[vsnet-chat 905] Re: NGC4462 sequence (Richmond)

[Taichi Kato <tkato>]

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Subject: [vsnet-chat 0] Re: NGC4462 sequence 
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 Taichi Kato asked:

> >   Thank you veru much!  I have tried your anonymous ftp file several times
> >without success.  Is this B-V=+0.27 color usual for an SN Ia at maximum?

  Arne Henden replied with some very nice data:

>   I'm not a supernovae expert by any means.  They redden as they age.
> The aperture differential results for the three nights I took data are:
> 
>  HJD          V     B-V    V-R     R-I
> 50935.7229  13.496  0.268  0.175  -0.135
> 50936.7160  13.498  0.276  0.189  -0.197
> 50937.6754  13.532  0.313  0.178  -0.220
> 50937.6814  13.535  0.307  0.177  -0.235

  I've compared the values above to those for the relatively normal
type Ia SN 1994D in NGC 4526.  The (B-V) color listed above matches
that of SN 1994D at about 12 days after max B light.  The (V-R) and
(R-I) colors match those of SN 1994D somewhat later, about 20 days
past max B light.

  I'd say that this new SN, SN 1998bn, is about 2 or 3 weeks past
maximum.  It's unlikely to be reddened much, I'd say, because dust
should make the (B-V) value change the most (i.e. B-V would be more
different from a "normal" B-V than the V-R would be from a "normal"
V-R) ... but the current (B-V) of this new SN is a bit _bluer_ than
one would expect if it were presently at maximum, and merely reddened
by dust.

  If you watch it for another two weeks or so, you should see the
color trend reverse; after about 25 days past max B light, normal
SNe Ia stop getting redder, and start slowly to become BLUER.


-- 
-----                                      
Michael Richmond                   "This is the heart that broke my finger."
mwrsps@rit.edu                     http://p674p06.isc.rit.edu/richmond/

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