A Quick Guide to CCD Imaging at the OAN/SPM Alan Watson & Michael Richer August 2004 Contents Planning Your Observations 2 Telescopes 2 CCDs 2 Filter Wheels, Filters, and Focal Reducers 2 Computers 2 Estimating Performance 3 Observing 5 Simple Rules for Happy Observing 5 Start-of-Night Check List 5 End of Night Check List 6 Planning Your Observations Telescopes Table 1 summarizes of the characteristics of the telescopes. Note that all of the telescopes have restricted northern declination limits. All of the telescopes have finders equiped with video cameras and guiders. The two smaller telescopes are generally operated by the observer. The control program is simple to use. See the WWW page of the OAN/SPM for more details of the telescope optics and manuals for the control programs and guiders. CCDs Table 2 summarizes of the characteristics of the CCDs. The Thomson is awful. The Marconi is hot in U and B, the SITe3 and Marconi have fringes in I, but otherwise there is not too much difference between the two SITe CCDs and the Marconi. Note that the observatory will often restrict the use of CCDs to certain telescopes; see the call for proposals. There is an program of CCD characterization every fall that measures zero points, gain, read noise, and linearity. The SITe and Thomsons CCDs are controlled using a comercial program called PMIS. The Marconi is controlled using with a program written at the OAN. See the WWW page of the OAN/SPM for the report of the latest characterization run and the manuals for the control programs. Filter Wheels, Filters, and Focal Reducers The filter wheels are summarized in Table 3. The observatory doesn't like to move filter wheels unless there is a scientific reason, so you're most likely to get the Mexman at the 84-cm, the Ruca at the 1.5-m, and either the Mexman or the Italiana at the 2.1-m. The complement of filters in the Italiana are fixed. Johnson-Cousins UBV RI, Stromgren-Crawford uvbyBeta, Thuan-Gunn uvgriz, and nebular filters are available for use with the other filter wheels. See the WWW page of the OAN/SPM for filter curves and manuals for the filter wheels. Computers The telescope and ancillary equipment is controlled from a Linux computer. The CCD is controlled either from the same Linux computer or from a Windows computer. IRAF is installed on the Linux computer to allow you to quick-look your data. There is another Linux computer available with IRAF for more detailed reduction. Data can be transfered to an anonymous FTP area on haro.astrossp.unam.mx or be written to CD-ROMs. Estimating Performance If you're working in UBV RI, you're in luck; there is a simulator. If you're working with other broadband filters, you could try scaling from the simulator. If you're working with narrow band filters, you'll probably have to use the approximate zero-points given the reports of the CCD charaterization runs. See the WWW page of the OAN for the broad-band simulator, filter curves, and the report of the CCD characterization run. Table 1: Telescope Summary ======================================================= Telescope f/ dec Limits HA Limits ======================================================= 84-cm 15 -45. <= d <= +65. -5.0 <= HA <= +5.0 1.5-m 13.5 -40. <= d <= +59. -5.0 <= HA <= +5.0 2.1-m 7.5 -40. <= d <= +69. -5.5 <= HA <= +5.5 Table 2: CCD Summary ====================================================================== CCD SITe1 SITe3 Marconi Thomson ====================================================================== Size 25mm 25mm 28mm 31mm Format 1024 x 1024 1024 x 1024 2048 x 2048 2048 x 2048 QE in U Good Okay Excellent Poor QE in BVR Good Good Good Good QE in I Good Good Okay Okay Read noise Okay Okay Good Good Non-linearity < 1% < 1% < 1% 3% Fringes None in I in I in VRI Read time Fast Okay Fast Slow Normally used at 1.5-m/84-cm 2.1-m 1.5-m anywhere Table 3: Filter Wheel Summary ================================================================ Mexman Ruca Italiana ================================================================ 84-cm yes possibly no 1.5-m no yes no 2.1-m yes no yes Filter size 50-mm round 50-mm square or round 50-mm round Number 14 8 10 Focal reducer x 1.5 x 1.6 at 84-cm only no Observing Simple Rules for Happy Observing * Plan your observations. Arrive at the observatory having read the manuals, with coordinates and finding charts for your objects and standards, and knowing what filters you wish to use. * Remember to fill the dewar as needed. * Make sure the fans are on and the doors open or closed as appropriate. * Close when the humidity gets to 85% or when there is condensation on metal surfaces. * Check the focus after every image. IMEXAM is your friend. * Carefully center your object before looking for guide stars. * Correct the telescope coordinates after centering an object and before moving to a new one. * Back up your data onto haro.astrossp.unam.mx at the end of each night. Start-of-Night Check List This check list applies to the 84-cm and 1.5-m only; at the 2.1-m the telescope operator handles start-of-night activities. * Check that the fan in the the observing room is on. It should be left on permanently. * 84-cm only: Check that the fan in the communications room is on. It should be left on permanently. * Turn on the telescope console. Wait 3 minutes then turn on the motors and fans. Start the telescope control program. * Open the dome. Remove the covers for the two finders. * 84-cm only: Turn on the mirror cell fans. Open the two doors to the balcony. * 1.5-m only: Open the two doors to the north. * Move the telescope to the south. * Remove the telescope cover. * Now is a good time to fill and take twilight flats. * Start the finder control program. Turn on automatic dome movement and tracking. Move to a first magnitude star. Center the star in the video camera. If you can't find the star, center it first using the small finder. Correct the telescope coordinates. * Move the a sixth magnitude star. Center it on the CCD and focus roughly. Correct the telescope coordinates. * Start the guider control program and turn on the guider intensifier. Select the center. Insert the mirror. Center and focus the star. Define the center. Remove the mirror. End of Night Check List This check list applies to the 84-cm and 1.5-m only; at the 2.1-m the telescope operator handles end-of-night activities. * Remove the guider mirror, turn off the guider intensifier, and stop the guider control program. * Stop the finder control program. * Now is a good time to take twilight flats. * Move to the zenith. Replace the covers on the finders. * 84-cm only: Turn off the fans on the mirror cell. * Move to the south. * Replace the cover on the telescope. Close the dome. * Now is a good time to fill the dewar. * Move the the zenith. Stop the telescope control program. Turn off the fans, motors, and console. * Leave the building fans on.