[vsnet-chat 342] Re: any black-hole transient candidates?

[Taichi Kato <tkato>]

Erik Kuulkers wrote in [vsnet-chat 340]:

> The only obvious potential black-hole transient progenitors are those which 
> have been shown outbursts before, such as V616 Mon (Nova Mon 1975) and
> V404 Cyg (Nova Cyg 1989). V616 Mon has had an outburst in 1917 and 1975
> suggesting a recurrence time of ~58 years, while V404 Cyg showed outbursts 
> in 1938 and 1989.

   I should comment that V404 Cyg experienced at least one more outburst
in 1956 (Richter 1989, IBVS 3362).

   Their positive observations from 1462 Sonneberg plates between 1928
and 1989.

              JD             B
    1938   2429193.34      13.7:
              9194.36      13.5
              9216.28      13.3
    1956   2435685.40      14.1::
              5691.41      14.3
              5694.52      14.5:
    1979   2444142.93      13.4? uncertain
    1989   2447706.43      16.2
                  .44      16.3
                  .45      16.3
                  .47      16.2

   My concern is whether we can discern such sources before any outbursts
occur.  Have there been any attempts?  Or are there more dormant beuties
among known galactic novae?

> Such objects are very faint in quiescence (V~18 mag for V616 Mon, while
> typically fainter than 19-20 mag for others), and are therefore very 
> difficult to find. 

   I believe X-ray Nova Sco (GRO J1655-40) is brighter.  Aren't they
well within the reach of recent massive variable star surveys, like MACHO
or OGLE?

Regards,
Taichi Kato

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