[vsnet-chat 1221] Re: [vsnet 1575] Re: (fwd) On SN1998dm (Howerton) - by Larry

[Taichi Kato <tkato>]

Re: [vsnet 1575] Re: (fwd) On SN1998dm (Howerton) - by Larry

> I viewed MCG+01-04-044 at approximately 9:30 UT (4:30 a.m. CDT) August 30,
> 1998 with a 13.1" (33.3cm) f/4.5 dobsonian at 202x.  After making a visual
> examination of the field, I have concluded there is some incorrect
> information as to the exact position of the galaxy MCG-01-04-044.
> 
> The chart provided at the address listed below incorrectly positions the
> galaxy.  Furthermore, my software (Guide 6.0) also plots the galaxy at the
> same position (1h 26.319m, -6d 4.433m).  Both show a star (GSC 4684 1696 per
> Guide 6.0) in the south-southwestern tip of the galaxy when this star
> actually lies some 1/2' following the northeastern tip of the galaxy.
> However, an examination of the software RealSky reveals a position of
> approximately 1h 26m 14s, -6d 5m 44s for the galaxy.
> 
> Others may make the same mistake I did this morning in believing there is a
> foreground star in the SSW tip and be frustrated in not being able to detect
> the supernova when, in fact, this star is probably the supernova.
> 
> Thus if I am correct, the only star visible in the SSW tip of MCG+01-04-044
> is SN1998dm.  Since I mistook it for a foreground star I did not make an
> estimate of its brightness.  However, I had made a mental note that it was
> about 14.0 to 14.5 as I was wondering why this "foreground" star was much
> fainter than expected.
> 
> Am I correct in my conclusion?

    Your finding is correct; most star chart plotting program seem to use
the original MCG coordinates.

  Original MCG coordinates (precessed to J2000.0) and RC3 ones:

012618.0 -060359 (2000.0) RC3_A0123-06 PGC5341 .SB.5*.
012619.0 -060426 (2000.0) CfA_A0123-0620 v=1968km/s Bmag=13.1
012619.1 -060425 (2000.0) M-01-04-044

  GSC and USNO entries for this galaxy (detected in IRAS also):

GSC4684.2075 012614.03 -060555.4 (2000.0) 11.11 0 N
GSC4684.1578 012614.46 -060538.0 (2000.0) 10.48 0 N
USNO0825.00327490 012614.037 -060555.43 (2000.0) 11.1 99.9
USNO0825.00327515 012614.466 -060538.01 (2000.0) 10.5 99.9
USNO0825.00327522 012614.546 -060536.88 (2000.0)  9.3  9.7
012613.8 -060543 (2000.0) IRAS01237-0621 0.475L 0.296L 0.725 2.171 -1%
012613.8 -060543 (2000.0) SSC01237-0621 0.475L 0.296L 0.725 2.171
012614.8 -060537 (2000.0) FSC01237-0621 0.130L 0.145L 0.683 2.001

  Regarding the supernova itself, the reported position seems to be a few
arcsec off, as I posted earlier -- could someone confirm this astrometry?

  There is a 15.5 mag star west to the SN.  So observers are requested
to avoid confusion and/or contamination of this foreground star.

  GIF image kindly provided by S. Massaro is at

  http://ftp.kusastro.kyoto-u.ac.jp/vsnet/SNe/sn1998dm/sn1998dm.gif

Regards,
Taichi Kato

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