Abstract
If accretion disc emission results from turbulent dissipation, then
axisymmetric accretion theory must be used as a mean field theory:
turbulent flows are at most axisymmetric only when suitably averaged.
Spectral predictions therefore have an intrinsic imprecision that must
be quantified to interpret the variability exhibited by a source
observed at different epochs. We quantify contributions to the
stochastic imprecision that come from azimuthal and radial averaging and
show that the imprecision is minimized for a particular choice of radial
averaging, which in turn, corresponds to an optimal spectral resolution
of a telescope for a spatially unresolved source. If the optimal
spectral resolution is less than that of the telescope then the data can
be binned to compare to the theoretical prediction of minimum
imprecision. Little stochastic variability is predicted at radii much
larger than that at which the dominant eddy turnover time ($\sim$ orbit
time) exceeds the time interval between observations; the epochs would
then be sampling the same member of the stochastic ensemble. We discuss
the application of these principles to protoplanetary discs for which
there is presently a paucity of multi-epoch data but for which such data
acquisition projects are underway.
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | arXiv |
| ISSN | 1229-2370 |
| Status | Accepteret/In press - 1 okt. 2010 |