[vsnet-chat 1662] Re: on the fast rise to maximum of U Sco

[Ulisse Munari <munari@astras.pd.astro.it>]

> On the event itself:
> Is this fast evolution a known fact for NRs or are these first such
> data?  There is the possibility of a wrong observation from my part,
> but I seriously doubt this to be the case... 

this is quite usual for recurrent novae. They should harbour a VERY
massive white dwarf (i.e. very close to the Chandrasekar limit around 1.4 
solar masses) with a minimal accreted envelope which reaction time to the 
onset of the nuclear reactions is therefore very fast (a matter of hours)

Berto's observation (I understand it caught U Sco during rise to
maximum, the quiescence brightness being around 19 mag if my memory
is still supporting me) is indeed perhaps unique in the U Sco history
of previous outbursts (1863, 1906, 1936, 1979, 1987), because it is
strategically placed in time to set a firm value on the onset time of such
spectacular events.

Being so little the accreted material on the white dwarf, you may also
expect that the outburst will take little time to process that material,
and therefore the return to quiescence should be quite fast.
Indeed U Sco is the nova with the shortest outburst duration:
C. Payne-Gaposchkin in 1964 reported U Sco as the record keeper with
a fantastic 0.67 mag/day decline.

Ulisse

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