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[vsnet-obs 4121] (repost) some more about DO Dra (YY Dra)

   Repost of vsnet 574 (1996 Mar. 13), when DO Dra showed a minor brightening.

   (Sorry the VSNET Home Page is currently unavailable.)

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   DO Dra is recently reported (cf. vsnet-obs postings, VSNET home page)
to be siginificantly brighter than its usual quiescence (esp. "low" state
quiescence).  As it has been already 5.5 years since its last major
outburst (probably long overdue), the observers should keep a close eye
on this dwarf nova to see whether the current enhanced quiescent activity
may be a precursor of a major outburst or not.

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   Although this might be a well-known history ...

   DO Dra was originally an optically identified X-ray source 3A1148+719,
independently by Green et al. during their course of the famous Palomar-
Green (PG) Survey of ultraviolet-excess objects, and by Patterson (1982).
They soon (?) identified the X-ray source with a 15-16 mag star exhibiting
a CV spectrum.  However, the X-ray error box also contained an already
designated eclipsing variable, YY Dra.  Wenzel (1983) examined the Sonneberg
plate collection for the period 1928-1982, and concluded there is no
corresponding eclipsing variable designated in GCVS; indeed he found
an apparent dwarf nova with recorded outbursts.  Upon these, the optical
counterpart was designated as a variable star, DO Dra, in the 67-th Name
List of Variable Stars (1984), with a statement in its remark that the CV
is not identical with YY Dra; this later caused a lot of confusion in
nomenclature of the CV.  Please read DO Dra = YY Dra when necessary.

   A summary of historical outbursts (Wenzel 1983, Hazen IBVS No. 2880):

   JD (2400000+)   mpg
         28262.7  <12.2
         28266.7   10.8:
         28267.7   11.1
         28273.7  <12.2

         31498.7  <14.5
         31499.7  <12.2
         31504.7   10.0:
         31505.8   10.8:
         31506.7   11.2
         31511.6  <12.2
         31519.9  <13.7

         33242.9   11.2
         33279.8  <14.4

         37761.4  <12.0
         37764.4   10.0
         37785.5  <12.0

         40153.4  <12.5
         40171.3   10.8
         40173.3   13.0
         40187.4  <13.8
         40188.7  <14.4

         42717.3  <13.5
         42740.3   10.5
         42750.4  <12.0
         42756.4  <13.0

         46364.3  <13.8  (IAUC 4130)
         46367.3   10.5      "
         46367.7   10.6      "

   The variable has been extensively monitored by visual observers,
yielding a successful detection of a new outburst in 1985 Oct. (the last
one in the table).  [I remember it was an exceptionally clear night in
Japan, when I was observing Comet Halley -- and missed the outburst.
To me the year of 1985 sounds like the most memorable -- chance detection
of eclipses in IP Peg during an outburst, first encounter with Comet Halley,
totally unexpected burst of Giacobinids..]

   DO Dra is notable for its low outburst frequency and outburst duty
cycle.  In Sonneberg plate collections, DO Dra was detected on only
four nights out of a total of 2175 nights.  The outburst duty cycle
of ~0.002 is the second smallest to that of WZ Sge (~0.001).  Another
characterstic of this dwarf nova can be found in its extreme shortness
of the duration of outbursts, as already evident in the table above.
[From the VSOLJ record for the period of 1984-1990, the object was
observed in outburst on only three nights out of 912 nights and 1677
observations.  At the meetings of variable star observers, sad stories
of missed outbursts are often the topics among experienced observers.]

Regards,
Taichi Kato