The NOAO SQIID Infrared Camera (Simultaneous Quad Infrared Imaging Device) produces simultaneous images of the same field in the J, H, K, and narrowband L filters, using individual 512X512 quadrants of ALADDIN InSb arrays and is designed for use at the f/15 Cassegrain foci of the KPNO 2.1-m and 4-m telescopes. The observations are generally background (photon statistics) limited. The designated array for each channel is selected for characteristics (read noise, settling time, and dark signal) appropriate to background limited operation under actual observing conditions for its single filter. SQIID, which serves as its own acquisition camera, is a good match to "point and shoot" observing at the 2.1-m without a telescope operator. The filters are fixed in place and dark slide and window covers are the only moving parts. SQIID employs closed cycle refrigeration instead of liquid cryogens and in its prior configuration operated flawlessly for periods as long as 40 days, providing an unparalleled degree of system stability. Typical observing programs include:
Each detector is a Raytheon Infrared Operations (nee SBRC) ALADDIN 1024X1024 indium antimonide (InSb) hybrid focal plane array with 27 micron pixels (90% geometric and 100% optical fill factors) produced under contract to the ALADDIN Consortium. The ALADDIN Consortium, consisting of NOAO/KPNO and the US Naval Observatory, Flagstaff, under the engineering guidance of Al Fowler, has designed, developed, characterized and optimized the performance of the ALADDIN array for the wider community. Since each SQIID channel illuminates a single 512X512 quadrant, devices need only one otherwise excellent operable quadrant to be acceptable. The optics for each channel are independently optimized with a relatively narrow bandpass (apart from the entrance window, which is shared in common), permitting high efficiency AR coatings to deliver high instrumental throughput. The four separate channels are co-focused and co-aligned with a minimum overlap region of roughly 500X500 pixels common to all channels and are physically edge-masked to stop stray light from entering (or leaving) the readout. The detectors are of sufficiently high quality and uniformity that the dark/sky subtracted raw data are useful in assessing data quality in near real-time.
Detector area, stability, uniformity, quantum efficiency, low read noise and dark signal combine to make SQIID the system of choice for any observation which requires multi-color (JHK) imaging over large areas of the sky, quick look at transient targets, and for deep observations of selected regions. IR observations of necessity consist of sequences of frames with interspersed telescope motions. Each set includes a subset of small telescope motions (dithering) to dodge bad pixels and provide better image sampling and may require equal time spent off target (especially when observing extended sources and/or crowded fields). Typically the minimum time spent on taking a complete set of frames at a given field (within detector FOV) can be on the order of 10 minutes or more. With a single channel imager, the same set of pointings needs to be repeated for each filter. Since variations in observing conditions - seeing, airmass, sky transparency, and atmospheric background - ultimately limit the cohesiveness of a data set, multi-color observations are necessarily limited in depth and/or areal extent by the mechanics of taking the observations and the systematic effects of combining them into a single coherent data set. The advantage of SQIID is self-evident. During the time necessary to take the observations at the most time consuming wavelength, one in effect gets the other channels for free under the same observing conditions. Systematic effects are limited and determinate. This is why SQIID competes favorably with larger format arrays for multi-color applications. In addition, wide field L band imaging is possible (albeit with restricted bandpass) with sufficient sensitivity to detect and accurately locate red sources in the field. This feature is particularly important for detecting and indentifying for further study sources with IR excess, highly reddened sources, and intrinsically cold sources near the galactic plane where the star formation process is still active.
Details of the prior SQIID system are discussed by Ellis et al. 1992 ("The Simultaneous Quad-color Infrared Imaging Device (SQIID): A Leap Forward in Infrared Cameras for Astronomy" by T. Ellis, R. Drake, A. M. Fowler, I. Gatley, J. Heim, R. Luce, K. M. Merrill, R. Probst, & N. Buchholz, 1992, in Proc. SPIE, 1765, pp. 94-106.) and the ALADDIN detectors are discussed by Fowler et al. 1996 ("ALADDIN, The 1024x1024 InSb Array: Design, Description, and Results", by A. M. Fowler, Ian Gatley, P. McIntyre, F. J. Vrba, & A. Hoffman, 1996, in Proc. SPIE,2816, pp 150-160).
The SQIID optical system, which is matched to f/15, has a demagnification of 4. The pupil masks are fixed (i.e., not selectable), but a reasonable compromise for the 2.1-m and the 4-m telescopes has been implemented (n.b., by design, the KPNO IR secondaries handle the central obscuration without requiring a separate cold stop within the pupil mask.) According to Charles Harmer (who has the current design available), the worst case blur circle for SQIID is about 75 microns with 90% encircled energy. The optical layout of SQIID is shown in Fig. 1. The f/15 telescope focal plane is located inside the entrance window near the top of the instrument. A series of dichroics and flat mirrors separates the incoming beam into four separate wavelength channels, each with its own camera (Lyot stop, filter, optics) and focal plane array. Dichroic #1 passes L and reflects JHK. Dichroic #2 passes H and reflects JK. Dichroic #3 passes J and reflects K. The telescope exit pupil is imaged at the Lyot stops which are sized to the exit pupil image diameter to serve as an optical cold stop. Standard astronomical passband filters located at the Lyot stops restrict the range in wavelength passed to the array.
The system of dichroics is matched to natural atmospheric windows, adequately spaced in wavelength so that their inband transmission and outband reflectivity is very high. Since each camera is designed for optimum performance over a limited wavelength range, the AR coatings provide unusally high transmission. The opportunity for optimizing each channel for operation over a restricted wavelength compensates for transmission losses within the dichroic system and has yielded high throughput in all channels, comparable to that of a single camera system.
SQIID, which was built in an era where 58X62 was standard and initially deployed (1990-1995) with 256X256 Platinum Silicide arrays, was designed to smoothly accommodate larger devices. The optics was designed to illuminate a 512X512 array of 25 micron pixels. Since the ALADDIN array has 27 micron pixels, some vignetting is inevitable. In addition, upon seeing the full FOV for the first time, we discovered some unintended vignetting in RA within the instrument that would require a substantial effort to rework. The pixel scale and the unvignetted spatial coverage at the two telescopes are summarized in Table 1.
Telescope | f/ratio | arcsec/pixel | # pixels | RA X DEC field (arcsec) |
---|---|---|---|---|
2.1-m | 15 | 0.69 | 440 X 460 | 304 X 317 |
4-m | 15 | 0.39 | 440 X 460 | 172 X 179 |
Each channel of SQIID has its own fixed filter. We are unable to accommodate other filters tailored to specific programs. The deployed filter complement as of February, 2002 is summarized in Table 2. Note: Prior to February 2002 the K channel contained a Barr K filter.
channel | vendor ID | midpoint (microns) | FWHM bandpass (microns) | HP short (microns) | HP long (microns) |
---|---|---|---|---|---|
J | Barr J | 1.267 | 0.271 | 1.131 | 1.402 |
H | Barr H | 1.672 | 0.274 | 1.535 | 1.809 |
K pre 02/2002 | Barr K | 2.224 | 0.394 | 2.027 | 2.421 |
K post 02/2002 | OCLI Ks | 2.225 | 0.35 | 1.95 | 2.30 |
L | Barr PAH | 3.299 | 0.074 | 3.262 | 3.336 |
J filter data are estimated from the manufacturer's warm tracing by applying 1.63% shortward shift. Other data are from manufacturer's 77K tracings. Dichroic transparency has not been applied.
The geometric distortion is comfortably small within the unvignetted area, so that the data from the different channels can be brought to a common basis using a superposition of linear transforms (position shift, rotation and magnification) and a modest amount of pincushion/barrel distortion. (Note: J has pincushion distortion and HK have nearly identical barrel distortion.) The geometric distortion appears to be radially symmetric and is well represented by the addition of a cubic term. This simplifies the data reduction enormously, as spatial registration at any channel can be directly translated into registration at all channels.
Since the individual channels of SQIID illumine a single quadrant of a four quadrant array (which is has to be physically mounted within a small volume so as to not interfere with its neighbors) and the best quadrant of each device is selected, the relative orientation on the sky on the array is channel specific. From the point of view of the array, which is read from the outside corner (see Fig. 13, rows are oriented along the horizontal and columns along the vertical), the sky is "natively" seen oriented as follows:
J H K L W N S E S N W E E W N S E S N W
Initially, SQIID data where displayed and saved oriented as shown. As of September 2000, the saver task correctly handles the orientation issue during the saver process. Images saved to disk (and automatically displayed) are properly oriented with North up and East to the left.
Located at the telescope focal plane are the imager cryostat, the mechanical interface, and the associated warm electronics in two boxes mounted to the instrument. Fig. 2 shows a side view of the instrument and identifies the important parts. SQIID communicates with a remotely located instrument computer and ultimately with the user in a remote observing room (Fig. 3). Even though the f/15 focal plane at the 4-m is well back from the "nominal" focal plane of the telescope, a re-imaging lens in each guide probe assembly permits them to be used for guiding and precision offsetting.
SQIIDs temperature is maintained by a pair of Closed Cycle Cryogenic Coolers that employ pressurized helium gas as a refrigerant. Most of the internal parts, including the dichroics, optics, and filters, are cooled below 70 K with the first stage of the Closed Cycle Cryogenic Coolers. Each array is operated at ~30 K by a thermal strap to the second stage of the Closed Cycle Cryogenic Coolers plus a closed loop heater circuit.
Refer to Fig. 2 to identify the external features of the instrument. SQIID will be cabled upon installation, and should not be uncabled for any reason without contacting KPNO staff first. The only necessary user contacts with the focal plane instrument are the instrument power switch located on the electronics box and the mechanisms for inserting the internal and external dark slides.
3. Command, Communication, and Control
SQIID operates through a distributed computer network that has slowly evolved to the meet changing needs of computer support. Historically SQIID was operated by the user from a SUN workstation in the telescope control room through the WILDFIRE system, a transputer based system that communicates over optical fibers. WILDFIRE supports fast co-adding in place, movie mode, and data transfer directly to the SUN. Since WILDFIRE is tied to Sbus based hardware and a SunOS host system there is little room for growth in the core machine. The system was hard pressed by the upgrade from four 256X256 arrays to four 512X512 arrays during the SQIID upgrade. Movie mode was dropped owing to I/O delays associated with this upgrade.
The current configuration has SQIID remotely operated from a Linux-based Workstation (physically located in the control room) that connects to the SQIID host Sun Workstation (now completely in the computer room) through a VNC server.
The WILDFIRE system uses transputers and transputer links to control and acquire data from SQIID. A transputer is a single-chip microcomputer with its own local memory and communication links, which can operate either by itself or in conjunction with other elements linked to form computing arrays and networks. The WILDFIRE system consists of three main hardware components:
Communications between SQIID and the DSP take place over transputer links implemented on an optical fiber cable. The B016 interconnects the transputer DSP to the SUN SparcStation computer via a VME to SBUS converter within the Heurikon box.
The WILDFIRE user interface on the SUN is implemented within the TCL (tool command language) environment. On startup, one can configure the image save to produce either FITS images or IRAF images (via IMFORT routines) so that they can be manipulated and archived to tape within IRAF. The image data are generated in IEEE 32-bit floating point format. It is important to note that these images are NOT PROTECTED in any way and can be overwritten if the full path names of existing and new images are the same. (Currently the saver task attempts to manage conflicting filenames by appending ".nnn" to the incoming conflicting filename.) The data may be written to Exabyte or DAT tapes on local tape drives or sent via 'ftp' to one's home institution. Depending on the amount of header information, a single FITS file of a 512 X 512 image is about 1.057MB and a single 4 color exposure is 4 images (4.2MB).
Under the present version of WILDFIRE data acquisition:
A separate Linux based system serves as the telescope control, with a terminal at the LTO station; a hardwire link between the TCS and instrument control computers is used to send TCS commands to the telescope (singly, or within TCL scripts) and to retrieve telescope information for the image header. A schematic depiction of this arrangement is shown in Fig. 3.
Important Note: The disks within the primary workstations khaki and lapis are designated /data1. At the 2.1-m, WILDFIRE is run on the secondary workstation royal, whose partition is /data2. The disks are cross-mounted so that access to both is possible from either machine. However, such cross-access (e.g., /data1 from royal) is significantly slower than accessing the disk resident in the workstation. Therefore, it is imperative that the partition used for storing data taken by WILDFIRE be /data2 on the 2.1-m telescope! While it is possible to designate /data1 as the WILDFIRE data partition, operation will be much slower and subject to crashes, so don't do it. At the 4-m, one may designate either /data1 or /data2 as the data partition.
