Taichi Kato
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.
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 (see below, we should call the CV DO Dra, and should reserve YY Dra for the missed variable; the VSNET reports will stick to using DO Dra until the identification problem is settled).
Despite polemic in the literature, the GCVS team strongly insists that the cataclysmic star should be called DO Dra, whereas the name YY Dra is reserved for the (apparently lost) eclipsing variable originally discovered by Tsessevich. Interesting enough, Tsessevich claimed he had not forgotten the field, but the plate from the Moscow collection on which we had asked him to mark the star did not arrive in time - he died!
Tsessevich's observations used Simeiz plates. A part of Simeiz collection perished in the World War II, another part survived and is now in Pulkovo. The Pulkovo collection does not contain plates around the dates of minima originally announced by Tsessevich. Also, some plates could survive and be taken to Odessa, but, again, they could not be found so far.
Tsessevich was a VERY experienced person and could not mix up an eclipser with a dwarf nova.
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
Return to Daisaku Nogami's page
Return to HomePage