scholarly journals Spectroscopic studies of OB stars in the Magellanic Clouds with VLT-UVES

2003 ◽  
Vol 212 ◽  
pp. 176-177
Author(s):  
Christopher J. Evans ◽  
Paul A. Crowther ◽  
Alexander W. Fullerton ◽  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Model Atmosphere ◽  
Spectroscopic Studies ◽  
Magellanic Clouds ◽  
Ob Stars ◽  
Plane Parallel ◽  
Parallel Models ◽  
Cno Abundances ◽  
Loss Rates

We present results from optical and ultraviolet analysis of nine LMC/SMC supergiants. Temperatures, mass-loss rates and CNO abundances are obtained using the non-LTE, line-blanketed model atmosphere code of Hillier & Miller (1998). In general, the derived temperatures are significantly lower than those determined from unblanketed, plane-parallel models.

scholarly journals Herschel/PACS: Constraining clumping in the intermediate wind region of OB stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 137-139
Author(s):  
M. M. Rubio-Díez ◽  
F. Najarro ◽  
J. O. Sundqvist ◽  
A. Traficante ◽  
J. Puls ◽  
...  
Keyword(s):  
Mass Loss ◽  
Far Infrared ◽  
Initial Estimate ◽  
Ob Stars ◽  
Wind Region ◽  
Loss Rates

AbstractAt present, it is well established that previously accepted mass-loss rates (Ṁ) of luminous OB stars may be overestimated when clumping is neglected. Our Herschel/PACS Far-Infrared (Far-IR) observations of a set of OB stars allow us to improve our knowledge of clumping stratification, constraining clumping properties in intermediate wind regions. In this work, better sampled clumping structure estimates are provided for ι Ori, ε Ori and ξ Per as well as an initial estimate of the clumping properties of the wind from τ Sco. These observations will allow us to obtain reliable mass-loss rates and improve our understanding of the wind physics.

scholarly journals Luminosities and mass-loss rates of carbon stars in the Magellanic Clouds

2007 ◽  
Vol 376 (1) ◽  
pp. 313-337 ◽  
Author(s):  
M. A. T. Groenewegen ◽  
P. R. Wood ◽  
G. C. Sloan ◽  
J. A. D. L. Blommaert ◽  
M.-R. L. Cioni ◽  
...  
Keyword(s):  
Mass Loss ◽  
Magellanic Clouds ◽  
Carbon Stars ◽  
Loss Rates

scholarly journals FeII in the UV Spectrum of Luminous Emission Line Stars

1986 ◽  
Vol 116 ◽  
pp. 275-276
Author(s):  
G. Muratorio ◽  
M. Friedjung ◽  
R. Viotti
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Velocity ◽  
Previous Analysis ◽  
Magellanic Clouds ◽  
Absorption Lines ◽  
High Dispersion ◽  
Uv Spectrum ◽  
Loss Rates

Following the excessive mass loss rates we derived in a previous analysis of the FeII emission and absorption lines of some luminous Magellanic Clouds stars, assuming the two components formed in the same region (Muratorio et al., 1984), we again analysed the FeII data using the same method (Muratorio, 1985), but taking into account the presence of high velocity winds detected in some stars (R66, R126) by the study of the high dispersion IUE spectra (Stahl et al., 1983; Zickgraf et al., 1985).

scholarly journals Evolution of 1–5 Mm⊙ Stars by Mass Loss

1993 ◽  
Vol 155 ◽  
pp. 478-478
Author(s):  
E. Vassiliadis ◽  
P.R. Wood
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Star Clusters ◽  
Magellanic Clouds ◽  
Pulsation Period ◽  
Agb Stars ◽  
Loss Formula ◽  
Loss Rates

