PDS_VERSION_ID = PDS3 OBJECT = DATA_SET DATA_SET_ID = "IUE-C-LWR-3-EDR-IUECDB-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "IUE LWR DATA OF COMETS" DATA_SET_TERSE_DESC = " IUE Long-Wavelength Redundant (LWR) observations of comets" DATA_SET_COLLECTION_MEMBER_FLG = Y START_TIME = 1978-10-15T23:38:36.000 STOP_TIME = 1983-09-07T22:39:53.000 DATA_SET_RELEASE_DATE = 2001-02-19 ABSTRACT_DESC = "This data set contains spectral observations of 18 comets obtained with the Long-wavelength redundant (LWR) spectrograph on the International Ultraviolet Explorer (IUE) satellite. Both low dispersion data from 1910-3300 A and high dispersion data from 1845-2980A (with partial coverage from 2980-3230) are included." ARCHIVE_STATUS = "LOCALLY ARCHIVED" CITATION_DESC = "Grayzeck, Edwin J. (ed.), IUE LWR Data of Comets, IUE-C-LWR-3-EDR-IUECDB-V1.0, NASA Planetary Data System, 2005." DATA_OBJECT_TYPE = IMAGE PRODUCER_FULL_NAME = "EDWIN J. GRAYZECK, JR" DETAILED_CATALOG_FLAG = N DATA_SET_DESC = " Raw Image Data and Label Parameters =================================== Each raw image consists of an array of 8-bit picture elements or 'pixels'. Each vidicon scan line consists of 768 pixels or 'samples' obtained in minor frame units of 96 pixels; 768 such scan lines compose the entire image. Line 1, sample 1 is at the upper left corner of the image; line 768, sample 768 is at the lower right corner of the image. Each raw pixel value lies in the range 0 to 255 (integers only). The units of raw pixel values are data numbers (DN), which are proportional (up to the telemetry system limit of 255) to the integrated charge read out from the SEC Vidicon target in the camera scanning process. Since the telemetry system saturates at 255, the DN/charge proportionality breaks down at that level. Associated with each raw image is a set of 20 header, or label, records. Each record is 360 8-bit bytes long (a concatenation of five 72-byte logical records). This set of 20 label records is generated by the Operations Control Center (OCC) software during image acquisition and contains various identifying parameters and scientific/engineering data pertinent to the image. Raw images must be corrected for the instrumental effects of the SEC Vidicon camera system before quantitatively meaningful data can be extracted from them. The methods of compensation for the radiometric (photometric) non-linearities and non-uniformities and the geometric distortion introduced by the vidicon system are described in the NEWSIPS Manual, Chapters 5 - 11(Garhart et al., 1997 [GARHARTETAL1997]). In addition, figures 2.1-15 of the same manual illustrate schematically the spectral formats in both dispersion modes, for both apertures and for all operational cameras. IUE Final Archive Data Products for Comets ====================================================== The output files for the IUE Final Archive are fundamentally different from those produced by IUESIPS, both in content and format. They are based on the Flexible Image Transport System (FITS) format (NOST 1995) and incorporate the FITS binary table extensions (NOST 1995) and FITS image extensions (Ponz, Thompson, and Munoz 1994). Although some FITS reading routines may not yet support these new FITS extensions, it was felt that there was no convenient alternative FITS format available for storing IUE data. Note that only those features included in the basic binary table proposal (i.e., excluding the conventions described in the appendices of the proposal) have been used in the Final Archive file formats. The formats described below (as originally described in DCG 1995) have been approved by the IUE Three Agencies as well as the NOST FITS Support Office. --------------------------------------------------------------------------- * IUE Filename Conventions * Resampled Low Image (SILO) * Resampled High Image (SIHI) * Extracted Low-Dispersion Spectra (MXLO) * Extracted High-Dispersion Spectra (MXHI) --------------------------------------------------------------------------- IUE Filename Conventions ======================== The basic FITS keywords define the structure and content of the files. These basic keywords include both the required FITS keywords and, when appropriate, certain optional reserved FITS keywords. A project-defined keyword that needs to be mentioned is FILENAME. This keyword describes the camera image number and the type of data contained in the particular FITS header-and-data unit (HDU) and appears in every HDU containing data. One purpose of the FILENAME keyword is to provide users with a naming convention when separating FITS file. FILENAME is useful for verifying the