Var73 Dra superoutburst
Dear Colleagues,
The Kyoto observations (observers: M. Uemura and R. Ishioka) have detected a bright outburst of Var73 Dra, a long-period (probably in the period gap) SU UMa-type dwarf nova recently discovered.
The object is located at 20 23 38.193, +64 36 26.91 (J2000.0) reference Antipin and Pavlenko, A&A 391, 565 (2002). (See also vsnet-campaign-dn 2761, 2762). The superhump period has been reported to be P=0.0954 d.
The object was rising on October 4, and likely attained its maximum around October 9-10 (the data reduction was delayed because of the occurrence of GRB 021004). The maximum was around 15.0 or possibly brighter. The object has been confirmed to be still bright on October 11. Preliminary analysis of the recent data shows variations of 0.2-0.3 mag, which are likely superhumps. Further observations are strongly encouraged, since the period and period derivative of this astrophysically interesting object has not been yet well established. More detailed analysis is presently ongoing, and the results will be later reported by Uemura-san.
When sending time-series observations, please also send them to Uemura-san and Ishioka-san (uemura@kusastro.kyoto-u.ac.jp and ishioka@kusastro.kyoto-u.ac.jp) in order to avoid a delay of communication.
Good observations!
Regards, Taichi Kato VSNET Collaboration team
Var73 Dra superhump period
Dear Colleagues,
A preliminary analysis of Starkey's data (+alpha) now favors a superhump period of 0.1051(2) d. This period would make Var73 Dra a "twin" system with the NY Ser, an SU UMa-type dwarf nova in the period gap (Nogami et al. (1998) 50, L1), although other aliases are still possible. We will be able to refine the period with an upcoming combined analysis of the entire data.
Regards, Taichi Kato VSNET Collaboration team
Var73 Dra outburst again!
Dear Colleagues,
From the Kyoto observation last night (observers: R. Ishioka and M. Uemura), the SU UMa-type dwarf nova Var73 Dra is confirmed to be undergoing another outburst. The brightness is comparable to that of the October superoutburst. If the present outburst turns out to be a superoutburst, Var73 Dra may become the first object having a supercycle length between usual SU UMa stars and ER UMa stars. Although the season is slightly late, we encourage further follow-up observations of the current outburst. Even nightly snapshot observations would be very helpful in determining the properties of this outburst. Please send your observations to the VSNET Collaboration team.
Happy observing!
Regards, Taichi Kato VSNET Collaboration team
Var73 Dra: first ER UMa-like dwarf nova in the period gap?
Donn Starkey's most recent observation almost certainly confirms that the present outburst is a superoutburst(!). This finding suggests that the minimum supercycle length of Var73 Dra is around 60 d (or possibly slightly shorter). This shortness of the supercycle is comparable to those of ER UMa-type dwarf novae. In conjunction with Antipin and Pavlenko (2002) A&A 391, 565, the supercycle of this object may not be as stable as in ER UMa stars. Such a variation of the supercycles was also recorded in the in-the-gap SU UMa-type dwarf nova, NY Ser (Nogami et al. 1998, PASJ 50, L1).
Further observations of Var73 Dra during the present outburst is planned. We also strongly encourage multi-longitude observations to compensate the short visibility in this season.
Regards, Taichi Kato VSNET Collaboration team
Authors: D. Nogami, M. Uemura, R. Ishioka, T. Kato, K. Torii, D.R. Starkey,
K. Tanabe, T. Vanmunster, E.P. Pavlenko, V.P. Goranskij, E.A. Barsukova,
O. Antoniuk, B. Martin, L.M. Cook, G. Masi, F. Mallia
Abstract:
An intensive photometric-observation campaign of the recently discovered
SU UMa-type dwarf nova, Var73 Dra was conducted from 2002 August to 2003
February. We caught three superoutbursts in 2002 October, December and
2003 February. The recurrence cycle of the superoutburst (supercycle)
is indicated to be ~60 d, the shortest among the values known so far
in SU UMa stars and close to those of ER UMa stars. The superhump
periods measured during the first two superoutbursts were 0.104885(93) d,
and 0.10623(16) d, respectively. A 0.10424(3)-d periodicity was
detected in quiescence. The change rate of the superhump period during
the second superoutburst was 1.7x10^-3, which is an order of
magnitude larger than the largest value ever known. Outburst activity
has changed from a phase of frequent normal outbursts and infrequent
superoutbursts in 2001 to a phase of infrequent normal outbursts and
frequent superoutbursts in 2002. Our observations are negative to an
idea that this star is an related object to ER UMa stars in terms of the
duty cycle of the superoutburst and the recurrence cycle of the normal
outburst. However, to trace the superhump evolution throughout a
superoutburst, and from quiescence more effectively, may give a fruitful
result on this matter.
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