[vsnet-chat 1107] Re: [vsnet 1499] Larry Robinson's SN1998dh image

[Taichi Kato <tkato>]

Re: [vsnet-chat 1105] Re: [vsnet 1499] Larry Robinson's SN1998dh image

> This magnitude is quite brighter than other estimates.  He wrote he
> have used Astrometrica and USNO-SA as reference stars, but it is
> uncertain which stars are choosed as a photometry reference.  

   USNA-SA catalog is an astrometric catalog, which is not always suitable
for astrometry: many bright stars missing, while very faint stars (down to
20th mag) included.  USNO-SA is even more unsuitable for calibrating CCD
frames than USNO A1.0 or GSC.  The GSC magnitudes of this field seem
to give rather consistent results between observers and frames, and I
propose to use them for photometry.

Regards,
Taichi Kato

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