Dear Colleague,
As you may know, we are in charge of one of the Primary Working Groups at the ITP Conference on Black Holes. The topic we have been asked to cover is:
How Do We Measure The Physical Properties Of Outer Disks?
Our Group will meet on the afternoon of Wednesday, February 3.
We have tried to come up with a list of topics that may be appropriate for our Working Group. Based on this, we thought that you may perhaps be interested in participating in the discussions. It would be useful to have a head count, so please let us know if you will be able to join us. Please also tell us if you would like to add or delete any topics from the list given below.
We have not yet decided exactly how we will organize the Working Group Session. Our thinking at the moment is not to have formal presentations, but to have informal discussions centered around a set of topics. There will be a viewgraph machine, so that anyone who would like to show a transparency to illustrate a point will be able to do so.
Tentative list of topics for the Outer Disk Working Group
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In most of the following, we assume that the "outer disk" is a
Shakura-Sunyaev thin accretion disk, perhaps modified by S-curves and
limit cycles due to opacity effects.
We decided that we would ignore the "torus" which is found in Seyferts
and other AGN, since the torus is located at such a large radius that
it probably has very little to do with the central black hole.
I. The inner radius of the disk
If we are going to concentrate on the "outer disk," then by definition
there is something else on the inside. Our Working Group will not
discuss what is on the inside, but some important questions are:
At what radius does the outer disk change to the inner region?
What physics determines this transition radius?
How can we measure the transition radius?
How does the transition radius depend on black hole mass, accretion
rate, etc.?
II. The mass accretion rate in the outer disk
How can we measure the mass accretion rate?
Is the accretion rate constant or does it vary with radius?
What kinds of physics might cause the rate to vary with radius?
III. Effect of Irradiation
What effect does irradiation have on the dynamics and warping of
the outer disk?
What can we tell from observations about the geometry of the disk,
its scale height and the degree of warp?
How does irradiation affect the thermal state of the disk?
How do shadowing effects modify the behavior of a time-dependent
disk or a warped disk?
IV. Mass Evaporation, Corona, Winds
How much mass loss is there in outer disks?
What is the physics of the mass loss? Thermal evaporation, irradiation?
What role do magnetic fields play in the dynamics of the outflow?
What effect does irradiation have on the outflow?
What kind of coronae do we find above outer disks?
V. Variability
Is there any evidence for variability associated with the outer disk?
What kinds of quasi-periodic oscillations do we expect in the disk?
What kinds of noise phenomena do we expect in the disk?
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Please send us your comments on the above topics.
We look forward to seeing you in Santa Barbara!
Yours sincerely,
Ramesh Narayan (narayan@cfa.harvard.edu)
Jan van Paradijs (jvp@astro.uva.nl)
PS: Please send your reply to both of us