Re: question about aglc

From: David P. Huenemoerder <dph_at_email.domain.hidden>
Date: Wed, 3 Dec 2008 22:06:34 -0500
Hi Juan,

    juan> -I'm using aglc to extract light curves doing:

    juan> a=aglc_read_events("evt2.fits","../secondary/stat1.fits");
    juan> aa=aglc(a,6.6,[9.1457,9.2052],[9.1917,9.2542],"meg",[-1,1]);
    juan> aglc_write_curve("lc.fits",a.fevt_1a,aa,"light curve");


    juan> why the first row of the time column is different than 0.0?,
    juan> is it possible to have the number of seconds since
    juan> 2450814.5?

I offset the time to 0.0 at the start of the observation, just so a
plot's time axis is easier to read by eye.  The FITS header keyword,
TIMEZERO, gives the number of seconds since MJDREF.

Both "timezero" and "mjdref" are fields of the structure returned by
aglc. 

While TIMEZERO is a FITS convention, it is possible that other
software ignores the keyword.

If you want to make the time column absolute, you can do something
like this:

  aa.time     += aa.timezero ; 
  aa.time_min += aa.timezero ; 
  aa.time_max += aa.timezero ;
  aa.timezero -= aa.timezero ; 

  aglc_write_curve( ... );

I hope that helps,


--Dave

David Huenemoerder  617-253-4283 (o); -253-8084 (f); http://space.mit.edu/home/dph
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar St., NE80-6065,
Cambridge, MA  02139
[Admin. Asst.: Elaine Tirrell, 617-253-7480, egt_at_email.domain.hidden
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Received on Wed Dec 03 2008 - 22:06:41 EST

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