COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3685

                                                Konkoly Observatory
                                                Budapest
                                                2 December 1991

                                                HU ISSN 0374 - 0676


    Detection of a faint variable with Delta m > 4.5m in Andromeda


As a by-program in the course of studies on the galactic structure, we have
started a search for new variable stars on Palomar Observatory Sky Survey
(POSS) prints. The search is done by comparison of overlapping regions of POSS
fields (using positive and negative transparent copies) around alpha ~ 00h,
where the largest overlap occurs. Here we present our most obvious candidate.

The star was discovered on POSS O and E839, but is absent on O and E368. Its
coordinates are alpha = 23h47m47s, delta = +46d 42'40"; +-0.1' (1950). In
Figure 1, finding charts are given.


                              [FIGURE 1]

 Figure 1: Reproductions from blue-sensitive (O) and red-sensitive (E) POSS
 prints. From left to right: O839, O386, E839, and E368.


To estimate the brightness of the variable, we measured the size of the star
image and used the mean magnitude - diameter relations published by King and
Raff (1977) and Humphreys et al. (1991). The weighted means are:

               m_b = 17.2, m_r = 17.6,

with an error of approximately +-0.5m, respectively.

On several plates taken with the Schmidt telescopes of the Sonneberg 
Observatory [m_b(lim) ~= 18] and the Karl Schwarzschild Observatory [m_b(lim)
~=20m], in the SE corner of the very recently delivered (1st shipment) POSS II
transparency B240 [m_b(lim) ~= 22], as well as on a CCD V frame [m_v(lim) ~=
22] the region in question is contained, but no trace of the star is visible.

The variable thus only appears on the plate pair E and 0839. These exposures
were taken on Oct. 1/2 1953 (45min E plate, break of 6min, followed by the
12min O plate). A comparison of the star images in O and E shows, by far more
convincing than the rather inaccurate brightness data from above, the blueness
of the object. Stars with such an extremely blue colour can at best be found
among central stars (T_eff~=10^5K) of planetary nebulae. A variable of this
amplitude is, however, not known among central stars; besides, there is no
nebula visible on the POSS.

As a consequence, it is plausible that the star underwent a brightness change
during the exposure of the plate pair, with a rapid increase in brightness
during < 1 hour.

By taking the large amplitude (Delta m > 4.5m) into account, it is tempting to
speculate whether the variable is an eruptive star of some kind. In this
connection it might be of interest that there is no sign of any dark cloud or
star forming region in or near the area on the POSS and that there is no IRAS
point source at the position of the star. The variable is located just outside
the error box of the X-ray source 1H2353+471 (Wood et al. 1984).

It might be rewarding to obtain a very deep exposure (CCDs) in order to gain
more information on this object.

A part of this work was supported by the Austrian "Fonds zur Förderung der
wissenschaftlichen Forschung" (project P6345). The advice and support by Dr.
W. Gotz from the Sonneberg Observatory is gratefully acknowledged.


                            R. WEINBERGER
                            Institut fur Astronomie
                            Technikerstrasse 25
                            A-6020 Innsbruck, AUSTRIA

References:

Humphreys, R. M., Landau, R., Ghigo, F.D., Zumach, W., and LaBonte, A. 1991, AJ,
   102, 395 [BIBCODE 1991AJ....102..395H ]
King, I.R., & Raff, M.I. 1977, PASP, 89, 120 [BIBCODE 1977PASP...89..120K ]
Wood, K.S., Meekins, J. F., Yentis, D.J., Smathers, H. W., McNutt, D.P., Bleach, R.
   D., Byram, E.T., Chubb, T.A., Friedmann, H., and Meidav, M. 1984, ApJS, 56, 507 [BIBCODE 1984ApJS...56..507W ]