Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...489..601g&link_type=abstract
Astrophysical Journal v.489, p.601
Astronomy and Astrophysics
Astronomy
26
Galaxies: Evolution, Galaxies: Starburst, Galaxies: Stellar Content, Line: Profiles, Stars: Early-Type, Ultraviolet: Stars
Scientific paper
Evolutionary synthesis models of a stellar population in the far-ultraviolet are presented. The spectra include the lines O VI lambda lambda 1032, 1038, Ly beta , and C II lambda lambda 1036, 1037. They are based on a stellar library built with observations of O and B stars collected with Copernicus and the Hopkins Ultraviolet Telescope (HUT). This library is used as input into an evolutionary synthesis code. The line profile of O VI + Ly beta + C II is computed for different star formation histories (instantaneous burst and continuous star formation) and different assumptions about the initial mass function (IMF). The metallicity is near the solar value. O VI lambda lambda 1032, 1038 is a very sensitive indicator of the presence or absence of O stars. O VI develops a P Cygni profile when formed in stellar winds of the most massive stars. When these stars are absent, no O VI is formed. In contrast, Ly beta and C II are very sensitive indicators for B stars. If these stars dominate, as is the case in poststarburst galaxies, Ly beta and C II are present as strong absorption features, and they are formed in the photosphere of B stars. An equivalent width of Ly beta + C II larger than 1 Angstroms always indicates a population younger than 1 Gyr. Because of the universal strength of O VI in O stars, O VI is not a good discriminator between instantaneous versus continuous star formation for ages in the starburst phase, but the absence of O VI and the presence of stellar Ly beta and C II is a good indicator of a short burst duration and for the galaxy being in a poststarburst phase. Application of this technique to starburst or poststarburst galaxies will require careful attention to interstellar absorption.
Gonzalez Delgado Rosa Maria
Heckman Timothy
Leitherer Claus
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