contents of the various data sets. The value of the FILENAME keyword is formed by the concatenation of the following codes: * Camera: 3 letter code (LWP, LWR, SWP). * Image number: 5 digits. * File type: 2 letter code as: RI raw image RO original RI (low dispersion only, in the case of partial-read images) VD vector displacements XC binary table extension of the VD file containing the cross correlation coefficients LI linearized image LF nu flag image extension of the LI file SI resampled image WL binary table extension of the high-dispersion SI file containing spectral wavelengths and spatial centroid positions of the orders SF nu flag image extension of the high-dispersion SI file CR cosmic ray image extension of the high-dispersion SI file MX merged extracted image (large, small or both apertures) * Dispersion: 2 letter code (HI, LO). Resampled Image (SILO) ====================== The resampled low-dispersion image is an array produced by resampling the photometrically corrected portion of the LILO/LIHI image using the modified Shepard algorithm taken from the Numerical Algorithms Group (NAG) software package. Each pixel is resampled to the position determined by the summation of the vectors needed for: 1. shift to photometric correction (ITF) raw space, 2. shift from ITF space to geometrically-rectified space, 3. rotation such that orders are horizontal, 4. wavelength linearization, 5. detilting of large-aperture spectra for low-dispersion extended sources only, 6. alignment of the low-dispersion apertures for constant wavelength in the line direction, 7. adjustment so that both LW cameras provide coverage of the same spectral range, 8. adjustment to maintain the spectrum at approximately the same location in the file in the spatial direction (low dispersion only), 9. adjustment to LWP data to put the large-aperture data at the top of the file, 10. corrections for the spatial deviations (cross-dispersion wiggles) for the LWP and LWR low-dispersion data, The low-dispersion SI is stored in the SILO as a 2-D (640 samples x 80 lines) primary array, with the y coordinate in pixels and the x coordinate in in Angstroms. Each pixel represents a flux number (FN) scaled up by a factor of 32 for storage purposes. The pixels are coded as 16-bit, two's complement integers, with the bits stored in decreasing order of significance. When the image is displayed with the origin in the lower left corner, the large-aperture data appears at the top of the file and the wavelengths increase from left to right. The associated pixel quality flags are stored as an image extension which has the same dimensions as the primary array. Table 12.8 in the NEWSIPS Manual (Garhart et al., 1997 [GARHARTETAL1997]) shows the basic FITS keywords for the main header and the image extension header. High-Dispersion Resampled Image FITS File (SIHI) ================================================ The SIHI contains more information than stored in the corresponding low-dispersion file and, as a result, the FITS format is slightly more complex. Overall, the SIHI is comprised of a primary array containing the resampled image, a binary table of wavelengths and both predicted and found line positions, an image extension of nu flags, and a second image extension of background cosmic ray flags. The high-dispersion SI data is similar to the low-dispersion SI data except that the high-dispersion wavelength linearization varies with spectral order, and the entire image is stored in the primary array. Each pixel is resampled to the position determined by the summation of the vectors computed for: * shift to photometric correction (ITF) raw space, * shift from ITF space to geometrically-rectified space, * rotation such that orders are horizontal, * wavelength linearization, * adjustment to maintain the echelle orders at approximately the same locations in the file in the spatial direction, * corrections for the spatial deviations (cross-dispersion wiggles) for LWP, LWR, and SWP data, * heliocentric velocity correction, and * de-splaying correction. The high-dispersion SI is stored in the SIHI as a 2-D (768 samples 768 lines) primary array. Each pixel represents an FN scaled up by a factor of 32 for storage purposes. The pixels are coded as 16-bit, two's complement integers, with the bits stored in decreasing order of significance. When the image is displayed with the origin in the lower left corner, the short-wavelength, closely-spaced high order numbers appear at the bottom, and the long-wavelength, low order numbers appear at the top. Within each order, the wavelengths increase from left to right. Because the wavelength linearization