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

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.

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

10.1017/s0074180900211893 ◽

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 ◽

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.

Probing the hidden atomic gas in Class I jets with SOFIA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937242 ◽

2020 ◽

Vol 642 ◽

pp. A216

Author(s):

T. Sperling ◽

J. Eislöffel ◽

C. Fischer ◽

B. Nisini ◽

T. Giannini ◽

...

Keyword(s):

Mass Loss ◽

Mass Loss Rate ◽

Far Infrared ◽

Class I ◽

Ejection Rate ◽

Almost Everywhere ◽

Atomic Gas ◽

Protostellar Outflows ◽

Mass Ejection ◽

Context. We present SOFIA/FIFI-LS observations of five prototypical, low-mass Class I outflows (HH111, SVS13, HH26, HH34, HH30) in the far-infrared [O I]63μm and [O I]145μm transitions. Aims. Spectroscopic [O I]63μm,145μm maps enable us to study the spatial extent of warm, low-excitation atomic gas within outflows driven by Class I protostars. These [O I] maps may potentially allow us to measure the mass-loss rates (Ṁjet) of this warm component of the atomic jet. Methods. A fundamental tracer of warm (i.e. T ~ 500–1500 K), low-excitation atomic gas is the [O I]63μm emission line, which is predicted to be the main coolant of dense dissociative J-type shocks caused by decelerated wind or jet shocks associated with protostellar outflows. Under these conditions, the [O I]63μm line can be directly connected to the instantaneous mass ejection rate. Thus, by utilising spectroscopic [O I]63μm maps, we wish to determine the atomic mass flux rate Ṁjet ejected from our target outflows. Results. Strong [O I]63μm emission is detected at the driving sources HH111IRS, HH34IRS, SVS13, as well as at the bow shock region, HH7. The detection of the [O I]63μm line at HH26A and HH8/HH10 can be attributed to jet deflection regions. The far-infrared counterpart of the optical jet is detected in [O I]63μm only for HH111, but not for HH34. We interpret the [O I]63μm emission at HH111IRS, HH34IRS, and SVS13 to be coming primarily from a decelerated wind shock, whereas multiple internal shocks within the HH111 jet may cause most of the [O I]63μm emission seen there. At HH30, no [O I]63μm,145μm was detected. The [O I]145μm line detection is at noise level almost everywhere in our obtained maps. The observed outflow rates of our Class I sample are to the order of Ṁjet ~ 10−6M⊙ yr−1, if proper shock conditions prevail. Independent calculations connecting the [O I]63μm line luminosity and observable jet parameters with the mass -loss rate are consistent with the applied shock model and lead to similar mass-loss rates. We discuss applicability and caveats of both methods. Conclusions. High-quality spectroscopic [O I]63μm maps of protostellar outflows at the jet driving source potentially allow a clear determination of the mass ejection rate.

Radiatively driven winds of OB stars

10.1017/s0074180900215684 ◽

1994 ◽

Vol 162 ◽

pp. 487-489 ◽

Cited By ~ 2

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 ◽

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.

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

The Astrophysical Journal ◽

10.1088/0004-637x/710/1/549 ◽

2010 ◽

Vol 710 (1) ◽

pp. 549-566 ◽

Cited By ~ 43

Author(s):

Henry A. Kobulnicky ◽

Ian J. Gilbert ◽

Daniel C. Kiminki

Keyword(s):

Mass Loss ◽

Stellar Mass ◽

Ob Stars ◽

Bow Shocks ◽

Mass loss rates of OB stars derived from infrared observations

International Astronomical Union Colloquium ◽

10.1017/s0252921100094574 ◽

1981 ◽

Vol 59 ◽

pp. 51-56 ◽

Cited By ~ 2

Author(s):

E.G. Tanzi ◽

M. Tarenghi ◽

N. Panagia

Keyword(s):

Mass Loss ◽

Near Infrared ◽

Broad Band ◽

Early Type ◽

Model Calculations ◽

Infrared Observations ◽

Ob Stars ◽

Wide Range ◽

Early Type Stars ◽

In this paper we report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types (Fig. 1).37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined indipendently by various Authors for stars in common. Our data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity.

