[vsnet-chat 2944] [FWD] about SN? 2000ch (W. Li)

[Hitoshi YAMAOKA <yamaoka@rc.kyushu-u.ac.jp>]

>Date: Wed, 17 May 2000 02:07:49 -0700 (PDT)
From: weidong li <weidong@urania.Berkeley.EDU>
Subject: SN 2000ch

Hi all,

I finally got to do something with the KAIT monitoring images
of NGC 3432. A big surprise is that the progenitor of the SN
(or a super nova, or whatever you call it) has probably been
in KAIT images since we began to monitor the galaxy in 1999. 
Here is a breakdown of the details:

1999:  Feb 24, 20.5 (?)
       Apr 18, hint 
       May  8, 20.5 (?)
       Dec 29, hint
2000:  Apr 19, hint
       Apr 24, 20.5 (?)
       May  3, 17.4 DISCOVERY
       May  4, 18.2
       May  5, 19.0 (?)

While the nature of the object, and whether it should be called
a genuine supernova are in question,  it should be noted that 
several SNe (1961V in NGC 1058, 1999bw in NGC 3198, and 1997bs
in NGC 3627) have about the same absolute brightness. SN 2000ch
in NGC 3432 is probably a superoutburst of a very massive luminous
blue variable star (the progenitor, with mag 20.5 at the distance
of NGC 3432 - 7.8Mpc, has an absolute magnitude of about -9),
analogous to eta Carinae. The star probably survived the outburst
(as in the case of 1961V; See Filippenko et al. 1995, AJ 110,2261
for the recovery of 1961V in HST images). HST observations of 
1997bs also indicate that the star probably survived the explosion
(Schuyler Van Dyk et al., in preparation).

The case of SN 2000ch is peculiar since the star didn't appear in 
the DSS images taken in 1996. The very luminous progenitor of 
SN 2000ch perhaps had experienced a gradual brightening since sometime
after 1996, or it brightened to a somewhat stable  magnitude (20.5?)  
at some point. The superoutburst of the star on May 3, 2000 is perhaps
caused by the explosion of the outer shells of the massive star. 
The ultimate fate of this kind of star is still uncertain, some say
they will eventually become TRUE supernovae,  some say they will fail
to go supernovae and core collpse to directly form black holes.

What should these objects be called is the IAUC people's headache 
(not mine, ;o)). It is clear, however, that the subclass of "SN IIn"
have been contaminated by some "impostors".

Cheers,
Weidong

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