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Astron. Astrophys. 353, 715-721 (2000)

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COMPTEL limits on 26Al 1.809 MeV line emission from [FORMULA] Velorum

U. Oberlack 1,6, U. Wessolowski 1, R. Diehl 1, K. Bennett 4, H. Bloemen 2, W. Hermsen 2, J. Knödlseder 5, D. Morris 3, V. Schönfelder 1 and P. von Ballmoos 5

1 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching, Germany
2 SRON Utrecht, 3584 CA Utrecht, The Netherlands
3 Space Science Center, University of New Hampshire, Durham, NH 03824, USA
4 Astrophysics Division, ESTEC, 2200 AG Noordwijk, The Netherlands
5 Centre d'Etude Spatiale des Rayonnements (CNRS/UPS), 31028 Toulouse, France
6 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA

Received 18 June 1999 / Accepted 28 October 1999

Abstract

The Wolf-Rayet binary system [FORMULA] Vel (WR 11) is the closest known Wolf-Rayet (WR) star. Recently, its distance has been redetermined by parallax measurements with the HIPPARCOS astrometric satellite yielding [FORMULA] pc, significantly lower than previous estimates (300 - 450 pc). Wolf-Rayet stars have been proposed as a major source of the Galactic uc26Al observed at 1.809 MeV. The gamma-ray telescope COMPTEL has previously reported 1.8 MeV emission from the Vela region, yet located closer to the Galactic plane than the position of [FORMULA] Vel. We derive an upper 1.8 MeV flux limit of [FORMULA] [FORMULA] cm-2s-1 ([FORMULA]) for the WR star. With the new distance estimate, COMPTEL measurements place a limit of [FORMULA] [FORMULA] on the uc26Al yield of [FORMULA] Vel, thus constrains theories of nucleosynthesis in Wolf-Rayet stars. We discuss the implications in the context of the binary nature of [FORMULA] Vel and present a new interpretation of the IRAS Vela shell.

Key words: gamma rays: observations – nuclear reactions, nucleosynthesis, abundances – stars: individual: fl2 Vel – stars: Wolf-Rayet – ISM: individual objects: IRAS Vela shell

Send offprint requests to: Uwe Oberlack (oberlack@astro.columbia.edu)

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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