[vsnet-chat 3154] CVs & Faint Xray Sources...

[no name <crawl@zoom.co.uk>]

In vsnet-id 236 Berto Monard makes an interesting point re red dwarfs in
the RASS-PSC.

Sufficient RASS [ROSAT All Sky Survey] objects appear to match tightly
some nearby eclipsing binaries, red dwarf / flare stars, and for the FSC
even just "normal" visual binaries [and I _mean_ binaries, not optical
doubles] that maybes the following can also be the case. [FSC & BSC =
Faint and Bright Source Catalogues respectively].

That is, that some of the Faint sources aren't telling us that the white
dwarf is a faint xray source, but that the secondary is
"chromospherically" active.

I'm a bit behind on my reading re CV secondaries, and am not sure
whether they are capable of having *true* chromospheres, but can't see
why they shouldn't be equatable to flare stars in some respects.

But such sources wouldn't really be expected to be as xray hard as CVs,
so inappropriate hardness values may not be a problem...

...a red dwarf / flare star type xray signature where no appropriate
nearby star or EB is listed could be a secondary indicator of a secret
CV [??].

A lot of the CVs Taichi Kato is noting as in the RASS-FSC have broad
detection ranges [ie equally "bright" across the full (investigated)
xray bandpass.  Then again, most FSC objects do...].  I assume xrays
from bright sources are thermally produced on the white dwarf boundary
layer &/or accretion disk, which'd suggest black body profiles, and thus
a tighter peak range...

Then there's the possibility of brehmstrahlung xrays I suppose, with
some secondaries known to show reflection effects in the visual at
least?

So, we could have xrays _induced_ by the white dwarf, however
indirectly, but not necessarily from it.

You'd think a natural consequence would be for some CVs to be in both
the BSC & FSC. At best I could only find around half a dozen CVs that
came close to being in both cats, and _none_ of those had FSC & BSC
positions better than 2 arcmin despite the CVs being well known, so
probably just coincidental alignments.

However, the catalogues and/or their experimental aspects may well be
mutually exclusive.  The _only_ decent pairing I could find for the
_entirety_ of the BSC versus FSC was no closer than 8" and is for GSC
8885 0021.  You'd expect more than this single case just from plain
chance alignment.

[Anyone feel free to correct any glaring gaffs in the above : including
the spelling of "brehmstrahlung" ;-)].

John

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