[vsnet-chat 344] Re.:

[geckeler@ait730.ait.physik.uni-tuebingen.de]

>Dear readers,
>maybe this won't be very smart question but I'm interested if it will be
>(or WAS???) possible to observe directly some accretion disk. Maybe
>interferometry should help. But I don't know which CVs is too close to
>Sun's possition to be some chance to do it.
>Have a nice day
>Rudolf 

Howdy Rudolf,
The spatial resolution of accretion disks is currently only
possible with indirect methods, e.g. doppler tomography and
eclipse mapping.
Doppler tomography is acomplished using observations of
emission lines over one orbital period of the system. The
laboratory wavelengths of the emitting atoms are shifted by
the orbital rotation of the system & by the keplerian motion
of the disk itself. Doppler tomography allows to map
the emission back only to velocity space, not to spatial
coordinates. It has been used to detect density waves
in CV accretion discs and to map the free falling accretion
stream in polars (magnetic CVs). See Horne 1988, MNRAS, 235, 269
for a detailed view at the method, an impressing example
for a magnetic CV can be found in Schwope et al. 1997,
A&A, 319, 894.

Eclipse mapping uses the fact, that the secondary in eclipsing
systems scans twice across the surface brightness distribution
of the disk during eclipse ingress & egress. Knowledge about the
general system geometry allows to reconstruct a map of the
disk & hot spot. Multi-color photometry allows to reconstruct
the temperature distribution of the accretion disk. See Horne 1985,
MNRAS, 213, 129 (Keith again, he also has develloped echo tomography)
for the method and Baptista et al. 1995, for UX Uma data. 

Best regards, Ralf

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