Standard files

The main Figaro data directory (corresponding to environment variable FIGARO_PROG_S) contains a number of files giving the published flux densities of standard stars, all with a `.tab' extension. In addition Jeremy Walsh has made available the Oke and HST standards and copies can be retrieved by anonymous ftp. 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) (Preprint, submitted to P.A.S.P.)
   *   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 UNITS = "micro-Janskys"
   SET 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', which contains the lines

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

The functions of the UNITS and LABEL lines should be fairly obvious. Setting MAGFLAG to 1 in a file indicates to `splot' that the data are in magnitude units and so should be plotted with the flux scale reversed. (Note that most `.tab' files actually used by Figaro in fact use `.Z.UNITS' rather than just `UNITS'; these were written for the original version of `gspike' where you were allowed to assume that data units always were held in a file in an item called `file.Z.UNITS'. Now that Figaro supports NDF format files, this is no longer the case, and the abstract term UNITS is preferred-however, the original format files still work, since the new `gspike' uses a conversion table to handle these explicitly named items.) Tables based on data from, for example, Oke & Gunn's 1983 paper will also include the line

   SET BANDWIDTH = 40

to indicate the 40 Angstrom bandwidth used by their data. The Filippenko & Greenstein data represent fitted continuum fluxes, so do not have a bandwidth-a point we shall have to return to very shortly. From the `.tab' files already supplied, it should be possible for you to deduce how to create your own, should that be necessary.

There is a Figaro convention regarding the naming of the table files. The `ls' command may be used to find which files are available as tables. The command

   % ls $FIGARO_PROG_S/*.tab

will list all the table files supplied in the main directory. Note that not all of these are intended for flux calibration; some may be extinction tables, etc. If in doubt, these are all text files, and should have comments at the start describing their function. So, the command

   % more $FIGARO_PROG_S/file.tab

will list the file for you. You should find that most flux files exist in two incarnations, as implied above, one in a Jansky based unit, one in AB magnitudes. The name of the AB magnitude file ends with `a'. So, for example, the files `l74546.tab' and `l74546a.tab' both represent the standard star L745-46A, but the former is in Jansky units-and is therefore probably the one you should use-while the latter is in AB magnitudes. The fact that the name of the object itself ends in `A' is an unfortunate complication that may be misleading.