Line shape diagnostics of Galactic Al

Free access article

Issue		A&A Volume 412, Number 2, December III 2003


Page(s)		L47 - L51
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20034604

A&A 412, L47-L51 (2003)
DOI: 10.1051/0004-6361:20034604

Letter

Line shape diagnostics of Galactic $\mathsf{^{26\!}}$ Al

K. Kretschmer¹, R. Diehl¹ and D. H. Hartmann²

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
² Department of Physics & Astronomy, Clemson University, Clemson, SC 29634-0978, USA

(Received 7 July 2003 / Accepted 6 November 2003)

Abstract
The shape of the gamma-ray line from radioactive $\element[][26\!]{Al}$ , at 1808.7 keV energy in the frame of the decaying isotope, is determined by its kinematics when it decays, typically 10 ⁶ y after its ejection into the interstellar medium from its nucleosynthesis source. Three measurements of the line width exist: HEAO-C's 1982 value of (0+3) keV FWHM, the GRIS 1996 value of $(5.4\pm 1.3)$ keV FWHM, and the recent RHESSI value of $(2.0\pm 0.8)$ keV FWHM, suggesting either "cold", "hot", or "warm" $\element[][26\!]{Al}$ in the ISM. We model the line width as expected from Galactic rotation, expanding supernova ejecta, and/or Wolf-Rayet winds, and predict a value below 1 keV (FWHM) with plausible assumptions about $\element[][26\!]{Al}$ initial velocities and expansion history. Even though the recent RHESSI measurement reduces the need to explain a broad line corresponding to 540 km s ^-1 mean $\element[][26\!]{Al}$ velocity through extreme assumptions about grain transport of $\element[][26\!]{Al}$ or huge interstellar cavities, our results suggest that standard $\element[][26\!]{Al}$ ejection models produce a line on the narrow side of what is observed by RHESSI and INTEGRAL. Improved INTEGRAL and RHESSI spatially-resolved line width measurements should help to disentangle the effects of Galactic rotation from the ISM trajectories of $\element[][26\!]{Al}$ .

Key words: nuclear reactions, nucleosynthesis, abundances -- gamma rays: observations -- supernovae: general -- ISM: supernova remnants -- stars: formation

Offprint request: K. Kretschmer, kkr@mpe.mpg.de

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