[vsnet-chat 2320] Re: Overlap of variable star survey

[aah@nofs.navy.mil]

Berto wrote:
>All you need doing is to download USNO-A1.0 and USNO-A2.0 data for certain areas and compare 
>them. With an alert brain and a feel for B and R magnitudes and their expected differences you 
>will soon spot a number of stars that show every promise to be variable. Just follow them up 
>with the scope...
  Most of USNO-A1.0 and USNO-A2.0 are based on the exact same photographic
plate material, so comparing 1.0 vs. 2.0 only tells you the difference in two
calibrating algorithms on the same star images and not any variability.
The exception is the north/south overlap region, where 1.0 used the POSS-I
plates and 2.0 uses the ESO plates.
  I agree that most of the visible variables have yet to be discovered.
We found ~5000 in the SDSS calibration regions (~300 square degrees on
the equator) down to R=17; about 99percent were previously unknown.
A rough estimate is that one or two percent of stars
are easily confirmed to be variable.  Since the GSC contains ~14M stars
to V=14 (well within the limit of an 8" + CCD), that means about 100-200K variables
should be observable, most unknown, especially in the south.
Arne

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