NSSDC/WDC-A-R&S 83-02 DOCUMENTATION FOR THE MACHINE-READABLE VERSION OF THE STELLAR SPECTROPHOTOMETRIC ATLAS, 3130 - 10800 A OF GUNN AND STRYKER (1983) Wayne H. Warren Jr. March 1983 (Revision 1, November 1984) National Space Science Data Center (NSSDC)/ World Data Center A for Rockets and Satellites (WDC-A-R&S) National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 DOCUMENTATION FOR THE MACHINE-READABLE VERSION OF THE STELLAR SPECTROPHOTOMETRIC ATLAS, 3130 - 10800 A OF GUNN AND STRYKER (1983) ABSTRACT A detailed description of the machine-readable version of the Atlas as it is currently being distributed from the Astronomical Data Center is given. The data were obtained with the Oke multichannel scanner on the 5-meter Hale re- flector for purposes of synthesizing galaxy spectra, and the digitized atlas contains normalized spectral energy distributions, computed colors, scan line and continuum indices for 175 selected stars covering the complete ranges of spectral type and luminosity class. The documentation includes a byte-by-byte format description, and a table of the indigenous characteristics of the machine-readable file. ii TABLE OF CONTENTS Section 1 - INTRODUCTION AND SOURCE REFERENCE ....................... 1-1 Section 2 - FILE CONTENTS ........................................... 2-1 Section 3 - FILE CHARACTERISTICS .................................... 3-1 Section 4 - REMARKS, ACKNOWLEDGMENT AND REFERENCE ................... 4-1 LIST OF TABLES Table 1 File Contents .................................................. 2-1 2 File Characteristics ........................................... 3-1 iii SECTION 1 - INTRODUCTION AND SOURCE REFERENCE The machine-readable version of the Stellar Spectrophotometric Atlas, 3130 - 10800 A contains normalized spectral energy distributions for 175 selected stars. The data were obtained for purposes of synthesizing galaxy spectra, but may be generally useful for other applications (although the source reference should be consulted prior to using the data). This document describes the machine version of the atlas as it is currently being distributed from the Astronomical Data Center. It is intended to enable users to read and process the data without problems or guesswork. For additional information concerning the observations, data reductions, accuracy and limitations, computation of the scanner colors, and for graphical representation of the scans, the user should refer to the source reference (Gunn and Stryker 1983). A copy of this document should accompany any machine-readable copy of the catalog. SOURCE REFERENCE Gunn, J. E. and Stryker, L. L. 1983, Astrophys. J. Suppl. 52, 121. 1-1 SECTION 2 - FILE CONTENTS The machine-readable Stellar Spectrophotometric Atlas, 3130 - 10800 A file consists of groups of logical records for each star. There are 175 groups of 142 logical records each, with a group consisting of two header records followed by 140 data records. Since all record groups are identical in format, Table 1 contains byte-by-byte descriptions of the two header records only, followed by a general description of the data records. For more detailed information on the data in the header records, the source paper should be consulted. Table 1. File Contents. Stellar Spectrophotometric Atlas. Suggested Byte(s) Units Format Description Record 1 -------- 1- 4 --- I4 Sequential number from 1 to 175. 5-64 --- 15A4 or equivalent. Star identification, spectral type and other miscellaneous information entered or taken at the telescope: AV = visual absorption; AP = aperture size; G, R, B = green, red, and blue filters; plus codes for object and day of the observing run. The AV values given in bytes 73-80 should be used rather than the reference values given here. 65-72 mag F8.3 V magnitude, as calculated in the scan reductions. Although these data are recorded to a precision of 0.001 mag, they are accurate only to 0.1 mag. 73-80 mag F8.3 Visual absorption, AV, as calculated in the scan reductions. The thousandths column (always zero) is insignificant. Record 2 -------- 1- 7 mag F7.3 U-B color as found from the scan (the scans were convolved with the standard filter functions to determine the colors). 8-14 mag F7.3 B-V scan color. 2-1 Table 1 (concluded) Suggested Byte(s) Units Format Description 15-21 mag F7.3 V-R scan color. 