taken from STScI Newsletter 1992, 9, No. 2, p. 19. UPDATES TO HST STANDARD STAR FLUXES Ralph Bohlin and Don Lindler Space Telescope Science Institute Instrument Science Report on Standard Calibration Sources 001 July 1992 As part of an ongoing effort to develope a thoroughly checked and consistent set of reference spectrophotometry from 1050 to 10000A, the composite stellar spectra that are used for the fundamental flux standards for HST calibrations have been updated. See Appendix B of the HST Cycle 1 Calibration Plan, version 1.0 of 1990 May for additional documentation. These data are in an STScI data base named CRCALSPEC and have been divided into two categories to help the user understand the origin and accuracy of these flux distributions. The Category 1 HST standard star flux tables listed below were redelivered on June 24, 1992. Standard stars are classified as Category 1, if both IUE (Bohlin et al. 1990, ApJ Suppl, 73, 413) and Oke (1990, AJ, 99, 1621) spectra are available. Oke (1990) used the Double Spectrograph on the 5 m Hale Telescope to obtain these spectra for HST calibration; and these data are identified in the HST data bases by the keyword OBSMODE=OKE DBSP. Also listed are the Category 2 flux tables, some of which were last updated in August, 1991. Category 2 standard stars do not have Oke DBSP data and should not be used for HST calibrations longward of the IUE cutoff. Three additional flux tables, installed into the ST ScI CRCALSPEC data base in August 1989, are 10-LAC_001.TAB, ETA-AUR_001.TAB, and LAM-LEP_001.TAB. These three stars are not HST flux standards and their pedigree is unknown. ----------------------------------- | Category 1 Standard Star Tables | ----------------------------------- Summary of changes for the June 24, 1992 delivery: 1) Replace any Oke Literature, Stone, or Model data with the available Oke DBSP data between 3200 and 8800 Angstroms. 2) Oke DBSP flux values are decreased by 0.04 magnitude units. (note: HZ44 already had the adjustment since 1990 Mar 7.) 3) The long wavelength cutoff for Oke has been increased to 8800 Angstroms in all cases. We chose 8800 Angstroms to retain the the data for the Paschen jump at 8200 Angstroms and to avoid the second order contamination reported by Oke above 8800 Angstroms. 4) Statistical errors less than 0.0005 magnitude units were rounded to 0.0 on the tape delivered by Oke and were propagated as NULL into CRCALSPEC. These 0.0 values are changed to 0.0005 magnitudes, while interpolated data are distinguished as NULL statistical errors. 5) In the following wavelength regions, Oke (1990) has supplied interpolated data. 5150 - 5210 Angstroms 6846 - 6950 7550 - 7690 The statistical errors for the interpolated regions are set to NULL: The interpolated regions can be distinquished from model data, which have both the statistical error and the FWHM set to NULL. 6) All wavelengths above 2000 Angstroms are converted from air to vacuum. 7) All model data are extracted from the previous CALSPEC data set for each star. Scale factors are applied to the model data above 8800A to make the average flux in the model equal to the average flux observed by Oke in the 8500-8800A wavelength region. 8) Scale factors applied to the VOYAGER data are the same as in the previous delivery of Aug 1, 1991 and match the VOYAGER to the IUE flux levels. 9) The new CALSPEC data sets have flux units of FLAM in erg s^-1 cm^-2 A^-1 instead of STMAG. The following table gives the source of the data for each wavelength region of the new CALSPEC data sets. The wavelength ranges are for the source data set and are given in air above 2000 A. MODEL data were computed by the model atmosphere program XCAL by Keith Horne. ---------------- ----- ------- ------ Wavelength Range SCALE OBSMODE SOURCE ---------------- ----- ------- ------ AGK+81D266_003.TAB 970.0 1155.0 0.9200 VOYAGER2 CALOBS:AGK_81D266_003.TAB 1155.0 3200.0 1.0 IUE CALOBS:AGK_81D266_005.