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Calibration Database System

CALSPEC contains the composite stellar spectra that are flux standards on the HST system. 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 file, which can be read with the IRAF hedit task or by mrdfits.pro in IDL. Table 1 below summarizes this set of standard star spectra. Columns 2-4 give the spectral type, V, and B-V magnitudes of the stars. 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". 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 eight A-stars for JWST calibration were developed by Bohlin & Cohen (2008) from NICMOS observations, and similarly, Bohlin (2010) fit models to STIS and NICMOS data for seven solar analogs. The eight A stars have Spitzer IRAC observations; and their coordinates are documented in Reach et al. (2005). Coordinates for stars that cannot be found by name in Simbad are in Table 2.

High fidelity models are available for a few stars, as listed in column 6 of Table 1. The modeled IR fluxes for 13 stars are compared to Spitzer IRAC photometry in Bohlin et al. (2011). Models for the three fundamental primary standards GD71, GD153, and G191B2B (Bohlin 2003) are calculated with the NLTE code of Rauch et al. (2013), which includes metal line blanketing for G191B2B. Previous to November 2013, pure hydrogen models calculated with the Hubeny NLTE code were used for all three stars. This change results in a wavelength dependent shift of the HST/STIS flux scale but by <~1%.

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 consists of IUE data from 1152-1675A, STIS CCD fluxes from 1675-5350A, and a specially tailored Kurucz 9400K model longward of 5350A (Kurucz 2005). From 900-1152A, 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 extended to 2.5microns with NICMOS data.

Column 7 lists the CDBS suffix names for the standard stars with STIS or NICMOS fluxes (Bohlin, Dickinson, & Calzetti 2001, hereafter BDC; 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. Even though the column 7 flux distributions are the best observational spectral energy distributions (SEDs), caution is still required, because some SEDs flagged with an asterisk are not entirely from the gold standard STIS or NICMOS data. Additional IUE, FOS, or Oke observations have lower signal-to-noise, wavelength precision, and photometric accuracy, as discussed in BDC. Thus, the fits headers of any SED used for precision science applications should be checked to be certain that the wavelength region of interest is identified as STIS or NICMOS.

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, the composite of Rieke et al. (2009), and the solar model from the website of R, Kurucz are additional choices for a solar reference spectrum.

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.

New Content

Also in the CALSPEC data directory are two new products. Rauch et al. (2013) combined FUSE and STIS high resolution spectra of G191B2B ( g191b2b_stisfuse_001.fits), and the covariance matrix ( WDcovar_001.fits) for the uncertainty of the HST flux system as a function of wavelength is included. As explained in more detail by Bohlin & Gordon (2014), the uncertainty is relative to the reference wavelength of 5556A, where this relative uncertainty is zero and the absolute uncertainty is 0.5% (Bohlin 2014).
Table 1: CDBS Files of the Flux(1) Standards with Columns in Order of Preference
--------------------------------------------------------------------------------
Star name    Sp. T.    V     B-V    CDBS name	Model	   STIS        FOS+Oke  IUE+Oke
  (1)          (2)    (3)    (4)       (5)	 (6)	    (7)          (8)      (9)

