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Adding in sidereal time to image headers

 
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massey
Esteemed IRAF Fellow


Joined: 10 Feb 2006
Posts: 135
Location: Flagstaff

PostPosted: Wed Dec 31, 2008 9:39 pm    Post subject: Adding in sidereal time to image headers Reply with quote

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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fitz
Site Admin


Joined: 30 Sep 2005
Posts: 3256
Location: Tucson

PostPosted: Wed Dec 31, 2008 10:22 pm    Post subject: Reply with quote

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

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


Then running as

Code:
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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massey
Esteemed IRAF Fellow


Joined: 10 Feb 2006
Posts: 135
Location: Flagstaff

PostPosted: Sun Jan 11, 2009 5:20 pm    Post subject: Reply with quote

Mike---this is great. THANK YOU!

---phil
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AnTaR3s
Active IRAF User


Joined: 24 Oct 2009
Posts: 56

PostPosted: Wed Jun 01, 2011 7:48 pm    Post subject: Reply with quote

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

Code:
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:

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


and then it works. Smile

cheers
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