Aggiornamenti sulla SN 1999 gn in M61

A due giorni dalla scoperta la comunità scientifica ha cominciato a fornire dati più completi su sn1999gn. Innanzitutto è stato determinato il tipo, II, e la magnitudine, 15,5, ma in forte crescita tanto che si prevede possa toccare un massimo di 13,4. La velocità di espansione della Supernova è stata calcolata di 5300 Km/sec. [vsnet-alert 3842].

• Index of Images of Supernova 1999gn in M61
• Supernova 1999gn resources by David Bishop
• Messier Galaxies and their Supernovae
• Supernovae in Messier Catalog Galaxies
• AAVSO finder chart

SUPERNOVA 1999gn IN M61
Alessandro Dimai, Cortina, Italy, reports his discovery of an apparent supernova (mag 16.0) on an arm of the host galaxy (NGC
4303 = M61), found on a CCD frame taken on Dec. 17.22 UT with a 0.50-m telescope. He reported the new object as being 35" east and
25" south of the galaxy nucleus; the new star is not present in J. Wray's Color Atlas of Galaxies. W. Li, University of California at
Berkeley, reports that an image taken on Dec. 18.5 with the Katzman Automatic Imaging Telescope (KAIT) shows SN 1999gn at mag about
15.5. Li measured a position for SN 1999gn: R.A. = 12h21m57s.02, Decl. = +4o27'45".6 (equinox 2000.0), which is 31".7 east and 39".8
south of the nucleus of M61. A KAIT image taken on Nov. 26.5 showed nothing at the position of the new star (limiting mag about
19.0). Previous supernovae in M61 were 1926A, 1961I, and 1964F.

           THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
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                AAVSO ALERT NOTICE 268 (December 20, 1999)

1216+05 SUPERNOVA 1999gn IN NGC 4303 = M61

We have been informed by the Central Bureau for Astronomical Telegrams (IAU
Circular 7335 - http://cfa-www.harvard.edu/iau/cbat.html) that Alessandro
Dimai, Cortina, Italy, discovered an apparent supernova in NGC 4303 (= M61) on
Dec. 17.22 UT at unfiltered CCD magnitude 16.0, using a 0.50-m telescope.
Dimai reported that nothing was visible at the location of the supernova
in J. Wray's Color Atlas of Galaxies.

W. Li, University of California at Berkeley, reported that the supernova was
unfiltered CCD magnitude 15.5 on an image taken with the Katzman Automatic
Imaging Telescope (KAIT) on Dec. 18.5 UT.  Nothing was visible at the position
of the supernova down to magnitude 19.0 on a KAIT image of NGC 4303 taken on
Nov. 26.5 UT.

A precise position of SN 1999gn, which is 31.7" east and 39.8" south of the
nucleus of the galaxy, was measured by Li as:

     R.A. = 12h 21m 57.02s   Decl.= +04 degrees 27' 45.6" (Equinox 2000.0)

Accompanying is a chart prepared by K. Malatesta, AAVSO Headquarters, using
an image from the Digitized Sky Survey and comparison star magnitudes from the
Hipparcos and Tycho Catalogues and from R. Buta (Thompson and Bryan, The
Supernova Search Charts and Manual).  Please use this chart to observe
1216+05 SN 1999GN and report your observations to AAVSO Headquarters so we
may inform the astronomical community.  Please be sure to indicate which
comparison stars you used.

Congratulations to Alessandro Dimai on his discovery!

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