Radioactive 26Al from the Scorpius-Centaurus association
Abstract
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2010
- DOI:
- 10.1051/0004-6361/201014302
- arXiv:
- arXiv:1007.4462
- Bibcode:
- 2010A&A...522A..51D
- Keywords:
-
- stars: massive;
- supernovae: general;
- evolution;
- solar neighborhood;
- gamma rays: ISM;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 7 figures