Bright OB stars in the Galaxy

Маркова, Н.; Puls, J.; Scuderi, S.; Markov, H.

doi:10.1051/0004-6361:20041774

Cited by 65 publications

(72 citation statements)

References 32 publications

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“…Another potential source of bias in determinations ofṀ (Hα) is the high frequency of variability (Ebbets 1982;Kaper et al 1998;Markova et al 2005). Many of these variations are characterized by changes in the equivalent width of the emission, which implies that either the amount of material or its density distribution changes.…”

Section: Biases In Measurements Ofṁ (Hα)mentioning

confidence: 99%

The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

Fullerton

Massa

Prinja

2006

ApJ

348

415

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We have determined accurate values of the product of the mass-loss rate and the ion fraction of P 4+ ,Ṁ q(P 4+ ), for a sample of 40 Galactic O-type stars by fitting stellar-wind profiles to observations of the P v resonance doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P 4+ is the dominant ion in the wind (i.e., 0.5 q(P 4+ ) ≤ 1),Ṁ q(P 4+ ) approximates the mass-loss rate to within a factor of 2. Theory predicts that P 4+ is the dominant ion in the winds of O7-O9.7 stars, though an empirical estimator suggests that the range from O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P v wind profiles are systematically smaller than those obtained from fits to Hα emission profiles or radio free-free emission by median factors of ∼130 (if P 4+ is dominant between O7 and O9.7) or ∼20 (if P 4+ is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from "ρ 2 " diagnostics have been systematically over-estimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.

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Section: Biases In Measurements Ofṁ (Hα)mentioning

confidence: 99%

The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

Fullerton

Massa

Prinja

2006

ApJ

348

415

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“…Generally, for the line profiles studied here, the influence of rotation is important for the recombination lines, but not for the resonance lines. We use observed uv fuse spectra from Fullerton et al (2006), and optical spectra from Markova et al (2005) and A. Herrero (described in Herrero et al 2000). In addition to H α , He ii 4686, and PV, we also consider the wind sensitive cores of H β and H γ .…”

Section: A Multi-diagnostic Study Of λ Cepmentioning

confidence: 99%

“…The H α time series of Markova et al (2005) reveal that both the height of the emission peak and the depth of the absorption trough depend on the observational snapshot, variations can reach 0.04 in residual flux units. Therefore it is not critical that neither the peak nor the trough is perfectly reproduced by our models in Fig.…”

Section: Constraints From Empirical Stochastic Modelsmentioning

confidence: 99%

Mass loss from inhomogeneous hot star winds

Sundqvist¹,

Puls²,

Feldmeier³

et al. 2011

A&A

Self Cite

117

168

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Context. Mass loss is essential for massive star evolution, thus also for the variety of astrophysical applications relying on its predictions. However, mass-loss rates currently in use for hot, massive stars have recently been seriously questioned, mainly because of the effects of wind clumping. Aims. We investigate the impact of clumping on diagnostic ultraviolet resonance and optical recombination lines often used to derive empirical mass-loss rates of hot stars. Optically thick clumps, a non-void interclump medium, and a non-monotonic velocity field are all accounted for in a single model. The line formation is first theoretically studied, after which an exemplary multi-diagnostic study of an O-supergiant is performed. Methods. We used 2D and 3D stochastic and radiation-hydrodynamic wind models, constructed by assembling 1D snapshots in radially independent slices. To compute synthetic spectra, we developed and used detailed radiative transfer codes for both recombination lines (solving the "formal integral") and resonance lines (using a Monte-Carlo approach). In addition, we propose an analytic method to model these lines in clumpy winds, which does not rely on optically thin clumping. Results. The importance of the "vorosity" effect for line formation in clumpy winds is emphasized. Resonance lines are generally more affected by optically thick clumping than recombination lines. Synthetic spectra calculated directly from current radiationhydrodynamic wind models of the line-driven instability are unable to in parallel reproduce strategic optical and ultraviolet lines for the Galactic O-supergiant λ Cep. Using our stochastic wind models, we obtain consistent fits essentially by increasing the clumping in the inner wind. A mass-loss rate is derived that is approximately two times lower than what is predicted by the line-driven wind theory, but much higher than the corresponding rate derived when assuming optically thin clumps. Our analytic formulation for line formation is used to demonstrate the potential importance of optically thick clumping in diagnostic lines in so-called weak-winded stars and to confirm recent results that resonance doublets may be used as tracers of wind structure and optically thick clumping. Conclusions. We confirm earlier results that a re-investigation of the structures in the inner wind predicted by line-driven instability simulations is needed. Our derived mass-loss rate for λ Cep suggests that only moderate reductions of current mass-loss predictions for OB-stars are necessary, but this nevertheless prompts investigations on feedback effects from optically thick clumping on the steady-state, NLTE wind models used for quantitative spectroscopy.

