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From: allan@noao.UUCP
Newsgroups: net.physics
Subject: Re: pulsing large objects
Message-ID: <365@noao.UUCP>
Date: Mon, 2-Jul-84 12:56:34 EDT
Article-I.D.: noao.365
Posted: Mon Jul  2 12:56:34 1984
Date-Received: Tue, 3-Jul-84 02:53:14 EDT
References: <2292@mit-eddie.UUCP>
Organization: Natl. Optical Astronomy Obs.  Tucson AZ USA
Lines: 22


  One of the problems with interpreting quasars' light curves is that they are
not periodic. The best that you can do is give a typical time for a quasars
to vary by a significant amount. This time goes from about an hour upto several
years depending on the individual object. The expected timescale for variations
depends on what model you believe in. The favourite model consists of an
accretion disk around a black hole, in which case the quasar cannot vary
faster than the light travel time across the black hole (unless relativistic
beaming is important).

  Part of the problem in measuring quasar variability is that most quasars 
are not very variable. Here at Kitt Peak, Bill Keel and I are trying to measure
the variability of a (hopefully) unbiased sample of quasars. We can detect 
variation as small as 0.05 magnitudes (5 percent for you non astronomers).
The project is going fairly well and a few more observing runs should complete
the data acquisition.


Peter (theories to go) Allan
Kitt Peak National Observatory
Tucson, Az
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