From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Fri Mar 14 2003 - 20:43:47 PST
On Fri, Mar 14, 2003 at 01:48:35PM -0800, Lifan Wang wrote:
> Isn't it true that we plan observations in terms of S/N ratio ? I will be
> very surprised if anyone is observing the same SN with constant exposure
> time.
Sure, we increase the exposure time as the flux goes down.
But we don't increase it by a factor of 400 by the time we expect the
flux to be 5% of its initial value...! That's what you'd have to do in
order to keep the same magnitude errors all the way down.
Anyway, generally, we talk about the S/N ratio where we use S at peak.
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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