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Flux Standards

With the proliferation of linear detectors on Cassegrain spectrographs, spectrophotometry has become a common byproduct of many spectroscopic observations. The cornerstone of such studies is the system of spectrophotometric standards. Useful references are:

1pt

3em Filippenko, A.V., Greenstein, J.L., 1984. , 96, 530

3em Oke, J.B., Gunn, J.E., 1983. , 266, 713

3em Massey , 1988. , 328, 315

For observers with access to a STARLINK node, the main Figaro directory (logical name FIGARO_PROG_S) contains a number of files, including those recently compiled by Roderick Johnstone (IoA) giving the published flux densities of standard stars, all with a .TAB extension according to FIGARO convention.

The VMS DIRectory command may be used to find which files are available as tables. The command

$DIR FIGARO_PROG_S:*.TAB

will list all the table files supplied in the main directory. Not all of these are intended for flux calibration; some may be extinction tables, etc. These are all text files, and have comments at the start describing their function. For most of the flux standards for which Figaro supplies tables, two tables are provided: one in AB magnitudes, usually a direct copy of the published data, and one in (milli- or micro-) Janskys, usually the result of a semi-automatic conversion from the former. If you particularly like , then you can either provide your own flux tables in these units and work from them directly, or you can use the FLCONV command to convert from a spectrum calibrated in Janskys into these units.

The command

$TYPE FIGARO_PROG_S:file.TAB

will list the file. For example, the file G158M100.TAB begins as follows -

*                   G 1 5 8 - 1 0 0
     *
     *   Table file for G158-100, faint object flux standard,
     *   based on Filippenko and Greenstein (1984) P.A.S.P.
     *   96, 530. Note that these are fitted continuum 
     *   fluxes, not directly measured fluxes, and should 
     *   be used accordingly.   This file is designed for
     *   use with the Figaro routine GSPIKE.  The data here is
     *   given to 3 decimal places and was supplied directly by
     *   Alex Filippenko.
     *
     SET .Z.UNITS = "micro-Janskys"
     SET .Z.LABEL = "Flux"
     *
      3300   891.251
      3400   990.831
      3500  1135.534
      3600  1282.331
      3700  1432.187
      3800  1599.556
      3900  1770.110

The lines beginning with asterisks are treated as comments, and the lines that begin with `SET' are used to set data objects in the file created from this table.

An alternative version of this file is G158M100A.TAB, the A added after the star name indicates that the list is in AB magnitudes. It contains the lines

SET .Z.UNITS = "AB Magnitudes"
     SET .Z.LABEL = "Flux"
     SET .Z.REVSCALE = 1
     SET .Z.MAGFLAG = 1
     *
      3300   16.525
      3400   16.410
      3500   16.262
      3600   16.130
      3700   16.010
      3800   15.890

The functions of the .Z.UNITS and .Z.LABEL lines should be fairly obvious. Setting .Z.REVSCALE to 1 in a file indicates to SPLOT that the data should be plotted with the flux scale reversed, and setting .Z.MAGFLAG indicates that the scale is in logarithmic units. Tables based on data from, for example, Oke and Gunn's 1983 paper will also include the line

SET .Z.BANDWIDTH = 40

to indicate the 40 Angstrom bandwidth used by their data. The Filippenko and Greenstein data represents fitted continuum fluxes, so does not have a bandwidth. From the .TAB files already supplied, it should be possible for you to deduce how to create your own, should that be necessary.

Table 1 lists the stars available in FIGARO main directory (Column 1), name of the file (Column 2), wavelength coverage (Column 3) and comments (Column 4).

The files listed contain stellar fluxes in milli-janskys. AB magnitude files have the same name, but with an A after the star's name. Files are called after the star with + and - signs replaced by P and M respectively. Some files have been included more than once under aliases of the star name.

Numerical values of wavelength, flux, bandwidth and order changeover wavelengths have been checked and are believed to be correct.

Note that there are several different magnitude systems which determine the fluxes presented in these tables. These are defined through different calibrations of the primary standard Vega and use different ways of transferring the magnitude system from Vega to the fainter secondary standards. In general the stars listed here are not actual standards but are just good calibrations of non-variable stars. The user is strongly advised to read the paper from which the numbers come (listed at the top of each file) to gain an idea of both the random and the systematic errors in the fluxes as well as the magnitude system from which the fluxes derived.

Special thanks to Doreen Oliver at RGO who typed in most of the original files and to Carolyn Crawford who gave invaluable help checking the numbers.

