[vsnet-alert 1739] Re: SN 1998ar confusion

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

Dear SN fans,

  Dr. Rodrigues, M1 group, Spain, has pointed out the confusion in
identification of SN 1998ar in NGC 2916. I have checked his image and
I perfectly agree with him. I guess it is necessary for those who have
observed this SN to check out whether the observed star was truely SN
or not. 

  I have measured the locations of point-like sources around NGC 2916
with DSS-1 image and 5 GSC stars. Belows are the results, adding the
position of SN 1998ar reported on IAUC 6877. 

                     R. A. (2000.0)  Decl.    offset from core
Core of NGC 2916   9h34m57s.69  +21o42'18".8    --------
Star A             9h34m57s.88  +21o42'30".7    2"E, 12"N
Star B             9h34m57s.08  +21o42'54".5    8"W, 32"N
SN 1998ar          9h34m58s.86  +21o42'57".5   17"E, 39"N

  Star A seems to be a foreground star. The magnitude of this star is
estimated as 15.5 mag or so on DSS1 image. Besides, Star B looks like
a condensation (bright region) of the host galaxy. It is about 16 mag
or so on the same image. 

  I have also checked the image taken by Dr. Wentworth, which can be
accessed at http://vsnet.ggw.org/asras/snimages/sn98ar1.html . It was
taken on Apr 24.1UT (its caption was referred), which time is
consistent to the time of magnitude reported by himself on vsnet as 
15.35C. His image has clearly shown Star A and Star B, and
stellar-looking knot exists near the location of SN 1998ar (Star C).
Star C seems to be dimmer than Star B, and comparing GSC 14.8 mag star
and fainter neighbouring stars, its magnitude is about 1.5 mag dimmer
than GSC 14.8 mag star; which tells that SN was about 16.3 mag.
However, on the DSS image, there are the blobby knots near to the
location of SN. Star C can be the integrated spot of these blobs and
SN, so this magnitude should be taken as an upper limit.

  This discrepancy can be due to mis-identification of SN. Could the
observers of this SN check the images and the identifications?

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan
yamaoka@rc.kyushu-u.ac.jp

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