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Mr. McDonald asked whether the stars "96" and "104" near Nova Cas 1995 are still valid.
The problem may lie with "104" (GSC 3668-1745), which is fairly red (B-V ~1.75), and so will appear fainter visually than the V magnitude by about 0.3-0.4 mag. This happens because the dark-adapted eye has a peak sensitivity somewhat to the blue side of standard V, and so red stars appear fainter than expected from their V magnitudes.
It is also possible that such a red star is somewhat variable, although strong reddening is not ruled out. The Goranskij and Shugarov UBV photometry, sent out via vsnet about the same time as my results, agrees very closely, however.
The particular star was observed simply because it is close to the nova and had already been chosen as a "lettered" comparison star by variable-star organizations. Obviously it would be useful to poke around the field for another star of similar brightness that is not so red. If I have a chance I'll try to do so in the coming dark run, but no guarantees as usual. If anyone else can do photometry in at least two colors, then by all means try it yourself.
\Brian Skiff (bas@lowell.edu)
Nova Cas 1995 observers,
I was able to make some observations tonight in the field of Nova Cassiopeiae 1995, mainly to try to find a replacement star for the comparison star "104" = GSC 3668-1745, which seems too faint visually because of its red color. The nearest stars of similar brightness and ordinary color that I could find are BD+53 227 and BD+53 223. These are added to the table below, which is amended from the one I sent out a couple months after the nova erupted. The first-mentioned star is slightly brighter than "104" and the other slightly fainter, but considering the persistent activity of the nova around this magnitude level, the additional stars are certainly not redundant. It's too bad they're as far away as they are, but we can't do anything about that!
I took the ooprtunity to reobserve "104" and also GSC 3668-1121, which was suspected of being slightly variable in the original series. I confirm that "104", although fairly red, is not obviously variable: my mean from three V measurements has little scatter and agrees closely with the UBV results sent out by Goranskij & Shugarov late in 1995.
GSC 3668-1121 is another story. In the 1995 series, I indicated that one of my three observations was possibly in error. My fourth observation tonight suggests that measurement was not off, but that the star is indeed somewhat variable, with a full amplitude of about 0.1 mag. (The rms scatter on the b-y colors is less than 0.004 mag., so the far larger scatter in V is likely to be real.) Goranskij & Shugarov's UBV colors suggest it is a reddened mid-B star. The amplitude and relatively short implied period suggests it is possibly a beta Cepheid-type star. Since the star is immediately adjacent to the nova, perhaps someone in the vsnet group already has the necessary CCD frames to examine the variability more closely. Also, if you've been using this star as a comparison for CCD observations of the nova, you might want to look through your data again! If the nova seems to be varying by ~0.1 mag. on timescales of one day or so, it might be due to the comparison star instead. Finally, since the star is never more than ~0.05 mag. from the mean value, it's probably just fine as a comparison for visual observers. Of course, the nova hasn't got that faint since it was discovered, so it hasn't come into use for them yet!
Note again that the observation of the nova itself is not strictly on the standard system because of the mismatch of the emission-line spectrum to that of ordinary standard stars.
Photometry of stars in the field of Nova Cassiopeiae 1995
(version: 1 November 1996)
Name RA (2000) Dec V b-y n spec remarks
N Cas 1995 1 05 05.4 +54 00 41 9.05 0.44 1 1995 Sep 11.3 UT
HD 6250 1 04 17.3 +54 12 18 6.837 0.341 5 G0 (1)
.002 .002
HD 7178 1 13 05.5 +54 24 13 8.528 0.060 2 A0
.004 .007
HD232365 1 04 17.3 +54 27 43 8.701 0.471 2 K0(v)
.007 .006
HD232354 1 02 30.0 +54 15 16 8.844 0.747 1 K0
HD232382 1 09 04.0 +54 08 54 8.954 0.762 1 K2
HD232357 1 03 13.5 +53 54 48 9.104 0.103 2 A0
.002 .005
BD+53 212 1 04 39.4 +54 13 04 9.351 0.708 1
HD232374 1 05 36.2 +54 07 52 9.584 0.127 2 B9
.001 .008
BD+53 227 1 07 23.8 +53 48 12 10.153 0.435 1 (2)
GSC 3668-1745 1 04 36.8 +54 01 29 10.352 1.216 3
.010 .020
BD+53 223 1 06 31.6 +54 25 23 10.485 0.602 1 (3)
BD+53 215 1 05 28.1 +53 56 50 11.011 1.143 2 (4)
.012 .022
GSC 3668-1121 1 05 07.4 +53 59 12 11.584 0.204 1995 Sep 11 UT
11.561 0.197 1995 Sep 12 UT
11.490 0.200 1995 Oct 3 UT
11.500 0.205 1996 Nov 1 UT
average 11.53 0.202
.05 .004
GSC 3668-0884 1 04 49.8 +53 59 44 13.228 0.504 1
(.026) (.033)
Notes
1 V = 6.833, b-y = 0.342 (Olsen 1983, A&A Suppl 54, 55); V = 6.846
(Kornilov et al. 1991, Trudy Astr. Inst. Sternberg, vol. 63).
2 GSC 3669-0041.
3 GSC 3672-0006.
4 GSC 3668-2028.
\Brian Skiff (bas@lowell.edu)
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