COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3331

                                           Konkoly Observatory
                                           Budapest
                                           24 May 1989

                                           HU ISSN 0374 - 0676


  SEARCH FOR OPTICAL BRIGHTENINGS OF THE X-RAY TRANSIENT EXO 0748-676


The transient X-ray source EXO 0748-676 detected by Parmar et al. (1985) was
identified with a faint (>=17 mag.) but variable (Delta_m >= 6 mag.) star by
Wade et al. (1985). The optical object exhibits a spectrum resembling those
of other low-mass binary X-ray transients and luminous cataclysmic variable
stars, such as nova-like variables and dwarf novae in outbursts.

The error box of EXO 0748-676 was examined on 351 plates (representing roughly
350 h of monitoring time) taken at the southern stations of the Bamberg
Observatory in the years 1963-1976. The typical limiting magnitudes on the
plates are between 13 and 15 (m_B). The proposed optical candidate is
invisible on all investigated plates and, similarly, no other variable optical
phenomena were found. We conclude that either the brightenings of the object
are infrequent or the maxima are fainter than m_v ~14.


RENE HUDEC
Astronomical Institute
Czechoslovak Academy of Sciences
251 65 Ondrejov
Czechoslovakia


References:

Parmar, A.N., White, N.E., Giommi, P., and Haberl, F. 1985, IAU Circ., No. 4039. [BIBCODE 1985IAUC.4039....1P ]
Wade, R.A., Quintana, H., Horne, K., and Marsh, T.R. 1985, Publ. Astron. Soc.
   Pacific, 97, 1092. [BIBCODE 1985PASP...97.1092W ]