Bright OB stars in the Galaxy

Маркова, Н.; Puls, J.

doi:10.1051/0004-6361:20077919

Cited by 185 publications

(343 citation statements)

References 74 publications

(143 reference statements)

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“…Mokiem et al (2007b) have analysed other fast rotators in the SMC, but they give no further clues because the authors could only derive upper limits that are above the mean WLR for the SMC. However, it is interesting to note that we do not find this situation in the Milky Way: the values derived by Mokiem et al (2007b) and Repolust et al (2004), whether actual values or upper limits, are close to or below the average WLR for the Milky Way and we are not aware of significantly A85, page 6 of 8 high β values needed to fit the spectra of Galactic O stars, although they are found for the slower winds of B-supergiants (Kudritzki et al 1999;Crowther et al 2006;Markova & Puls 2008). We note that determining of β from optical spectra rapidly rotating stars seen edge-on is in most cases very difficult because of the lack of spectral features sensitive to this parameter.…”

Section: The Wind Momentum Of Ghv-62024mentioning

confidence: 86%

A peculiar Of star in the Local Group galaxy IC 1613

Herrero¹,

García²,

Puls³

et al. 2012

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Context.Results from the theory of radiatively driven winds are nowadays incorporated in stellar evolutionary and population synthesis models, and are used in our interpretation of the observations of the deep Universe. Yet, the theory has been confirmed only until Small Magellanic Cloud metallicities. Observations and analyses of O-stars at lower metallicities are difficult, but much needed to prove the theory. Aims. We have observed GHV-62024, an O6.5 IIIf star in the low-metallicity galaxy IC 1613 (Z ≈ 0.15 Z ) to study its evolution and wind. According to a previous preliminary analysis that was subject to significant restrictions this star could challenge the radiatively driven wind theory at low metallicities. Here we present a complete analysis of this star. Methods. Our observations were obtained with VIMOS at VLT, at R ≈ 2000 and covered approximately between 4000 and 7000 Å. The observations were analysed using the latest version of the model atmosphere code FASTWIND, which includes the possibility of calculating the N iii spectrum. Results. We obtain the stellar parameters and conclude that the star follows the average wind momentum-luminosity relationship (WLR) expected for its metallicity, but with a high value for the exponent of the wind velocity law, β. Comparing this with values of other stars in the literature, we suggest that this high value may be reached because GHV-62024 could be a fast rotator seen at a low inclination angle. We also suggest that this could favour the appearance of the spectral "f"-characterictics. While the derived β value does not change by adopting a lower wind terminal velocity, we show that a wrong V ∞ has a clear impact on the position of the star in the WLR diagram. The N and He abundances are very high, consistent with strong CNO mixing that could have been caused by the fast rotation, although we cannot discard a different origin with present data. Stellar evolutionary model predictions are consistent with the star being still a fast rotator. We find again the well-known mass-discrepancy for this star. Conclusions. We conclude that the star follows the WLR expected for its metallicity. The results are consistent with GHV-62024 being a fast rotator seen close to pole-on, strongly contaminated at the surface with CNO products and with a wind structure altered by the fast rotation but without modifying the global WLR. We suggest that this could be a general property of fast rotators.

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Section: The Wind Momentum Of Ghv-62024mentioning

confidence: 86%

A peculiar Of star in the Local Group galaxy IC 1613

Herrero¹,

García²,

Puls³

et al. 2012

A&A

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“…Recent estimates of the effective temperature of early B-type supergiants have shown that the values obtained with non-LTE blanketed models including winds (hereafter non-LTE BW models) are systematically lower than those derived with models without winds (hereafter wind-free models) (Lefever et al 2007;Crowther et al 2006). Differences range roughly from 0 to 6000 K and they tend to be lower the later the B-sub-spectral type (Markova & Puls 2008). On the other hand, Morossi & Crivellari (1980) noted that the effective temperatures of B-supergiants derived with photometric methods are in general higher than those obtained spectroscopically.…”

Section: Introductionmentioning

confidence: 99%

“…Later, effective temperature determinations for these stars were made using the silicon lines in the optical spectral region, either by fitting the line profiles or by measuring their equivalent widths (Becker & Butler 1990;McErlean et al 1999;Trundle et al 2004). Nowadays, methods based on adjustments of He i and He ii line profiles, and/or the line intensity ratio Si iv/Si iii are preferred (Herrero et al 2002;Repolust et al 2004;Martins et al 2005;Crowther et al 2006;Benaglia et al 2007;Markova & Puls 2008;Searle et al 2008). Recent estimates of the effective temperature of early B-type supergiants have shown that the values obtained with non-LTE blanketed models including winds (hereafter non-LTE BW models) are systematically lower than those derived with models without winds (hereafter wind-free models) (Lefever et al 2007;Crowther et al 2006).…”