Stars of mass 1–5 MM⊙ and composition Y=0.25 and Z=0.016 have been evolved from the main-sequence to the white dwarf stage with an empirical mass loss formula based on observations of mass loss rates in AGB stars. This mass loss formula (Wood 1990) causes the mass loss rate to rise exponentially with pulsation period on the AGB until superwind rates are achieved, where these rates correspond to radiation pressure driven mass loss rates. The formula was designed to reproduce the maximum periods observed for optically-visible LPVs and it also reproduces extremely well the maximum AGB luminosities observed in star clusters in the Magellanic Clouds (see Vassiliadis and Wood 1992 for details).

scholarly journals Probing the weak wind phenomenon in Galactic O-type giants

2019 ◽  
Vol 628 ◽  
pp. A36 ◽  
Author(s):  
E. S. G. de Almeida ◽  
W. L. F. Marcolino ◽  
J.-C. Bouret ◽  
C. B. Pereira
Keyword(s):  
Mass Loss ◽  
Model Atmosphere ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Energy Distributions ◽  
Conservation Of Energy ◽  
Predicted Values ◽  
Weak Winds ◽  
Weak Wind ◽  
Loss Rates

Aims. Analyses of Galactic late O dwarfs (O8-O9.5V stars) raised the “weak wind problem”: spectroscopic mass-loss rates (Ṁ) are up to two orders of magnitude lower than the theoretical values. We investigated the stellar and wind properties of Galactic late O giants (O8-O9.5III stars). These stars have luminosities log (L⋆ ∕ L⊙) ~ 5.2, which is the critical value (onset of weak winds) proposed in the literature. Methods. We performed a spectroscopic analysis of nine O8-O9.5III stars in the ultraviolet (UV) and optical regions using the model atmosphere code CMFGEN. Results. Stellar luminosities were adopted using calibrations from the literature. Overall, our model spectral energy distributions agree well with the observed ones considering parallaxes from the latest Gaia data release (DR2). The effective temperature derived from the UV region agrees well with the ones from the optical. As expected, the analysis of the Hertzsprung–Russell (HR) diagram shows that our sample is more evolved than late O dwarfs. From the UV region, we found Ṁ ~ 10−8 − 10−9M⊙ yr−1 overall. This is lower by ~0.9 − 2.3 dex than predicted values based on the (global) conservation of energy in the wind. The mass-loss rates predicted from first principles, based on the moving reversing layer theory, agree better with our findings, but it fails to match the spectroscopic Ṁ for the most luminous OB stars. The region of log (L⋆ ∕ L⊙) ~ 5.2 is critical for both sets of predictions in comparison with the spectroscopic mass-loss rates. CMFGEN models with the predicted Ṁ (the former one) fail to reproduce the UV wind lines for all the stars of our sample. We reproduce the observed Hα profiles of four objects with our Ṁ derived from the UV. Hence, low Ṁ values (weak winds) are favored to fit the observations (UV + optical), but discrepancies between the UV and Hα diagnostics remain for some objects. Conclusions. Our results indicate weak winds beyond the O8-9.5V class, since the region of log (L⋆ ∕ L⊙) ~ 5.2 is indeed critical to the weak wind phenomenon. Since O8-O9.5III stars are more evolved than O8-9.5V, evolutionary effects do not seem to play a role in the onset of the weak wind phenomenon. These findings support that the Ṁ (for low luminosity O stars) in use in the majority of modern stellar evolution codes must be severely overestimated up to the end of the H-burning phase. Further investigations must evaluate the consequences of weak winds in terms of physical parameters for massive stars (e.g., angular momentum and CNO surface abundances).

scholarly journals Long Period Variables in the Magellanic Clouds and the Galaxy

1993 ◽  
Vol 139 ◽  
pp. 192-200 ◽  
Author(s):  
S.M.G. Hughes
Keyword(s):  
Mass Loss ◽  
Galactic Disk ◽  
Magellanic Clouds ◽  
Pulsation Mode ◽  
Long Period ◽  
Long Period Variables ◽  
The Galaxy ◽  
Loss Rates

