Adding in sidereal time to image headers

Philip Massey wrote on Dec 31, 2008

I'm just back from a Magellan run, and discovered to my chagrin that my headers all have a bogus value for the sidereal time. Everything else is fine, including the airmass, UT time, date, etc. I actually discovered this after running setjd and doslit, and somewhere along the line some IRAF task recomputed the airmasses based on my bogus sidereal times, with the result that my airmasses are now wacky as well.

Given that I know the longitude, time, and data, it should be possible to put valid sidereal time values into my headers, and then run setairmass. I've gotten as far as determining that either astedit or astcalc might be able to do this, but I confess that after multiple readings of the help pages, I'm still scratching my head.

Any additional guidance would be greatly appreciated.
cheers,
phil

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Mike Fitzpatrick wrote on Dec 31, 2008

Hi Phil,

ASTHEDIT is probably the task you need, specifically the 'mst' function will help: Create a command file called 'cmd' that contains the following

st = mst (@'date-obs', ut, obsdb ("lco", "longitude"))

Then running as

cl> asthedit *.fits cmd

should update the 'ST' keyword (assuming the default parameters and that the obsdb value for Las Campanas is good enough for you, if not you can enter a more precise longitude). Let me know if you still have questions.

Cheers and Happy New Year,
-Mike

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Philip Massey wrote on Dec 31, 2008

Mike---this is great. THANK YOU!

---phil

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AnTaR3s wrote on Dec 31, 2008

Just in case anyone encountered the same problem as I have:

st = mst (@'date-obs', ut, obsdb ("lco", "longitude"))

This above did not work for me, IRAF didn't accept the keyword, so my file now looks like this:

observatory = "act"      
date = imget(clget("keywpars.date_obs"))
mst = mst (date, obsdb (observatory, "longitude"))

and then it works. :)

cheers

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Last post on Dec 31, 2008