(fwd) M51 field comparison stars

>From bas@lowell.edu Sun Apr  3 07:50:44 1994
>Subject: M51 Field Comparison Stars
>To: nova@nova.la.asu.edu

     The most useful comparison for the supernova in M51 for CCD observers
is likely to be the fairly bright star about 90 arcsec southwest of the
center of the galaxy in the interarm region.  The Longo & de Vaucouleurs
aperture photometry catalogues list several values for this star, all due to
otherwise unpublished measures by Harold Corwin (unpublished):

     V    B-V   U-B   V-R   R-I   V-I
   13.48  0.59  0.17  0.36  0.33  0.69
   13.46
   13.41  0.59  0.04

Presumably the discrepancies in V and U-B are due mainly to the difficulty of
subtracting the background light with single-channel photometers.  This star
does not appear in the Guide Star Catalogue.
     Visual observers are not so well served over the likely magnitude range,
so I will try (no promises) to measure a few more of the brighter stars in
the field soon.

sources:
Longo, G., and de Vaucouleurs, A.  1983.  A General Catalogue of Photoelectric
     Magnitudes and Colors in the UBV System of 3578 Galaxies Brighter Than
     the 16th V Magnitude (1936-1982); University of Texas Monographs in
     Astronomy, no. 3.
Longo, G., and de Vaucouleurs, A.  1985.  Supplement to the General Catalogue
     of Photoelectric Magnitudes and Colors of Galaxies in the UBV System;
     Univeristy of Texas Monographs in Astronomy, no. 3A.
de Vaucouleurs, A., and Longo, G.  1988.  Catalogue of Visual and Infrared
     Photometry of Galaxies from 0.5$\mu$m to 10$\mu$m (1961-1985); University
     of Texas Monographs in Astronomy, no. 5.


\Brian