[vsnet-chat 2716] Re: SNe observations (Skiff)

[Taichi Kato <tkato>]

From bas@lowell.edu Mon Mar  6 09:37 JST 2000
Date: Sun, 5 Mar 2000 17:36:52 -0700 (MST)
From: Brian Skiff <bas@lowell.edu>
To: f.m.ewalt@snet.net
Subject: Re: Supernova Magnitude Observations
Cc: tkato@kusastro.kyoto-u.ac.jp, yamaoka@rc.kyushu-u.ac.jp
Content-Type: text
Content-Length: 1332

     All this sounds fine.  Be aware that if the original GSC version 1.1
positions are being used as reference for astrometry, then the results are
subject to systematic errors of sometimes over an arcsecond (even if internal
errors are small) due to the way in which the GSC v1.1 was reduced.  It is
much preferable to use either GSC v1.2 or Bill Gray's GSC-ACT.  These both
can be accessed via the data centers, such as:

http://vizier.u-strasbg.fr

The catalogues are items i/254 and i/255, respectively.  Better still is to
use the new Tycho-2 catalogue (i/259), which will have vanishingly small
errors for nearly all astrometric purposes.
     Remember also that the magnitudes in the GSC are not on the standard
system, and have zero-point variations from plate to plate that range over
a full magnitude, again even though internal errors for small regions can
be acceptably small.  It is best if possible to try shooting stars in one
of the GSPC regions or some other sequence, such as are contained in my
large photometric reference file:

http://ftp.lowell.edu/pub/bas/starcats/loneos.phot

In most cases one a random field is not more than one or two degrees from
the nearest sequence of stars.  These are suitable for getting zero-points
in magnitude to 0.05 mag. or better on a standard system, such as V or R.

\Brian

VSNET Home Page

Return to Daisaku Nogami

---

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