varies with spectral order, the starting wavelength and wavelength increment values vary with each order. This information is stored in a binary table extension to the SIHI, which follows the primary array. The entire contents of the binary table extension include: * Order Number, one 8-bit integer. * Starting wavelength, one double-precision floating point number. Heliocentric velocity correction has been applied. * Wavelength increment, one double-precision floating point number. * predicted line position of order centroid, one single-precision floating point number. * line position where spectral centroid is found, one single-precision floating point number. (This is determined by the high-dispersion spectral flux extraction module and written back into the SIHI file retroactively.) The associated nu flags and cosmic ray flags are stored in the SIHI image extensions with the same dimensions and orientation as the high-dispersion SI data contained in the primary array. The pixel quality flags are stored as unscaled 16-bit integers, and the cosmic ray flags are unscaled 8-bit integers. Table 12.9 from Garhart et al. (1997) shows the basic FITS keywords for the main and extension headers for the SIHI. Extracted Low-Dispersion Spectra (MXLO) ======================================= The extracted low-dispersion file uses the binary 3-D table extension with fixed-length floating point vectors to contain the extracted fluxes and associated data quality flags. Since no primary data are included, the extension header immediately follows the primary FITS header. Each row of the binary table includes the following columns: 1. Aperture designation as 'LARGE' or 'SMALL', stored in 5 ASCII characters. 2. Number of extracted points, one 16-bit integer. The number of extracted points is 640. 3. Starting wavelength, one single precision floating point value. 4. Wavelength increment, one single precision floating point value. 5. Net flux spectrum, array with 640 single precision floating point values. 6. Background flux spectrum, array with 640 single precision floating point values. 7. Sigma vector, array with 640 single precision floating point values. 8. Data quality flags, array of 640 16-bit integers. 9. Absolutely calibrated net flux spectrum, array with 640 single precision floating point values. Wavelengths are linearly sampled, and referenced to vacuum. Double aperture low-dispersion spectra will contain two rows in the above format, with one row for each aperture. Table 12.10 in the NEWSIPS Manual (Garhart et al., 1997 [GARHARTETAL1997]) shows the basic FITS keywords for the MXLO file. Note: The keyword NAXIS1 in the table extension defines the number of bytes per row in the table. High-Dispersion Merged Extracted Image FITS File (MXHI) ======================================================= The wavelengths, nu flags, and fluxes extracted from the SIHI are stored in the MXHI as a binary table extension using fixed-length floating point vectors. No primary data or additional extensions are included. The binary table contains 17 fields of various data types. All vectors are padded with zeroes (both before and after the extracted data) to maintain a fixed length of 768 points. Wavelengths are uniformly sampled for each order, are measured in vacuum, and have had the heliocentric velocity correction applied. The width of each row (i.e., 65 + 22 * 768 = 16961) bytes, and the number of rows (i.e., NAXIS2) is equal to the number of extracted orders. In this manner, all the information pertaining to one spectral order is contained in one row of the binary table. The fields are defined in the order shown below: * Order number, one 8-bit byte. * Number of extracted points n, one 16-bit integer. * Starting wavelength, one double-precision floating point value. * Starting pixel at starting wavelength, one 16-bit integer. * Wavelength increment, one double-precision floating point value. * Slit height in pixels, one single-precision floating point number. * Line number for found centroid of spectrum, one single-precision floating point number. * Net flux spectrum, 768 single-precision floating point numbers with n extracted data points. * Background flux spectrum, 768 single-precision floating point numbers with n extracted data points. * Noise vector, 768 single-precision floating point numbers with n extracted data points. * nu flags as n 16-bit integers stored in two's complement form. * Ripple-corrected net flux spectrum, 768 single-precision floating with n extracted data points. * Absolutely-calibrated, ripple-corrected net flux spectrum, 768 single-precision floating point numbers. with n