Supernova 1998bu in M96

Supernova 1998bu occurred in M96 on May 9, 1998 and was discovered by

Italian amateur astronomer Mirko Villi, one of the maintainers of the

Network, on CCD image when it was at 13th

magnitude, and rapidly brightening to 11.8 mag. This supernova is

situated about 1 arc minute north of the center of M96, and is the first

one ever discovered in this galaxy.

Our image was obtained by Norbert Stapper on May 14, 1998 at 21:53 UT with

a 8-inch SC telescope, LPR filter and ST7 CCD camera at 1.86 arc seconds

per pixel, under modest observing conditions. Norbert estimated the

brightness of the supernova as 12.0 +/- 0.1 at that time.

Spectral investigations indicated that this supernova is of type Ia,

as there is no hydrogene, but helium present in the spectrum (see e.g.

In case of Supernova 1998bu, this may be of particular interest with

respect to the cosmic distance scale determination, as supernovae of this

type are often regarded as one of the more reliable “standard candles” for

determining distances of more remote galaxies, and M96 has a Cepheid

distance determined by the Hubble Space Telescope. Therefore, the

brightness of SN type Ia might be better “gauged” by this supernova.

These investigations have been actually carried out by Nick Suntzeff and

co-workers and have been submitted for publication;

Type Ia supernovae are commonly interpreted as explosions of a White Dwarf

which acquires too much mass from a companion star, so that its mass

exceeds the Chandrasekhar limit of stability (about 1.4 solar masses) and

finally collapses, causing a thermonuclear explosion, or as the result of

a collision of two White Dwarf stars. As this process is thought to occur

under very similar conditions each time, it is assumed that all type Ia

supernova explosions are similar, i.e. are of similar luminosity and show

similar light curves. Observational results give supplementary evidence to

this assumption.

Last Modification: 23 May 1998, 10:00 MET