The Ultraviolet and Optical Spectra of Metal-deficient O Stars in the Small Magellanic Cloud

Details The Ultraviolet and Optical Spectra of Metal-deficient O Stars in the Small Magellanic Cloud The Ultraviolet and Optical Spectra of Metal-deficient O Stars in the Small Magellanic Cloud

Sep 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000pasp..112.1243w&link_type=abstract

The Publications of the Astronomical Society of the Pacific, Volume 112, Issue 775, pp. 1243-1261.

Astronomy and Astrophysics

Astronomy

80

Galaxies: Magellanic Clouds, Open Clusters And Associations: Individual (Ngc 346), Stars: Early-Type, Stars: Fundamental Parameters, Stars: Winds, Outflows, Ultraviolet: Stars

Scientific paper

An ultraviolet and optical spectral atlas of 15 O stars in the Small Magellanic Cloud (SMC) is presented and described. The echelle data have resolving powers of order 104; they were obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph in the UV, and at the Anglo-Australian Telescope or the European Southern Observatory 3.6 m in the optical. The ultimate objective is to develop metal-deficient templates for the interpretation of distant starbursts, but here we discuss interesting new properties of the SMC stars themselves, revealed by the high quality of these data. The SMC metal deficiency produces anomalously weak stellar-wind profiles along the entire O main sequence, as well as at intermediate luminosities; the first intermediate Si IV λ1400 wind profile in the SMC is shown. The second known Of star in the SMC displays wind peculiarities that are identical to those of its spectral classmate, again likely due to the low systemic metallicity. Several objects display marked CNO anomalies, including the first cases of C III λ4650 emission without N III λ4640 in O-type spectra. The N/C ratio appears to increase with mass, extent of evolution away from the zero-age main sequence, and/or rotational velocity in the young cluster NGC 346. In addition, the first examples of Onfp (Oef) and Of?p spectra in the SMC have been found (the latter being only the fourth member of its peculiar shell category known anywhere). The UV wind characteristics of these objects correlate with their optical peculiarities. All these spectroscopic phenomena provide diagnostics of the evolutionary status of metal-deficient massive stars. Based in part on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Also based on observations obtained at the Anglo-Australian Observatory, Siding Spring, and at the European Southern Observatory, La Silla.

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