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“…S.-D. et al: Low-frequency photospheric and wind variability in HD 2905 Meanwhile, important advances can be also achieved using ground-based time-resolved spectroscopy (e.g., Kraus et al, 2015;Aerts et al, 2017). Indeed, these complementary observations will become decisive for disentangling the intricate -and most likely interconnected -photospheric and wind variability present in the whole massive star domain (see Ebbets, 1982;Prinja et al, 1996;Fullerton et al, 1996;Kaufer et al, 1996Kaufer et al, , 1997Rivinius et al, 1997;Morel et al, 2004;Markova et al, 2005Markova et al, , 2008Martins et al, 2015, for some illustrative examples). Such data are in any case needed to perform a reliable seismic characterization of these extreme stellar objects.…”

Section: Introductionmentioning

confidence: 99%

Low-frequency photospheric and wind variability in the early-B supergiant HD 2905

Diaz

Aerts

Urbaneja

et al. 2018

A&A

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Context. Despite the important advances in space asteroseismology during the last decade, the early phases of evolution of stars with masses above ∼15 M (including the O stars and their evolved descendants, the B supergiants) have been only vaguely explored up to now. This is due to the lack of adequate observations for a proper characterization of the complex spectroscopic and photometric variability occurring in these stars. Aims. Our goal is to detect, analyze and interpret variability in the early-B type supergiant HD 2905 (κ Cas, B1 Ia) using long-term, ground based, high resolution spectroscopy. Methods. We gather a total of 1141 high-resolution spectra covering some 2900 days with three different high-performance spectrographs attached to 1 -2.6m telescopes at the Canary Islands observatories. We complement these observations with the Hipparcos light curve, which includes 160 data points obtained during a time span of ∼1200 days. We investigate spectroscopic variability of up to 12 diagnostic lines by using the zero and first moments of the line profiles. We perform a frequency analysis of both the spectroscopic and photometric dataset using Scargle periodograms. We obtain single snapshot and time-dependent information about the stellar parameters and abundances by means of the fastwind stellar atmosphere code. Results. HD 2905 is a spectroscopic variable with peak-to-peak amplitudes in the zero and first moments of the photospheric lines of up to 15% and 30 km s −1 , respectively. The amplitude of the line-profile variability is correlated with the line formation depth in the photosphere and wind. All investigated lines present complex temporal behavior indicative of multi-periodic variability with timescales of a few days to several weeks. No short-period (hourly) variations are detected. The Scargle periodograms of the Hipparcos light curve and the first moment of purely photospheric lines reveal a low-frequency amplitude excess and a clear dominant frequency at ∼0.37 d −1 . In the spectroscopy, several additional frequencies are present in the range 0.1 -0.4 d −1 . These may be associated with heat-driven gravity modes, convectively-driven gravity waves, or sub-surface convective motions. Additional frequencies are detected below 0.1 d −1 . In the particular case of Hα, these are produced by rotational modulation of a non-spherically symmetric stellar wind. Conclusions. Combined long-term uninterrupted space photometry with high-precision spectroscopy is the best strategy to unravel the complex low-frequency photospheric and wind variability of B supergiants. 3D simulations of waves and of convective motions in the sub-surface layers can shed light on a unique interpretation of the variability.

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Bright OB stars in the Galaxy

Cited by 65 publications

References 32 publications

The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

Mass loss from inhomogeneous hot star winds

Low-frequency photospheric and wind variability in the early-B supergiant HD 2905

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