22-28 mag F7.3 R-I scan color. 29-35 --- F7.3 An approximation to the airmass (the actual quantity is sec z) at mid-observation. 36-56 --- 3F7.3 (21X) Internal data used for plotting purposes. 57-63 rad F7.3 Right ascension (1950) taken from various sources. 64-70 rad F7.3 Declination (1950) taken from various sources. 71-80 --- F10.3 The cosecant of the Galactic latitude b. 2-2 Records 3-142 The data records contain three arrays of data, as described below: Array 1: Flux (K), K = 1, 509, the normalized fluxes at 509 wavelengths. Elements 1-3, 507-509 always zero. Energy distribution data are given per unit frequency interval, 1/Lambda, at each wavelength. Array 2: Sigma (K), K = 1, 509, the flux error estimates at the 509 wavelengths. Elements 1-3, 507-509 always zero. Array 3: XBL (K), K = 1, 102, miscellaneous data. Element 1 contains an internal tape number, element 2 contains 777. if variable atmospheric cycles have been removed (see Gunn and Stryker 1983, section II); otherwise zero. Element 3 contains 888. if reddening problems were encountered (see Gunn and Stryker 1983); otherwise zero. Elements 4-10 are zero, while elements 11-28 contain the scan "continuum" colors: 33-37, 37-40, 40-46, 46-V, V-70, 70-87, 87-99 and the feature indices: Balmer break, CN38+, 41-42, Ca H, Ca K, Ti61+, Ti71+, Ca42, CH43, Mg51 and Na D, respectively. Elements 29-102 are zero. The elements of the three arrays are located in contiguous positions starting at the beginning of record 3. A sample FORTRAN statement to read a complete group of records for a star from unit 1 might be: READ (1,100) ID,(AL(K),K=1,15),V,VA,(BBCOL(K),K=1,4), (STUFF(K),K=1,7),(F(K),K=1,509),(S(K),K=1,509),(XBL(K),K=1,102) 100 FORMAT (I4,15A4,2F8.3 / 10F7.3,F10.3 / (8E10.3)) It is important to note and take into consideration the fact that the wave- length increment changes from the blue to the red; thus, in order to assign wavelength values to the fluxes and their errors, the following algorithm should be used: DIMENSION LAMBDA(509) DO 1 I=1,262 1 LAMBDA(I) = 3130 + 10 * (I-1) DO 2 I=263,509 2 LAMBDA(I) = 5740 + 20 * (I-262) 2-3 SECTION 3 - FILE CHARACTERISTICS The information contained in Table 2 is sufficient for a user to describe the indigeneous characteristics of the machine-readable Stellar Spectrophotometric Atlas to a computer. Information easily varied from installation to installation, such as block size (physical record length), blocking factor (number of logical records per physical record), total number of blocks, tape density, number of tracks, and internal coding (EBCDIC, ASCII, etc.) is not included, but should always accompany secondary copies if any are supplied to other users or installations. Table 2. File Characteristics. Stellar Spectrophotometric Atlas. NUMBER OF FILES ................................................... 1 LOGICAL RECORD LENGTH (BYTES) ..................................... 80 RECORD FORMAT ..................................................... Fixed TOTAL NUMBER OF LOGICAL RECORDS ................................... 24850 3-1 SECTION 4 - REMARKS, ACKNOWLEDGMENT AND REFERENCE The magnetic tape version of the Stellar Spectrophotometric Atlas was received from Dr. L. L. Stryker of the Dominion Astrophysical Observatory on 21 October 1982. A brief description of the format was supplied with the tape, the latter being written with 84-byte logical records having the digits "0084" in bytes 1-4 of each record. The atlas was transferred to disk storage and changed to 80-byte logical records by elimination of the "0084". A computer program to print and plot spectra from the atlas is available and can be obtained from Dr. Stryker. An error in the name identification for star number 115 has been found and transmitted by Dr. Stryker: HD 113439 should be HD 113493. The error has not been corrected in the machine-readable version. ACKNOWLEDGMENT Appreciation is expressed to Dr. Linda L. Stryker for supplying the original magnetic tape of the atlas, for sending a preprint of the published paper, and for replying quickly in response to questions about the format description. Dr. Stryker kindly reviewed the completed document. REFERENCE Gunn, J. E. and Stryker, L. L. 1983, Astrophys. J. Suppl. 52, 121. 4-1