extracted data points. * Start pixel for background fit, one 16-bit integer number. * * End pixel for background fit, one 16-bit integer number. * * Chebyshev scale factor, one single-precision floating point number. * * Chebyshev polynomial coefficients for global background correction, 7 single-precision floating point numbers. * Note that unlike the MXLO, SILO, and SIHI, the starting wavelengths listed in the MXHI table do not refer to the first data point in the flux vectors, but rather the starting pixel listed in field four. In this manner, the 768-point flux vector can be mapped directly to the 768-pixel wide high-dispersion SI array. As in low dispersion, since the absolute calibration covers the range of 1150-1980 for short-wavelength spectra and 1850-3350 for long-wavelength spectra, data points outside this wavelength range are set to 0 in the absolutely-calibrated flux vector. The net, background, and noise vectors are not affected. (Note that unlike the sigma vector in the MXLO file, the MXHI noise vector is uncalibrated.) Uncalibrated data points are also flagged in the nu flag vector with a value of -2. *IMPORTANT NOTE: Several adjustments must be made to the last four parameters (fields 14-17) if the user wishes to evaluate the Chebyshev coefficients in order to reproduce the background fluxes as stored in the ninth field of the MXHI extension header. First, the parameters have inadvertently been stored in the reverse order (i.e., the parameters written in the first row of the table should have been stored in the last row, the parameters for the second row in the second to last row, etc.). So, for example, in the case of the LWR camera, the starting and ending pixels, Chebyshev scale factor, and Chebyshev coefficients found in row 1 (echelle order 127) actually pertain to row 61 (echelle order 67). Second, the true starting pixel is 768 minus the stored ending pixel and the true ending pixel is 768 minus the stored starting pixel. These true pixel values must be used to correctly evaluate the Chebyshev coefficients. Third, once the Chebyshev coefficients have been evaluated, the resultant background ``fluxes'' must be scaled in the following manner: multiply each background value by both the Chebyshev scale factor and the corresponding extraction slit height then divide this result by 32. Finally, the resultant array of background fluxes which are produced upon evaluation of the Chebyshev coefficients must be reversed (i.e., the computed background flux for pixel 1 becomes the background flux for pixel 768 and vice versa). We emphasize that these reversals and scalings are needed only when using the Chebyshev parameters in fields 14-17 to reproduce the background fluxes-the background fluxes themselves as contained in the ninth field are correct. " CONFIDENCE_LEVEL_NOTE = "N/A" END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "COMET" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "140P/BOWELL-SKIFF 1 (1980 E1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "19P/BORRELLY 1 (1904 Y2)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "22P/KOPFF 1 (1906 Q1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "26P/GRIGG-SKJELLERUP 1 (1922 K1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "2P/ENCKE 1 (1818 W1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "38P/STEPHAN-OTERMA 1 (1942 V1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "67P/CHURYUMOV-GERASIMENKO 1 (1969 R1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "6P/D'ARREST 1 (1851 M1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "8P/TUTTLE 1 (1858 A1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "9P/TEMPEL 1 (1867 G1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/AUSTIN (1982 M1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/BRADFIELD (1979 Y1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/CERNIS (1983 O1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/IRAS-ARAKI-ALCOCK (1983 H1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/MEIER (1980 V1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/PANTHER (1980 Y2)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/SEARGENT (1978 T1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "C/SUGA-SAIGUSA-FUJIKAWA (1983 J1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_MISSION MISSION_NAME = "INTERNATIONAL ULTRAVIOLET EXPLORER" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "IUE" INSTRUMENT_ID = "LWR" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "BOGGESSETAL1978B" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "GARHARTETAL1997" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END