10 Lac        O9V    4.88   -0.21  10lac                 _STIS_002
1732526       A4V    12.53   0.12  1732526               _STISNIC_002
1740346       A6V    12.48   0.20  1740346		 _STISNIC_002
1743045       A8III  13.52   0.28  1743045		 _STISNIC_002
1757132       A3V    12.01  -0.10  1757132               _STIS_002
1802271       A2V    11.98   0.08  1802271               _STISNIC_002
1805292       A4V    12.28   0.14  1805292		 _STISNIC_002
1808347       A3V    11.69   ...   1808347               _STIS_002
1812095       A5V    11.74   0.20  1812095		 _STISNIC_002
1812524       A4V    12.27   0.18  1812524		 _NIC_004
2M0036+18     L3.5   21.34   ...   2M003618		 _STISNIC_005
2M0559-14     T4.5   I=19.14	   2M055914		 _STISNIC_005
AGK+81 266    sdO    11.95  -0.36  AGK_81D266		 _STISNIC_005*		 _005
ALPHA LYR     A0V     0.031  0.00  ALPHA_LYR   _MOD_001	 _STIS_007*		 _004
BD+02D3375    A5      9.93   0.45  BD02D3375             _STIS_002
BD+17 4708    sdF8    9.47   0.44  BD_17D4708		 _STISNIC_005
BD+21D0607    F2      9.22   0.44  BD21D0607             _STIS_002
BD+25 4655     ?      9.69  -0.31  BD_25D4655					 _002
BD+26D2606    A5      9.73   0.39  BD26D2606             _STIS_002
BD+28 4211(2) Op     10.51  -0.34  BD_28D4211		 _STIS_003*    _FOS_003  _005
BD+29D2091    F5     10.22   0.50  BD29D2091             _STIS_002
BD+33 2642    B2IV   10.83  -0.17  BD_33D2642			       _FOS_003  _004
BD+54D1216    sdF6    9.71   0.48  BD54D1216             _STIS_002
BD+60 1753    A0-A1V  9.65   0.07  BD+60D1753            _STIS_002
BD+75 325     O5p     9.55  -0.33  BD_75D325		 _STIS_003*    _FOS_003  _005
C26202        F8IV   16.64   0.26  C26202		 _STISNIC_005
ETA UMA       B3V    1.85   -0.10  ETAUMA                _STIS_002
FEIGE110      D0p    11.83  -0.30  FEIGE110		 _STISNIC_005*		 _005
FEIGE34       sdO    11.14  -0.23  FEIGE34		 _STIS_003*		 _005
FEIGE66       sdO    10.51  -0.29  FEIGE66					 _002
FEIGE67       sdO    11.82  -0.34  FEIGE67					 _002
G191B2B       DA.8   11.781 -0.33  G191B2B     _MOD_009  _STISNIC_005* _FOS_003  _005
G93-48        DA3    12.74  -0.01  G93_48					 _004
GD108         sdB?   13.56  -0.22  GD108                                         _005
GD153         DA1.2  13.346 -0.29  GD153       _MOD_009  _STISNIC_005  _FOS_003
GD50          DA2    14.06  -0.28  GD50                                          _004
GD71          DA1    13.032 -0.25  GD71        _MOD_009  _STISNIC_005  _FOS_003
GJ754.1A      DBQA5  12.29   0.05  GJ7541A               _STIS_002
GRW+70 5824   DA3    12.77  -0.09  GRW_70D5824           _STISNIC_005            _005
HD009051      G7III   8.92   0.81  HD009051              _STIS_002
HD031128      F4V     9.14   0.41  HD031128              _STIS_002
HD074000      sdF6    9.66   0.45  HD074000              _STIS_002
HD106252      G0      7.36   0.64  HD106252              _STIS_002
HD111980      F7V     8.38   0.53  HD111980              _STIS_002
HD116405      A0V     8.34  -0.07  HD116405              _STIS_002
HD14943       A5V     5.91   0.19  HD14943               _STIS_002
HD158485      A4V     6.50   0.13  HD158485              _STIS_002
HD159222      G1V     6.56   0.65  HD159222              _STIS_002
HD160617      F	      8.73   0.45  HD160617              _STIS_002
HD163466      A6V     6.85   0.19  HD163466              _STIS_002
HD165459      A4V     6.86   0.13  HD165459              _STISNIC_002
HD180609      F-A0V   9.42   0.15  HD180609              _STIS_002
HD185975      G3V     8.10   0.68  HD185975              _STIS_002
HD200654      G	      9.11   0.63  HD200654              _STIS_002
HD205905      G2V     6.74   0.62  HD205905              _STIS_002
HD209458      G0V     7.65   0.59  HD209458              _STISNIC_005
HD37725       A3      8.31  -0.19  HD37725               _STIS_002
HD37962       G2V     7.85   0.65  HD37962               _STIS_002
HD38949       G1V     7.80   0.57  HD38949               _STIS_002
HD60753       B3IV    6.68  -0.09  HD60753               _STIS_002
HD93521       O9Vp    6.99  -0.27  HD93521		 _STIS_003*		 _005
HS2027+0651   DO     16.9    ...   HS2027                _STIS_003
HZ2           DA3    13.88  -0.09  HZ2                                           _005
HZ21          DO2    14.69  -0.33  HZ21                  _STIS_003*              _005
HZ4           DA4    14.51   0.09  HZ4                   _STIS_004*              _004
HZ43 (3)      DA     12.91  -0.31  HZ43        _MOD_009  _STIS_003*    _FOS_003
HZ43B (3)     M3Ve   14.30   ...   HZ43B                 _STIS_003
HZ44          sdO    11.67  -0.29  HZ44                  _STIS_003*    _FOS_003  _005
KF01T5        K1III  13.56   ...   KF01T5		 _NIC_003
KF06T1       K1.5III 13.52   ...   KF06T1		 _NIC_003
KF06T2       K1.5III 13.8    ...   KF06T2		 _STISNIC_002
KF08T3       K0.5III 13.5    ...   KF08T3		 _NIC_003
ksi2 Ceti     B9III   4.28  -0.04  KSI2CETI              _STIS_002
LAM LEP       B0.5IV  4.27  -0.23  LAMLEP                _STIS_002
LB227         DA4    15.32   0.06  LB227                                         _004
LDS749B       DBQ4   14.674 -0.04  LDS749B     _MOD_004	 _STISNIC_005		 _005
LTT9491       DC     14.10   0.03  LTT9491					 _002
MU COL        O9.5V   5.15  -0.26  MUCOL                 _STIS_002
NGC7293       DAO.5  13.52  -0.36  NGC7293					 _005
P041C         GOV    12.16   0.68  P041C                 _STISNIC_005*  _001
P177D         G0V    13.36   0.60  P177D                 _STISNIC_005*  _001
P330E         G2V    12.92   0.64  P330E                 _STISNIC_005*  _001
SF1615+001A   G      16.75   0.49  SF1615_001A		 _STISNIC_005
SIRIUS        A1V    -1.46   0.00  SIRIUS      _MOD_001  _STIS_001*
SNAP-1        sd:B   15.40   0.20  SNAP1                 _STISNIC_005
SNAP-2        G      16.23   ...   SNAP2                 _STISNIC_005
VB8           M7V    16.70   2.0   VB8                   _STISNIC_005
WD0308-565    sdB    14.07  -0.11  WD0308_565  _MOD_002  _STIS_003
WD0320-539    DA     14.9    ...   WD0320_539            _STIS_003
WD0947+857    DA     16.4    ...   WD0947_857            _STIS_003
WD1026+453    DA     16.13  -0.04  WD1026_453            _STIS_003
WD1057+719    DA1.2  14.68   ...   WD1057_719  _MOD_004  _STISNIC_005
WD1657+343    DA1    16.1    ...   WD1657_343  _MOD_004  _STISNIC_005
SUN           G2V   -26.75   0.63  SUN_REFERENCE         _STIS_002*