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:AGK_81D266_006.TAB 8800.0 12000.0 0.9386 MODEL CALSPEC:AGK_81D266_002.TAB BD+28D4211_003.TAB 970.0 1155.0 0.9600 VOYAGER2 CALOBS:BD_28D4211_007.TAB 1155.0 3200.0 1.0 IUE CALOBS:BD_28D4211_012.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:BD_28D4211_017.TAB 8800.0 12000.0 0.9879 MODEL CALSPEC:BD_28D4211_002.TAB BD+33D2642_002.TAB 970.0 1155.0 1.0 MODEL CALSPEC:BD_33D2642_001.TAB 1155.0 3200.0 1.0 IUE CALOBS:BD_33D2642_008.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:BD_33D2642_012.TAB 8800.0 12000.0 0.9769 MODEL CALSPEC:BD_33D2642_001.TAB BD+75D325_003.TAB 970.0 1155.0 0.8000 VOYAGER2 CALOBS:BD_75D325_004.TAB 1155.0 3200.0 1.0 IUE CALOBS:BD_75D325_006.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:BD_75D325_007.TAB 8800.0 12000.0 0.9497 MODEL CALSPEC:BD_75D325_002.TAB FEIGE110_003.TAB 970.0 1155.0 1.0 VOYAGER2 CALOBS:FEIGE110_016.TAB 1155.0 3200.0 1.0 IUE CALOBS:FEIGE110_012.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:FEIGE110_015.TAB 8800.0 12000.0 0.9535 MODEL CALSPEC:FEIGE110_002.TAB FEIGE34_003.TAB 970.0 1155.0 1.0 VOYAGER2 CALOBS:FEIGE34_016.TAB 1155.0 3200.0 1.0 IUE CALOBS:FEIGE34_013.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:FEIGE34_015.TAB 8800.0 12000.0 1.0224 MODEL CALSPEC:FEIGE34_002.TAB G191B2B_003.TAB 970.0 1155.0 0.8900 VOYAGER2 CALOBS:G191B2B_011.TAB 1155.0 3200.0 1.0 IUE CALOBS:G191B2B_014.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:G191B2B_015.TAB 8800.0 12000.0 0.9761 MODEL CALSPEC:G191B2B_002.TAB G93-48_002.TAB 970.0 1155.0 1.0 MODEL CALSPEC:G93-48_001.TAB 1155.0 1190.0 1.0 IUE CALOBS:G93-48_003.TAB 1190.0 1230.0 1.0 MODEL CALSPEC:G93-48_001.TAB 1230.0 3200.0 1.0 IUE CALOBS:G93-48_003.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:G93-48_005.TAB 8800.0 12000.0 1.0377 MODEL CALSPEC:G93-48_001.TAB GD108_003.TAB 970.0 1155.0 1.0 MODEL CALSPEC:GD108_002.TAB 1155.0 3200.0 1.0 IUE CALOBS:GD108_007.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:GD108_008.TAB 8800.0 12000.0 0.9777 MODEL CALSPEC:GD108_002.TAB GD50_002.TAB 970.0 1155.0 1.0 MODEL CALSPEC:GD50_001.TAB 1155.0 3200.0 1.0 IUE CALOBS:GD50_008.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:GD50_009.TAB 8800.0 12000.0 1.0176 MODEL CALSPEC:GD50_001.TAB GRW+70D5824_003.TAB 970.0 1175.0 1.0 MODEL CALSPEC:GRW_70D5824_002.TAB 1175.0 1190.0 1.0 IUE CALOBS:GRW_70D5824_006.TAB 1190.0 1230.0 1.0 MODEL CALSPEC:GRW_70D5824_002.TAB 1230.0 3200.0 1.0 IUE CALOBS:GRW_70D5824_006.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:GRW_70D5824_008.TAB 8800.0 12000.0 1.1015 MODEL CALSPEC:GRW_70D5824_002.TAB HD93521_003.TAB 970.0 1135.0 1.0 VOYAGER2 CALOBS:HD93521_006.TAB 1155.0 3200.0 1.0 IUE CALOBS:HD93521_008.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:HD93521_010.TAB 8800.0 12000.0 1.0023 MODEL CALSPEC:HD93521_002.TAB HZ21_003.TAB 970.0 1155.0 1.0 MODEL CALSPEC:HZ21_002.TAB 1155.0 3200.0 1.0 IUE CALOBS:HZ21_009.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:HZ21_011.TAB 8800.0 12000.0 0.9859 MODEL CALSPEC:HZ21_002.TAB HZ2_003.TAB 970.0 1155.0 1.0 MODEL CALSPEC:HZ2_002.TAB 1155.0 1200.0 1.0 IUE CALOBS:HZ2_009.TAB 1200.0 1225.0 1.0 MODEL CALSPEC:HZ2_002.TAB 1225.0 3200.0 1.0 IUE CALOBS:HZ2_009.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:HZ2_010.TAB 8800.0 12000.0 1.2787 MODEL CALSPEC:HZ2_002.TAB HZ44_003.TAB 970.0 1155.0 1.0 VOYAGER2 CALOBS:HZ44_010.TAB 1155.0 3200.0 1.0 IUE CALOBS:HZ44_012.