High mass-loss asymptotic giant branch stars detected by the Midcourse Space Experiment in the `intermediate' and `outer' Galactic bulge

Details High mass-loss asymptotic giant branch stars detected by the Midcourse Space Experiment in the `intermediate' and `outer' Galactic bulge High mass-loss asymptotic giant branch stars detected by the Midcourse Space Experiment in the `intermediate' and `outer' Galactic bulge

Nov 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007mnras.381.1219o&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 381, Issue 3, pp. 1219-1234.

Astronomy and Astrophysics

Astronomy

8

Stars: Agb And Post-Agb, Circumstellar Matter, Stars: Mass-Loss, Dust, Extinction, Infrared: Stars

Scientific paper

We present a study of Midcourse Space Experiment (MSX) point sources in the Galactic bulge (|l| < 3°,1° < |b| < 5°), observed in the A, C, D and E bands (8-21μm), with a total area ~48 deg2 and more than 7000 detected sources in the MSX D band (15 μm). We discuss the nature of the MSX sources [mostly asymptotic giant branch (AGB) stars], their luminosities, the interstellar extinction, the mass-loss rate distribution and the total mass-loss rate in the bulge. The mid-infrared data of MSX point sources have been combined with the near-infrared (J,H and Ks) data of Two Micron All Sky Survey. The cross-identification was restricted to Ks-band detected sources with Ks<= 11 mag. However, for those bright MSX D-band sources ([D] < 4.0 mag), which do not satisfy this criterion, we have set no Ks-band magnitude cut-off. The bolometric magnitudes and the corresponding luminosities of the MSX sources were derived by fitting blackbody curves. The relation between and (Ks - [15])0 was used to derive the mass-loss rate of each MSX source in the bulge fields. Except for very few post-AGB stars, planetary nebulae and OH/IR stars, a large fraction of the detected sources at 15 μm (MSX D band) are AGB stars well above the red giant branch tip. A number of them show an excess in ([A]- [D])0 and (Ks - [D])0 colours, characteristic of mass-loss. These colours, especially (Ks - [D])0, enable estimation of the mass-loss rates of the sources in the bulge fields which range from 10-7 to 10-4Msolaryr-1. Taking into consideration the completeness of the mass-loss rate bins, we find that the contribution to the integrated mass-loss is probably dominated by mass-loss rates larger than 3 × 10-7Msolaryr-1 and is about 1.96 × 10-4Msolaryr-1deg-2 in the `intermediate' and `outer' bulge fields of sources with mass-loss rates, . The corresponding integrated mass-loss rate per unit stellar mass is 0.48 × 10-11yr-1. Apart from this, the various mid- and near-infrared colour-colour and colour-magnitude diagrams are discussed in the paper to study the nature of the stellar population in the MSX bulge fields.

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