Properties of the Scenario for the Formation of WR Stars as Post-Red Supergiants

10.1017/s0074180900029090 ◽

1982 ◽

Vol 99 ◽

pp. 371-375

Author(s):

André Maeder

Keyword(s):

Mass Loss ◽

The Other ◽

Evolutionary Models ◽

Constant Mass ◽

Ob Stars ◽

Red Supergiants ◽

Grids of evolutionary models for single stars in the range 9–120 M⊙ have been computed up to the end of the central C-burning phase with up-to-date stellar physics. In addition to other results these models allow us to study the main properties of the formation of WR stars as post-red supergiants (Maeder, 1981c). Three grids of models have been computed: one for constant mass evolution (grid A) and the other two (B and C) with mass loss. As there exists no unique parametrization representing, over the various spectral types, the mass loss rates as a function of basic stellar parameters, we have used mass loss rates fitted on the observations, applying different laws for a) OB stars, b) B-G supergiants, c) red supergiants (RSG) and d) WR stars. At a given luminosity, the rates in grid C are twice as large as in grid B and both grids encompass the central bulk of the observed mass loss rates.

Radio Observations of Massive OB Stars

10.1017/s0074180900045368 ◽

1991 ◽

Vol 143 ◽

pp. 315-315 ◽

Cited By ~ 1

Author(s):

Ian D. Howarth ◽

Alexander Brown

Keyword(s):

Mass Loss ◽

Main Sequence ◽

Thermal Emission ◽

Stellar Winds ◽

X Ray ◽

Ob Stars ◽

Hydrogen Recombination ◽

Flux Limit ◽

Model Independent ◽

The mass-loss rates of O stars and B supergiants are of interest because of their influence on the evolution of these massive stars (among other matters). In principle, the ‘safest’ (i.e. most model-independent) method of determining M is to measure the free-free emission from stellar winds at radio wavelengths. This method is complicated, however, by the existence of poorly understood non-thermal emission in some stars, and by the possibility of hydrogen recombination in the winds of B supergiants.We are in the process of carrying out a VLA survey of OB stars, initially at 3.5cm, to a flux limit of ~0.1mJy. Because all our targets should have thermal emission at detectable levels (based on mass-loss rates from Howarth & Prinja 1989 and terminal velocities from Prinja, Barlow & Howarth 1990), the survey is yielding an unbiassed estimate of the frequency of non-thermal emission. The improved sensitivity of our survey over earlier work defines the log M – log L relationship much more precisely than was previously possible, over a large range in luminosities; and allows us to make definitive statements on recombination in B supergiant winds. Our sample includes the first radio detections of an OC star, of a massive X-ray binary, and of thermal emission from a main-sequence star.

The Theory of Radiation Driven Stellar Winds and the Wolf-Rayet Phenomenon

10.1017/s0074180900028850 ◽

1982 ◽

Vol 99 ◽

pp. 185-196

Author(s):

David C. Abbott

Keyword(s):

Chemical Composition ◽

Mass Loss ◽

Radiation Pressure ◽

Stellar Winds ◽

List Type ◽

Ob Stars ◽

Wind Theory ◽

Peter Conti has a tradition of always talking about 0-type stars at Wolf-Rayet symposia, and Wolf-Rayet stars at 0 star symposia. Since there is no well-developed theory for the origin of the winds of WR stars, it is my pleasure to join Peter's tradition, and to talk mainly about the theory of radiation driven winds in OB stars. The advantage of OB stars is that there exists a fairly complete wind theory, which agrees well with the available observations. The question is, can the mass loss observed from Wolf-Rayet stars be explained by a version of this wind theory which is scaled to the conditions found in the envelopes of Wolf-Rayet stars? The topics I consider are: —The calculated radiation pressure in OB stars, and its dependence on temperature, density, and chemical composition.—A comparison between predicted and observed mass loss rates and terminal velocities for OB stars.—The applicability of the standard radiation driven wind models to Wolf-Rayet stars.—Speculations on how Wolf-Rayet stars achieve their enormous mass loss rates within the context of the radiation pressure mechanism.

Discussion – Circumstellar environment of active OB stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311010805 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 378-379

Author(s):

Douglas R. Gies ◽

Richard H. D. Townsend

Keyword(s):

Mass Loss ◽

X Ray ◽

Ob Stars ◽

Circumstellar Gas ◽

Circumstellar Environment ◽

This session dealt with the circumstellar gas surrounding active OB stars, and the discussion broadly focused on disks, wind morphology and structures, X-ray emission, and mass loss rates.