[vsnet-chat 2057] Re: Supernovae estimates using USNO SA2.0

[Taichi Kato <tkato>]

    One of my concerns using USNO SA series rather than USNO A series stems
from whether conventional (commercial) photometry softwares can properly
handle sparse "local standard stars" with a wide range of magnitudes.
Assuming the CCD linearlity, one will be able to obtain magnitudes of faint
objects using an ensemble of bright standards (it is probably the case
for USNO A users).  I wonder what happens if the photometry software is
instead forced to use sparsely populated bright stars and sometimes very
faint (17-19 mag) stars.  Although the existence of such faint stars may
not significantly affect the astrometric accuracy, I suspect photometry can
be affected.  If the software has a only freedom of zero-point adjustment,
the existence of a large number of low S/N (and maybe affected by selection
effect) stars can lead to a scatter or a systematic bias).

Regards,
Taichi Kato

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp