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Astron. Astrophys. 346, 831-842 (1999)

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44Ti: its effective decay rate in young supernova remnants, and its abundance in Cassiopeia A

Y. Mochizuki 1, K. Takahashi 2, H.-Th. Janka 2, W. Hillebrandt 2 and R. Diehl 3

1 The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako, Saitama 351-0198, Japan
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching, Germany
3 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85740 Garching, Germany

Received 18 February 1999 / Accepted 30 March 1999

Abstract

Radioactive isotopes such as 44Ti offer probably the most direct probe into nucleosynthesis environments in the interior of exploding stars, when the associated [FORMULA]-ray activities in the explosion remnant are detected and translated back to the isotopic abundances at the time of the explosion. In this paper, we assert that the procedure may not necessarily be straightforward, at least in the case of 44Ti, an orbital-electron capture decay isotope. Using the analytic model of McKee & Truelove (1995) for young supernova remnants, and assuming the existence of overdense 56Fe-dominated clumps that contain also 44Ti, we show that a high degree of ionization may be caused by the reverse shock so that the electron-capture rate of 44Ti could be significantly reduced from its laboratory value. When applied to Cas A, this increases under certain conditions the current 44Ti-activity by a factor [FORMULA], which yields a better compatibility between the COMPTEL observation of the 1.16 MeV line activity associated with the 44Ti decay and the SN model predictions of the initial 44Ti abundance. This possibility is, however, subject to various uncertainties, and in particular to the unknown properties and radial distribution of the clumps in the ejecta.

Key words: stars: supernovae: general – stars: supernovae: individual: Cas A – ISM: supernova remnants – nuclear reactions, nucleosynthesis, abundances

Send offprint requests to: Y. Mochizuki (motizuki@postman. riken.go.jp)

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© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999
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