4. The InSb Detector Array
The four detectors in SQIID are ALADDIN 1024X1024 hybrid focal plane InSb arrays
produced by Raytheon Vision Systems (nee Santa Barbara Research Center).
They consist of a photovoltaic InSb detector array mated to a silicon direct readout
multiplexer via indium bumps. The readout is a p-channel MOSFET device. The
ALADDIN array was cooperatively designed and developed at RIO/SBRC with the ALADDIN
Consortium, consisting of NOAO and the US Naval Observatory, Flagstaff.
The device is presently operated in a non-destructive readout mode providing double correlated sampling. A representation of the voltage on a single pixel during an integration and readout is shown in Fig. 4. An address cycle consists of a "reset" to the canonical detector bias voltage, a non-destructive "read", followed by a second "read". During the reset operation, the voltage on each pixel is set to the value VR. When the reset switch is opened, the voltage left on the sense node will differ slightly from VR, due to charge spillback from the reset gate and from "kTC" noise. After a time 'fdly', the voltage on the pixel is sampled nondestructively (i.e., without resetting), yielding V1. After a second time interval, defined as the integration time, the voltage is again sampled, yielding V2. The "signal" is the difference between the two reads. Note that this technique, known as "double correlated sampling" eliminates the effect of the transient following the reset operation. The intervals indicated (not to scale) at the bottom of Fig. 4 represent the time required to carry out each operation on the entire array; thus, on an absolute frame, the time at which a given pixel is reset and read depends on its location in the array.
The operating microcode for ALADDIN arrays includes a provision for "multiple correlated sampling" (frequently referred to as Fowler sampling in deferrence to its discovery, Al Fowler of NOAO) in which the "reads" consist of a series of N nondestructive reads coadded to yield the values V1 and V2. This greatly reduces (by approximately N0.5) the array read noise on long, low-background integrations. Since SQIID observations are generally background limited (specifically, they are not detector limited), we only use "Fowler 1" which corresponds to double correlated sampling. At the shortest integrations (within the SQIID environment) selecting "coadds >= 2" also improves S/N (by approximately N0.5).
Table 3 summarizes the device characteristics and measured performance levels (according to standard lab protocol) of the ALADDIN arrays assigned to SQIID. SQIID was designed for background limited performance at low to moderate backgrounds. The ALADDIN array has 27 X 27 micron pixels with 90% geometric fill factor (100% optical fill factor) and a 1024 X 1024 format comprised of 4 electrically independent quadrants. The ALADDIN2/ALADDIN3 readout designation corresponds to improvements in the readout design. Note: Table 3 reflects the array assignments within SQIID as of February 2002. The prior configuration was SCA49484_Q3 at H channel, SCA41375_Q3 at K channel and SCA414107_Q3 at L channel. The bias values listed are effective as of January 2005.
Characteristic | J | H | K | L | Comments |
---|---|---|---|---|---|
SBRC Indentification (Quadrant) | SCA 45986 (Q3) | SCA 46888 (Q4) | SCA 414375 (Q2) | SCA 415412 (Q3) | ALADDIN InSb |
Readout type | ALADDIN2 | ALADDIN2 | ALADDIN3 | ALADDIN3 | version |
Response uniformity | +/-5% | +/-5% | +/-5% | +/-5% | within FOV |
Quantum efficiency | 95% | 95% | 95% | 85% | in band |
Bias | 700 | 700 | 700 | 900 | mv |
Full well | >200000 | >160000 | >200000 | >300000 | electrons |
lab read noise | 40 | 45 | 35 | 35 | electrons rms |
lab dark signal @ 300mv bias | 0.3 | 0.4 | 0.6 | 0.1 | electrons/sec |
Conversion gain | 10 | 10 | 11 | 11 | electrons/ADU |
Cosmetics | isolated regions | isolated pixels | reduced QE region | isolated pixels | primary defects |
It is useful to note that "dark current" is a function of applied bias and because both "dark current" and read noise are temperature dependent in opposite senses (below 40K "dark current" decreases with decreasing temperature to a minimum near 30K and read noise increases with decreasing temperature from a minimum near 40K) they cannot both be minimized. Hence the array operating temperature is generally selected to provide an application (background) specific compromise. Further information on the array design and operation may be found in Fowler et al., Proc. SPIE, 2268,340-345 (1994), and in Fowler et al., Proc. SPIE, 2816,150-160 (1996). The multiple correlated sampling technique used for read noise reduction is described in Fowler and Gatley, Ap. J. (Letters), 353, L33 (1990).
Telescope performance is covered in Section 5. The relatively high dark signals listed in Table 4 - which do not compromise performance - are indicative of compromises in the instrument design (not intended for low backgrounds), the need to operate at high bias, and the freedom to deploy specific arrays that might be unsuited to more demanding applications.
The limiting performance of SQIID depends on a number of factors.
Typical observed fluxes for a 10.0 magnitude star at the 2.1-m telescope are listed in Table 4. By direct measurement the fluxes are a factor of 3.21 higher at the 4-m telescope and the sky background per pixel is essential the same. The conversion gain is a detector-specific 10-11 electrons/ADU. Note: the biases listed are not necessarily the current bias values.
channel | J | H | K | L | comments |
---|---|---|---|---|---|
10 mag star within aperture | 3.25e4 | 2.90e4 | 1.78e4 | ? | ADU/sec |
Sky brightness level | 98 | 421 | 387 | ??? | ADU/sec/pixel |
Sky brightness origin | OH airglow, scattered light | OH airglow, scattered light | OH airglow, thermal emission | thermal emission | Note: components vary in intensity |
Conversion gain | 10 | 10 | 11 | 11 | electrons/ADU |
Bias | 600 | 600 | 700 | 800 | mv |
Full well | >200000 | >200000 | >200000 | >250000 | electrons |
in situ read noise | 40 | 40 | 35 | 35 | electrons rms |
in situ dark signal | 21 | 32 | 197 | 26 | electrons/sec |
Minimum integration time | 0.84 | 0.84 | 0.84 | 0.11 | seconds |
The estimated limiting magnitude for S/N = 3 in 60 sec integration time for a point-source (pt: mag) and a diffuse-source (diff: mag/square_arcsec) under average conditions (temperature = 50F; 3mm PWV; midrange OH background) sans sky subtraction is summarized in Table 5. For the purposes of this calculation, a 10 pixel collecting area on the sky is assumed. In practice, observing limits are dependent on the mode of sky subtraction employed. When mapping an extended region, the number of frames available for producing sky frames significantly exceeds the depth at a given position, virtually eliminating the sky subtraction "penalty". However, for the case where sky frames are exposed for an aggregate time comparable to that of the source frames, sensitivity is reduced by 0.376*mag (2.5*(log(sqrt(2))) from the values listed in Table 5 . Such is often the case for deep integrations of individual fields.
Channel | 2.1-m pt | 2.1-m diff | 4-m pt | 4-m diff |
---|---|---|---|---|
J | 19.8 | 20.2 | 21.1 | 21.3 |
H | 18.9 | 19.7 | 20.2 | 20.4 |
K | 18.3 | 19.2 | 19.6 | 19.8 |
PAH | 12.3 | 13.1 | 13.5 | 13.7 |
One must be prepared for the simple fact that IR observations are subject to a wider range of sensitivity variations linked to changing environmental conditions (OH airglow and temperature) than the optical, where phase of the moon and sky transparency predominate. Table 6 estimates the relative sensitivity for SQIID for three levels of OH airglow.
Airglow | J | H | K | L | Comments |
---|---|---|---|---|---|
low | +0.25 | +0.25 | +0.08 | +0.00 | magnitudes improvement |
medium | +0.00 | +0.00 | +0.00 | +0.00 | magnitudes improvement |
high | -0.24 | -0.20 | -0.10 | +0.00 | magnitudes improvement |
Estimates of the relative background and sensitivity variation for SQIID for three different ambient temperatures and 4 values of Precipitable Water Vapor are summarized in Table 7 and Table 8 respectively. At KPNO, 1mm PWV is a winter rarity and 9mm PWV is a Monsoon Season staple. It is useful to remember that the thermal background comes from both the atmosphere (which varies with airmass) and the telescope (which does not vary with airmass) in comparable quantities. Although observations at JHK are onscale under all conditions, at high temperature the L channel can saturate and become unusable. The primary symptom of saturation is an East/West gradient in the L background at the shortest integration times. If one desperately needs to perform L channel observations under higher temperature conditions, insertion of the cold internal polarizer element (it is the third choice in the open/dark/polarizer position controlled by the hand crank on the instrument) drops the background (and the signal!) by a factor of two, with edge vignetting (because it is too small to service the full FOV). Although one can obtain useful data at JHKL within the central field with the polarizer in place, the vignetting near the edge (which is variable, since we do not put a close tolerance on the indication when the polarizer is in position) is problematic. It is also worth remembering that for polarized sources your signal loss will be larger.
Ambient Temperature | J | H | K | L | comments |
---|---|---|---|---|---|
30 F | +0.00 | +0.00 | +0.21 (0.7) | +0.35 (0.5) | magnitudes improvement (background relative to 50F) |
50 F | +0.00 | +0.00 | +0.00 (1.0) | +0.00 (1.0) | magnitudes improvement (background relative to 50F) |
70 F | +0.00 | +0.00 | -0.30 (1.7) | -0.31 (1.8) | magnitudes improvement (background relative to 50F) |
PWV | J | H | K | L | comments |
---|---|---|---|---|---|
9mm | +0.00 | +0.00 | -0.02 (1.02) | -0.19 (1.12) | magnitudes improvement (background relative to 6mm) |
6mm | +0.00 | +0.00 | +0.00 (1.00) | +0.00 (1.00) | magnitudes improvement (background relative to 6mm) |
3mm | +0.00 | +0.00 | +0.03 (0.98) | +0.26 (0.84) | magnitudes improvement (background relative to 6mm) |
1mm | +0.00 | +0.00 | +0.06 (0.95) | +0.54 (0.67) | magnitudes improvement (background relative to 6mm) |
To optimize observing efficiency, it is important to keep the two distinctly different system overheads in mind, related to:
The preferred method for improving observing efficiency involves internal co-addition, since co-addition of JHK frames entails an overhead of only 10 millisec. By co-adding integrations to produce the equivalent of a 1 to 3 minute integration, the effect of data pipeline flow overhead is minimized.
The mode of array operation also has a significant impact on observing efficiency. In particular, it is important to understand the role of minimum JHK integration time in the JHK observing efficiency. SQIID currently employs global reset and double correlated sampling to produce an image: each image is the difference between two reads of the array and the minimum integration time is roughly the time to read the array once. Consequently, at the shortest integration times (approaching the minimum integration time of oreder 1 sec) the observing efficiency declines to 50% and for integration times of order 10 seconds, the JHK observing efficiency approaches 90%.
It is equally important to understand the relationship between JHK integration time and L integration time that affects L observing efficiency. During the course of an integration, SQIID simultaneously resets the JHK arrays, then simultaneously performs a non-destructive read (equivalent to a CCD bias frame) on the JHK arrays, waits roughly an integration time then reads out the JHK arrays again. Between JHK reads, the L band array is read out (in pairs and differenced) as often as will fit between the JHK read pair and the results co-added. Since there is some dead time before running L and since the minimum integration time is roughly the readout time, the maximum time spent integrating at L within a JHKL cycle is less than half the JHK integration time. One could use a different technique to read L (e.g., row reset) to improve efficiency, but we have yet to produce the complex code required to read L differently than JHK and will most likely produce a code employing row reset for all channels. The situation is summarized in Table 9 for the case of the shortest L time:
L time per coadd (sec) | JHK time (sec) | L coadds | total L time (sec) | % time (L/JHK) |
---|---|---|---|---|
0.11 | 1.00 | 1 | 0.11 | 11.0% |
0.11 | 2.00 | 6 | 0.66 | 33.0% |
0.11 | 3.00 | 10 | 1.10 | 36.6% |
0.11 | 5.00 | 19 | 2.09 | 41.8% |
0.11 | 10.00 | 42 | 4.62 | 46.2% |
0.11 | 15.00 | 65 | 7.15 | 47.7% |
Object Coordinates for any epoch can be entered into the telescope computer for use during the run. Although this task could be done by the telescope operator during the course of the night, lengthy observing lists are best entered by electronic submission (see below). These may include objects, standards, offset and guide stars, etc. Acquisition of optically faint or invisible objects might require initial acquisition and coordinate updating on a nearby bright star, so advance selection of these offset stars can save considerable time while observing. SQIID does not use a guider.
