[fitsbits] Re: EXPOSURE or OBSTIME?

[Doug Mink]

Tom Kuiper wrote:
> I'm working on a radio spectral line data acquisition package and need to decide
> what keyword to use for integration time. An example FITS file that I have from
> the SEST telescope at La Silla uses OBSTIME. The OGIP Spectral File Format
> specifies EXPOSURE.  Are there any other keywords in use for this parameter?
> Is there any hint of a convergence on a standard?

I looked through all of the files I have collected for testing WCS software,
and EXPTIME was used by almost all optical telescopes for exposure in seconds.
In my sample, only the Digitized Sky Survey uses EXPOSURE, and its units are
minutes.

Release 2.8.0 of WCSTools, a suite of programs for creating and using world
coordinate systems in FITS (and IRAF .imh) image files, is now out.  Most of
the changes are minor, but support for Tycho-2, a 2.5-million star catalog
based on Hipparcos and other data, has been added.  Documentation and
installation
instructions are at http://tdc-www.harvard.edu/software/wcstools/ .

-Doug Mink
 Telescope Data Center
 Harvard Smithsonian Center for Astrophysics
 Cambridge, Massachusetts USA