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CALSPEC: 2004 June 15
CALSPEC contains the composite stellar spectra that are the fundamental flux standards for HST calibrations. All files are in machine independent binary FITS table format. Information about the pedigree of a given spectrum is in the header of the FITS table file, which can be read with the IRAF hedit task or by mrdfits.pro in IDL.
The Table below summarizes the set of recommended standard star spectra. Columns 2 and 3 give the V and B magnitudes of the stars. More documentation on these stars, eg. coordinates, finding charts and spectral types can be found in Turnshek et al. (1990), Bohlin, Colina & Finley (1995), and Colina & Bohlin (1997). Column 4 is the computer compatible file name with the plus and minus signs converted to underscores. Thus, the actual CALSPEC file name is the prefix in column 4, plus one of the suffixes in columns 5-8, plus ".fits". For example, a standard that has STIS data is "bd_28d4211_stis_001.fits".
The pure hydrogen WD model LTE spectra of Bohlin (2000) are now Hubeny NLTE models calculated with his Tlusty code (Bohlin 2003). These fundamental primary standards GD71, GD153, and G191B2B are listed by Calibration Data Base System (CDBS) suffix in column 5 of the Table and provide the basis for the secondary flux standards. The observational spectra from columns 6-8 can be compared with the models; and in the case of G191B2B, there is ultraviolet line blanketing at the ~1 percent level. The model calculations extend to 30 microns and cover the long wavelength limits of 2.7 microns for NICMOS, 1.1 microns for STIS and ACS, and 27 microns for JWST. Vega was observed by STIS (Bohlin & Gilliland 2004a); and the new composite flux standard alpha_lyr_stis_002.fits consists of IUE data from 1256-1675A, STIS CCD fluxes from 1675-4200A, and a specially tailored Kurucz model longward of 4200A (Kurucz 2003) and from 900-1256A. The STIS and ACS observations of the SDSS standard BD+17d4708 are documented in Bohlin & Gilliland (2004b).
Column 6 lists the 20 CDBS suffix names for the second choice standard stars with STIS data from Bohlin, Dickinson, & Calzetti (2001). Tabulated in column 7 are the next best standard star flux distributions, which are composed of FOS spectra in the UV and Oke spectra at the longer wavelengths. Also appearing in column 7 are the three solar analogs that are comprised of FOS observation but do not have "_FOS" in the CALSPEC file name.
The names for the last, but largest, set of standard stars appear in column 8 of the Table. The application of corrections to the original IUE and optical fluxes produces a consistent set of spectrophotometric standards from 1150 to 9200A (Bohlin 1996 and references therein). This set of standards is composed of IUE+Oke data only.
CALSPEC also contains the ultraviolet to near-infrared absolute flux distribution of the Sun (filename: sun_reference_stis_001.fits) to 2.7 microns, which is used to model the IR spectrum of the three solar analog stars. The solar reference spectrum combines absolute flux measurements from satellites and from the ground with a model spectrum for the near-infrared (Colina, Bohlin, & Castelli 1996).
The order of preference for the choice of a standard flux distribution is from left to right in the Table, i.e. from the best in column 5 to the last choice with the lowest quality in column 8.
CDBS Files of the Flux Standards with Columns in Order of Preference(1) ------------------------------------------------------------------------------- Star name V B-V CDBS name Model STIS FOS+Oke IUE+Oke (1) (2) (3) (4) (5) (6) (7) (8) AGK+81D266 11.94 -0.34 AGK_81D266 _STIS_001 _005 ALPHA-LYR 0.03 0.00 ALPHA_LYR _STIS_002 _004 BD+17D4708 9.47 0.44 BD_17D4708 _STIS_001 BD+25D4655 9.69 -0.31 BD_25D4655 _002 BD+28D4211 10.51 -0.34 BD_28D4211 _STIS_001 _FOS_003 _005 BD+33D2642 10.83 -0.17 BD_33D2642 _FOS_003 _004 BD+75D325 9.55 -0.33 BD_75D325 _STIS_001 _FOS_003 _005 FEIGE110 11.83 -0.30 FEIGE110 _STIS_001 _005 FEIGE34 11.18 -0.34 FEIGE34 _STIS_001 _005 FEIGE66 10.51 -0.29 FEIGE66 _002 FEIGE67 11.82 -0.34 FEIGE67 _002 G191B2B 11.77 -0.33 G191B2B _MOD_004 _STIS_001 _FOS_003 _005 G93-48 12.74 -0.01 G93_48 _004 GD108 13.56 -0.22 GD108 _005 GD153 13.35 -0.29 GD153 _MOD_004 _STIS_001 _FOS_003 GD50 14.06 -0.28 GD50 _004 GD71 13.03 -0.25 GD71 _MOD_005 _STIS_001 _FOS_003 GRW+70D5824 12.77 -0.09 GRW_70D5824 _STIS_001 _005 HD93521 6.99 -0.27 HD93521 _STIS_001 _005 HZ21 14.69 -0.33 HZ21 _STIS_001 _005 HZ2 13.88 -0.09 HZ2 _005 HZ43 12.91 -0.31 HZ43 _MOD_004 _STIS_001 _FOS_003 HZ43B 14.30 ... HZ43B _STIS_001 HZ44 11.67 -0.29 HZ44 _STIS_001 _FOS_003 _005 HZ4 14.51 +0.09 HZ4 _STIS_001 _004 LB227 15.32 +0.06 LB227 _004 LDS749B 14.68 -0.04 LDS749B _005 LTT9491 14.10 +0.03 LTT9491 _002 NGC7293 13.53 -0.37 NGC7293 _005 P041C 12.00 0.62 P041C _STIS_001 _001 P177D 13.47 0.66 P177D _STIS_001 _001 P330E 13.00 0.64 P330E _STIS_001 _001 SUN -26.75 0.63 SUN_REFERENCE _STIS_001
(1) The unit of flux in all files is erg s-1 cm-2 A-1.
SUPPLEMENTAL CALSPEC contains previous CALSPEC versions and spectrophotometry that may be useful for special purposes.
PREVIOUS UPDATES: 96feb22, 99jul19, 01Jun5, 04Feb27
REFERENCES
Bohlin, R.C. 1996, AJ, 111, 1743 Bohlin, R.C. 2000, AJ, 120, 437 Bohlin, R. 2003, 2002 HST Calibration Workshop, ed. S. Arribas, A. Koekemoer, & B. Whitmore, (Baltimore:STScI), p. 115 Bohlin, R. C., & Gilliland, R. L. 2004a, AJ, 127, 3508 Bohlin, R. C., & Gilliland, R. L. 2004b, AJ, submitted in June Bohlin, R.C., Colina, L., & Finley, D.S. 1995, AJ, 110, 1316 Bohlin, R. C., Dickinson, M. E., & Calzetti, D. 2001, AJ, 122, 2118 Colina, L., & Bohlin, R. 1994, AJ, 108, 1931 Colina, L., & Bohlin, R. 1997, AJ, 113, 1138 Colina, L., Bohlin, R.C., & Castelli, F. 1996, AJ, 112, 307 Kurucz, R. 2003, http://kurucz.harvard.edu/ Oke, J.B. 1990, AJ, 99, 1621 Turnshek, D.A., Bohlin, R.C., Williamson, R., Lupie, O., Koornneef, J., & Morgan D. 1990, AJ, 99, 1243
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