Star File Coverage Comments ==== ==== ======== ========

40 Eri B 40ERIB.TAB 3320-9880 AM CVn HZ29.TAB 3340-8720 BD+25 3941 BDP253941.TAB 3200-8370 BD+28 4211 BDP284211.TAB 3200-8370 BD+33 2642 BDP332642.TAB 3200-8370 BD+40 4032 BDP404032.TAB 3200-8370 BD+82 2015 BDP82015.TAB 3200-8370 EG 5 VMA2.TAB 3260-10640 Used 2nd order values at overlap EG 11 L870M2.TAB 3210-7220 EG 28 LB1240.TAB 3210-7220 EG 29 LB227.TAB 3210-7220 EG 31 HZ2.TAB 3210-7220 EG 33 40ERIB.TAB 3320-9880 EG 39 HZ7.TAB 3210-7220 EG 42 HZ14.TAB 3230-7420 EG 50 HE3.TAB 3340-9440 EG 54 L745M46AA.TAB 3320-10520 Cosmetic change to lambda_double EG 63 LDS235B.TAB 3320-8920 Cosmetic change to lambda_double EG 67 SA29M130.TAB 3210-10200 EG 76 AL970M30.TAB 3180-7040 40A bins in 2nd order EG 76 BL970M30.TAB 3320-9880 80A bins in 2nd order EG 77 TON573.TAB 3340-8160 EG 79 R627.TAB 3160-10840 EG 86 HZ21.TAB 3340-9660 EG 91 HZ29.TAB 3340-8720 EG 98 HZ43.TAB 3320-10520 EG 99 W485A.TAB 3320-9880 EG 102 GRWP705824.TAB 3210-10200 EG 119 ROSS640.TAB 3320-10520 EG 129 GRWP708247.TAB 3340-9200 EG 133 L1573M31.TAB 3336-10073 EG 139 W1346.TAB 3210-10640 EG 144 GRWP738031.TAB 3340-9440 EG 148 L1363M3.TAB 3316-10520 EG 149 L930M80.TAB 3320-9240 Cosmetic change to lambda_double and correct value at 4510 EG 162 L1512M34B.TAB 3210-10040 EG 182 G47M18.TAB 3340-9280 EG 184 GD140.TAB 3160-10560 EG 192 AGD185.TAB 3200-7240 80A bins 2nd order EG 192 BGD185.TAB 5820-9780 360A bins EG 247 G191B2B.TAB 3320-10520 Feige 110 F110.TAB 3200-8370 _S: file seems to have wrong bandwidth and lambda_double Feige 15 F15.TAB 3200-8370 Feige 25 F25.TAB 3200-8370 Feige 34 F34.TAB 3200-8370 Feige 56 F56.TAB 3200-8370 Feige 92 F92.TAB 3200-8370 Feige 98 F98.TAB 3200-8370 G191B2B G191B2B.TAB 3320-10520 G47-18 G47M18.TAB 3340-9280 GD 140 GD140.TAB 3160-10560 GD 185 AGD185.TAB 3200-7240 80A bins 2nd order GD 185 BGD185.TAB 5820-9780 360A bins GD-248 GDM248.TAB 3300-10000 Not from SPICA Grw+70 5824 GRWP705824.TAB 3210-10200 Grw+70 8247 GRWP708247.TAB 3340-9200 Grw+73 8031 GRWP738031.TAB 3340-9440 He 3 HE3.TAB 3340-9440 HZ 14 HZ14.TAB 3230-7420 HZ 15 HZ15.TAB 3200-8370 HZ 2 HZ2.TAB 3210-7220 HZ 21 HZ21.TAB 3340-9660 HZ 29 HZ29.TAB 3340-8720 HZ 43 HZ43.TAB 3320-10520 HZ 44 HZ44.TAB 3316-10520 Ambiguity in bandwidth at changeover to first order HZ 7 HZ7.TAB 3210-7220 Kopff 27 KOP27.TAB 3200-8370 L1363-3 L1363M3.TAB 3316-10520 L1403-49 TON573.TAB 3340-8160 L1512-34B L1512M34B.TAB 3210-10040 L1573-31 L1573M31.TAB 3336-10073 L745-46A L745M46AA.TAB 3320-10520 Cosmetic change to lambda_double L870-2 L870M2.TAB 3210-7220 L930-80 L930M80.TAB 3320-9240 Cosmetic change to lambda_double and correct value at 4510 L970-30 AL970M30.TAB 3180-7040 40A bins in 2nd order L970-30 BL970M30.TAB 3320-9880 80A bins in 2nd order LB1240 LB1240.TAB 3210-7220 LB227 LB227.TAB 3210-7220 LDS235B LDS235B.TAB 3320-8920 Cosmetic change to lambda_double R627 R627.TAB 3160-10840 Ross 640 ROSS640.TAB 3320-10520 SA29-130 SA29M130.TAB 3210-10200 Ton573 TON573.TAB 3340-8160 VMa 2 VMA2.TAB 3260-10640 Used 2nd order values at overlap W1346 W1346.TAB 3210-10640 W485A W485A.TAB 3320-9880

Table 2 has been compiled for the WHT manual by Janet Sinclair (RGO) and includes 1950.0 positions, proper motions, m and spectral type of spectrophotometric standards.

Technical Note 100
Technical Note 85

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Wed Apr 6 22:56:39 BST 1994