Atlas of Synthetic Ultraviolet Spectra of Massive Star Populations

Details Atlas of Synthetic Ultraviolet Spectra of Massive Star Populations Atlas of Synthetic Ultraviolet Spectra of Massive Star Populations

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apjs...99..173l&link_type=abstract

Astrophysical Journal Supplement v.99, p.173

Astronomy and Astrophysics

Astronomy

136

Atlases, Stars: Early-Type, Stars: Mass Loss, Stars: Wolf-Rayet, Ultraviolet: Stars

Scientific paper

An atlas of synthetic ultraviolet spectra of a population of massive stars is presented. The spectra are based on a stellar library of lUE high-dispersion spectra of O and Wolf-Rayet stars, coupled to an evolutionary synthesis code. Later spectral types are included via low-dispersion spectra. Line profiles of N V λ1240, Si IV λ1400, C IV λ1550, He II λ1640, and N IV λ1720 have been computed for star-formation histories and initial mass functions typically found in starburst regions.
It is found that the lines are sensitive indicators for the presence or absence of massive stars. C IV λ1550 is the strongest stellar line in the ultraviolet spectrum of a typical starburst. If O stars with zero-age main-sequence masses above 50 Msun are present, C IV always shows a P Cygni profile. In the absence of such stars, only a blue- shifted absorption is present. During later epochs of the starburst, when late-O/early-B stars dominate, an un-shifted photospheric absorption appears.
Si IV λ1400 shows a conspicuous wind profile when luminous O supergiants are present. A strong P Cygni profile is found only for an instantaneous burst observed at 3 to 5 Myr, which has a top-heavy IMF. The velocity of the blueshifted absorption is strongly correlated with the age and the upper cutoff mass (or slope) of the IMF.
N V λ1240 traces the most massive stars and behaves rather similar to Si IV λ1400. Its usefulness as an indicator of very massive stars is limited due to the strong blending effect of the nearby Lyα line. Nevertheless, strong N V λ1240 emission in a starburst suggests the presence of stars with masses in excess of 60 Msun.
He II λ1640 and N IV λ1720 are produced by very hot and luminous O and Wolf-Rayet stars. Both lines can have weak absorption or emission in a typical starburst but are predicted to be observable only under rare circumstances, such as in an instantaneous burst at t ≍ 3 Myr.
The profiles presented in the atlas can be compared to high-quality ultraviolet observations of galaxies with active star formation in order to constrain the massive star population. The atlas is published in its entirety in computer-readable form in the AAS CD-ROM series, Vol. 5.

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