Infrared giants vs. supergiants

Free access article

Issue		Astron. Astrophys. Suppl. Ser. Volume 129, Number 1, April I 1998


Page(s)		45 - 68
DOI		http://dx.doi.org/10.1051/aas:1998396

DOI: 10.1051/aas:1998396

A&A Supplement series, Vol. 129, April I 1998, 45-68

Received March 21; accepted September 17, 1997

II. CO observations

E. Josselin - C. Loup - A. Omont - C. Barnbaum - L.-Å. Nyman - F. Sèvre

Send offprint request: E. Josselin

Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, F-75014 Paris, France
STScI, 3700 San Martin Dr., Baltimore, MD 21218, U.S.A.
European Southern Observatory, Casilla 19001, Santiago 19, Chile

Abstract:

We report systematic observations of millimeter CO emission from a sample of 109 oxygen-rich evolved stars (AGB and supergiants), colour-selected from the IRAS Point Source Catalog . CO(1-0) has been searched with good sensitivity in 81 sources (74% of the sample). CO(1-0) is detected in 54 sources and a significant upper limit has been achieved in 27 sources.

In our previous paper we reported on the statistical results of these observations. We showed that in almost 50% of the sources, the ratio of the IRAS flux to CO intensity, , is larger by a factor of 3 to more than 10 than what is expected according to the correlation found by Nyman et al. (1992). Supergiants only exhibit very high values (). In most cases, the observed spread in the values of this ratio can be explained by a large range of luminosities. This leads to a new criterion to identify AGB stars: an object with must have a low mass progenitor.

Here we study the correlations between and various physical properties of the sources. Most sources with high values of also have low galactic latitudes, small IRAS variability indices, and early spectral types (typically M1-M5). Conversely, there is no dependence on the IRAS colours, nor on the intensity of silicate emission. However, a few AGB stars exhibit large ; other factors than luminosity are required to explain these values. Different hypotheses, such as the possible presence of a chromosphere, a low ¹²C abundance or a variable mass-loss rate, are examined. Considering the global high OH detection rate , we studied the correlations with CO and OH emission. The detection of OH seems to be a useful discriminator of mechanisms that enhance .

keywords: molecular processes -- stars: circumstellar matter -- stars: mass loss -- stars: supergiants -- radio lines: stars

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.