archive: SETI FW: [ASTRO] Spectra question

SETI FW: [ASTRO] Spectra question

Larry Klaes ( lklaes@zoomtel.com )
Tue, 15 Sep 1998 09:16:30 -0400

----------
From: Ka Chun Yu
Sent: Monday, September 14, 1998 5:21 PM
To: astro@lists.mindspring.com
Subject: Re: [ASTRO] Spectra question

> In a message dated 9/14/98 4:07:10 AM Pacific Daylight Time, jega@ziplink.net
> writes:
> 2. In
> practical terms, we are trying to null the signal of a star which has
> some diameter, say 1.5 million km. What resolution can we expect to get
> of the diameter of the region nulled, considering that 150 million km (or
> 1 au) will subtend only a small fraction of an arc second at our
> telescope(s)?
>
> * That depends on the baseline(s) of the interferometer. In any case, a model
> of the structure of the star can be included in the nulling process; one not
> need demand that the star be point-like.
>
> * The inteferometer is not being used here as an IMAGING device (although it
> could) but as a 'notch' filtering device. My impression is that resolution is
> not the issue, far away from the null spatially. I believe the idea is to look
> at the residual spectra for spectral lines--without regard to spatial
> (angular) resolution per se.

NC has answered the questions quite well so I won't add much more.

I will note that the person whose webpage to look up on the web is
Roger Angel at the University of Arizona. He pioneered the
spin-casting of telescope mirrors and is in the forefront of coming
up with answers to the problems of detecting and imaging extrasolar
planets. He a Neville Woolf came up a few years back a simulation of
a "movie" showing planets orbiting a nearby star as seen with an
infrared interferometer. There's a picture from that movie at their
article for Scientific American, "Searching for Life in Other Solar
Systems", available at:

http://www.sciam.com/1998/0398cosmos/0398angel.html

The article is also a very good lay introduction to the problem of
taking spectra of extrasolar planets and of imaging interferometers.

> *Cordially,
> *NC

--kachun +** Center for Astrophysics and Space Astronomy, CB 389 **+
+** University of Colorado, Boulder, CO 80309 **+
+** Email: kachun@casa.colorado.edu **+
+** http://casa.colorado.edu/~kachun **+