COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3079


                                          Konkoly Observatory
                                          Budapest
                                          31 August 1987

                                          HU ISSN 0374-0676


                        LET'S FORGET DO Dra


  A 16th magnitude cataclysmic variable has recently been identified as the
optical counterpart of a HEAO-1 and HEAO-2 X-ray source (Patterson et al.1982).
Because the X-ray and optical positions agree to within the 1' accuracy of the
X-ray position, and because the X-ray flux and spectrum are about what is 
expected from cataclysmic variables, there is essentially no doubt that the star
is the X-ray source. Hazen (1985) and Wenzel (1983) have searched plate collections
and found brightenings to m ~12 which are probably dwarf nova eruptions.
  What is perhaps less clear, at first glance, is that this star is extremely
likely to be the variable star noted by Tsesevich (1934) and catalogued as
"YY Dra" in all editions of the General Catalogue of Variable Stars. In particular,
Wenzel (1983) has expressed doubt on this point, prompting the assignment 
of a new variable star name (DO Dra) to the dwarf nova. This seems quite
ill-advised, because, as we shall see, the confusion probably arises from
fairly routine errors in position and photometric classification.
  The positional data are shown in Figure 1 and Table I. The lower circle and
various diagonal lines show the X-ray positions, and (I leave out the detailed
arguments, but they can be found in Patterson et al. (1987)) are all consistent
with the position of the dwarf nova, star D. The upper circle, drawn with an
arbitrary 40" error radius, shows Tsesevich's stated position for YY Dra. The
other constraint on the problem comes from Tsesevich's analysis of the brightness
variations; he suggested an Algol-type binary varying from m = 12.9 to >14.5
with a period of 4.21123 days. But we have scanned over 500 plates in the
Harvard plate collection, and have found no Algol-type light variations for
any star in the field (covering typically about 20' by 20'). Wenzel (1983)
reports the same result from 700 additional archival plates. We can envision
only two solutions: either the reported position of YY Dra is grossly in error,
and the star is now lost; or the reported position is in error by 53", and
YY Dra is identical to the dwarf nova. We strongly favor the second hypothesis,
for these reasons:


                             [FIGURE 1]


           TABLE 1. Measured positions (1950.0)
   

   star D (+/- 1.5")                11h40m48.83s  71d 57' 59"
   HEAO-2 X-ray (+/-1')             11h40m44.7s   71d 58' 3"
   (E1140.8+7158)
   GCVS "YY Dra"                    11h40m45s     71d 58' 48"

(1) AC these high galactic latitudes, the incidence of variable stars is about
0.03/deg^2, so the probability that an erroneous position would accidentally.
fall within 1' of a true variable star is ~ 10^5.
(2) A 13th magnitude Algol binary at high latitude is intrinsically somewhat
suspicious. For a typical M in the range -1 to +3, one obtains distances of
1-6 kpc -- placing the star well out in the galactic halo, where binaries of
any kind seem to be quite rare (Batten 1973). Inspection of the entire Variable
Star Catalogue reveals only 3 Algol-type ("EA") stars with m.> 12.5 in
the 10^4 deg^2 at the galactic poles (b>45deg).
(3) A positional error of 53" is not unusual. The accurate coordinates of 23
cataclysmic variables measured by Lopez (1985) showed an rms offset of 41",
compared to the GCVS positions.
(4) It is not difficult to imagine how a sparse set of photographic magnitudes,
for a star never observed before or since, could have produced a spurious 
period and light curve. There are hundreds of precedents.

  Thus we have substantial confidence that the star we now recognize as a
dwarf nova is YY Dra, the star observed by Tsesevich. The point may seem 
somewhat academic, but is made here in the interests of accuracy and reasonable
nomenclature. Variable stars are commonly re-classified, but that does not
warrant re-naming them.
   Let's consign the name of DO Dra to a richly deserved oblivion.




                          JOSEPH PATTERSON

                          NINA EISENMAN

                          Department of Astronomy
                          Columbia University
                          New York, NY 10027

References:

Batten, A.H. 1973, Binary and Multiple Systems of Stars (Pergamon:Oxford). [BIBCODE 1973bmss.book.....B ]
Hazen, M. 1985, IBVS No. 2880.
Lopez, C. 1985, IBVS No. 2837.
Patterson, J., Schwartz, D.A., Bradt, H., Remillard, R., McHardy, I.I., Pye, J.P.,
         Williams, G., Fesen, R.A. and Szkody, P. 1982, B.A.A.S., 14, 618. [BIBCODE 1982BAAS...14Q.618P ]
Patterson, J. 1987, in preparation.
Tsesevich, W. 1934, Variable Stars, 4, 291.
Wenzel, W. 1983, IBVS No. 2262.