* WARNING. Some wavelength coverage from sources of lower precision, such as IUE, FOS, or Oke.
(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 (BDC).

Table 2: Coordinates not found by star name in Simbad
              R.A.  (2000)  Decl.          PM (mas/yr)
1732526     17 32 52.574 +71 04 42.74
1740346     17 40 34.684 +65 27 14.97
1743045     17 43 04.48  +66 55 01.6
1757132     17 57 13.242 +67 03 40.85
1802271     18 02 27.17  +60 43 35.7
1805292     18 05 29.291 +64 27 51.92
1808347     18 08 34.704 +69 27 28.70
1812095     18 12 09.604 +63 29 42.16
1812524     18 12 52.371 +60 02 31.85
2M0036+18   00 36 16.176 +18 21 10.47      883  108
2M0559-14   05 59 19.143 -14 04 48.88	   563 -346
C26202      03 32 32.84  -27 51 48.6
P041C       14 51 57.985 +71 43 17.38     -48.4 18.4
P177D       15 59 13.57  +47 36 41.9
P330E       16 31 33.82  +30 08 46.5
SF1615+001A 16 18 14.23  +00 00 08.63       4   -12
Snap-1      16 29 35.76  +52 55 53.2       -2   -20
Snap-2      16 19 46.11  +55 34 17.8

History

2009 January Update

The 2009 January CALSPEC delivery encompassed six new models and 22 standard star flux distributions. 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. The correction of a V bandpass error made all stars fainter by a constant 0.35%, independent of wavelength. 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). 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, and a lot of new NICMOS observations are included.

2010 February Update

The 2010 February CALSPEC delivery included six revised models, 22 revised standard star flux distributions, and four new SEDs from STIS observations. 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). 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). For seven G stars (Bohlin 2010), the 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.

2011 December Update

Calibration standard WD0308-565 derived from STIS data was added to the list of CALSPEC data.

2013 November Update

The low dispersion (R~500) CALSPEC database is expanded from 60 to 93 members with 19 new SEDs for JWST flux calibration (programs 12428 and 12682), 13 new southern standards (12813), and one partial flux distribution from the MAST HST archive. The new stars are measured with STIS and have preliminary extensions to 40microns from model atmosphere fits. The basis for the wavelength dependence of the fluxes is switched from Hubeny pure hydrogen to Rauch model atmosphere calculations, and all dependence on ground based V magnitudes is removed. This delivery encompasses an update for 48 stars with STIS or NICMOS spectrophotometry, the 32 new standards with complete STIS coverage, and eta UMa with archival STIS G230LB data. In addition, 8 high fidelity stellar models are new or updated. For the first time, high dispersion observations of G191B2B and an uncertainty covariance matrix are included.

2013 December Update

Added coordinates for Reach et al. (2005) stars to Table 2.

2014 March Update

A STIS flux distribution for the primary IR standard Sirius (Bohlin 2014) is added to CALSPEC with an IUE extension to shorter wavelengths and with a special Kurucz model beyond 1 micron. The specially tailored Kurucz models for both Sirius and Vega, as normalized to STIS, are also now included. Bohlin (2014) reconciled the absolute visible and IR flux measures, resulting in a 5556A flux reduction from 3.46 to 3.44 e-9 erg s-1 cm-2 A-1. Thus, all of the STIS and NICMOS SEDs are reduced by 0.6% at all wavelengths.

UPDATES: 1996Feb22, 1999Jul19, 2001Jun5, 2004Feb27, 2006Sep1, 2007Oct LDS749B (Bohlin & Koester 2008), 2008Jul Bohlin & Cohen (2008), 2009Jan, 2010Feb, 2011Dec WD0308-565, 2013Nov, 2013Dec, 2014Mar

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Last modified, December 2013