On the importance of the wind emission to the optical continuum
of OB supergiants

KRAUS, Michaela, Jiří KUBÁT and Jiří KRTIČKA. On the importance of the wind emission to the optical continuum of OB supergiants. Astronomy and Astrophysics. Les Ulis Cedex, France: EDP Sciences, 2008, vol. 36, No 481, p. 499-506. ISSN 0004-6361.

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TY  - JOUR
ID  - 762570
AU  - Kraus, Michaela - Kubát, Jiří - Krtička, Jiří
PY  - 2008
TI  - On the importance of the wind emission to the optical continuum of OB supergiants
JF  - Astronomy and Astrophysics
VL  - 36
IS  - 481
SP  - 499-506
EP  - 499-506
PB  - EDP Sciences
SN  - 00046361
KW  - stars: early-type -- stars: supergiants -- stars: winds outflows -- stars: mass-loss -- stars: circumstellar matter
UR  - http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2008/14/aa8991-07/aa8991-07.html
N2  - Context. Thermal wind emission in the form of free-free and free-bound emission is known to show up in the infrared and radio continuum of hot and massive stars. For OB supergiants with moderate mass loss rates and a wind velocity distribution with $\beta$$\simeq$ 0.8 ... 1.0, no influence of the wind to the optical continuum, i.e. for $\lambda \la$ 1.0 $\mu$m, is expected. Investigations of stellar and wind parameters of OB supergiants over the last few years suggest, however, that for many objects $\beta$ is much higher than 1.0, reaching values up to 3.5. Aims. We investigate the influence of the free-free and free-bound emission on the emerging radiation, especially at optical wavelengths, from OB supergiants having wind velocity distributions with $\beta \ge$ 1.0. Methods. For the case of a spherically symmetric, isothermal wind in local thermodynamical equilibrium (LTE) we calculate the free-free and free-bound processes and the emerging wind and total continuum spectra. We localize the generation region of the optical wind continuum and especially focus on the influence of a $\beta$-type wind velocity distribution with $\beta$ > 1 on the formation of the wind continuum at optical wavelengths. Results. The optical wind continuum is found to be generated within about 2 $R_{\rm *}$ which is exactly the wind region where $\beta$ strongly influences the density distribution. We find that for $\beta$ > 1, the continuum of a typical OB supergiant can indeed be contaminated with thermal wind emission, even at optical wavelengths. The strong increase in the optical wind emission is dominantly produced by free-bound processes.
ER  -

Basic information
Original name	On the importance of the wind emission to the optical continuum of OB supergiants
Name in Czech	O důležitosti emise větru pro optické kontinuum OB veleobrů
Authors	KRAUS, Michaela (276 Germany), Jiří KUBÁT (203 Czech Republic) and Jiří KRTIČKA (203 Czech Republic, guarantor, belonging to the institution).
Edition	Astronomy and Astrophysics, Les Ulis Cedex, France, EDP Sciences, 2008, 0004-6361.

Other information
Original language	English
Type of outcome	Article in a journal
Field of Study	10308 Astronomy
Country of publisher	France
Confidentiality degree	is not subject to a state or trade secret
WWW	URL
Impact factor	Impact factor: 4.153
RIV identification code	RIV/00216224:14310/08:00040362
Organization unit	Faculty of Science
UT WoS	000254515800025
Keywords in English	stars: early-type -- stars: supergiants -- stars: winds outflows -- stars: mass-loss -- stars: circumstellar matter
Tags	International impact, Reviewed
Changed by	Changed by: prof. Mgr. Jiří Krtička, Ph.D., učo 8714. Changed: 30/4/2011 17:02.

Abstract

Context. Thermal wind emission in the form of free-free and free-bound emission is known to show up in the infrared and radio continuum of hot and massive stars. For OB supergiants with moderate mass loss rates and a wind velocity distribution with $\beta$$\simeq$ 0.8 ... 1.0, no influence of the wind to the optical continuum, i.e. for $\lambda \la$ 1.0 $\mu$m, is expected. Investigations of stellar and wind parameters of OB supergiants over the last few years suggest, however, that for many objects $\beta$ is much higher than 1.0, reaching values up to 3.5. Aims. We investigate the influence of the free-free and free-bound emission on the emerging radiation, especially at optical wavelengths, from OB supergiants having wind velocity distributions with $\beta \ge$ 1.0. Methods. For the case of a spherically symmetric, isothermal wind in local thermodynamical equilibrium (LTE) we calculate the free-free and free-bound processes and the emerging wind and total continuum spectra. We localize the generation region of the optical wind continuum and especially focus on the influence of a $\beta$-type wind velocity distribution with $\beta$ > 1 on the formation of the wind continuum at optical wavelengths. Results. The optical wind continuum is found to be generated within about 2 $R_{\rm *}$ which is exactly the wind region where $\beta$ strongly influences the density distribution. We find that for $\beta$ > 1, the continuum of a typical OB supergiant can indeed be contaminated with thermal wind emission, even at optical wavelengths. The strong increase in the optical wind emission is dominantly produced by free-bound processes.

Abstract (in Czech)
Ukázali jsme, že optické kontinuum OB veleobrů vzniká ve vzdálenosti menší než 2 R_* od hvězdy. Pro pomalu urychlované větry podstatná část kontinua vzniká ve hvězdném větru.

Links
KJB300030701, research and development project	Name: B[e] veleobři: kde je jejich místo ve vývoji velmi hmotných hvězd?

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On the importance of the wind emission to the optical continuum of OB supergiants

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