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 2-4 give the spectral type, V, and B magnitudes of the stars. More documentation on some of these stars, eg. coordinates, finding charts and spectral types are in Turnshek et al. (1990), Bohlin, Colina & Finley (1995), and Colina & Bohlin (1997). A set of A-stars for JWST calibration were developed by Bohlin & Cohen (2008) from NICMOS observations, while all 8 of these stars (HD165459 and 1*_nic_002.fits) have Spitzer IRAC observations and coordinates documented in Reach et al. (2005). Column 5 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 5, plus one of the suffixes in columns 6-9, plus ".fits". For example, a standard that has STIS data is "bd_28d4211_stis_001.fits".
High fidelity models are available for a few stars, as listed in column 6. Models for the three fundamental primary standards GD71, GD153, and G191B2B (Bohlin 2003) provide the basis for the secondary flux standards and are calculated with the Hubeny NLTE code for pure hydrogen. The observational spectra from columns 7-9 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 or 40 microns and cover the long wavelength limits of 2.7 microns for NICMOS, 1.1 microns for STIS and ACS, and >30 microns for some JWST or Spitzer filters. Vega was observed by STIS (Bohlin & Gilliland 2004a) and revised by Bohlin(2007). The composite flux standard alpha_lyr_stis_005.fits consists of IUE data from 1256-1675A, STIS CCD fluxes from 1675-5337A, and a specially tailored Kurucz 9400K model longward of 5337A (Kurucz 2005). From 900-1256A, the hotter Kurucz (2003) 9550K model is more continuous with the IUE flux. The STIS and ACS observations of the SDSS standard BD+17 4708 are documented in Bohlin & Gilliland (2004b) and are now extended to 2.5microns with NICMOS data.
Column 7 lists the CDBS suffix names for the second choice standard stars with STIS data from Bohlin, Dickinson, & Calzetti (2001) and NICMOS fluxes per Bohlin (2007). The naming convention in column 7 is _STIS_ for STIS only, _NIC_ for NICMOS only, and _STISNIC_ for stars with both types of spectrophotometry. Tabulated in column 8 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 8 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 set of standard stars appear in column 9 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. The solar reference spectrum combines absolute flux measurements from space and from the ground with a model spectrum for the near-infrared (Colina, Bohlin, & Castelli 1996). The newer absolute solar flux measurements of Thuillier (2003) from 1990-23975A and the composite of Rieke et al. (2009) are additional choices for a solar reference spectrum.
2009 January Update
The 2009 January CALSPEC delivery encompasses six new models and 22 standard star flux distributions. The model flux distributions are for pure hydrogen in NLTE and are computed with the TLUSTY code, version 203, while the previous models used the outdated version 200. The calculated SEDs for the three primary standards G191B2B, GD153, and GD71 are placed on an absolute flux scale using a synthetic calculation of the V magnitudes relative to Vega and provide the flux calibrations for both the STIS and the NICMOS spectrophotometry. The switch to TLUSTY203 caused a small change in the continuum fluxes with a 0.3% increase in the 1300A/10000A flux ratio. In a narrow region around 4000A between H-delta and H-epsilon, the new models are up to ~0.9% fainter. In addition, the synthetic V magnitude calculation was corrected to remove an extra factor of wavelength that had been included explicitly but was discovered to be already included in the Cohen et al. (2003) V filter transmissions. The correction of this error made all stars fainter by a constant 0.35%, independent of wavelength. A new model for the historical standard HZ43 is included for completeness. Pure hydrogen NLTE models are provided for the first time for the faint stars WD1057+719 and WD1657+343; and these models include a small amount of interstellar reddening (Bohlin 2007).
The above changes that make the three primary WD models fainter by a few tenths of a percent affect all 22 newly measured SEDs by the same amount. There is one new standard, HD209458, delivered to CALSPEC for the first time. The G230LB STIS spectra of G191B2B have replaced the FOS fluxes at 1700-3850A in g191b2b_stisnic_002. A lot of new NICMOS observations are included in the updates of the stisnic_001 to stisnic_002 measurements; and all stars in this delivery have NICMOS fluxes measured to 2.5 microns, except for Vega, which is too bright for any NICMOS mode, and except for WD1657+343, which is too faint for the NICMOS G206 mode that covers the 1.9-2.5 micron range. Two stars AKG+81 266 and GRW+70 5824 have more STIS observations included and now also have NICMOS spectrophotometry, which promotes these two SEDs into the STISNIC category. All of the NICMOS spectra have been reprocessed with the new CALNICA algorithm (Dahlen et al. 2008) and the new 2008 flat fields. A correction for the correlation of the NICMOS sensitivity with temperature is also applied.
2010 February Update
The 2010 Febuary CALSPEC delivery encompasses six revised models, 22 revised standard star flux distributions, and four new SEDs from STIS observations. A new model SED for HZ43 has not been delivered, because HZ43 was demoted from its primary standard category some years ago because of its bright cool companion.
