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Date: Thu, 20 May 93 19:47:14 GMT
From: gav@astro.as.utexas.edu (Gerard de Vaucouleurs)
Subject: SNnote4
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>From G. de Vaucouleurs (gav@astro.as.utexas.edu) (5.20.93)
Note 4 on SN1993J comparison star GSC4383.0340 (Richmond *C):
After much exchange of correpondence with H. Corwin, W. Neely, B. Skiff
and reviewing the e-mail of the past six weeks, it would seem that we are
converging to a plausible mean V magnitude for this comparison star, but
its color(s) and possible variability are still moot. The zero point is set
by *A = 11.41, B-V = 0.56 (GSC 0565), *B = 11.90, B-V = 0.50 (GSC 0928).
---------------------- Mean V magnitude --------------------------
Source <V> Remarks
AAVSO, TB chart (14.0) Old visual estimates
GSC (14.59) Transformed by HC to ...
............... (14.96) with GV's formula
Corwin ....... 14.4 inferred from J-K colors
Richmond ...... 14.51 CCD, Berkeley, *A + 3.10
Kato .......... 14.45 CCD, Kiso
Neely ......... 14.48 unfilt. CCD, *B + 2.58
Skiff ......... 14.68 var.? from b,y ptm, Lowell, 7n
Unweighted mean 14.51 N = 8, no rej.
14.52 +/- .04 N = 6, () rej., s.d. = 0.11
Median ........ 14.50 Adopted
-------------------------------------------------------------------
---------------------- Color index --------------------------------
Corwin + GV .... B - V = + 0.46 +/- 0.05, mean inferred from
U. Hawaii (4/2/93) J - K = + 0.36 with *A: + 0.39, *B: + 0.44
Skiff .......... B - V = + 0.37 +/- 0.05, mean (4n) inferred from del(b-y)(*C-*A) = - 0.08
Provisional mean B - V = + 0.41: Adopted
---------------------------------------------------------------------
With these values the pre-discovery observation of the supernova by
Neely on March 28.3 = JD 074.8 (SN 0.8 mag brighter than *C, as
published in IAUC5740, assuming *C = 14.6 GSC) would become 13.7,
but an improved reduction of the original CCD frame with *C = 14.5,
as above, still gives 13.8 (Neely, private communication, 5/19/93)
subject only to the as yet unknown color effect between the comparison
stars (B - V ~ 0.5) and the supernova (possibly B - V ~ -0.2 at that
time).
We urgently need bona fide UBVRI photoelectric or CCD observations
of ALL the comparisons stars on the AAVSO, TA, TB and other charts.
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