[vsnet-chat 3431] Re: Permanent Superhumpers...

[Alon Retter <ar@astro.keele.ac.uk>]

>    It seems (also from the paragraphs above and below) that you assume
> "the observed signals in long-period systems having periods different
> from orbital periods" are the same superhumps as those in short-period
> systems.  Yes, this may be a matter of the definition of the "superhump"
> terminology, but it is not well established whether this modulation is
> caused by the same mechanism which produces well-established SU UMa-type
> superhumps.  For example, period vs. "superhump" excess relation is
> different from that of short-period systems.  This might suggests that
> a completely different mechanism may be relevant.  In such a case, the
> classification based on tidal stability may make no sense.  The in-the-gap
> system V795 Her is perfectly on the SU UMa-type superhump excess relation;
> this is why this system is a natural extension of SU UMa systems toward
> novalike or longer period systems, but the situation is less clear in
> even longer period systems.  Some recent simulations suggest that these
> "superhumps" need to be reconsidered (not on the naive extension of
> short-period systems) using more detailed fluid treatment [NB the original
> tidal instability does not require fluid as an essential part].
> Remebering this, one should be more conservative in observationally
> determining the tidal stability limit from "superhumps" in long-period
> systems.

I'm sorry, but I completely disagree. The relation between the superhump
period excess and the orbital period in CVs above the gap is not
significantly different from that of SU UMa systems, and may result simply
because of low statistics, higher mass ratios above the gap (see Murray
2000) or from the possibility that in superoutbursts of SU UMa systems the
accretion discs become more elliptical than in permanent superhump systems
(thus having higher period excess). Remember that in SU UMa systems, when
decaying from a superoutburst, the superhump period is typically
decreases.

The fact that we don't have SU UMa systems just above the gap (P=3-4 h),
can be understood within the current models. In fact, in our preprint
on TV Col (MNRAS, submitted), we actually predict the presence of SU UMa
systems with orbital periods above the gap (and up to at least 5.5 h -
the orbital period of TV Col. I believe that SU UMa system and permanent
superhump systems are the same binaries with a small mass ratio but just
at different stages in its life time. Therefore there should be any
significant difference between superhumps in SU UMa systems and superhumps
in permanent superhump systems.

>    Keeping this and original definition in mind, Osaki's "permanent
> superhumpers" should be better understood in a narrower sense, as thermally
> stable systems which show superhumps having the same properties as our
> familiar SU UMa-type superhumps.

Again, I believe that superhumps are the same superhumps whether they
appear in SU UMa systems, permanent superhump systems or other CVs.
 
Regards,
Alon
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