Volume 535, November 2011
|Number of page(s)||25|
|Section||Interstellar and circumstellar matter|
|Published online||27 October 2011|
Centro de Astrobiología, (CSIC-INTA), Ctra. Torrejón Ajalvir km 4, 28850 Torrejón de Ardoz, Spain
2 Department of Physics, University of Cincinnati, PO Box 21001, Cincinnati, Ohio, 45221-0011, USA
3 Universitätssternwarte München, Scheinerstr. 1, 81679 München, Germany
Received: 26 October 2010
Accepted: 18 August 2011
Context. Mass-loss, occurring through radiation driven supersonic winds, is a key issue throughout the evolution of massive stars. Two outstanding problems are currently challenging the theory of radiation-driven winds: wind clumping and the weak-wind problem.
Aims. We seek to obtain accurate mass-loss rates of OB stars at different evolutionary stages to constrain the impact of both problems in our current understanding of massive star winds.
Methods. We perform a multi-wavelength quantitative analysis of a sample of ten Galactic OB-stars by means of the atmospheric code cmfgen, with special emphasis on the L-band window. A detailed investigation is carried out on the potential of Brα and Pfγ as mass-loss and clumping diagnostics.
Results. For objects with dense winds, Brα samples the intermediate wind while Pfγ maps the inner one. In combination with other indicators (UV, Hα, Brγ) these lines enable us to constrain the wind clumping structure and to obtain “true” mass-loss rates. For objects with weak winds, Brα emerges as a reliable diagnostic tool to constrain Ṁ. The emission component at the line Doppler-core superimposed on the rather shallow Stark absorption wings reacts very sensitively to mass loss already at very low Ṁ values. On the other hand, the line wings display similar sensitivity to mass loss as Hα, the classical optical mass loss diagnostics.
Conclusions. Our investigation reveals the great diagnostic potential of L-band spectroscopy to derive clumping properties and mass-loss rates of hot star winds. We are confident that Brα will become the primary diagnostic tool to measure very low mass-loss rates with unprecedented accuracy.
Key words: infrared: stars / stars: early-type / stars: winds, outflows / stars: mass-loss
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program ms ID 076.D-0149 (L-band ISAAC) and 266.D-5655(A) (UVES optical spectra).
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011
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