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                AAVSO ALERT NOTICE 263 (November 1, 1999)

0436-03 SUPERNOVA 1999em IN NGC 1637

We have been informed by the Central Bureau for Astronomical Telegrams (IAU
Circular 7294) that W. D. Li, University of California at Berkeley, on
behalf of the Lick Observatory Supernova Search team, reports the discovery
of a bright supernova in NGC 1637 on October 29.44 UT at an unfiltered CCD
magnitude about 13.5, using the 0.8-m Katzman Automatice Imaging Telescope.

SN 1999em was confirmed at the Beijing Astronomical Observatory (BAO) on
October 20.45 UT. No star was recorded down to magnitude 19.0 at the
location of the supernova on a KAIT image of the same field taken on October
20.45 UT.

The position provided by K. Stanek with the F. L. Whipple Observatory (FLWO)
1.2-m telescope shows the supernova located at:

R.A. = 04h 41m 27.05s     Decl. = -02 51' 45.8"      (2000)

and about 15.4" west and 17.0" south of the nucleus of NGC 1637 (IAU
Circular 7296).

Additional spectroscopic confirmation was obtained by M. Calkins (IAU
Circular 7296), with the FLWO 1.5-m telescope (+ FAST spectrograph),
revealing SN 1999em to be a Type II supernova at an early epoch. The
spectrum exhibits a very blue continuum with P-Cyg profiles of H-alpha,
H-beta, H-gamma, and He I. The spectrum also shows narrow interstellar Na I
D at the redshift of NGC 1637, implying that the supernova may be partly
obscured by dust.

J. S. Deng, H. L. Cao, D. W. Xu, Y. Lu, H. B. Li, Y. L. Qiu, and J. Y. Hu,
Beijing Astronomical Observatory (BAO), report that the low-dispersion
spectrum of SN 1999em was obtained on October 29.7 UT with the BAO 2-m
telescope (IAU Circular 7296). This again shows the supernova to be an early
Type II event.

Accompanying is a chart of NGC 1637 from the Thompson/Bryan Supernova Search
Charts. Until an AAVSO chart is prepared, please use this chart to observe
the supernova, and report your observations of 0436-03 SN 1999em to AAVSO
Headquarters, making sure you indicate which comparison stars you used.

Congratulations to Lick Observatory Supernova Search team on their


Electronic copies of the SN 1999em chart mentioned in this Alert Notice are
available through our web site at the following address:


The chart may also be obtained directly from our FTP site:

             ftp.aavso.org (, in /alerts/alert263)

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Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Janet A. Mattei

Kerriann Malatesta
Technical Assistant