[vsnet-alert 4586] BC UMa superhumps and early superhumps

[Taichi Kato <tkato>]

BC UMa superhumps and early superhumps

Dear Colleagues,

    A preliminary analysis of the combined data set on BC UMa submitted to
the VSNET Collaboration team, including the Kyoto data, until Apr. 7 has
revealed the remarkable growth of "true" superhumps (see also vsnet-obs
27154, vsnet-alert 4584).  The long delay of the superhump growth, the
detection of "early superhumps" (vsnet-alert 4562) and their subsequent
decay are all characterstic of a WZ Sge-type superoutburst.

    A preliminary analysis of fully grown superhumps has yielded a refined
superhump period of 0.06426 d.  The analysis of the second to third night
of the outburst (early superhumps) has yield a period of 0.0621 d, which is
remakably close to the previously determined "superhump" period (0.0619 d)
by Iida (1994).  If we assume these period reflect common superhump and
orbital period, the fractional superhump excess becomes ~3 percent.
The periodicity in the earliest data (vsnet-alert 4562) thus can be
"negative superhump", whose existence in the early superoutbursting stage
has been recently suggested (Gao et al. 1999, ApJ 527, L55).  The present
observation may be the second exmplification of such a phenomenon.

    A more complete analysis and further observations are under way (with
a strong competition with XTE J1118+480!).  We hope we can present a more
detailed matter as the progress of the observations.  Observations of both
remarkable sources (BC UMa and XTE J1118+480) are strongly encouraged and
we would be happy to hear any more reports.

Regards,
Makoto Uemura, Taichi Kato, Sergei Shugarov, Elena Pavlenko, Patrick Schmeer,
Rudolf Novak, Gianluca Masi
On behalf of the VSNET collaboration team

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp