RE: Mark IV data off by one day

[Thomas Droege <tdroege2@earthlink.net>]

The clocks are set by hand, and there is always the possibility that I
could set them one day off.  I don't always set them every night if they
are tracking the GPS well, so the tendency is to run several nights in a
row with the same clock setting.

A way to tell, if it is recorded is to check offset added to the image to
get it to line up with WCS.  The mechanics is rarely changed.  There is a
parameter that tells the program where the RA home position iswith respect
to the meridian.   If the clock is off by a day, then the WCS correction
will change by 360degrees/365.25 days or nearly a degree.  If the data is
available, then one just looks at a long sequence of days and see if the
WCS correction changes by a degree on the day of interest.  This would
surely indicate that the clock was off by a day.

What say, Michael, are we recording what is needed?

Tom Droege


> [Original Message]
> From: Stupendous Man <richmond@stupendous.cis.rit.edu>
> To: <tass@listserv.wwa.com>
> Cc: <mwrsps@rit.edu>
> Date: 6/6/2004 10:56:10 AM
> Subject: Mark IV data off by one day
>
>
>   The affair of GSC 3493-1324 suggested that at least one
> night's worth of Mark IV data has a date off by exactly one day.
> I checked this in a quick way by looking at Mark IV measurements
> of another variable star, AR Her, which is an RR Lyr variable
> with period of 0.47 days, close to GSC 3493-1324 in the sky.
> I used SIMBAD to look up the ephemeris of AR Her, phased
> the Mark IV data with that ephemeris, and plotted the points.
> The Mark IV data show a periodic curve, but it isn't as
> tight as I'd like.  
>
>   The two measurements made on the same night as the disputed
> GSC 3493-1324 measurements -- JD 2453109.8 -- did indeed lie
> off the main locus by about 0.10 in phase.  When I changed
> the date to JD 2453110.8, they lined up better with
> the main locus.  This adds weight to the hypothesis that
> the computer's clock was off by one day on that night.
>
>   Hmmm.  This brings up the unpleasant possibility that there
> could be more occasions on which the Mark IV computer's date
> was off by one day.  I'm not sure how best to look for other
> such errors.  It might be as easy as checking the markings
> on various disks or files which Tom created against the dates
> stored in the Mark IV database -- that would take an hour or
> two, I would guess, if the information were gathered in one
> place.  Another way to do it, much harder, would be to look
> at a sample of 10 or 20 good variable stars and examine their
> phased Mark IV light curves for points which fall far from
> the locus.  If several stars share similar bad points on the
> same dates, and if changing the date improves the light
> curves, then that might indicate another error.
>
>                                               Michael 
>
>