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Re: Hubble pinpoints red supergiant that exploded (Forwarded)

Subject: Re: Hubble pinpoints red supergiant that exploded Forwarded
From: Steve Willner
Date: 8 Mar 2006 13:53:04 -0500
Newsgroups: sci.astro
In article <F7yaP8BXd1CEFwI+@xxxxxxxxxxxxxxxxxxx>,
 Jonathan Silverlight <jsilverlight@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
>  could we have missed a 
> supernova a few degrees from the Sun in the past?

To be obscured by the Sun, a SN would have to be near the ecliptic.
That at first glance seems unlikely because the ecliptic and Galactic
planes are inclined, but in fact they cross in Sagittarius, only a
few degrees from the Galactic center.  So the Sun obscures a fair
fraction of the Milky Way for a month or more each year.

On the other hand, supernovae decay only a few magnitudes in 60 days.
An _unobscured_ SN Ia at the distance of the Galactic center would
have an observed peak magnitude of -4 and could hardly be missed even
several months later.  If, on the other hand, you allow interstellar
extinction, you can make the SN as faint as you want.  The Galactic
center itself suffers about 27 or so magnitudes of visual extinction,
and there are even more heavily obscured regions not far from it.  So
it's possible to imagine a SN that was, say, magnitude +3 at peak but
was behind the Sun then, and by the time the Sun moved out of the way
the SN was too faint to be seen.  This strikes me as a fairly special
set of conditions, and I suppose it's a matter of taste whether you
say the SN was missed because of extinction or because of the Sun.

All in all, I'd say extinction is more likely to account for missing
Galactic SNe than "behind the Sun," but the latter may have
contributed.

-- 
Steve Willner            Phone 617-495-7123     swillner@xxxxxxxxxxxxxxx
Cambridge, MA 02138 USA                 
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