Conscientious observers may send coordinate lists via email (two weeks or more before the run) to coords@noao.edu. Files should be ASCII text, no longer than 2000 lines. Start the file with your name, a cache name, telescope, and dates of the observing run. Coordinates will be checked for format, loaded into the appropriate telescope computer, and acknowledgement will be sent. Each object should be one line of text. The format is object name, RA (starting column 16 or greater, delimited by first blank after col 15; hours, minutes, seconds), DEC (degrees, minutes, seconds), and epoch. Each field should be separated by one or more spaces (NO TABS); the delimiter in the RA and DEC fields may be spaces or colons. Example:
Standards are a subject of continuing discussion, and probably will remain so for some time. For the purposes of determining and removing the effects of telluric absorption and throughput in the instrument, it is desirable to observe a calibration star as near as possible to the object in both space and time. Owing to its high sensitivity and relative coarse pixel scale, SQIID must be calibrated using standard stars fainter than JHK=9mag. Recent compendia of faint standards are extremely useful in this regard:
Visitors should arrive on the mountain at least by early afternoon of the first night. This will allow time to become familiar with the instrument, create and test observing parameter sets, and enter object coordinates into a cache. First-time users of SQIID may wish to arrive a day early and spend some time in the evening looking over the shoulder of the previous observer, with his/her prior permission.
6. The IR Instrument Control System -- WILDFIRE
Note: This contains a SQIID-specific synopsis of the WILDFIRE manual written by Nick Buchholz.
As of December 2006, the SQIID operating environment at the 2.1-m telescope has changed with the incorporation of a Linux-based workstation as the console for operations in the control room:
The optical CCD (ICE) and infrared (WILDFIRE) environments are both operated from the same account on the 2.1-m (2meter) and 4-m (4meter) telescopes. The all-important obsinit command performs a number of functions relevant to this operating procedure.
On the first night of an IR block, the ICE environment might still be active (the presence of the "CCD Acquisition" and "CCD Reduction" windows will verify this). It will be necessary to run obsinit as detailed below to change to the WILDFIRE environment; since the hardware may be in an unknown state, it is also recommended to run through a complete hardware initialization on the first night of an IR block as part of the obsinit process. This will involve rebooting the observer's SUN workstation with the DSP (in the computer room) powered on and the SQIID instrument power off.
The "First Night" procedure is detailed within Appendix IX. Installation Issues. Since this procedure differs both in complexity and detail from the situation normally comforting the observer, we will not recount it here.
The following assumes that the change from ICE to Wildfire has already occurred and that Wildfire is already running properly.
On subsequent SQIID runs, obsinit is run only to enter the new observer and proposal ID information. It is NOT necessary to power down SQIID or reboot the computer. After typing exit in the Instrument Control window, logging out of all IRAF processes and running obsinit, simply exit OpenWindows from the desktop menu and log back in when the login window appears.
At the 2.1meter telescope, PROPID and OBSERVER can be modified without running obsinit. One can either run the newobserver command within the Wildfire Instrument Window or one can change the appropriate environmental variables within the ".cshrc2" file used by Royal on /data1/2meter/.
Note: The SQIID instrument power supply is located on the instrument itself. The (rocker) switch is on the right (South) side (near the top by the power cord) of the electronics box mounted on SQIID.
After a few seconds, OpenWindows will automatically load and present the login window shown below:
Login as [telescope] (where telescope is "2meter" or "4meter" as appropriate) with the current password posted on the workstation terminal. The WILDFIRE system will then load automatically, resulting in a terminal screen layout approximately like Fig. 5 below; the dashed window labeled Instrument Status will appear in the approximate position shown only after the instrument microcode has been loaded.
Once the environment has been set to WILDFIRE by obsinit, it will remain in that state, even if it is necessary to reboot the instrument computer for any reason. There should be no reason to execute obsinit more than once during a run. If a reboot is required, the login procedure in the window displayed above will automatically bring up the WILDFIRE windows.
A brief description of the windows follows:
There are three basic steps in the complete startup of WILDFIRE: hardware initialization; starting WILDFIRE; instrument initialization. The procedure below will go through all three steps, as would be necessary on the first night the instrument is on the telescope.
Hardware Initialization
This procedure establishes the link between the DSP box and the computer, by rebooting the observer's SUN workstation with the SQIID power off. The obsinit procedure for the first night of an SQIID block (described above) includes these steps.
HISTORIC NOTE: The startup script for WILDFIRE was simplified significantly in 1999. The microcode will be loaded automatically and the bias for SQIID set to the default values. The dialog during a typical WILDFIRE/SQIID initialization is recorded in Appendix VIII.
Starting WILDFIRE
At this point, the windows should be present as in Fig. 5. Go to the Instrument Control Window and enter:
This will lead you through an interactive startup procedure. READ THE QUESTIONS CAREFULLY; simply entering [cr] will return the default, which may not be appropriate. For the full startup, the replies are:
At this point, the transputer nodes will bootstrap, and four .tld files will load. Eventually (when the startup script automatically executes "setup sqiid") you will see messages regarding the downloading of the microcode, setting of 4 values of VddCl1 (-1.3), VddCl2 (-3.5), VggCl1 (-4.9), VggCl2 (-2.8), and Vset (-1.8). When this is completed, the final message will appear:
You will see messages reporting 4 biases being set, followed by:
If you want to use a different parameter file than the default "sqiid" parameter file that was executed by the startup script, you can enter "puse parameter_filename" at this time.
SQIID is now ready for operation.
If difficulties are encountered in startup, entering trouble in any of the windows (except the Instrument Control) will open a troubleshooting diagnostic, listing symptoms and possible solutions. However, most problems occur during the initial installation, and are often hardware related. The most common problems are listed below:
red LED(s) in DCU | Bad fiber connection. With the instrument power on, the green LED in the DCU should be on, and the two red LEDs off. If either or both red LEDs is lit, there is a fiber problem which must be repaired. A similar set of LEDs in the DSP box can diagnose fiber problems at that end. |
halt after "Configuring C004" | Bad fiber optic connection (see above). Even if red LEDs are off, one or more fibers may have poor throughput, which must be measured. Power supplies may be connected improperly. Check that the analog connector goes to "CCD Power" and not "PS-10 Power" on the telescope. |
halt after "bootstrapping node 100" | Bad fiber optic connection (see above). C004 may not be configured and a full startup may be necessary (DSP cycle, reboot, startwf). |
"error #16 (cannot open link)" | System stuck in funny state. Full startup may be required. If that does not help, check for proper power connection and fiber throughput. |
"cannot read telescope status" | Link to TCP computer is down. This is usually solved by rebooting the TCP computer. WILDFIRE will still work, but cannot move telescope or retrieve telescope status information for header. |
In addition, comments, suggestions, and descriptions of persistent problems should be emailed to wfire@lemming, which has been set up as an equivalent to service for WILDFIRE instrumentation.
"parameter sets" are used to control the attributes of data acquisition. A listing of the parameters is given below. Because the data are saved directly as IRAF images, note that parameters include not only observation-specific items such as integration time, but archiving items such as the IRAF filename and the header and pixel directories.
Observing Parameters | |
---|---|
title coadds * lnrs pics integration_time * filename header_dir pixel_dir mode nextpic ucode display ra dec epoch offset imag_typ airmass comment im_list save archive |
IRAF header title number of coadded integrations per image number of low noise reads (1 for SQIID) number of pictures per observation integration time (seconds) IRAF filename image header directory pixel file directory process mode [stare, sep, hphot] picture index microcode channels to display (j, h, k, or l for SQIID) RA of object # DEC of object # epoch of object # observation offset type of observation [object,dark,flat..] airmass of object # comment filename of image list channels to be saved to disk ([j h k l] or subset for SQIID) channels to be archived ([j h k l] or subset for SQIID) |
* WARNING: Use 'set-time' to set coadds and integration time rather than responding to the individual 'coadds' and 'integration_time' queries from 'ask'.
In general, the parameters fall into three categories:
When this is complete, save the parameter set with the command psave [filename]. This will save both the edited parameter set and the menu selected by eask in the file '[filename].par'. Should the system crash, this information may be retrieved by the command puse [filename]. Should major changes be made to the parameter file, such as change of header or pixel directory (say on another night of the run), it is a good idea to psave the updated file so it, and not the previous version, will be recovered by puse.
The basic observation is initiated by the command observe. The system will print on the screen, one at time, those parameters selected by eask, and the current value [], prompting for entry of a new value or [cr], which will enter the current value. The command go will begin an observation, but will use the current values for the parameters (except the picture index, which will be automatically incremented). The command movie will begin a loop consisting of an observation (using the current parameters!) and a display; this may be terminated with end at any time. The observation in progress will be completed and displayed. Movie observations are stored on disk! This is unfortunately necessary to prevent orphaned pixel files from filling up the disk. A recommended procedure is to include the 'filename' parameter in the ask menu and change to a dummy filename at the beginning of a movie. When returning to data taking, one may reset the filename to that used for the data. If one wishes to retain continuity in the index number, it is also necessary to reset 'nextpic' to the value before the movie observations. Keep good logs!!
The ask command will cycle through the selected parameters, prompting for changes, just as with obs, but will NOT begin an observation. This command is useful for checking parameters, and is essential before executing movie, which will use the parameters for the previous observation, even if it were 600s in length. The combination of ask and go is a perhaps preferable alternative to observe.
One may abort an observation (such as an unintentional 600s movie) by entering abort in the Instrument Control window; the system should respond by acknowledging the abort and the observation should terminate gracefully in a few seconds. This can sometimes turn off the display and save operations, so it is advisable to re-enter save j h k l (or whichever subset you have been using) and display k (or whichever channel you have been using after an abort.
The user interface is written in the Tool Command Language (tcl), which
is well-suited to the construction of scripts for data taking.
Scripts are a powerful tool for executing a sequence of tcl commands,
including telescope motions, instrument motor commands, and observations,
as a single executable program. Even for those who are not veteran
programmers (most of us), simple scripts are fairly easy to construct.
Scripts are highly recommended for spatial sampling (dithering) and
linearity calibrations.
The best recipe for starting out is to copy an existing script to a new
file and then edit that file as desired. The first line of the script file
contains the basename of the script file ("proc
source /data2/2meter/tclSamples/[scriptname].tcl
To execute the script, enter the basename [scriptname] as a command
in the Instrument Control window. A sample script is given in
Appendix IV.
Scripts may be found in directory "tclSamples" under the "[telescope]"
directory, as in the path above, and also in /usr/wfire/tcl. This
latter path is the system response to query pwd in the Instrument
Control window. When creating a custom script, please copy a system script
into an observer directory and then rename and modify it, to avoid
confusion.
Scripts copied into the user home script directory (/data2/2meter/wfire at the 2.1-m
and /data2/4meter/wfire at the 4-m) and sourced can be marked for automatic inclusion in
subsequent invocations of "startwf" by entering "mkIndx".
For the more sophisticated (or daring) observer, a TCL manual is available.
WILDFIRE presently uses TCL version 6.7 and properly written code should
run with no special limitations. Please note we will not debug or otherwise
support user code, nor will user supplied TCL routines be saved within
WILDFIRE from one observing run to the next.
The following WILDFIRE default scripts are useful for various observing
programs, and as templates for user-constructed modification. They
are initiated by entering the script name as a command, and going
through a series of interactive queries to set internal parameters.
Alternatively, several have command line versions for faster use.
These are default scripts which do not require sourcing.
Refer to the Appendices for listings of WILDFIRE
and SQIID commands (Appendix II)
and troubleshooting procedures (Appendix III).
Michael Merrill's provisional IRAF script tmove may be used for centering
stars on the array, using an image displayed in the ximtool window. Because
this is not yet a standard IRAF task, it will probably have to be
manually installed for an observing run.
task tmove =   /data1/4meter/tmove.cl
Michael Merrill's provisional IRAF script idisp may be used to display
sky-subtracted images in the ximtool window. Because this is not yet a standard IRAF task,
it will probably have to be manually installed for an observing run.
The installation of the instrument and cables will be handled before
the beginning of the run by the mountain technical staff and are not
of concern to the user. The SQIID Reference Manual
provides coverage of the details of installation and setup for those who
are interested. SQIID remains on the telescope (with power on, under normal circumstances)
for the entire observing run.
