HST Spectrophotometric Standards

The HST project has identified six types of calibration target essential to the good calibration of HST results:
1. UV spectrophotometric calibrations stars
2. Optical photometric and spectrophotometric calibration stars
3. Wavelength calibration targets
4. Astrometric calibration fields
5. Polarimetric calibration targets
6. Spatial flat field targets
Turnshek et al. (AJ, 99, 1243, 1990) list the calibration targetsand provide finding charts. Bohlin et al. (ApJS, 73, 413, 1990) discuss the UV calibration of HST standards from IUE data. The basic data for the UV and optical spectrophotometric standards is held in the database CALOBS at STScI. The data is also available through anonymous ftp (ftp@stsci.edu in cdbs/cdbs2/calobs). Bohlin and Lindler (1992) provide details of the calibration data that is available.

The conversion of the IUE, HST FOS and optical spectra into standard starspectra on the white dwarf primary spectrophotometric scale (Bohlin, Colina & Finlay, AJ, 110, 1316, 1995) is described by Bohlin (Proceedings of STScI HST Calibration Workshop, eds. A. Koratkar & C. Leitherer, p. 49, 1994)and Bohlin (AJ, 111, 1743, 1996). There are spectra available for 23 starsin this white dwarf flux system and the data is held in the CALSPEC data base at STScI.

The data for the 23 stars in the white dwarf spectrophotometric system anda further 7 stars with IUE and model fluxes (indicated by an M in thelast column of the table below) has been converted to ABMAG and to flux (ergs/cm/cm/s/A) using the formula
ABMAG = -2.5 alog10(Fnu) - 48.59
(Hamuy et al., PASP, 104, 533, 1992), where Fnu is in ergs/cm/cm/s/Hz.

  Star Name          alpha  (2000)  delta   Spec.    STMAG  Oke (1990)  Model opt.
Type (5460A) fluxes spectra
------------------------------------------------------------------------------------
Zeta Cas (HR153) 00 36 58.30 +53 53 48.9 B2 IV 3.63 M
BPM 16274 00 50 03.18 -52 08 17.4 DA2 14.36 M
GD 50 03 48 50.06 -00 58 30.4 DA2 14.05 *
Hz4 03 55 21.70 +09 47 18.7 DA4 14.45 *
LB227 04 09 28.76 +17 07 54.4 DA4 15.24
Hz2 04 12 43.51 +11 51 50.4 DA3 14.02
Mu Col (HR1996) 05 45 59.92 -32 18 23.4 O9 V 5.15 M
HD 49798 06 48 04.64 -44 18 59.3 O6 8.31 M
HD 60753 07 33 27.26 -50 35 03.7 B3 IV 6.60 M
BD+75d325 08 10 49.31 +74 57 57.5 O5p 9.51 *
AGK+81d266 09 21 19.06 +81 43 28.6 sdO 11.88
GD 108 10 00 47.33 -07 33 31.2 sdB 13.57 *
Feige 34 10 39 36.71 +43 06 10.1 DO 11.12 *
HD 93521 10 48 23.51 +37 34 12.8 O9 Vp 6.95 *
Gamma UMa (HR4554) 11 53 49.83 +53 41 41.1 A0 V 2.59 M
Hz21 12 13 56.42 +32 56 30.8 DO2 14.67 *
Hz44 13 23 35.37 +36 08 00.0 sdO 11.68 *
GRW+70d5824 13 38 51.77 +70 17 08.5 DA3 12.80 *
Eta UMa (HR5191) 13 47 32.44 +49 18 48.0 B3 V 1.83 M
BD+33d2642 15 51 59.86 +32 56 54.8 B2 IV 10.73 *
Alpha Lyr (HR7001) 18 36 56.33 +38 47 01.1 A0 V -0.01
LDS749B 21 32 15.75 +00 15 13.6 DB4 14.71
BD+28d4211 21 51 11.07 +28 51 51.8 Op 10.47 *
G93-48 21 52 25.33 +02 23 24.3 DA3 12.74
NGC 7293 Star 22 29 38.46 -20 50 13.3 Hot 13.48 *
Feige 110 23 19 58.39 -05 09 56.1 DOp 11.80 *

STMAG = -2.5 log10(F(lam)) - 21.10 where F(lam) is in ergs/cm/cm/s/A.