[vsnet-chat 1124] Re: helium dwarf novae (SN1998di)

[Taichi Kato <tkato>]

Re: helium dwarf novae

>   I've been querying the General Catalog of Variable Stars (4th Ed) and
> have seen some errors, according with your data. First, there is no entry
> for CR Boo; second, V803 Cen is clasified as RCB. CP Eri is UG: (dwarf
> nova, right?).

    You are all right.  The category of this variable has been established
(I believe so) after the latest edition of the GCVS.  CR Boo, originally
PG 1346+082, was revealed in 1986; V803 Cen was discovered as a hydrogen-
deficient variable star with faint episodes (thus was considered as an
RCB variable).  The properties of CP Eri was not known until 1992.
These stars are, in a broad sense just as our familiar "CV" classification,
generally called as "AM CVn stars".  Yet confusing is in some literatures
the class abbreviation "AM" is used both for AM Her-type (polars) and
AM CVn-types.  This explains why AAVSO newflashes continue designating
CR Boo as a "magnetic variable".

    AM CVn stars, or short-period helium CVs, believed to consist of white
dwarfs and mass-supplying helium white dwarfs can be categorized as below:

    AM CVn, HP Lib : disk is thermally stable; corresponding to NLs in
                     hydrogen-rich CVs
    CR Boo, V803 Cen, CP Eri: disk is thermally unstable; corresponding to
                     UG stars in hydrogen-rich CVs (helium dwarf novae)
    GP Com: disk is almost steadily in a low state.  No one knows whether
                     this star has ever or will be in outburst.
                     Claimed to correspond to WZ Sge in hydrogen-rich CVs.

    SN1998di apparently undergoes a large (>4 mag or so) variation in a short
period.  So it is most likely the system belong to the second subgroup.
Of course, there is a possibility the new star comprises a totally new
subgroup....

>   Also, is there any updated edition of GCVS where the new variables and
> parameters are introduced? I have downloaded it recently from
> cdsweb.u-strasgb.fr. 

    I have heard the GCVS team is continuously updating the original file.
You may hear more details from Prof. N. Samus (samus@sai.msu.su), the chief
of the GCVS editorial.

Regards,
Taichi Kato

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