SN 1998bu in M96 (NGC 3368)
SN 1998bu in M96 (NGC 3368)
Mirko Villi in Italy has found (on May 9.9 UT) an apparent supernova in the bright galaxy Messier 96. He reports that it is located about 50 arcsec north of the center of the galaxy and about mag. 13.5.
I have made a visual confirmation of this object using the Lowell 53cm telescope at May 10.33 UT. The position estimate seems to be correct based on offsets using the telescope's photometer diaphragms. If anything, the star has become quite a bit brighter in the intervening 6-8 hours, and must be at least mag. 12.5 if not 12.0---because of the Full Moonlight and high aerosols scattering it, I could see nothing in the field except the galaxy nucleus and the new star.
There is no asteroid here in either the Minor Planet Center's search widget or from our local asteroid database. The object does not appear on various images of the galaxy (Vickers, Hubble/Carnegie, POSS, Wray color atlas, etc.).
\Brian
Dear SN fans,
There appears the nearest supernovae in these five years! My article intends to summarize the information available up to now.
Mirko Villi, Italy has discovered an apparent supernova (mag about 13.5) on the CCD image he had taken on May 9.9 UT in NGC 3368 = Messier 96. He reports that it locates about 50" north of the center of the host galaxy. Visual confirmation was made by B. Skiff, at Lowell observatory on May 10.33 UT. There has been no preveously-existing stars up to 18 mag, nor any known bright asteroids.
Preliminary astrometry was brought out by Yasuo Sano, Nayoro Observaroty, Hokkaido, Japan, which gives the position of the new star as R.A. = 10h46m46s, Decl = +11o50'07" (2000.0, using 11 GSC stars), which is about 49" north (east-west offset is not certain because of the accuracy but it should be less than 7") from the center of the host. It agrees with Mirko's position.
Magnitude estimates up to now:
UT(YYMMDD) mag observer 980509.9 13.5C Villi 980510.33 12.5: Skiff (visual) 980510.48 12.49C Sano
which indicate a remarkable brightning in about a half-day.
The host galaxy (type Sab) belongs to Leo group and the distance of it has been estimated as 8.1 Mpc for H_0 = 75 km s-1 Mpc-1 (Turry, Nearby Galaxy Catalog). It is a nearest supernova after SN 1993J. If it is of type Ia, it can reach 10.7 mag on its maximum. Also, it is nearer than (bright) SN Ia 1991T. Spectroscopy had not carried on (it crouds almost all Japan without Hokkaido...). The observation with wide wavelength is deadly urged.
Sincerely Yours, Hitoshi Yamaoka, Kyushu Univ., Japan yamaoka@rc.kyushu-u.ac.jpP.S. Please forward this article to anyone who would be interested.
As far as I know, there is no published photometric sequence around M96. On the relevant chart from the Thompson & Bryan "Supernova Search Charts" are shown V magnitudes evidently from several professional observers. Below are the positions and IDs for these stars (except a faint star very close to the galaxy). The name indicates the magnitude rounded to 0.1, e.g. "114" means V = 11.4.
ID RA (2000) Dec GSC 114 10 46 23.9 +11 56 54 0849-0685 126 10 46 21.7 +11 44 29 0849-0703 131 10 46 32.7 +11 50 55 0849-0841 135 10 46 10.4 +11 42 50 0849-0887 143 10 46 52.9 +11 43 22 0849-0306 149 10 46 52.9 +11 52 42 0849-0206 150 10 46 32.7 +11 52 06 0849-0931
T&B give the sources for this data as Peter Birch et al. (Perth Observatory, Western Australia), Bill Liller and Gonzalo Alcaino (CTIO?), and Marion Frueh (probably McDonald Observatory).
Since I complain that the IAUC's don't give a precise position for the host galaxies of supernovae, the center of M96 is at: 10 46 45.6 +11 49 18 (2000), according to NED, which cites 1996 ApJS 107, 215, and claims an accuracy of +/- 5 arcsec.
\Brian
Finding chart with magnitudes (kindly provided by M. Funada)
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