[vsnet-chat 4028] Re: on the presence of helium novae (V445 Pup)

[Taichi Kato <tkato>]

Re: on the presence of helium novae (V445 Pup)

Dear Alon and all,

> Dr. Kato might remember
> that I speculated the presence of helium novae in a talk given in
> the Kyoto conference in 1998.

    Yes, I vividly remember your presentation of your "unification theory"
of novae.

> However, it should be noted that according
> to (Mariko) Kato, Saio & Hachisu  (1989) a helium nova is possible if
> the mass transfer rates are very high - ~5^{-8} Msolar/yr. This limit
> exceeds by 2 factors the values estimated for the AM CVn systems.

    Since the mass-transfer rate of AM CVn systems (cataclysmic variables
with helium white dwarfs) is regarded as a consequence of angular momentum
removal by the gravitational wave radiation, there should be an even
tighter upper limit to mass-transfer rates than in hydrogen-rich
non-degenerate (i.e. usual) CVs.  So the progenitor would be unlike
'classical' AM CVn systems.  If the requested high value of mass-transfer
was achived, the progenitor system may well have transferred matter
via Roche-lobe overflow of an evolving secondary (as in the helium star
path depicted by Iben 1991).  Perhaps the sole point not all of us agree
is the consequence of the helium ignition on the surface of a white dwarf.

    I might add a comment on the supposed existence of Ca I line (the strong
line close to the wavelength close to H alpha).  This species seems to be
rarely met in (classical) novae, but its existence is proposed in some
SNe Ia.  Together with the apparent (complete?) absence of hydrogen, the
environment may have been similar to those producing SNe Ia.

    The spectrum is in some degree similar to the hydrogen deficient hot
R CrB star MV Sgr, though this object is not known as an erupting object,
and though the velocity in V445 Pup is far larger than that of MV Sgr.
A missing link to MV Sgr-type star? -- yet another speculation.

Regards,
Taichi Kato

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