[vsnet-chat 4538] Re: [vsnet 2103] Photometric problem using USNO-A2.0

["Bruce Sumner" <b.sumner@bom.gov.au>]

	Do not use USNO-A2.0 as a source of photometric data, it IS NOT 
a photometric cataloge. The USNO-2.0 magnitudes are representative 
only, and even though the internal accuracy is sometimes quite high, 
the external accuracy is abysmal.

	There is no photometric catalogue of faint stars presently 
available. The best would be the GSPC-II data set, of which a 
preliminary version, known as GSPC2.1, is available at:

http://vsnet-gsss.stsci.edu/gspc/GSPChome.htm

	This dataset contains accurate V and R photometric calibration
stars for GSC-II, down to about magnitude 19. The current version 
contains only about one third the stars of the final version. You
can download the lists is you desire.

Bruce Sumner

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