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:HZ44_014.TAB 8800.0 12000.0 0.9724 MODEL CALSPEC:HZ44_002.TAB HZ4_002.TAB 970.0 1300.0 1.0 MODEL CALSPEC:HZ4_001.TAB 1300.0 3200.0 1.0 IUE CALOBS:HZ4_013.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:HZ4_015.TAB 8800.0 12000.0 1.0054 MODEL CALSPEC:HZ4_001.TAB LB227_002.TAB 970.0 1250.0 1.0 MODEL CALSPEC:LB227_001.TAB 1250.0 3200.0 1.0 IUE CALOBS:LB227_003.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:LB227_004.TAB 8800.0 12000.0 1.0478 MODEL CALSPEC:LB227_001.TAB LDS749B_003.TAB 970.0 1249.0 1.0 MODEL CALSPEC:LDS749B_002.TAB 1250.0 3200.0 1.0 IUE CALOBS:LDS749B_003.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:LDS749B_007.TAB 8800.0 12000.0 1.1061 MODEL CALSPEC:LDS749B_002.TAB NGC7293_003.TAB 970.0 1155.0 1.0 VOYAGER2 CALOBS:NGC7293_002.TAB 1155.0 3200.0 1.0 IUE CALOBS:NGC7293_004.TAB 3200.0 8800.0 1.0 Oke DBSP CALOBS:NGC7293_006.TAB 8800.0 12000.0 0.9446 MODEL CALSPEC:NGC7293_002.TAB The CALSPEC and CALOBS data sets are located in the following directories on the STScI science cluster: CALSPEC: DISK$REFERENCE:[CDBSDATA.REFER.CALSPEC] CALOBS: DISK$REFERENCE:[CDBSDATA.REFER.CALOBS] ----------------------------------- | Category 2 Standard Star Tables | ----------------------------------- Category 2 flux tables are not recommended for HST calibration longward of the IUE limit. Some of these tables were redelivered on Aug 1, 1991 to: 1) Replace model data with VOYAGER2 data shortward of 1155 Angstroms. 2) Scale the VOYAGER2 or Model data to improve the match with IUE. 3) Adjust the short wavelength IUE wavelength cutoff. 4) Replace OAO-2 data in ZETA-CAS with IUE data. Category 2 flux tables are listed below along with their installation dates. ---------------- ----- ------- ------ Wavelength Range SCALE OBSMODE SOURCE ---------------- ----- ------- ------ ALPHA-LYR_001.TAB 4-Oct-1989 500.0 1170.0 1.0 MODEL 1170.0 3100.0 1.0 IUE CALOBS:ALPHA-LYR_010.TAB 3100.0 12000.0 1.0 MODEL BPM16274_001.TAB 2-Aug-1989 500.0 1160.0 1.0 MODEL 1160.0 1200.0 1.0 IUE CALOBS:BPM16274_002.TAB 1200.0 1225.0 1.0 MODEL 1225.0 3150.0 1.0 IUE CALOBS:BPM16274_002.TAB 3150.0 12000.0 1.0 MODEL ETA_UMA_002.TAB 1-Aug-1991 925.0 1155.0 0.9000 VOYAGER2 CALOBS:ETA-UMA_011.TAB 1155.0 3200.0 1.0 IUE CALOBS:ETA-UMA_012.TAB 3200.0 12000.0 1.0 MODEL GAMMA-UMA_001.TAB 2-Aug-1989 500.0 1200.0 1.0 MODEL 1200.0 3200.0 1.0 IUE CALOBS:GAMMA-UMA_003.TAB 3200.0 12000.0 1.0 MODEL HD49798_002.TAB 1-Aug-1991 900.0 1155.0 1.0 VOYAGER2 CALOBS:HD49798_004.TAB 1155.0 3200.0 1.0 IUE CALOBS:HD49798_003.TAB 3200.0 12000.0 1.0 MODEL HD60753_002.TAB 1-Aug-1991 500.0 1155.0 1.3400 MODEL CALSPEC:HD60753_001.TAB 1155.0 3200.0 1.0 IUE CALOBS:HD60753_002.TAB 3200.0 12000.0 1.0 MODEL MU-COL_002.TAB 1-Aug-1991 900.0 1155.0 1.0 VOYAGER2 CALOBS:MU-COL_003.TAB 1155.0 3100.0 1.0 IUE CALOBS:MU-COL_004.TAB 3100.0 12000.0 1.0 MODEL ZETA_CAS_002.TAB 1-Aug-1991 925.0 1155.0 1.0 VOYAGER2 CALOBS:ZETA-CAS_005.TAB 1155.0 3200.0 1.0 IUE CALOBS:ZETA-CAS_001.TAB 3200.0 4000.0 1.0 MODEL 4000.0 6500.0 1.0 STONE CALOBS:ZETA-CAS_006.TAB 6500.0 12000.0 1.0 MODEL FUTURE WORK Without the complications of an intervening atmosphere, more accurate relative spectrophotometry should be possible with FOS than has been previously achieved over the wavelength range 1150-8500A. Therefore, a possible Category 3 of reference spectrophotometry could be created from HST observations of standard stars after the absolute calibration of FOS is fully characterized. Furthermore, the time may be ripe to include the adjustment of the IUE absolute scale to the white dwarf flux standard, as proposed by D. Finley and others.