The revisions to the flux distributions are all generally less than 1%. The main change was driven by the discovery of a small error of ~0.57% in the gain 4 to gain 1 ratio for the STIS CCD (Goudfroiij, et al. 2009). Depending on the mix of the gain 1 and 4 in the STIS CCD data, various small changes occur for each STIS flux distribution. The V mag for Vega changed from 0.026 to 0.031; and the models for the primary standards GD153 and GD71 got brighter by ~0.5%. The model for G191B2B would also have brightened by 0.5%, except that the Landolt & Uomoto (2007) V=11.781 is now adopted, replacing the V=11.773 from FOS measurements (Bohlin 2000). The computed model SEDs for the three primary standards G191B2B, GD153, and GD71 are placed on an absolute flux scale using a synthetic calculation of the V magnitudes relative to Vega and provide the flux calibrations for both the STIS and the NICMOS spectrophotometry. The weighting for the STIS sensitivity is changed from the total counts for each observation to equal weight for each star, regardless of the number of observations. A few stars have additional STIS observations included in their observed average SED. The NICMOS dispersion relations have been updated (Pirzkal, Bohlin, & Thatte 2009).
The primary motivation for this update is the modeling of seven G star flux distributions (Bohlin 2010). These observed flux distributions have been extended from the NICMOS long wavelength limit of ~2.5 microns to 40 microns, using the best fitting Castelli & Kurucz (2004) model SED.
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 6 to the last choice with the lowest quality in column 9.
2011 December Update
Calibration standard 'WD0308-565' derived from STIS data was added to the list of CALSPEC data.
CDBS Files of the Flux Standards with Columns in Order of Preference(1) -------------------------------------------------------------------------------- Star name Sp. T. V B-V CDBS name Model STIS FOS+Oke IUE+Oke (1) (2) (3) (4) (5) (6) (7) (8) (9) 1732526 A4V 12.53 0.12 1732526 _NIC_002 1740346 A6V 12.48 0.20 1740346 _NIC_002 1743045 A8III 13.52 0.28 1743045 _NIC_002 1802271 A2V 11.98 0.08 1802271 _NIC_002 1805292 A4V 12.28 0.14 1805292 _NIC_002 1812095 A5V 11.74 0.20 1812095 _NIC_002 1812524 A4V 12.27 0.18 1812524 _NIC_002 2M0036+18 L3.5 21.34 ... 2M003618 _STISNIC_003 2M0559-14 T5 I=19.14 2M055914 _STISNIC_003 AGK+81 266 sdO 11.94 -0.34 AGK_81D266 _STISNIC_003 _005 ALPHA-LYR A0V 0.026 0.00 ALPHA_LYR _STIS_005 _004 BD+17 4708 sdF8 9.47 0.44 BD_17D4708 _STISNIC_003 BD+25 4655 ? 9.69 -0.31 BD_25D4655 _002 BD+28 4211(2) Op 10.51 -0.34 BD_28D4211 _STIS_001 _FOS_003 _005 BD+33 2642 B2IV 10.83 -0.17 BD_33D2642 _FOS_003 _004 BD+75 325 O5p 9.55 -0.33 BD_75D325 _STIS_001 _FOS_003 _005 C26202 G 16.64 ... C26202 _STISNIC_003 FEIGE110 D0p 11.83 -0.30 FEIGE110 _STISNIC_003 _005 FEIGE34 DO 11.18 -0.34 FEIGE34 _STIS_001 _005 FEIGE66 sdO 10.51 -0.29 FEIGE66 _002 FEIGE67 sdO 11.82 -0.34 FEIGE67 _002 G191B2B DA0 11.781 -0.33 G191B2B _MOD_007 _STISNIC_003 _FOS_003 _005 G93-48 DA3 12.74 -0.01 G93_48 _004 GD108 sdB? 13.56 -0.22 GD108 _005 GD153 DA1 13.346 -0.29 GD153 _MOD_007 _STISNIC_003 _FOS_003 GD50 DA2 14.06 -0.28 GD50 _004 GD71 DA1 13.032 -0.25 GD71 _MOD_007 _STISNIC_003 _FOS_003 GRW+70 5824 DA3 12.77 -0.09 GRW_70D5824 _STISNIC_003 _005 HD165459 A4V 6.86 0.13 HD165459 _NIC_002 HD209458 G0V 7.65 0.59 HD209458 _STISNIC_003 HD93521 O9Vp 6.99 -0.27 HD93521 _STIS_001 _005 HS2027+0651 DO 16.9 ... HS2027 _STIS_001 HZ2 DA3 13.88 -0.09 HZ2 _005 HZ21 DO2 14.69 -0.33 HZ21 _STIS_001 _005 HZ4 DA4 14.51 +0.09 HZ4 _STIS_002 _004 HZ43 (3) DA 12.91 -0.31 HZ43 _MOD_005 _STIS_001 _FOS_003 HZ43B (3) M 14.30 ... HZ43B _STIS_001 HZ44 sdO 11.67 -0.29 HZ44 _STIS_001 _FOS_003 _005 KF01T5 K1III 13.56 ... KF01T5 _NIC_001 KF06T1 K1.5III 13.52 ... KF06T1 _NIC_001 KF06T2 K1.5III 13.8 ... KF06T2 _NIC_001 KF08T3 K0.5III 13.5 ... KF08T3 _NIC_001 LB227 DA4 15.32 +0.06 LB227 _004 LDS749B DBQ4 14.674 -0.04 LDS749B _MOD_002 _STISNIC_003 _005 LTT9491 DC 14.10 +0.03 LTT9491 _002 NGC7293 ... 