Rare Superoutburst of BC UMa in 2003 February

(BC UMa in superoutburst, V-band CCD image taken on Feb. 1 by K. Nakajima)


(vsnet-alert 7633)

BC UMa rare outburst!

Dear Colleagues,

Patrick Schmeer just reported an outburst of the rarely outbursting SU UMa-type dwarf nova BC UMa!!

Subject: [vsnet-outburst 5162] BC UMa in outburst

UMABC 20030201.205 127 Scp

The last outburst was in 2001 June (Simonsen, short outburst). The preceding outburst (superoutburst and a rebrightening) in 2000 March-April (detected during the rising stage by Schmeer). There had long been no confirmed outburst before the year 2000.



for the 2000 superoutburst.

Further time-resolved CCD photometry is very strongly encouraged! During the 2000 superoutburst, "early superhumps" were possibly observed (see vsnet-alert 4562, 4567, 4577). Urgent observations are most strongly needed!

Taichi Kato
VSNET Collaboration team

Early Observations

(vsnet-campaign-dn 3394)

BC UMa observation by Nakajima-san

Dear Colleagues,

We have received nearly 6-hour observation from K. Nakajima-san (Mie, Japan). Although there existed small light variations, no clear superhumps have been recorded. However, the characterstic time-scales of the variations seem to be similar to those of other short-period SU UMa stars before superhumps actually grow. These variations may suggest that the present outburst will evolve into a genuine superoutburst, and we are witnessing its earliest stage. We have also received a successful communication of observation from H. Maehara-san (Saitama, Japan). These observations will be reviewed when the results become available.

Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3402)

BC UMa: early superhumps?

Dear Colleagues,

We have received a complete set of data from Maehara-san. An analysis of the combined data on Feb. 1 reported up to now is consistent with the presence of low-amplitude double-wave modulations with a period close to the orbital period (the best period from the Feb. 1 data is around 0.062 d). This feature resembles those of "early superhumps" in WZ Sge-type dwarf novae (see Kato (2002) PASJ 54, L11; also see http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/wzsge01.html for the representative WZ Sge light curves).

If the current outburst indeed evolves into a genuine superoutburst, the present observation seems to illustrate a supposed link between WZ Sge-type stars and BC UMa (see Kato et al. (2001) PASJ 53, 1191 for more discussion).

Phase-averaged light curve on Feb. 1:

Taichi Kato
VSNET Collaboration team

Growing Superhumps!

(vsnet-alert 7636)

BC UMa: superoutburst! growth of genuine superhumps!

Dear Colleagues,

We have received new sets of data from David Boyd and Kazuhiro Nakajima-san. Boyd's observation covered the important part of the early stage, which showed a slightly decayed early modulations (early superhumps?). Nakajima-san's 8-hr long observation last night clearly shows the growth of genuine superhumps (ampliude growing to 0.1 mag). The period of the signal is slightly longer than 0.064 d, which qualifies the signal as the genuine superhumps! However, the profile of these humps is slightly unlike those of usual SU UMa-type superhumps, particularly in that the rise is slower and there is some tendency of a double wave. It is possible, as in the transition of WZ Sge from early superhumps to genuine superhumps, the major peak of the early double-wave modulations eventually developed into genuine superhumps. BC UMa would become a key object in clarifying the peculiar behavior of WZ Sge-type dwarf novae!

We have also received additional notes of successful observations during the past two days. We hope we will be able to fully illustrate the growth of superhumps in the very important system BC UMa.

Further observations are very strongly encouraged. Please also send your observations to Uemura-san (uemura@kusastro.kyoto-u.ac.jp) and Ishioka-san (ishioka@kusastro.kyoto-u.ac.jp) in order to avoid a delay in communication.

Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3409)

BC UMa: fully grown superhumps

Dear Collagues,

We have received further very impressive data from David Boyd, making a fully continous light curve on Feb. 3. The superhumps have a full amplitude of 0.3 mag. We have also received data from Kiyota-san, Torii-san (RIKEN) and usual data at Kyoto. Updated period and O-C analyses will be later reported by Uemura-san or Ishioka-san when the dataset becomes more complete.

Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3423)

BC UMa: superhump period change

Dear Colleagues,

We have received further extensive data from Nakajima-san and David Boyd, and regular additions from Torii-san (RIKEN) and Kyoto observations. The resultant analysis seems to show emerging evidence of a superhump period growth. Disregarding the initial stages of early superhumps? and genuine superhump growth, the period derivative has been determined to be dot(P)/P ~ 8*10^5. We hope we will soon be able to refine the value with the progress of the ongoing analysis. The present outburst is becming the best observed superoutburst of BC UMa in the history; further nightly observations are very strongly encouraged.

Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3431)

BC UMa superoutburst: superhump period change

Dear Colleagues,

We have received new BC UMa observations from Jochen Pietz (2 nights) and Nakajima-san (2 nights), further analyzed the Kyoto and Torii-san (RIKEN) observations. The superoutburst still continues even after 12 d of the detection of the outburst.

The period change of the superhumps is rather unusual and complex. After the initial period of the period increase, the period suddenly started shortening. Up to now, the mean period of the superhumps decrased by 0.5%, which is an unusually large value. The overall period bahavior somehow looks like that of AL Com in 1995, but the amplitude of the variation is larger.

Further analysis and observation are in progress. Thanks to the excellent midnight visibility, the coverage has been surprisingly good. Please keep the present excellent coverage and continue for some while even after the expected transition to quiescence.

Taichi Kato
VSNET Collaboration team

Related systems

(Mainly objects showing positive Pdot)

WX Cet
V1028 Cyg
AL Com
AL Com (2001 May)
RZ Leo
HV Vir
V485 Cen
1RXS J232953.9+062814
WZ Sge stars
WZ Sge
International TOAD watch

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Light curve

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