Section: Introductionmentioning

confidence: 99%

“…Effective temperatures are also necessary to study the physical processes in the atmosphere, such as non-radial pulsations or stellar winds (radiative forces; changes in ionization). Regarding the stellar winds, the effective temperatures are particularly useful in discussing terminal velocities, mass loss rates, the bi-stability jump, and the wind momentum luminosity relationship (Kudritzki et al 2003;Crowther et al 2006;Markova & Puls 2008).…”

Section: Introductionmentioning

confidence: 99%

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Fundamental parameters of B supergiants from the BCD system

Zorec¹,

Cidale

Arias

et al. 2009

A&A

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Context. Effective temperatures of early-type supergiants are important to test stellar atmosphere-and internal structure-models of massive and intermediate mass objects at different evolutionary phases. However, these T eff values are more or less discrepant depending on the method used to determine them. Aims. We aim to obtain a new calibration of the T eff parameter for early-type supergiants as a function of observational quantities that are: a) highly sensitive to the ionization balance in the photosphere and its gas pressure; b) independent of the interstellar extinction; c) as much as possible model-independent. Methods. The observational quantities that best address our aims are the (λ 1 , D) parameters of the BCD spectrophotometric system. They describe the energy distribution around the Balmer discontinuity, which is highly sensitive to T eff and log g. We perform a calibration of the (λ 1 , D) parameters into T eff using effective temperatures derived with the bolometric-flux method for 217 program stars, whose individual uncertainties are on average |ΔT eff |/T f eff = 0.05. Results. We obtain a new and homogeneous calibration of the BCD (λ 1 , D) parameters for OB supergiants and revisit the current calibration of the (λ 1 , D) zone occupied by dwarfs and giants. The final comparison of calculated with obtained T eff values in the (λ 1 , D) calibration show that the latter have total uncertainties, which on average are T eff /T f eff ±0.05 for all spectral types and luminosity classes. Conclusions. The effective temperatures of OB supergiants derived in this work agree on average within some 2000 K with other determinations found in the literature, except those issued from wind-free non-LTE plane-parallel models of stellar atmospheres, which produce effective temperatures that can be overestimated by up to more than 5000 K near T eff = 25 000 K. Since the stellar spectra needed to obtain the (λ 1 , D) parameters are of low resolution, a calibration based on the BCD system is useful to study stars and stellar systems like open clusters, associations or stars in galaxies observed with multi-object spectrographs and/or spectro-imaging devices.

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“…The wind influence on the B and V band fluxes cannot be expressed easily in terms of, e.g., the recently introduced windstrength related Q parameter (see Markova & Puls 2008). In fact, it was not possible to find a unique parameter, which would express the wind influence in a self-consistent way, and against which we could have plotted the deviations in A V .…”

Section: Resultsmentioning

confidence: 99%

Parameters of galactic early B supergiants

Kraus

Fernandes

Kubát

2009

A&A

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Context. The interstellar extinction, E(B − V), of OB supergiants is usually derived from the observed color index, (B − V), in comparison with the intrinsic one. This method works properly only if the stellar wind does not influence the optical continuum emission. Over the past years, many OB supergiants have been found to have wind-velocity distributions with rather high β values; i.e., their winds are only slowly accelerating, resulting in relative density enhancements within the wind-continuum forming region. It has been found that these kinds of winds might indeed influence the total continuum emission even at optical wavelengths. Aims. We investigate the influence of the wind on the observed color indices of OB supergiants, in order to distinguish between interstellar and circumstellar extinction contributions. Methods. We first tested the influence of the wind on the UBV band fluxes of a model O supergiant star with artificial winds of different β values and a fixed interstellar extinction value. From the UBV magnitudes of these systems, the apparent interstellar extinction was then derived by calculating the values of E(B − V), from the (B − V) as well as from the (U − B) color index. Then we turned to a sample of galactic early-type B supergiants for which the stellar and wind parameters are known. All except one of these stars have β values higher than 1.0, which makes this set the most suitable one for our investigation. We calculated each star's wind contribution to the BV band fluxes. The observed magnitudes were corrected for the wind contributions, and the interstellar extinctions were derived and compared with those derived purely from the (B − V) color index.Results. From our model supergiant, we find that with increasing β the wind starts to influence the observable color indices. The wavelength dependence of the wind contribution is thereby different from that of the interstellar extinction contribution. Thus, the interstellar extinction values derived from the two color indices of our reddened star plus wind systems disagree. This effect is stronger for higher β. In addition, E(B − V) derived from the (B − V) color index always overestimates the real interstellar extinction. This trend is also found for the investigated B supergiant sample. Consequently, the luminosities of these stars are systematically overestimated. Our wind model always computes lower limits to the real wind contributions. This means that the real interstellar extinction values, hence the stellar luminosities of the studied B supergiant sample, might well be lower.

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Bright OB stars in the Galaxy

Cited by 185 publications

References 74 publications

A peculiar Of star in the Local Group galaxy IC 1613

A peculiar Of star in the Local Group galaxy IC 1613

Fundamental parameters of B supergiants from the BCD system

Parameters of galactic early B supergiants

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