[vsnet-chat 358] Re: any black-hole transient candidates?

[Erik Kuulkers <e.kuulkers1@physics.oxford.ac.uk>]

Taichi Kato wrote in [vsnet-chat 342]:

>    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?

Certainly there will be a lot more dormant transients out there, but I 
don't know if there have been attempts to find them. It's probably a 
similar kind of search as you do for faint CVs. You look for blue 
objects, which show emission lines.

> > 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?

Indeed, X-ray Nova Sco is brighter in quiescence (V~17) mag), but it isn't 
a "normal" X-ray transient as many others which show one outburst (with 
maybe some rebrightenings) after decades of quiescence. 
I don't think MACHO reaches it, because they are mainly looking at stars 
in the LMC/SMC and the Galactic center (if I remember correctly).
I'm not sure about OGLE. 

Regards,

Erik Kuulkers

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