AbstractNew results (∼last two years) on mainly observational properties of Long Period Variables (LPVs) in the Magellanic Clouds and the Galaxy are reviewed. These properties include the effects of metallicity variations on their mass loss rates, the use of AGB LPVs to map the stellar distributions of the Galactic disk and bulge, and using detailed observations of nearby Miras to investigate their structure and to obtain new parallax distances, with implications for the pulsation mode of Miras.

scholarly journals The Mass Loss Rate of SK 80 (07Iaf) in the Small Magellanic Cloud

1986 ◽  
Vol 116 ◽  
pp. 269-270
Author(s):  
A J Willis ◽  
I D Howarth ◽  
K Nandy ◽  
D H Morgan
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Optical Spectra ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Small Magellanic Cloud ◽  
Ob Stars

The star SK 80 in the SMC is classified as 07Iaf by Walborn (1976) who notes that it is the only confirmed Of star in that Galaxy known to date. A knowledge of the mass loss properties of OB stars in the Magellanic Clouds is of interest because of the recent evidence that such stars show reduced mass loss properties than their galactic counterparts (Hutchings 1980) and for Of stars because of the possible link between such stars and Pop I transition WNL stars (Conti 1976).We have secured HIRES IUE and optical spectra of SK 80 and have attempted to derive the mass loss rate from these data.

scholarly journals Structure in the winds of O-Type stars: observations and inferences

2010 ◽  
Vol 6 (S272) ◽  
pp. 136-147
Author(s):  
Alex W. Fullerton
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Spatial Scales ◽  
Model Atmosphere ◽  
Theoretical Framework ◽  
Observational Evidence ◽  
Considerable Progress ◽  
Small Scale ◽  
Wind Structure ◽  
Loss Rates

AbstractThis review describes the observational evidence for structure in the winds of O-type stars due to large-scale perturbations and small-scale inhomogeneities. Despite considerable progress, a comprehensive theoretical framework that explains the origin. properties, and coexistence of wind structure on different spatial scales has yet to be constructed and incorporated into model atmosphere analyses. Consequently, it is not yet possible to assess the effect of non-stationary structures on different wind diagnostics in a rigorous way, with the result that accurate empirical determinations of mass-loss rates remain elusive.

scholarly journals Radiatively driven winds of OB stars

1994 ◽  
Vol 162 ◽  
pp. 487-489 ◽  
Author(s):  
Michihiro R. Shimada ◽  
Masaki Ito ◽  
Ryuko Hirata ◽  
Toshihiro Horaguchi
Keyword(s):  
Mass Loss ◽  
Radiative Force ◽  
Ob Stars ◽  
Temperature Range ◽  
Wind Velocities ◽  
Atomic Lines ◽  
Loss Rates

We newly calculated the line radiative force with 520,000 atomic lines, which is twice as many as those of Abbott (1982), for OB supergiants. Our results are as follows. (1) The mass loss rates for O stars with Teff = 50,000K are seven times as large as Abbott's (1982) because of contribution from Fe iv lines. (2) Contribution from many weak lines increases the mass loss rates and decreases the wind velocities of OB stars within a temperature range of 10,000K ≤ Teff ≤ 30,000K. This result is qualitatively in accordance with the results from the recent observations of O stars. (3) The mass loss rates of OB stars depend on metallicity with Ṁ ∼ Z.

scholarly journals OB STARS AND STELLAR BOW SHOCKS IN CYGNUS-X: A NOVEL LABORATORY ESTIMATING STELLAR MASS LOSS RATES

2010 ◽  
Vol 710 (1) ◽  
pp. 549-566 ◽  
Author(s):  
Henry A. Kobulnicky ◽  
Ian J. Gilbert ◽  
Daniel C. Kiminki
Keyword(s):  
Mass Loss ◽  
Stellar Mass ◽  
Ob Stars ◽  
Bow Shocks ◽  
Loss Rates
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