After SQIID is installed on the telescope, go through the WILDFIRE startup
procedure outlined previously. Once the system is operational and the
detector activated, check the detector and temperature status with
status s and compare with the nominal values below:
status s
Housekeeping information is reported via status screens. Additional status
screens for SQIID are:
status t
status v
status 3
SQIID acts as its own acquisition camera. Open up and acquire a star in SQIID. Stars with K
magnitude fainter than 6 are OK for initial acquisition, but stars fainter than
K = 9 are necessary to avoid saturation for final focus adjustments. [Note: When SQIID is
first installed, it is best to start with unambiguous stars to verify initial telescope
pointing. Stars brighter than K = 3 are best for this purpose.] Use individual 'go' exposures
(because of the 40 second delay, movie can be confusing), to get the star within
the central region of the array. Choose a wavelength channel for determining focus (preferably K
which suffers least from seeing) and stick with it through the run to avoid confusion.
The four SQIID channels are near parfocal, but differences in sensitivity to seeing (which
improves with increasing wavelength) and slight differences in image quality away from focus
can be confusing if you switch back and forth. Once the star is found, move the telescope until
it is centered and focus the telescope, resetting display limits and integration time as necessary,
until a tight image is obtained. For optimizing focus, it is best to obtain single images, using
observe or go, and analyze the image quality with
the IRAF task imexam using the 'r' command. Remember that it may be necessary to relocate
the beam when moving to a new object.
An example of excellent focus (K channel, 1.0 sec) can be seen in Figure 6. Note that the star
appears to be positioned at the center of a pixel. Since the geometric quality of the optics on
the order of 80% flux within two pixels radius and the profile fitting algoritms stall near
1.5 pixels, this is as good as it gets. FWHM of 1.8-2.0 is more typical.
(The rightmost three values at the bottom of the profile image are the FWM from different
profile fitting algorithms.) Naturally, longer exposures will have somewhat broader profiles.
Stars which are too bright will tend to be either flat topped or possibly even contain a central void as
seen in Figure 7.
NOTE: It is likely that the single pixel events (that occur at the roughly once
per second and are visible even in dark frames) are in response to alpha particles from the anti-reflection coating of the last
lens surface. We have since discovered that thorium fluoride is the coating of choice for
producing durable wide bandpass coatings. The magnitude of these single pixel events is typically
3000-5000 ADU with of order 5% leakage into the four nearest neighbors.
Figure 8 is the radial image profile for a typical single pixel event.
At the 2.1m telescope focus is a simple function of temperature. Best focus
as a function of temperature shifts as deltaF/deltaT = 0.025 per degree K with a focus at 5.10 for 8K.
After the temperature of the telescope structure stabilizes (it varies rapidly for roughly an hour
after opening), the relationship provides an accurate estimate for best focus, which generally shifts
towards smaller values as the night progresses. Pick a temperature (such as the secondary or the front
surface of the primary) and monitor that temperature to adjust focus. It appears that best focus
was a tolerance of at least +/- 0.01 focus units. It is useful to note that there appears to be no
backlash in the IR secondary. At the 4m telescope, nominal focus is -7300 with an as yet
undetermined temperature dependence.
SQIID will be installed and checked out at the start of each observing run
by a competent and cheerful support scientist. Users may confirm continued
proper operation during their run with software interrogation and by
comparing dark and flatfield frames against "standard" frames.
Detector status and temperature information is displayed with the word
status s; it is also automatically updated at the beginning
of an observation. Standard values for the default SQIID configuration
are displayed above. The cryogen temperature readouts
are displayed as temperature based on a generic relationship between voltage at constant current and temperature.\.
The heater power may vary somewhat around the typical value given.
However, a significant and persistent departure from this value
may indicate the dewar is losing its vacuum (going "soft") or that the Closed Cycle
Cooler System is losing efficiency. If this is suspected, contact the
instrument support scientist.
Finally, sky- or dark-subtracted frames may occasionally show a dark (or light)
potato-shaped artifact about 30 pixels wide. This "Phobos effect" (see Fig. 10)
results from a region of lower signal in one of the frames, and can appear
as a positive or negative image anywhere on the array. This occurs very infrequently,
and is apparently a crystal relaxation phenomenon in response to the array being warmed
after having been too cold (below 25K). This can happen over a span of a few hours
when the SQIID electronics have just been powered on after they have been off for
an extended period. (The array heater power is controlled by the same power supply
as the electronics.)
Atmospheric extinction must be calibrated by observations of
either a standard star as close as possible to the same zenith distance used for the object
or a series of stars that span the range in zenith distance for the observation.
Typical extinction for SQIID is summarized in Table 9.
Flatfield exposures are necessary to calibrate the pixel-to-pixel
gain variations in the array and the effects of the illumination of
the array by the internal optics. The system response is stable and is very flat across
the arrays, with a slight intrinsic column to column modulation of +/- a few percent
(owing to relative array orientations, columns may have either NS or EW orientations
in the saved and displayed images). Consequently, the flatfield for each channel should
be stable at the percent level under normal illumination and global
flatfields can be constructed which are viable for extended periods of
time. Since direct illumination of the array is possible (remember that
the secondary mirror is undersized), observations near bright sources,
such as the moon, which have atypical illumination, should not be use
to determine global flatfields. Observations during twilight will also
have illumination atypical of nighttime observations.
Because sky flats provide the same array
illumination as real observations, they are preferable in principle to dome flats
using the White Spot. It is, nonetheless, a good idea to obtain dome flats as
a backup. If one is observing in a sufficiently sparse star field, one may use
the same set of observations for the object, sky, and flatfield.
Because the sky flats will include the array dark current, it is necessary
to obtain separate "dark" observations for subtraction from the sky
observations. Unfortunately, what constitutes a "dark" frame for
creating flats is ill-determined due to the "memory" effect which
accumulates in time. For example, a series of observations in the dark
filter immediately following sky (or dome) flat observations will show
a monotonic decrease in mean value as the "memory" of the relatively
bright preceding observations decays over 5 to 10 integration times.
By the same token, a series of dome flats following dark or low-background
observations will show a monotonic increase in mean value as the "memory" of the
higher flux observations accumulates. One possible approach is to
take a larger number of dome flat or dark observations and reject
those early in the series, when the change in value from one frame to
the next is the greatest.
Should one decide to obtain "dome flats", it is recommended that
one take exposures when the dome is dark, to minimize the ambient
radiation at J and H. At the 2.1-m and 4-m telescopes, the dome screen is
illuminated by lamps mounted on the telescope top ring.
(The 4-m telescope is positioned by mountain technical
staff.) Darkening the dome may require waiting until visitor hours end
at 1600 hr. The lamp controls at these telescopes are on the LTO console.
One should obtain a relatively large number (7 or more)
of flatfield images for post-processing within IRAF, where floating point
arithmetic and sigma-clipping or median combining are possible (the latter to
eliminate noise artifacts which may appear in a single observation). Since the
illumination level differs markedly at J, H, K and PAH, one should anticipate
taking data at several settings of the lamps.
Within the K and PAH bands, one will be dominated by the thermal emission from
the dome screen, and at the PAH band, the lamps are not necessary.
Dark current and residual
illumination subtraction require obtaining an identical series of observations
with the flatfield lights off (for J,H,K) or the dark slide in the
beam (PAH). After subtraction of the "off" or "dark" frame, normalization
(using, for example the IRAF 'response' task) and median combining of these observations
should eliminate noise spikes or systematic features in the spectra.
To stay within the relatively linear portion of the array response, it is
preferable to turn down the lamp intensity and use exposure times relatively
long in comparison to the readout time of 0.84s (e.g., 3 - 5 s). Keeping the
flux at a modest signal level (< 5000 ADU) may also help in this
regard; with a read noise ~ 35 e, one is completely background limited
by signals > 500 ADU.
The time-dependent dark signal is generally small compared to the sky background
for all four arrays. However, higher-order spatial features, such as the
gradient on one side of the H channel, are significantly brighter and cannot be
neglected when contructing flatfields. "Dark" images contain both static and time
variable components with diverse causes that obviate simple scaling of dark frames to
alternate integration times. Consequently darks corresponding to the integration times
for data that will be used for defining flatfield and linearity issues should be taken.
A sequence of 9 exposures should be sufficient. Since the dark current is so low, you
will be able to see transient events, such as those due to cosmic rays that can be
removed by median filtering. Darks should be taken in the afternoon and/or in the morning.
Closing the cold internal darkslide (hand crank on the side of the instrument) is both
necessary and sufficient for taking darks. The time dependence of the median dark
current within [100:400,100:400] is shown in Figure 11. Note that the H channel
exhibits an apparently negative dark current at short integration times.
While the detectors are stable, the sky is not necessarily so. Under good conditions,
sky flux varies only with airmass and at a given position, the sky can be stable over an
hour or more. Naturally sky flux increases when you get near the moon. When airglow is high and
variable, the sky at H can vary by a factor of two over the course of an hour, while the sky at J
varies by 40%. Consequently it is prudent to monitor the sky (use imstat inside IRAF) to be
sure that you have sufficient data to perform sky subtraction on your targets.
In the IR (even at JHK) observations of all but the brightest stars
(9 mag) are background limited so that typical diffuse targets (such as
galaxies) are seen at very low contrast in individual frames. As noted
above, the sky background is constantly changing (slowly with airmass
and on slow to moderately rapid timescales with sky emission) so that
the contrast varies as a function of time. Since observations are
ultimately limited by inadequacies in the flatfield, one cannot simply
co-add such observations and obtain a meaningful result; median
filtering such data merely selects the middle frame. (For example, as
the contrast varies the illumination pattern on the array also varies
since the relative mix of radiation seen through the telescope optics
and that seen directly past the secondary changes.)
One must devote a comparable amount of time off-source, intermixed
throughout the on-source observations, to provide sky frames;
subtracting sky frames on a pixel by pixel basis reduces the contrast
problem and allows one to successfully co-add data taken over a long
interval of time. When the targets are much smaller than the array,
one can accomplish this sky subtraction by moving the target around
the array and in effect taking the sky and source data at the same time.
GHOSTING - Each channel has its ghost, whose position is opposite the optic
axis from its parent bright star. Only saturated stars are bright
enough to clearly show their ghost, which is out-of-focus, covering
about 25% of the chip. The out-of-focus ghosts that lie opposite the
optic axis from the primary have the following characteristics:
When a pixel is reset, the voltage difference (bias) between the pixel
and detector substrate creates a depletion region that acts as a potential
well for the collection of (mostly) photogenerated carriers. Electrically,
one may consider this potential well as a capacitor. As charge accumulates
in the pixel, the depletion region fills in, increasing its capacitance
and that of the entire pixel node. This changes the electrical gain of the system,
resulting in a sub-linear voltage-charge relationship,
which quickly rolls off (saturates) when the pixel voltage reaches that
of the detector substrate (zero bias). Technically, a pixel will continue
to accumulate charge even into forward bias, but its response by that time
will be significantly nonlinear. As a direct consequence, pixel
response departs from linearity in a predictable fashion for
accumulated signals above a device-specific level. Since the total capacitance
(which determines system gain) is the sum of the distributed
(non-varying) capacitance of the system and the (variable) capacitance
at each detector node, the degree of non-linearity is a function of the
ratio of nodal to total capacitance. Since key pixel
parameters such as quantum efficiency are very uniform, the linearity
appears to be a global property of the array rather than pixel specific.
Increasing the bias on a pixel will not only increase the depth of the
potential well, but by decreasing the capacitance of the depletion region
in relation to parallel components of the node capacitance, will result in
a more linear voltage-charge relation. As a result, a bias increase from
0.6 to 0.8 volts will effectively double the charge capacity of the pixel.
This comes, however, at a significant cost in dark current, which increases
dramatically with bias. Therefore, we recommended a bias of 0.6v for JH, 0.7
for K, and 0.9v for high-background (L band) observations, where the increased dark
current is not important. These were the default bias values for SQIID until
January, 2005 whrn we adopted the current bias values. To further improve
linearity, we currently use a bias 0.7v for jhk and 0.9v for L
In the following discussion, observed (output) values have not been
corrected for the unseen charge collected during delay between biasing
the detectors (reset) and the first (non-destructive) read of the bias. A
second (non-destructive) read is taken an integration time later. Only the
difference between reads is output. In detail, the global reset mode
used to operate SQIID resets all the pixels at the same time and then
performs a non-destructive read of the array. The first pixel is read out
shortly after the global reset and the last pixel is read out 0.61 sec after
the global reset. The charge accumulated at the time of the position
dependent first read is "lost", since its value does not get reflected in
the difference. Hence, the reported signal is always less than the total signal
on the array at the time of the second read. At short integration times and
high rates of photon arrival (bright stars and/or high background), this
unreported charge can lead to a significant underestimate of the signal
outside the scope of the usual linearity correction. The unseen charge can be
accurately estimated (apart from noise issues) on the basis of the timing, but
since the amount of unseen charge is position dependent, one is better off
not "going there"!
