Re: Tycho-2 catalog

[Tom Droege <tdroege2@earthlink.net>]

Yes, as I said in a previous note, we need to find a way of optimizing the 
use of the Tycho2 catalog for best results from my location.  I think some 
compromise between two few good stars and many bad stars is called for.

I am hoping that the experts will guide me as to how to do this.  In a few 
hours I should be able to put up some plots that will help to demonstrate 
the problem.

There are not many stars on the list with difference of 2 between the 
catalog and my measurement.  But there are lots of 1 mag differences in the 
I catalog.  The V catalog is better, but I just found a few with greater 
than 0.8 mag difference.

So far, Michael has done all the work.  Possibly someone else can join 
in.  (hint)  I am slowly getting to the point that I can do manipulations 
of the catalog if someone guides me as to what to do.

Hmmmm!  Good suggestion, Arne.  Possibly we need to use one catalog for the 
astrometry and another for the photometry.  I can see how to do this with 
some advice as to what to put in the photometry catalog.

Tom Droege

At 10:50 AM 1/27/03 -0700, you wrote:
>Ok, that star is listed in many catalogs, including the MarkIII tenx.
>Note that it has Tycho2 Bt/Vt of 12.095/11.052, well outside my
>normal cutoff of V=10.0 for Tycho2.  Michael has relaxed the reference
>catalog requirements far beyond my limits, mostly to provide sufficient
>astrometric reference stars.  As I stated in the Mark III days, for
>photometric calibration you have to restrict yourself to stars
>brighter than V=10 and within specified color limits (for accurate
>transformation to the standard system).
>   I don't think Michael has the option yet of using
>a restricted subset of the refcat when doing the photometric calibration,
>but that should be high on his list (or better yet, allowing for an
>entirely different catalog for photometric calibration).
>   Bottom line:  this star is too faint and too red to be even moderately
>correct.  Give me another example where the star is bright and not
>too red where you are getting comparable errors.
>Arne
>
>Tom Droege wrote:
>>Sorry, it was .586.  A next project for me is to get the data processing 
>>machine hooked up on the network to the internet.  Sigh!  I carry data 
>>between the two machines on bits of paper.