COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                               Number 2481

                                                    Konkoly Observatory
                                                    Budapest
                                                    22 February 1984

                                                    HU ISSN 0374-0676



         ON THE NATURE OF THE CATACLYSMIC BINARY V 2051 OPHIUCHI


  According to the literature V 2051 Oph belongs to the six cataclysmic
binaries (with late type secondaries) known to have orbital periods below 90
minutes. Two of them are known as of AM Herculis type, three are dwarf novae
with very long cycle lengths, but the long time photometric character of
V 2051 Oph has not been fully investigated as yet. Sanduleak and Bateson
report of unspecified brightness changes between V ~~ 13.0m and the Palomar O
print B value, which is 15.4m in Vogt's system ( Publ. Variable Star Sect.
RASNZ no. 8) rather than 16.5m estimated by Sanduleak (Inf.Bull. Variable Stars
No. 663). A number of high speed photometric series yielded eclipsing light
curves with periods near 89.9 minutes and a mean brightness outside eclipses
of V ~~ B ~~ 15.0m.
  I checked the region of the variable on about 400 blue sensitive plates of
the Sonneberg Sky Patrol taken from 1957 to 1983 by H. Huth of the field
centred at 17h, -20d. Because of the very low altitude above the horizon the
limiting brightness of must of these plates is nut better than 11.5m to 13m.
   The object is not visible on any exposure. That means that two alternative
explanations are possible: Either V 2051 Oph does represent a dwarf nova with
large range outbursts, but has an extremely long cycle length (several years) so
that eruptions can easily be missed even on extended plate material, or the
relatively small variations mentioned above and occuring below the threshold
of our exposures are due to an AM Herculis type for which, apart from eclipses,
an amplitude of about 2.5 mag is typical. Both possibilities would not be
in contrast with the character of the other five cataclysmic binaries of similar
orbital periods.


                   W. WENZEL
             Sternwarte Sonneberg
             Zentralinstitut für Astrophysik
             der Akademie der Wissenschaften
             der DDR