[vsnet-alert 9776] Re: BZ Cam outburst!

[Taichi Kato]

>   I have an impression that the long-term light curve more resembles
> that of a supersoft X-ray source, such as QR And.
> Given the rather unusual properties, including the presence of
> bow-shock nebula atypical for a CV and photo-ionized emission
> nebula (see Greiner et al. 2001 above), the object may be better
> understood as a (low-luminosity?) supersoft X-ray
> binary rather than a classical novalike system (see also discussion
> by Greiner et al.).

   Further to note, I have an impression that there are two types
of "VY Scl-type" stars.  One is "classical" VY Scl-type stars, which
normally stay at a relatively constant magnitude, but experience
long-lasting distinct low states.  The other is (essentially) supersoft
X-ray binaries (and analogs) whose shallow "low states" were
phenomenologically interpreted as classical VY Scl-type low states.

   By mechanism, the low states of the former are reduced mass-transfer
rate caused by the secondary (spots etc?), while those of the latter
could by caused by a limit cycle-type phenomenon.  As proposed by
Hachisu and Kato 2003 (ApJ 588, 1003), this cycle can be maintained
by the coupling of wind and orbital angular momenta.  If this
interpretation can apply to BZ Cam, the presence of atypically strong
wind (and thereby a shock nebula?) and QR And/RX J0513.9-6951-like
quasi-cyclic high/low transition may be naturally explained.

   By the way, the current rise is a bit too rapid -- wouldn't there
be a possibility of an ongoing nova outburst (?!) -- think if the object
is near the borderline of steady nuclear burning, as in T Pyx,
and let's see what is actually going on there, particularly in the
light that the object was considered a candidate ex-nova
(cf. Ellis et al. 1984, PASP 96, 283).