Ideally, the data fit are always within the regime where this correction for
unseen charge was small. This is not the case, for example, when doing
0.84 sec integrations on standards!
One normally expresses the departure from linearity in terms of the relative error
(input-observed) or the normalized relative error (input-observed)/observed
for each array and fits these data to an appropriate mathematical model. For SQIID,
the model fitted function for the relative error is:
Eventually, a pixel will accumulate sufficient charge to forward bias
it to the point where no more is collected, resulting in a condition known
as saturation. The reset-read-read address cycle used in
double correlated sampling (Fig. 4) results in a characteristic, but
unusual, saturation behavior. For a given integration time, the effect
of increased flux is a steeper slope of the voltage-time curve. As the
flux increases, the voltage V2 will eventually saturate, while
the voltage V1 will continue to increase because of the time
interval between the reset and the first read; the difference signal will
thus decrease with increasing flux. Finally, the detector will saturate
in the short interval between the reset and first read, resulting in
identical values for V1 and V2, or a difference value
of zero. Thus, the double-correlated signal relation with flux is initially
nearly linear, then increasingly nonlinear, and eventually decreasing to
an ultimate value of zero as one saturates. The A/D channels (2 for J,H,K and
8 for L) will saturate at slightly different levels, resulting in an evident odd-even
column pattern. These effects are evident in a
Saturation Image of the L band, in which the flux increases rapidly from the bottom
to the top of the array.
The telescope and dome are operated by the Telescope Operator (nights)
or the Technical Assistant (days). Arrange schedules with them in advance for
positioning for dome flats, and opening the telescope and dome
at the start of the night. The observer should:
Inside the control room there are a number of tasks to attend to:
SQIID is now ready to take data.
Although sky flats are generally adequate for reducing SQIID observations,
dome flats may be useful. Dome flatfields may be done either in the afternoon before
observing or in the morning. Remember that you will need dark frames taken the same
way (integration time and number of coadds) as your sky/dome exposures to properly
produce your sky flats. Since the temperature and operating conditions for SQIID are highly stable
by design, one should not have to repeat flatfields once they have been verified.
In any case, it may be desirable to take some short and long (30s) dark frames before the
first night of observing to verify performance.
While all channels are exposed simultaneously, one may find different lamp
settings are required to be properly onscale at each channel. Flatfield series should be
obtained for each bandpass (J, H, K) used for observing, as each wavelength channel
is serviced by its own array. Two settings, one for J/H and one for K should suffice.
The high background at L band obviates dome flats - use sky L band flats instead
Use an illumination level sufficient to give approximately 5000 ADU in 2 s
integration time. Higher signals in shorter integration times may
exacerbate nonlinearity effects. Read noise is sufficiently low that
200 ADU signal will be background limited.
Obtain 5 - 10 flats in each band desired for later median averaging.
Turn flatfield lights off and obtain an equal number of non-illuminated
bias images at each setting.
Telescope Operator will do final dome and telescope checks and
acquire stars, offset, etc. SQIID acts as its own acquisition camera.
Telescope motions are generally commanded from LTO terminal, although they
can also be entered from the observer's
terminal. For programs demanding frequent motions, agree on a mutually
compatible protocol with the LTO.
In the event of multiple observers, only one should serve as
the communication link to the LTO.
SQIID image names follow the naming convention:
where "filename" is an observer controlled parameter, "ch_id" is the approripate
designator from the set "j h k l", the number "XXX" is sequentially numbered
(being automatically incremented for each exposure until a new value is declared,
either at a new object or new night) and "image_extension" is either ".fits" or ".imh"
(depending on the saver setting declared at startup).
If you correctly set
'oldirafname = yes' when reading the data from tape, the image names will be restored
to their original names and match the log sheets.
A list of available commands within the WILDFIRE instrument control window is:
As with all Kitt Peak instrumentation, nothing is ever supposed to
malfunction.
On the rare occasions when something seems to go wrong,
either by pilot error, exquisite software gotchas, or hardware failures,
recovery can in many cases be fairly simple. In particular, hang-ups in
the instrumentation software can usually be corrected without resorting to
rebooting the computer, which should be considered a last resort.
The following tables cover situations that may arise with the Instrument
Computer or SQIID itself.
Some situations are not covered in this manual, since the recommended
recovery could involve procedures that are potentially harmful if done
incorrectly. In these cases, the user is requested to call for technical
assistance from the Observatory staff.
The following procedures are intended as a guide for restoring the WILDFIRE
system following various levels of system failure. Re-booting the computer and
cycling power to the instrument or DSP in the Heurikon box in the computer
room are not normal WILDFIRE operations and should not be done without
proper consultation, or unless the specific conditions below are valid.
These procedures are listed roughly in order of increasing severity, so unless
a specific condition has occurred (e.g., DSP power cycling), try the less dramatic
procedures first.
An extensive troubleshooting library may be consulted by entering trouble
in any active window (except the Instrument Control window).
The resulting interactive session can be used to diagnose and correct problems.
If the Instrument Status window has vanished, first check to see if it has simply
been closed. Type fireproc (or !fireproc if necessary)
from an active window and look for the "hkserv" process. If the "fireproc" task is unavailable,
type:
If the process is present, the window has been closed, and it will be necessary
to locate and open it. If the icon is not visible, it may be hiding behind one
of the open windows. In OpenWindows, one can check the "windows" item in
the menu for the status of all operating windows; if the Instrument Status
window is present, open it and continue observing.
If the Instrument Status window has died, perform the SIMPLE RESTART procedure
below.
If WILDFIRE has crashed (Instrument Status window has vanished and could not
be found by above procedures), and/or the "[hostcomputer]" prompt has returned
to the Instrument Control window, the following steps within the Instrument
Control window should restore operation:
[NOTE: If the power to the instrument and/or the Heurikon DSP box in the
computer room has been interrupted or the computer has been rebooted, this
procedure may not be sufficient. See below for more specific procedures]
If WILDFIRE is hung (Instrument Control window unresponsive - won't respond with
a system prompt after issuing a "CR" - and data collection stalled):
If the STALLED SYSTEM procedure fails to return the UNIX prompt, or an
examination of the operating processes by entering ps ax in the
Console window reveals a process which cannot be halted via the
kill -9 [process number] command, it will be necessary to reboot the
instrument computer. In detail, type fireproc (or !fireproc if necessary)
from an active window and look for the "hkserv" process. If the "fireproc" task is unavailable,
type:
If the STALLED SYSTEM procedure fails to return the UNIX prompt, or an
examination of the operating processes by entering ps ax in the
Console window reveals a process which cannot be halted via the
kill -9 [process number] command, it will be necessary to reboot the
instrument computer. In detail, type fireproc (or !fireproc if necessary)
from an active window and look for the "hkserv" process. If the "fireproc" task is unavailable,
type:
If the power to the instrument was interrupted but the black Heurikon DSP box
in the computer room remained powered up and the computer was not rebooted:
If the black Heurikon DSP box in the computer room has been powered down, then
it is necessary to do the following.
NOTE: The order of these steps is important.
If the dsp box is powered down, rebooting the instrument computer is necessary.
Make sure no one else is using the instrument computer at the time. If only the
power to the instrument has been interrupted, perform the procedure above.
Whenever the instrument computer is rebooted, the instrument power must be off
and the heurikon dsp power on!
By way of information, these are the WILDFIRE specific processes running on royal
at the 2.1-m under normal operations:
Given the large variety of observing programs being carried out SQIID,
no single approach to data reduction is universally applicable.
This section reviews the promising approaches to data reduction for several specific
observing scenarios: observations of a bright stellar source, a faint stellar
source, and an extended object.
IR imagery with the InSb array presents several problems not encountered
in visual imagery with an optical CCD. These include high background with strong variable
emission lines and regions of bad pixels. Fortunately, the frontside illuminated InSb
arrays to not suffer from fringing so that theTo overcome the bad pixels, we recommend taking
a large number (>5) of observations of a given object, spatially offset between exposures,
and deriving the median of the individual observations. True dark frames are generally
not necessary in the course of normal observing, since sky subtraction
removes the dark current as well, and flatfield exposures (except for L)
are best done by cycling the illumination lamps on and off. Most importantly,
the strong and variable background requires that sky subtraction be handled in
a two step process. First order sky subtraction is achieved by subtracting a
sky frame. The very high level of IR sky brightness precludes the "traditional"
CCD approach of flatfielding and background reduction on a single object frame, since even
a 1%uncertainty in the flatfield would produce effects large in comparison
to the object signal. The first order sky subtraction will typically
remove 95 - 99% of the sky, thus greatly reducing the effects of
flatfield uncertainties in the second order background removal.
The majority of experience with SQIID has been in the J, H, and
K bands, where the background consists of OH and O2 lines
superposed on the spectrum. Beyond 2.3 microns, the background
consists of a smooth continuum due to the emission from the telescope
as well as emission lines in telluric features. Thus, transitions that
produce telluric absorption lines in astronomical spectra will
produce emission lines in the sky background. Although this
scenario is more challenging, the same routines of sky subtraction
and off-object residual background subtraction work well, as long as one
operates in the linear (< 10000 ADU) region of the detector.
Proper data reduction requires accurate solutions for the small additive
effects of internal illumination and charge generation (DARK frames), the
large additive effects of sky illumination (SKY frames) and the multiplicative
effects of position dependent pixel sensitivity (FLATFIELD frames).
The creation of DARK, FLAT, and SKY calibration frames are the first step
in the data reduction process. The DARK frames are simple to obtain and
process but the FLAT and SKY frames are more difficult to create and are
crucial to the quality of the final images. Compared to optical band CCD
observations, infrared observations are extremely background limited.
Furthermore, the background in the near-infrared is variable at many
temporal and spatial scales.
System SKY frames are established from observations with the same integration
time and near in time and place to the source frames. This is done by
interspersing frames of off-source (ideally) blank sky fields in the sequence
of source observations. Many of these sky frames, each at different
position, are then median filtered to remove celestial sources to generate a
SKY frame, which is measure of the temporally stable illumination on the array,
including dark current and fixed pattern noise.
System FLATFIELD frames are established using the sky as a uniform external
illumination source. The background in the IR results in sky levels with S/N
of better than 100 in a single 3 minute exposure. By taking the median of a
reasonable number of blank fields (or target fields without large objects)
obtained at different times during the night and at different locations on the
sky, a satisfactory measure of the system flatfield can be derived.
Generally, DARK frames (taken with the internal cold dark slide in place) are
stable over a night (at about 1 electron/sec) and are probably stable over an
entire observing run. Changes in dark current can accompany changes in the
ALADDIN array temperature. Since the SQIID dark current has both a base level
and a time-dependent component, a dark frame must be created for each exposure
time (that you intend to use to determine flatfields or for dark subtraction)
during the observing run (it is assumed here that the observer has obtained
such dark exposures).
One may define a bright star as one that can be observed in frame
times of less than 10 s; in this case, the greatest limitations to
S/N are systematic effects rather than background limited statistics.
To overcome these, set coadds to 3 - 5 (to build up signal to noise on
each frame) and take 5 - 7 observations of the star, displacing it between
observations. The do_standard script is ideal for this operation.
Since the observations span a short time, the sky will not vary significantly,
and one can generate a sky frame from a median of the individual
observations. Subtracting this median sky from the individual
observations removes the dark and first order sky. Each image is
then divided by the flat.
SQIID produces simultaneous images of the same field in the J, H, K, and
narrowbnd L passbands, using individual 512X512 quadrants of ALADDIN InSb arrays.
The observations are generally background (photon statistics) limited.
Typical observing programs include:
These three kinds of observations are distinguished because they require
somewhat different data reduction strategies. This document describes a set of
IRAF programs (created by Michael Merrill at NOAO) designed to facilitate the
reduction of SQIID datasets. These programs reside in the IRAF package
"upsqiid". They have a number of imperfections in the user interface (especially
a large number of irrelevant parameters) and currently do not have help files.
NB: The SQIID package is not an officially released and supported IRAF package;
all queries should be directed to Michael Merrill at NOAO (merrill@noao.edu; 520-318-8319)
We will define a "dataset" to be the set of direct observations of a given
field. These may be dithered observations of a single target or a mosaic of a
larger region. In the extreme case, the dataset may contain only a single
exposure (and only steps A and B listed below would be required). The
basic path for the reduction of SQIID dataset can be described as follows:
Users are cautioned that IR image datasets often present a greater data
reduction challenge than optical CCD images both due to the superior
performance of optical CCD detectors (lower dark current, readout noise,
and pixel to pixel sensitivity variations) and especially due to the
extreme background limited nature of most IR observations. The results at
each step in the process should be carefully examined and problems
understood before proceeding. Many problems can be solved by the exclusion
of bad images from the datasets.
