Submillimeter Carbon Monoxide Observations of Mass Loss from Evolved Stars

Details Submillimeter Carbon Monoxide Observations of Mass Loss from Evolved Stars Submillimeter Carbon Monoxide Observations of Mass Loss from Evolved Stars

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........25w&link_type=abstract

Thesis (PHD). PRINCETON UNIVERSITY , Source DAI-B 59/01, p. 261, Jul 1998, 324 pages.

Astronomy and Astrophysics

Astronomy

Stellar Kinematics

Scientific paper

A sample of mass-losing evolved (primarily AGB) stars was selected from the Point Source Catalogue produced by the Infrared Astronomical Satellite (IRAS) and observed in the 345 GHz (J = 3-2) and 230 GHz (J = 2-1) lines of carbon monoxide (CO). The sample is magnitude limited at 25 μm with the limit varying according to location on the IRAS two colour ( (12) - (25), (25) - (60)) diagram. Mass-loss rates are derived for all the stars with detected CO line emission by matching the observed CO line profile to line formation models for a steady stellar wind. The sky distribution of post-main sequence IRAS sources was investigated, quantifying how the degree of concentration towards the galactic plane and galactic center changes with color. This demonstrates that the luminosities of stars increase as the colours get colder. A few stars with IRAS colours indicating no mass-loss were nevertheless detected in CO. These stars were found to have unusual K- (12) colours, high variability and are likely to be carbon rich. Stars without mass-loss and stars with low mass-loss rates appear in distinct regions of the K- (12), (12) - (25) two colour diagram. Some stars in these regions have anomalously large 60 μm fluxes, probably due to contamination by cirrus emission. The mass-loss rate and the CO to 12 μm ratio both correlate with (12) - (25), with different relationships for carbon and oxygen rich stars. The distributions of various infrared (IR) colours change abruptly at a mass-loss rate of 10-6/ Msolar/ yr-1. For low mass-loss rates, the colours show little variation and are independent of mass-loss. At high mass-loss, the colours vary greatly between sources. A maximum likelihood method is described to estimate the velocity dispersion (and hence age and initial mass) of a population of stars when there is a significant contribution from galactic differential rotation. Extensive Monte Carlo testing of the method demonstrates its robustness. The method is applied to the results of the CO survey. The initial stellar masses are found to increase with (12) - (25) and hence mass loss rate. This trend is broken at the hot end of the sequence by luminosity selection effects and at the cold end by the presence of planetary nebulae.

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