Radioactive 26Al from the Scorpius-Centaurus association

• Published in: Astronomy and astrophysics (Berlin) 2010-11, Vol.522
• Main Authors: Diehl, R., Lang, M. G., Martin, P., Ohlendorf, H., Preibisch, Th, Voss, R., Jean, P., Roques, J.-P., von Ballmoos, P., Wang, W.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; evolution; Exact sciences and technology; gamma rays: ISM; solar neighborhood; stars: massive; supernovae: general
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201014302

Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic γ-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays with a radioactivity lifetime τ ~ 1 My, 1809 keV γ-rays from its decay can be measured with current γ-ray telescopes. Aims. We aim to identify nucleosynthesis ejecta from the youngest subgroup of Sco-Cen stars, and interpret their location and bulk motion from 26Al observations with INTEGRAL’s γ-ray spectrometer SPI. Methods. Following earlier 26Al γ-ray mapping with NASA’s Compton observatory, we test spatial emission skymaps of 26Al for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate 26Al emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. Results. We find an 26Al γ-ray signal above 5σ significance, which we associate with the locations of stars of the Sco-Cen group. The observed flux of 6 × 10-5 ph cm-2 s-1 corresponds to  ~ 1.1 × 10-4 M⊙ of 26Al. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. Conclusions. We confirm through direct detection of radioactive 26Al the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate 26Al contributions from this association. Our 26Al signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of 26Al and compare this to other indications of Scorpius-Centaurus massive-star activity.