The upsqiid IRAF package is contained within a tar file called "upsqiid.tar"
at the SQIID web site
Restore the package using "tar upsqiid.tar" within your IRAF login directory
and follow the "README" directions for installing the package within your
system. Since the package consists entirely of IRAF cl procedures, no
recompiling is needed.
Assuming you copy the package somewhere in a directory called "upsqiid", you
would put the following definitions in your "loginuser.cl" file:
You also need to edit the file upsqiid.cl in the "upsqiid" package to point to
your path instead of my path:
One loads the "upsqiid" package by typing upsqiid in the IRAF xgterm
window where the cl is running.
At KPNO the "DATA REDUCTION" window would qualify.
Alternatively, you can bring up a new "xgterm" from the menu.
At the KPNO 2.1m one has the option of performing data analysis on lapis
(either directly or remotely on royal) or azure, since the /data1
and /data2 disks are accessible from all three machines. Since royal is busy with
data aquisition, lapis or azure are preferred. When running locally on
lapis, one also needs to bring up a local ximtool window from the menu. If the
"upsqiid" package is unavailable, type the following in your (lapis/azure) IRAF window:
Scripts are a powerful tool for executing a sequence of tcl commands, including
telescope motions, instrument motor commands, and observations, as a single
executable program. Many of the wildfire commands are simply protected
scripts within the wfire/tcl directory. Observers may generate their own
scripts in the "public" directory /data2/[telescope]/tclSamples. One approach
is to browse through the existing scripts to find one that performs a function
similar to that desired, copy it to a new file, and edit it as required. It is
important to note that the first line contains the base name of the script, and
must be edited to reflect the new name of a script created in this manner.
Scripts copied into the user home script directory (/data2/2meter/wfire at the 2.1-m
and /data2/4meter/wfire at the 4-m) and sourced can be marked for automatic inclusion in
subsequent invocations of "startwf" by entering "mkIndx".
Below is a typical script, "dotransit", used with SQIID. This will take 5
observations - one at the center and four corners of a box. This script employs a string
array (setup by the "set step" lines) to hold the commands, which are run within the
"while" loop. After each step, the loop recognizes a CR as a signal to
abort the script, leaving the telescope pointed wherever it was. Since the "reset_offset"
command zeroed the north and east position variables, these variables accurately report
the current position relative to that at the start of the script. The script "dotransit"
modifies the "do_standard" script to keep the header information current.
(To save time, the "do_standard" script, which takes five images, normally shuts off
the TCP info (RA, DEC, airmass, ZD) after the first position and turns it
back on at the end.)
The script "box5.tcl" does something similar to the "dotransit.tcl" and the
"do_standard.tcl" scripts, but organizes things for easier expansion. One could
fill a "set set() {} structure" with the position increments you want to visit.
It is recommended that you build a series of such scripts rather than set up one
that executes a massive generalized observing program in one fell swoop. Note that
the "ask" command is used to query the observation parameters (only once) before
the observations start and provision is made for a graceful exit before commiting
to the observation.
A number of operational issues are worthy of note:
During February 2002, the final planned upgrades to SQIID were installed.
The relative spatial orientation and offset amongst the channels has changed
and channel characteristics will need to be re-determined. The changes are
summarized as follows:
The following session is representative of starting up a WILDFIRE session with SQIID.
Actions on the part of the observer are set apart in bold type inside square
brackets: "->[ Enter "commands here" ]<-",
where one types the enters the quoted text at the keyboard followed by a carriage return.
Informational asides are set apart in bold ("[Note:]").
WILDFIRE presents choices as bracketed values [n], where the default value,
selected by answering with a "return", is the value inside the brackets. The proper answer
to yes and no questions is "y" or "n" (not "yes', "no", etc.) Generally, the boolean
values are defaulted to the most likely value.
WILDFIRE operates through parameter files. The default default parameter set is "sqiid".
If you are restarting the system and have saved your own parameter file "my_set", activate
it by typing
Examine parameter list by typing
One edits the "ask" sequence - the questions task "ask" will ask you by
Changes to ask and the parameter file are preserved using
The following interchange sets the bias on the K channel.
The sequence noted below sets all the biases:
As of December 2006, the SQIID operating environment at the 2.1-m telescope has changed with
the incorporation of a Linux-based workstation as the console for operations in the control room:
The optical CCD (ICE) and infrared (WILDFIRE) environments are both
operated from the same account on the 2.1-m (2meter) and 4-m
(4meter) telescopes. The all-important obsinit
command performs a number of functions relevant to this operating procedure.
On the first night of an IR block, the ICE environment will still be active
(the presence of the "CCD Acquisition" and "CCD Reduction" windows will
verify this). It will be necessary to run obsinit to change to the
WILDFIRE environment; since the hardware may be in an unknown state, it is also recommended
to run through a complete hardware initialization on the first night of an IR block as part of
the obsinit process. This will involve rebooting the observer's SUN
workstation with the DSP (in the computer room) powered on and the SQIID
instrument power off.
The SQIID instrument power supply is located on the instrument itself. The (rocker) switch is on the
right (South) side (near the top by the power cord) of the electronics box mounted on SQIID.
Once this is complete, it is necessary to reboot the instrument computer with the
instrument power off.
Login as [telescope] (where telescope is "2meter" or "4meter" as appropriate)
with the current password posted on the workstation terminal.
The WILDFIRE system will then load automatically, resulting
in a terminal screen layout approximately like Fig. 5 below; the dashed window labeled Instrument
Status will appear in the approximate position shown only after the
instrument microcode has been loaded.
Once the environment has been set to WILDFIRE by obsinit, it will
remain in that state, even if it is necessary to reboot the instrument
computer for any reason. There should be no reason to execute obsinit
more than once during a run. If a reboot is required, the login procedure in
the window displayed above will automatically bring up the WILDFIRE
windows.
A brief description of the windows follows:
There are three basic steps in the complete startup of WILDFIRE: hardware
initialization; starting WILDFIRE; instrument initialization. The procedure
below will go through all three steps, as would be necessary on the first
night the instrument is on the telescope.
Hardware Initialization
This procedure establishes the link between the DSP box and the computer,
by rebooting the observer's SUN workstation with the SQIID power off. The
obsinit procedure for the first night of an SQIID block (described
above) includes these steps.
HISTORIC NOTE: The startup script for WILDFIRE was simplified significantly
in 1999. The microcode will be loaded automatically and the bias for SQIID
set to the default values. The dialog during a typical WILDFIRE/SQIID initialization is recorded
in Appendix VIII.
Starting WILDFIRE the first night
NOTE: When starting SQIID the first night we have found that it is important to
thoroughly exercise the Wildfire distributed memory by bringing up IRIM, then PHOENIX,
and finally SQIID. The following sequence walks you through this task.
At this point, the windows should be present as in Fig. 5. Go to the
Instrument Control Window and enter:
This will lead you through an interactive startup procedure. READ THE QUESTIONS
CAREFULLY; simply entering [cr] will return the default, which may not be
appropriate. For the full startup, the replies are:
At this point, the transputer nodes will bootstrap, and .tld files
will load. Eventually (when the startup script automatically executes "setup irim")
you will see messages regarding the downloading of the microcode,
setting assorted voltages. When this is completed, the final message will appear:
You will see messages about assorted voltage failures and servo errors (since the IRIM task looks
for DACs and for motors that
SQIID does not have), but the housekeeping window and the saver task should successfully start.
Go to the Instrument Control Window and exercize the system by typing "status s", "status v",
and "status t", then exit the system by typing:
Continue by typing:
Answer the questions:
At this point, the transputer nodes will bootstrap, and ".tld" files
will load. Eventually (when the startup script automatically executes "setup phoenix")
you will see messages regarding the downloading of the microcode,
setting assorted voltages. When this is completed, the final message will appear:
You may see messages about assorted voltage failures and servo errors (since the PHOENIX task looks
DACS and for motors that
SQIID does not have), but the housekeeping window and the saver task should successfully start.
Go to the Instrument Control Window and exercise the system by typing "status s", "status v",
and "status t", then exit the system by typing:
Continue by typing:
Answer the questions:
At this point, the transputer nodes will bootstrap, and four ".tld" files
will load. Eventually (when the startup script automatically executes "setup sqiid")
you will see messages regarding the downloading of the microcode,
setting of 4 values of VddCl1 (-1.3), VddCl2 (-3.5), VggCl1 (-4.9), VggCl2 (-2.8),
and Vset (-1.8). When this is completed, the final message will appear:
You will see messages reporting 4 biases being set, followed by:
The housekeeping window and the saver task should successfully start.
If you want to use a different parameter file than the default "sqiid" parameter file that
was executed by the startup script, you can enter "puse parameter_filename" at this time.
SQIID is now ready for operation
One tests the system noise by taking 10 dark exposures with short (1 sec) integration time.
These data are combined with the IRAF imcombine task to determine the rms per pixel.
The IRAF phist can be used to examine the results (nbins=200, z1=0, z2=25). A typical result
is shown in Figure 12. Peak values significantly higher than the 3.5-4.0 shown are indicative of
excess noise. Either the array temperatures have not yet stabilized (detector heater power is
not on unless the instrument power is on) or there is a problem with the electrical ground. SQIID
should not be run with instrument power connected through an isolation transformer.
tmove
idisp
first_image = "test010j.fits" First image in sequentially numbered images
sky_image = "-1" Name or sequential number of sky frame
(frame = 2) Display frame #
(number_id = "000") image number template results image? 000
(listid = "/tmp/list") name of wildfire system image list?
(dolast = no) Repeat for most recent image
(dostats = yes) Perform imstats?
(statsec = "[100:400,100:400]") Image section for calculating statistics
(lthreshold = INDEF) Lower threshold for exclusion in statistics
(hthreshold = INDEF) Upper threshold for exclusion in statistics
(imsave = no) Save difference of each pair?
(saveid = "dpr_") String prepended to object name
(zscale = yes) automatic zcale on each frame?
(ztrans = "linear") intensity transform: log|linear|none
(z1 = 0.) minimum intensity
(z2 = 1000.) maximum intensity
Getting Started
--------------------------------------------------------------------------
SQIID Base Status Display 18:11:29
H detector K detector J detector L detector
Integ time (secs) = 0.855 0.855 0.855 0.185
CoAdds = 1 1 1 1x1
Lnrs = 1 1 1 1
Number of Pics = 1
Detector Temp = 29.81K 30.68K 29.81K 30.68K
Det Heat Pwr (mw) = 129.39 56.15 146.48 75.68
Observation Settings
Mode = stare stare stare stare
File name = "test%03d%s" Index = 95 Space Available
Header Dir = "/data2/2meter" 3046308kb
Pixel Dir = "/data2/2meter/pixels" 3046308kb
--------------------------------------------------------------------------
--------------------------------------------------------------------------
SQIID Temperature Display
H detector K detector J detector L detector
Detector Temp = 29.81K 30.68K 29.81K 30.68K
Det Heat Pwr (mw) = 136.72 61.03 153.81 78.12
Bench 0 (North) = 40.69K Bench 1 (South) = 39.61K
Wheel = 46.29K Sieve Plate = 18.15K
Cold Hd A 1st St = 32.17K Cold Hd B 1st St = 32.34K
Cold Hd A 2nd St = 11.53K Cold Hd B 2nd St = 13.47K
--------------------------------------------------------------------------
--------------------------------------------------------------------------
SQIID PRCD Voltage Status Display
H detector K detector J detector L detector
VSet = -1.783 -1.790 -1.779 -1.803
ISet = 0.266 0.297 0.257 0.322
VDet = -2.897 -2.815 -2.926 -2.701
VDesUR = -5.579 -5.589 -5.583 -5.587
BOK = -2.896 -2.815 -2.925 -2.698
VddUC = -3.475 -3.497 -3.488 -3.489
VddOut = -0.986 -0.992 -0.989 -0.991
VddCl1 = -1.315 -1.319 -1.303 -1.303
VddCl2 = -3.545 -3.560 -3.517 -3.514
VggCl1 = -4.867 -4.886 -4.861 -4.908
VggCl2 = -2.773 -2.786 -2.769 -2.791
Vp = -0.489 -0.494 -0.494 -0.493
VnRow = -6.207 -6.186 -6.179 -6.177
VnCol = -3.988 -3.993 -3.987 -3.987
VDesLr = -0.494 -0.489 -0.497 -0.494
VRowOn = -5.985 -5.983 -5.985 -6.002
VRowOff = -0.685 -0.694 -0.695 -0.688
VRstOn = -5.971 -5.989 -5.973 -5.970
VRstOff = -2.991 -2.991 -2.989 -2.991
--------------------------------------------------------------------------
--------------------------------------------------------------------------
SQIID Power supply Voltage Display
Gnd Ref H/K Box = -0.097 Gnd Ref J/L Box = -0.105
Vcc1 H/K Box = 4.740 Vcc1 J/L Box = 4.699
Vcc2 H/K Box = 4.750 Vcc2 J/L Box = 4.706
PRCD Card H detector K detector J detector L detector
+5v Sup = 4.951 4.951 4.945 4.944
+15v Sup = 14.866 14.906 14.893 14.922
-15v Sup = -15.100 -15.198 -15.078 -15.250
+7v VRef = 6.914 6.921 6.911 6.906
-7v VRef = -6.909 -6.914 -6.897 -6.897
PA Cards H detector K detector J detector L detector
+5v Sup = 4.952 4.950 4.944 4.947
+15v Sup = 14.968 14.923 14.960 14.804
-15v Sup = -15.188 -15.062 -15.295 -15.131
+5v VRef = 5.002 5.001 4.992 4.992
-5v VRef = -4.986 -4.986 -4.980 -4.978
H detector K detector J detector L detector
VOff1 = 0.675 0.675 0.669 0.669
VOff2 = 0.678 0.677 0.668 0.672
--------------------------------------------------------------------------
Techniques
Focus
Performance Checks
Responsivity Calibration
J
H
K
PAH
0.15
+0.06
+0.08
TBD
Sky Subtraction
CAUTION: One cannot expect to simply co-add observations of faint
surface brightness sources and allow the off-source portion of the
observations within the detector FOV to determine the presumably
constant level of the sky. At some level, defects in the flatfield
(pupil ghosts, object ghosts, or whatever) dominate the accuracy of the
results. This deficiency is typically overcome by subtracting
off-source observations of the sky, then flatfielding the differences.
