[vsnet-alert 3259] (fwd) Nova Oph 1998 (Goranskij)

[Taichi Kato <tkato>]

(fwd) Nova Oph 1998 (Goranskij)

Date: Tue, 20 Jul 1999 21:04:52 +0400
From: "Vitaliy P. Goranskiy" <goray@sai.msu.ru>
Subject: [vsnet-obs 21808] N Oph 1998

CCD observation of N Oph 1998

JD hel.24...  V       R
51285.5443  17.60   16.63   Crimean Station of Sternberg Institute
  285.5468  17.27     -     125-cm reflector, Newton focus,
  285.5481  17.37     -     CCD ST-6

Astrometric problem.

Our R magnitude is close to that of USNO A1.0 16.8R faint star
nearby the nova position. It was mentioned in VSNET that the position
of Nova differs the position of faint USNO star by 1".0. Does our
measurement belong to faint companion?

To solve the problem I measured the positions of nova in old
last-year CCD frame and the new frame relative to 8 nearby USNO
reference stars.

Date         R.A., Decl. 2000.0         Mean          R mag.
                                        discrepancy
                                        of ref. star
1998 Jul 20  17 31 59.794  -19 13 55.24  0".35        14.86
1999 Apr 17  17 31 59.801  -19 13 55.30  0".38        16.63
USNO A1.0    17 31 59.788  -19 13 55.04  0".27*)      16.8

*) mean descrepancy between modern and USNO positions.

The outburst and post-outburst positions coincide well within the
errors of observations. There is a small systematical difference
between pre-outburst and modern positions, but not as large as
1".0. This means that the faint USNO star may be a Nova precursor,
and Nova has reached its quescent phase at 16.6 R in April 1999!

The spectroscopic and photometric confirmation needed.

Vitaly Goranskij, SAI, Moscow, Russia

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