[vsnet-chat 1214] (fwd) color changes and of the light curve of SN1998S (Richmond)

[Taichi Kato <tkato>]

From villi@mbox.queen.it Sun Aug 30 06:38 JST 1998
Date: Sat, 29 Aug 1998 17:33:06 -0400
From: Stupendous Man <richmond@a188-l009.rit.edu>
To: 76620.1721@compuserve.com, isn_chat@mbox.queen.it,
        vsnet-chat@kusastro.kyoto-u.ac.jp
Subject: color changes and the light curve of SN 1998S
Content-Type: text
Content-Length: 2145


  Steve Lucas has put together a very nice note on the visual
observations of SN 1998S.  He points out the variations
in its light curve around a smooth line, both before and
after maximum light.

  I suspect that some of the variations after maximum light may
be due to strong changes in the color of the SN affecting the
perception of visual observers.  I looked at an example of
several well-observed events to see how each varied in (B-V)
color near maximum light.  (You can find Postscript versions
of papers on these events on my home page)

       SN 1994D (Ia):       B-V =  -0.1     at   d =  -5 
                                   +1.2              +25
                                   +0.8              +60

       SN 1994I (Ic):       B-V =  +0.5     at   d =   0
                                   +1.3              +10
                                   +0.8              +30

       SN 1993J (IIb):      B-V =  +0.0     at   d = -15
                                   +1.3              +15
                                   +0.9              +60

  All three behave in the same way: they are bluest before
maximum light, quickly redden during and just after maximum,
and then, after one to four weeks later, slowly begin to turn
bluer again.  The stellar atmosphere cools down as it expands,
which explains the reddening.  After it becomes sufficiently
thin, light from the inner portions of the SN -- which are
heated by the radioactive decay of Nickel-56 and other elements --
begins to peek through: as we see those hot inner regions,
we perceive the SN to become slightly bluer.

  The smaller the mass of the ejected envelope, the more quickly
the changes in color occur.

  Note that the event typically looks most red about 20 or so
days after maximum light.  That is suspiciously close to one
of the slight dips in the visual light curve.

  But the small jump before maximum light -- I have no idea
what might cause that!

  
-----                                      
Michael Richmond                   "This is the heart that broke my finger."
mwrsps@rit.edu                     http://a188-L009.rit.edu/richmond/

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