This improves the accuracy of the detected signal by at least an order
of magnitude.
J H K
90 108 56 pixels diameter
5.5 6.3 5.5 difference in integrated flux in magnitudes
In addition, the J channel has an in-focus ghost located 36.5 pixels
east of its parent and 5.4 magnitudes fainter.
Linearity
ym[x] = a(1) * x**2 + a(2) * x**3
where ym = relative error = (input - observed)
x = observed (adu)
The fit is valid for values < Xmax. For values beyond Xmax, the array is rapidly
approaching saturation. The fitted parameters for each channel are summarized in
Table 10 and the fitted linearity is plotted in Figure 12. A new array was
installed in the H channel in February 2002.
Valid from
Jun 2000
Jan 2005
Jan 2005
Mar 2002
Jun 2000
Jun 2000
Channel (bias)
Ks (700mv)
H (700mv)
J (700mv)
H (600mv)
J (600mv)
H (600mv)
a(1)
6.4864e-7
-1.3456e-8
1.2626e-6
8.4783e-7
1.2164e-6
4.5326e-6
a(2)
4.4790e-10
6.1010e-10
2.9498e-10
6.8416e-10
4.7829e-10
4.8759e-10
Xmax (ADU)
16000
16000
16000
16000
16000
14000
Data date
Apr 2003
Apr 2003
Apr 2003
Apr 2003
Apr 2003
Apr 2001
Saturation
Pixel Masks
Representative pixel masks for the J, H, K channels of SQIID are contained in
Supplement 1: Channel Specific Characteristics.
These masks include the combined effects of intrinsically bad pixels and instrumental vignetting.
Appendix I: Telescope Checklist
Computer Room Setup
Observing Platform / Cassegrain Cage Setup
Control Room Setup
Calibration Data
Final Setup at Start of Night
Observing Miscellany
Control Room Shutdown
Observing Platform / Cassegrain Cage Shutdown
Computer Room Shutdown
Appendix II: WILDFIRE Command List for SQIID
"filename"//"ch_id"//"XXX"//"image_extension" (e.g., n1_001j.fits)
SYSTEM LEVEL
! commands
execute the commands in csh or run csh
? command
give help on a command
ed name
call up an editor on a proc
help name
display help for one of these topics
man name
display a man page for a given topic
progress 0
minimize diagnostic output during integrations (**node...)
source program
temporarily include tcl program within recognized system;
need to source again after powerup or go (full path name required)
DETECTOR
activate
activate the detector
deactivate
deactivate the detector
setup sqiid
set up the default SQIID voltages and prompt for activation.
Alternative parameter named parameter files can also be invoked via
setup filename
?ucode
list array microcode currently in use (also in image header)
dl microcode_name
download specific array microcode
WILDFIRE
startwf
initiate bootstrapping and downloading of the WILDFIRE system
exit
deactivate the array and exit the WILDFIRE controller
trouble
open troubleshooting session (do NOT enter in Instrument Control window)
hung
attempts to complete link protocol; used as part of the restart
procedure when WILDFIRE is hung (INSTRUMENT CONTROL window unresponsive and
data collection stalled); must be entered in Console window
HOUSEKEEPING
newobserver
enter observer name and proposal ID for image header
status [|s|v|t|f]
display a status screen; (general status |s|; voltages|v|; temperatures|t|; filters |f|)
longheaders [on|off]
will disable/enable house keeping data in the header
tcp_on
enable link to TCP for telescope status info and offsetting
tcp_off
disable link to TCP for telescope status info and offsetting
PARAMETER FILES
Note: a parameter has two attributes, its value and flags indicating whether the
parameter and its value should be displayed and/or queried when the
ask or observe tasks are run.
lpar
list the names of the available parameter files
plist
list all the current parameters
psave filename
save the current parameter set (values and ask/display
flags) to the named parameter file
puse filename
load the named parameter file
ped
edit the current parameter file selected by puse asking all
questions regardless of query status
ask
prompt for the eask selected subset of parameters within
the current parameter set
eask
iterate through all the known parameters, allowing the
user to specify which parameters are queried and which are
displayed. After each question an "l" signifies display only;
"a" signifies query; "la" will list the current value (which may
be selected by [cr]) or accept a new entry
ACCESSING INDIVIDUAL PARAMETERS
Note: many SQIID parameters have 4 values (one per channel) which are entered on the
same line separated by whitespace. The last argument in a series is adopted for the rest of
the arguments: "1" yields "1 1 1 1", "1 2" yields "1 2 2 2"; "1 2 3" yields "1 2 3 3".
When no argument is given, task prompts with current value.
?coadds
returns the number of coadds for next image
pics [n]
sets the number of pictures to be taken at each observe/go
set-time [f f2 n]
prompts and sets the JHKL coadds and integration time (in seconds to millisec level)
sets JHK time to f sec, L time to f2 sec, and JHK coadds to n (task computes L coadds).
This is the preferred method to set integration time and/or coadds
setIntegration [f f2 n]
sets JHK time to f sec, L time to f2 sec, and JHK coadds to n (task computes L coadds)
nextpic [n]
sets the picture index appended to filename to [n]
header_dir
sets path for FITS image or IRAF image headers
pixel_dir
sets path for IRAF image pixel files (unused for FITS images)
mode
sets operational mode for array readout (stare/sep); sep is for observing
title
sets title field for IRAF/FITS image header
comment
sets comment line within IRAF/FITS image header
offset
relative telescope (RA,DEC) position parameter updated by TCL commanded motions
resetoffset
reset the position "offset" values in the IRAF/FITS image header to "0,0"
filename filename
sets the IRAF/FITS image "filename". The path is is not
included in "filename"; if no argument given, will
prompt with current value. For SQIID, a "%d" or "%03d"
should be inserted where the picture number should be
placed. If no field is given, "%03d" will be appended.
The format will be: "filename"//"nextpic"//"ch_id"//"image_extension"
(Note: when filenames conflict, the saver task attempts to create a unique name by
appending .nnn to conflicting filename.)
OBSERVING
ask
prompting for pre-selected observing parameters
go
initiate an observation using the previously set parameters
observe
perform one observation using current parameter set,
prompting for key parameters
abort
abort an observation (enter in Instrument Control window); follow with save
save [ch_id ...]
include all the channels you wish to save, eg.,"j h k"; be sure to re-issue after an
abort
display [ch_id ...]
display channel n after each coadded integration
east [n]
move telescope n arcseconds east
west [n]
move telescope n arcseconds west
north [n]
move telescope n arcseconds north
south [n]
move telescope n arcseconds south
toffset [e] [n]
move telescope e arcsecs east and n arcsecs north:
+ for north/east; - for south/west
zs [z1] [z2]
set zscale values [z1] and [z2] for the image display
zs 0 0
enables autoscaling for the image display
tcp_on
enable link to TCP for telescope status info and offsetting
tcp_off
disable link to TCP for telescope status info and offsetting
movie
begin observe/display loop. NOTE: parameters (filename, running number, integration time,
coadds, etc.) will be those of previous observation or 'ask' routine unless
specifically reset!!!! Movie frames are saved to disk and should be deleted periodically.
It helps to use a filename like "junk" when using movie.
Terminate movie with end [CR] in Instrument Control window.
Pay careful attention to the nextpic numbers, as movie increments nextpic for
only the selected channel and after movie terminates, nextpic for the channels will
no longer match.
Instrument Hardware
no signal
Internal cold dark slide closed. Check status s for proper
temperatures, voltages. Check that green LED in
analog electronics box is lit. If the detector has been accidentally
deactivated, program will not sense this; observe will work, but return
pixel values near zero in image. minimal signal at J/H; large signal at K
Telescope mirror covers, dust slide (top, South), and/or external dark slide (pull knob
at NorthEast) closed. Check status s for proper
temperatures, voltages. apparent vignetting
External darkslide may be partially in place or internal aperture wheel may
not be set to open position. Vignetting by external darkslide or dust cover
will elevate K background. If the internal polarization anaylzer
is in position, the image will be vignetted on all sides with half the signal.
Vignetting also results in higher backgrounds in the K and L channels.
bootstrap failure
If the startwf procedure fails during the "bootstrapping node ..."
process, a likely culprit is a bad (or incorrect, if the failure occurs on
the initial setup) fiber optic connection. Check the three status LEDs visible
through sight holes on the SQIID electronics. The left LED should be green if there is power
to the instrument; the middle and right LEDs should be off. If either the middle
(channel 1) or right (channel 2) LED is red, there is a fiber continuity problem
in that channel. There is a duplicate set of LEDs in the Heurikon DSP box
in the computer room (reporting on the other two fibers); it is necessary to remove
the front cover to view them. A bad fiber channel will require the substitution of one
of the spare fibers. Call for assistance. WILDFIRE RESTART PROCEDURES
FAST RESTART:
If WILDFIRE has been exited normally and the system is intact (neither instrument
power nor Heurikon DSP power has been interrupted), one can simply type the following within
the Instrument Control window to restore operation:
g sqiid
The startup script will run automatically to the point where the question about
array activation is presented.
