[vsnet-chat 5774] Re: [AAVSO-DIS] survey, pixy etc

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Re: [vsnet-chat 5768] Re: [AAVSO-DIS] survey, pixy etc

>      There could be many reasons for this:  poor coordinates for the
> variables, crowding, poor solution for the coordinates derived from the
> CCD frames, etc.

   One of the main reasons comes from the implementation of PIXY.
PIXY first picks up stellar images (as in daofind in IRAF), and measure
these images.  The magnitudes of variable stars are picked up from these
measurements.  PIXY does not try to measure the expected locations of the
variable stars, which can significantly reduce the detectability of faint
stars.  As is well-known, the initial detection limit suffers from the
local background, nearby stars etc.  Some variable stars may have escaped
the initial star detection because of these factors.  Since the limiting
magnitude of PIXY output is more globally defined, the resultant upper
limit for certain unfavorably located variables may be inaccurate.

Regards,
Taichi Kato

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