Re: Data reduction methodology for V-I colors

["Richard Miles" <rmiles.btee@btinternet.com>]

>>The good side of doing this is that we only use calibration stars of
>>high quality i.e. use the best 50 stars from the night (e.g. Landolt
>>and similar) instead of 50 stars from every frame of dubious quality.

>The last time I tried this, I ran immediately
>into problems with the statistics of small
>samples ... zero Landolt stars in several
>cases. To get enough calibration stars, I was
>forced to use all the Tycho2 sources for the
>initial calibration of each image.

>The Tycho2 magnitudes are not at all precise
>in the first place and the I magnitudes
>computed from BT and VT are even worse than
>the V magnitudes.

Guys,

I have a particular interest in TASS in that I am running two simultaneous V
and I scopes as I write this (2nd night of operation in fact).  The quality
of the images and photometry I am getting look to be extremely promising.

I can't understand why you are overlooking the Hipparcos stars.  I shall be
using this dataset even though my fields are much smaller than TASS' (1.6
sq.deg vs. about 16 sq.deg).  Do note that the Tycho photometry was
something of an afterthought exploiting the star tracker on board the
spacecraft.  The Hipparcos photometry dataset (Hp magnitudes) was the prime
photometric mission and is well calibrated against Landolt and Cousins.

I will want to get hold of a CD copy or two from Tom as it will be
interesting to monitor some of the same fields as TASS and see how the data
compare.  Anything in the +17 to +23 Dec. would do just fine, I suggest.

Richard Miles