INSTRUMENT STATUS WINDOW HAS VANISHED:
ps ax | egrep 'PID|hkserv' | egrep -v grep
SIMPLE RESTART:
STALLED SYSTEM RESTART:
until either the WILDFIRE "%" prompt or the UNIX "[hostcomputer]" prompt returns in the
Instrument Control window
TOTALLY STALLED SYSTEM QUICK RESTART:
ps ax | egrep 'PID|wfire' | egrep -v grep
Look for a "control" process in state "D". If you find such a process, then:
The startup script will run automatically to the point where the question about
array activation is presented - answer 'y' to question about detector activation
g sqiid
TOTALLY STALLED SYSTEM RESTART:
ps ax | egrep 'PID|wfire' | egrep -v grep
Look for a "control" process in state "D". If you find such a process, then:
RESTART AFTER INSTRUMENT POWER INTERRUPTION:
RESTART AFTER HEURIKON DSP BOX POWER INTERRUPTION:
WILDFIRE PROCESSES:
230 p1 IW 0:00 /bin/csh /usr/wfire/bin/startwf-lapis
242 p1 IW 0:00 /bin/sh /usr/wfire/bin/startwf
290 p1 R 7:25 /usr/wfire/bin/SQIID/control
249 p2 IWN 0:00 /bin/csh /usr/iraf/extern/ice/startup/config/fire/start.red
304 p3 IW 0:00 /bin/csh /usr/wfire/bin/sun_daemons SQIID -fits
311 p3 R 26:08 ./saver -fits
312 p3 S 0:07 ./hkserv ../config/SQIID DISPLAY=lapis:0.0 EXINIT=set optim
Appendix IV: Data Reduction Guide
INTRODUCTION
TRIMMING AND LINEARIZATION
FLATS, DARKS, & SKY FRAMES
BRIGHT STAR
SQIID Package
task upsqiid = "your_pathname/upsqiid/upsqiid.cl"
set upsqdir = "your_pathname/upsqiid/"
task upsqiid = "/data2/ir2meter/merrill/upsqiid/upsqiid.cl"
upsqiid
Appendix V: TCL Scripts
proc dotransit {} {
#*******************************************************************************
# (do_standard - take 5 images, starting at the initial position, then scanning
# the corners of the enscribed square. The telescope is returned
# to the initial position when done. Prompts for the side of the
# square in arcseconds.)
# based on do_standard without turning off tcp
#*******************************************************************************
global north east
if ![ yorn "Is the telescope set to the center of the field? "] then {
error "telescope not set"
}
# make sure the coordinates are centered
reset_offset
# turn tcp header information on
tcp_on
# get size of grid
puts stdout "What is the separation between pictures in arc seconds? "
set size [readline]
puts stdout "Side of enscribed square = $size arc seconds"
# observe (0, 0)
set step(1) { puts stdout "Taking Center field" ; go }
set step(2) { puts stdout "Taking SE field"; toffset [expr "$size/2"] [expr "-$size/2"] ; go }
set step(3) { puts stdout "Taking NE field"; toffset 0 [expr $size] ; go }
set step(4) { puts stdout "Taking NW field"; toffset [expr "-$size"] 0 ; go }
set step(5) { puts stdout "Taking SW field"; toffset 0 [expr "-$size"] ; go }
set step(6) { puts stdout "Returning to starting field"; toffset [expr "$size/2"] [expr "$size/2"] }
puts stdout "Hit return to abort Grid."
set i 1
while { $i <= 6 } {
eval $step($i)
if [select] then {
break;
}
incr i
}
# turn tcp header information on
tcp_on
puts stdout "TRANSIT GRID COMPLETE "
}
proc box5 {} {
#*********************************************************************
# box5.tcl does something similar to the dotransit.tcl/do_standard.tcl
# scripts, but organizes things for easier expansion.
#*********************************************************************
puts stdout "Starting object sequence"
global north east
# zero offet parameters
set north 0
set east 0
# set_offset
# make sure the coordinates are centered
reset_offset
# turn tcp header information on
tcp_on
# run through standard 5 position grid, one observation (picture) taken
# at each position. The sequence starts centered, but takes no data and
# ends with data at center.
set step(1) { east 30.0 ; south 30.0}
set step(2) { north 60.0}
set step(3) { west 60.0 }
set step(4) { south 60.0}
set step(5) { east 30.0 ; north 30.0}
# run through ask sequence
ask
# allow for graceful exit
if ![ yorn "Do you want to continue "] then {
error "Safe exit"
}
# issue exit procedure reminder
puts stdout "Hit return to abort Grid."
set i 1
while { $i <= 5 } {
eval $step($i)
go
if [select] then {
error "error in sequence"
}
incr i
}
# issue beep at end
puts stdout "Sequence completed"
beep 10
}
Appendix VI: Cautions and Caveats
Appendix VII: Changes to SQIID
Appendix VIII: Representative WILDFIRE Interchange
Starting WILDFIRE
->[In the Instrument Control window type "startwf"]<-
lapis% startwf
royal being added to access control list
[1] 18486
2meter@lapis% stty: TCGETS: Operation not supported on socket
[1] 27884
[2] 27885
[Note: at this point control passes to WILDFIRE. At the 2meter,
a new Instrument Control window running remotely on royal overlays the Instrument
Control window on lapis.]
WELCOME TO THE WILDFIRE INSTRUMENT CONTROL SYSTEM.
This procedure walks you through a startup of the instrument control program.
All yes/no questions should be answered with a "y" or an "n".
Instrument names can be typed in upper or lower case.
Should this procedure abort or hang during the start up, please use
another window to run the "trouble" routine. This will allow you to
search a TROUBLESHOOTING file to try determine why the startup failed.
Please mail trouble reports or suggestions for improvements to wfire@lemming
Press "return" to Continue
->[ Press "return" ]<-
*******************************************************************************
If the power to the WFire DSP box in the computer rack was interrupted,
a hardware setup procedure must be run before it can be used.
This procedure must be run if the power to the DSP box went off
for ANY reason.
Has the WFire DSP box power been off for any reason since the last
time you ran startwf or restart (if unsure try 'n')? [n]
->[ Press "return" ]<-
******************************************************************************
The Instrument hardware must be setup to allow correct data transfers
between the instrument and the DSP Box. This setup MUST only be done
once each time the instrument is turned on.
Has the instrument power been off since the last time you ran startwf
or restart? [n]
->[ Press "return" ]<-
******************************************************************************
The Instrument hardware must be setup to allow correct data transfers
between the instrument and the DSP Box. This setup MUST only be done
once each time the instrument is turned on.
Has the instrument power been off since the last time you ran startwf
or restart? [n]
->[ Press "return" ]<-
******************************************************************************
Which instrument are you using (enter PHOENIX, IRIM, CRSP, SQIID, etc.) ? SQIID
->[ Enter "SQIID"]<-
******************************************************************************
Do you want windows? [y] (type 'n' if not using X windows).
->[ Press "return" ]<-
******************************************************************************
Do you want to save in IRAF format ? [n] (default is FITS).
->[ Press "return" ]<-
FITS=-fits
[Note: at this point WILDFIRE bootstraps the system.]
sldnet-noio SQIID
LD-NET (Network Loader), Version 89.1 [Link I/O Driver: 'SCIO']
Copyright (c) 1986-1989 by Logical Systems
Loading first phase of bootstrap to root node 1
Finished loading first phase, awaiting first acknowledge
Loading second phase of bootstrap to root node 1
Bootstrap loaded, awaiting acknowledge
Successfully bootstrapped root node 1
[Note: If there are problems either establishing or linking
with the root node, the system hangs or exists here.
Hangups during "Bootstrappping node 100" are due to poor fiber communications or
failed memory in the SQIID electronics. Overheating or lack of power are the
most common cause of such "failures".]
Bootstrapping the remainder of the network:
Bootstrapping node 100
Bootstrapping node 101
Bootstrapping node 102
Bootstrapping node 103
Bootstrapping node 203
Bootstrapping node 202
Bootstrapping node 201
Bootstrapping node 200
Bootstrapping node 2
Bootstrapping node 10
Network successfully bootstrapped
Downloading program: ../tld/SQIID/b011.tld
Downloading program: ../tld/SQIID/inst.tld
Downloading program: ../tld/SQIID/seq.tld
Downloading program: ../tld/SQIID/dspw.tld
Program downloading completed
WILDFIRE SQIID SYSTEM CONTROL
LAST BUILT: Fri May 21 14:47:16 MST 1999
entering wfinit
[1] 28110
[2] 28111
NOTE: All parameters should be given in j h k l order.
j h and k integration time, lnr's & coadds must be identical.
Be sure to set itvoffset before using sqtv or sqiid.
Get_picture message received from Saver
number digital averages for { j h k l } set to 4 4 4 1.
Be sure to rerun settime to correct the sequence timing
Min time for j = 0.61
Min time for h = 0.61
Min time for k = 0.61
Min time for l = 0.061
L Integration Time = 0.321, L coadds = 1
JHK Integration Time = 0.321, JHK coadds = 1
Initialization Complete
[Note: at this point WILDFIRE accesses and loads the sqiid
parameter file. If the system stops here, ->[ Enter "setup sqiid" ]<-]
% setup sqiid
Min time for j = 0.61
Min time for h = 0.61
Min time for k = 0.61
Min time for l = 0.061
L Integration Time = 0.321, L coadds = 1
JHK Integration Time = 0.321, JHK coadds = 1
seq
Stopped.
here
0 128 256 384 512 640 768 896 1024 1152 1280 1408
1536 1664 1792 1920 2048 2176 2304 2432 2560
Min time for j = 0.61
Min time for h = 0.61
Min time for k = 0.61
Min time for l = 0.061
running
Please wait while voltages are set ...
setting VddCl1
Array 0, VddCl1 0 set to -1.306
Array 1, VddCl1 0 set to -1.319
Array 2, VddCl1 0 set to -1.323
Array 3, VddCl1 0 set to -1.300
setting VddCl2
Array 0, VddCl2 0 set to -3.518
Array 1, VddCl2 0 set to -3.551
Array 2, VddCl2 0 set to -3.576
Array 3, VddCl2 0 set to -3.513
setting VggCl1
Array 0, VggCl1 0 set to -4.881
Array 1, VggCl1 0 set to -4.870
Array 2, VggCl1 0 set to -4.892
Array 3, VggCl1 0 set to -4.921
setting VggCl2
Array 0, VggCl2 0 set to -2.785
Array 1, VggCl2 0 set to -2.797
Array 2, VggCl2 0 set to -2.786
Array 3, VggCl2 0 set to -2.791
setting VSet
Array 0, VSet 0 set to -1.784
Array 1, VSet 0 set to -1.790
Array 2, VSet 0 set to -1.810
Array 3, VSet 0 set to -1.816
Do you want to activate the array? (y or [n]) y
->[ Enter "y" ]<-
[Note: "n" is the safe value. However, one must type "y" to get the
arrays properly activated. The detector biases may vary from those indicated]
Array 1, Detector Bias 0 set to 0.575
Array 2, Detector Bias 0 set to 0.681
Array 0, Detector Bias 0 set to 0.571
Array 3, Detector Bias 0 set to 0.589
The arrays are now activated
Parameter files
->[ Enter "puse my_set" ]<-.
->[ Enter "plist" ]<-.
% plist
Title
Number of coadds 1 1 1 1
Number of lnrs 1 1 1 1
Number of pictures 1
Integration time (seconds) 0.321 0.321 0.321 0.321
Filename template a%03d%s
Header Directory /data2/2meter
Pixel Directory /data2/2meter/pixels
Process mode stare stare stare stare
Picture index 0 0 0 0
Microcode sqiid4d_2231_01
Channels to display
RA of object 0:00:00
DEC of object 0:00:00
EPOCH of object 1950
Observation offset 0
Image type object
Current airmass 1
Comment none
Image name list file /tmp/list
Header Var 1
Header Var 2
Header Var 3
Header Var 4
Channels to save j h k l
Channels to archive j h k l
->[Enter "eask" ]<-.
In this exchange "l" corresponds to list and "la" corresponds to list and ask during the "ask"
sequence. Representative choices are given below.
% eask
List/Ask params(title): [l] la
List/Ask params(coadds): [l]
List/Ask params(lnrs): [l]
List/Ask params(pics): [l]
List/Ask params(integration_sec): [la]
List/Ask params(filename): [la]
List/Ask params(header_dir): [la]
List/Ask params(pixel_dir): [la] l
List/Ask params(mode): [l]
List/Ask params(pic_num): [la]
List/Ask params(ucode): [l]
List/Ask params(display): [l]
List/Ask params(ra): [l]
List/Ask params(dec): [l]
List/Ask params(epoch): [l]
List/Ask params(offset): [l]
List/Ask params(type): [l]
List/Ask params(airmass): [l]
List/Ask params(comment): [l]
List/Ask params(im_list): [l]
List/Ask params(var1): [l]
List/Ask params(var2): [l]
List/Ask params(var3): [l]
List/Ask params(var4): [l]
List/Ask params(save): [l]
List/Ask params(archive): [l]
->[ Enter "psave my_set" ]<-
% psave
WARNING: Overwriting existing file ~/wfpar/SQIID/sqiid.par
OK to proceed ? (y or [n]) y
Saving to ~/wfpar/SQIID/sqiid.par.
Setting detector bias
->[ Enter "setbias 2 0.7" ]<-
% setbias 2 0.7
% Array 2, Detector Bias 0 set to 0.681
->[ Enter "setbias j .7"
Enter "setbias h .7"
Enter "setbias k .7"
Enter "setbias l .9" ]<-
Appendix IX: Installation Issues
Interim notes for operation at the 2.1-m telescope
Initializing the Environment with OBSINIT
First Night of SQIID Block
After rebooting, the UNIX login prompt "[hostcomputer] login:" will appear; IGNORE THIS.
After a few seconds, OpenWindows will automatically load and present the
login window shown below:
Normal WILDFIRE Startup
The Windows
Bringing up WILDFIRE
Checking system noise