EDP Sciences
Free access
Volume 384, Number 2, March III 2002
Page(s) 408 - 413
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011794

A&A 384, 408-413 (2002)
DOI: 10.1051/0004-6361:20011794

Strongly decelerated expansion of SN 1979C

J. M. Marcaide1, M. A. Pérez-Torres1, 2, E. Ros3, A. Alberdi4, P. J. Diamond5, J. C. Guirado1, L. Lara4, S. D. Van Dyk6 and K. W. Weiler7

1  Departamento de Astronomía, Universitat de València, 46100 Burjassot, Spain
2  Istituto di Radioastronomia/CNR, via P. Gobetti 101, 40129 Bologna, Italy
3  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4  Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
5  MERLIN/VLBI National Facility, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK
6  Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 100-22, Pasadena, CA 91125, USA
7  Remote Sensing Division, Naval Research Laboratory, Code 7213, Washington, DC 20375-5320, USA

(Received 20 July 2001 / Accepted 11 December 2001 )

We observed SN 1979C in M100 on 4 June 1999, about twenty years after explosion, with a very sensitive four-antenna VLBI array at the wavelength of $\lambda$18 cm. The distance to M100 and the expansion velocities are such that the supernova cannot be fully resolved by our Earth-wide array. Model-dependent sizes for the source have been determined and compared with previous results. We conclude that the supernova shock was initially in free expansion for $6\pm2$ yrs and then experienced a very strong deceleration. The onset of deceleration took place a few years before the abrupt trend change in the integrated radio flux density curves. We estimate the shocked swept-up mass to be $M_{\rm sw} \sim 1.6~
M_{\odot}$ , assuming a standard density profile for the CSM. Such a swept-up mass for SN 1979C suggests a mass of the hydrogen-rich envelope ejected at explosion no larger than $M_{\rm
env} \sim 0.9 ~M_{\odot}$ . If SN 1979C originated in a binary star, the low value of $M_{\rm env}$ suggests that the companion of the progenitor star stripped off most of the hydrogen-rich envelope mass of the presupernova star prior to the explosion.

Key words: techniques: interferometric -- supernovae: individual: SN 1979C -- ISM: supernova remnants -- radio continuum: stars -- galaxies: individual: M100

Offprint request: J. M. Marcaide, J.M.Marcaide@uv.es

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