13.53 -0.37 NGC7293 _005 P041C GOV 12.00 0.62 P041C _STISNIC_003 _001 P177D G0V 13.47 0.66 P177D _STISNIC_003 _001 P330E G0V 13.00 0.64 P330E _STISNIC_003 _001 SF1615+001A G 16.753 +0.66 SF1615_001A _STISNIC_003 SNAP-1 WD 15.6 ... SNAP1 _STISNIC_003 SNAP-2 G 16.2 ... SNAP2 _STISNIC_003 VB8 M7 16.81 ... VB8 _STISNIC_003 WD0308-565 sdB D 14.07 -0.11 WD0308_565 _STIS_001 WD0320-539 DA 14.9 ... WD0320_539 _STIS_001 WD0947+857 DA 16.4 ... WD0947_857 _STIS_001 WD1026+453 DA 16.13 -0.04 WD1026_453 _STIS_001 WD1057+719 DA1.2 14.8 ... WD1057_719 _MOD_002 _STISNIC_003 WD1657+343 DA1 16.1 ... WD1657_343 _MOD_002 _STISNIC_003 SUN G2V -26.75 0.63 SUN_REFERENCE _STIS_001
(1) The unit of flux in all files is erg s-1 cm-2 A-1.
(2) BD+28 4211 has a companion at 2.8arcsec (Landolt & Uomoto (2007).
(3) HZ43 and HZ3B are separated by ~3arcsec (Bohlin, Dickinson, & Calzetti 2001).
SUPPLEMENTAL CALSPEC contains previous CALSPEC versions and spectrophotometry that may be useful for special purposes.
UPDATES: 96Feb22, 99Jul19, 01Jun5, 04Feb27, 06Sep1, 07Oct-LDS749B (Bohlin & Koester 2008), 08Jul-Bohlin & Cohen (2008), 09Jan, 2010Feb, WD0308-565 2011Dec
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. 2007, in The Future of Photometric, Spectrophotometric, and Polarimetric Standardization, ASP Conf. Series, Vol. 364, p. 315 ed. C. Sterken; also Astro-Ph 0608715 Bohlin, R. C. 2010, AJ, 139, 1515 Bohlin. R. C., & Cohen, M. 2008, AJ, 136, 1171 Bohlin, R.C., Colina, L., & Finley, D.S. 1995, AJ, 110, 1316 Bohlin, R. C., Dickinson, M. E., & Calzetti, D. 2001, AJ, 122, 2118 Bohlin, R. C., & Gilliland, R. L. 2004a, AJ, 127, 3508 Bohlin, R. C., & Gilliland, R. L. 2004b, AJ, 128, 3053 Bohlin, R. C., & Koester, D. 2008, AJ, 135, 1092 Castelli, F., & Kurucz, R. 2004, IAU Symp. No. 210, Modeling of Stellar Atmospheres, eds. N. Piskunov, W. Weiss, & D. Gray 2003, poster A20; also arXiv:0405.087 [astro-ph] Cohen, M., Megeath, S.~T., Hammersley, P.~L., Martin-Luis, F., & Stauffer, J. 2003, AJ, 125, 2645 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 Dahlen, T.,McLaughlin, H., V. Laidler, M. Regan, E. Bergeron, R. Jedrzejewski, R. Bohlin, R. de Jong, & A. Viana 2008, Instrument Science Report, NICMOS 2008-02, (Baltimore:STScI) Goudfrooij, P., Wolfe, M. A., Bohlin, R. C., Proffitt, C. R., & Lennon, D. J. 2009, Instrument Science Report, STIS 2009-02, (Baltimore:STScI) Kurucz, R. 2003, http://kurucz.harvard.edu/ Kurucz, R. 2005, Vega spectrum at T=9400K, log g=3.90, [M/H]=-0.5, and zero microturbulent velocity, personal communication Landolt, A., & Uomoto, A. 2007, AJ, 133, 768 Oke, J.B. 1990, AJ, 99, 1621 Pirzkal, N., Bohlin, R., & Thatte D. 2009, Instrument Science Report, NICMOS 2009-006, (Baltimore:STScI) Reach, W. T., et al. 2005, PASP, 117, 978 Rieke, G. H., et al. 2008, AJ, 135, 2245 Thuillier, G., Herse, M., Labs, D., Foujols, T., Peetermans, W., Gillotay, D., Simon, P., & Mandel, H. 2003, Sol. Phys., 214, 1 Turnshek, D.A., Bohlin, R.C., Williamson, R., Lupie, O., Koornneef, J., & Morgan D. 1990, AJ, 99, 1243
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Last modified, December 2011