COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3154

                                      Konkoly Observatory
                                      Budapest
                                      10 March 1988

                                      HU ISSN 0374-0676



               SHOULD WE REALLY FORGET DO Dra?

  In a recent paper (Patterson and Eisenman, 1987) it is argued that the
HEAO-2 X-ray source E1140.8+7158, recently identified with a 16th magnitude
cataclysmic variable, is in fact identical with the variable star YY Dra
(discovered by Tsesevich, 1934, and classified by him as an Algol-type star
with a period of 4.21123 d). So Patterson and Eisenman consider the decision
taken by us (Kholopov et al., 1985) to assign a new variable star name (DO Dra)
to the dwarf nova to be erroneous.
  The problem of YY Dra is really a complicated one; our attempts to get
additional information from Prof. Tsesevich have been described elsewhere
(Samus, 1988 ab). Evidence for the identity of E1140.8+7158 and YY Dra presented
by Patterson and Eisenman is surely of considerable interest and will be taken
into account in our work. However, this evidence is not absolutely convincing
(this is discussed in some more detail below), and we feel that some misunderstanding
exists about principles of assigning (or not assigning) new names to
variable stars. In fact, in dubious cases we always tend to not to assign a new
name to a star not sufficiently studied and not easily identified on the sky
if a possibility exists of its being identical with a better studied and readily
identified named variable star. On the contrary, we tend to assign a new name to
a well studied and easily identified star if there is a grounded possibility
of its being not identical with a poorer studied and not readily identified star.
  Now, the main reasons for Patterson and Eisenman's belief that the X-ray source
and YY Dra cannot be different stars are of statistical nature. It is well known
that such arguments are valid only a priori, and if it turns out that the 
improbable case of YY and DO Dra being not identical does take place in reality,
any such argument will be of no use. Moreover, some of Patterson and Eisenman's
points of argument could be criticised. The incidence of variable stars at high
galactic latitudes is in fact the incidence of known variable stars, and the
completeness at these latitudes may not be good. We also would recommend, when
discussing the number of bright Algols in the GCVS, to consider also "E", not
only "EA" stars.

  Finally, we agree that Tsesevich could probably give a wrong position;
quite obviously his magnitudes could be too bright (many similar cases are known
in the publications of the 30s). However, an active researcher of variable stars
would never take a dwarf nova (almost always in minimum light!) for an Algol
star (almost always in maximum light!) and never find a period with many decimals
unless it is at least an alias period.

  To conclude, we do not recommend to forget DO Dra, and we do not recommend
to forget YY Dra, either. If one really wants to forget something, it would be
better to forget YY Dra until it is proven that DO Dra and YY Dra are the same,
or until the real YY Dra is found. As a group responsible for the names of
variable stars we are very much interested in avoiding confusion and strongly
recommend to use the name DO Dra for E1140.8+7158.





P.N. KHOLOPOV

Sternberg Astronomical
Institute
13, University Avenue,
Moscow 119899, USSR

N.N. SAMUS

The Astronomical Council
of the USSR Academy of Sci.
48, Pyatnitskaya Str.,
Moscow 109017, USSR




References;
Kholopov, P.N., Samus, N.N., Karazovets, E.V., Perova, N.B. 1985, 
  I.B.V.S. No. 2681.
Patterson, J., Eisenman, N. 1987, I.B.V.S., No. 3079.
Samus, N.N. 1988a, in "Istoriko-Astronomicheskiye Issledovaniya" ("Studies in
  the History of Astronomy", in Russian), Moscow, "Nauka" Publishers
  (in press). [BIBCODE 1988IAIss..20..216S ]
Samus, N.N. 1988b, l'Astronomia (in Italian; in press).
Tsesevich, W. 1934, Variable Stars, 4, 291.