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Date: Tue, 13 Jul 93 11:07:26 EDT
From: Stupendous Man <richmond@astro.Princeton.EDU>
Subject: comparison stars very close to SN 1993J
Gerard de Vaucouleurs and Harold Corwin have made a very useful table
of magnitudes of stars scattered around the field of M81. I'd like to
add Johnson-Cousins UBVRI values for the three stars closest to the
SN itself, which may be of use to people who are making photoelectric
or CCD measurements. Here's a map of the area, about five arcminutes
on a side; the "*" marks the position of the SN.
N
-------------------
| . |
| .... | Star other names
| ..... | ------- --------------------
| .M81 | A GSC 0565
| ..... | MAA "E"
| ... |
E | A | W B GSC 0928
| * | MAA "F"
| C | The Astronomer "F"
| B | Corwin star 4
| |
------------------- C GSC 340
S
And here are Johnson UBV, Cousins RI magnitudes for each of these
three stars, based on measurements made at Kitt Peak on the MDM 1.3
meter telescope on eight nights between Apr 15-26, 1993, by Eric Schulman
and Caroline Cox. Please note that the I-band filter used for this
measurement was simply a long-pass filter, so it's not likely to be very
accurate. The values were derived using Landolt standards
(AJ 104, 340 (1992)). I also list Corwin's values for star "B":
star U B V R I
------------------------------------------------------------------
A 12.02 (03) 11.96 (01) 11.40 (04) 11.11 (03) 10.80 (05)
B 12.33 (03) 12.41 (02) 11.89 (05) 11.61 (03) 11.30 (05)
12.32 12.40 11.90 11.60 11.30 Corwin
C 15.08 (08) 15.10 (07) 14.58 (11) 14.21 (12) 13.83 (05)
I suggest that we all use star B (= Corwin star 4) as the primary
calibrator; it is in a much less bright region of M81 than star A,
and considerably brighter than star C. Further, I suggest that
we adopt Corwin's UBVRI values (with which Schulman's measurements
are consistent), since they were released very early on and many people
have already been using them.
Michael Richmond
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
