Spectroscopic Analyses of Hot Extreme Helium Stars

AbstractSpectroscopic fine analyses of hot extreme helium stars are reviewed. The chemical composition is discussed in detail and conclusions as to the nuclear history of the atmospheric material are drawn. Evidence of inhomogeneities among the hot extreme helium stars is presented and it is concluded that the extreme helium stars can be found in the halo population (BD+10°2179) as well as in the disc population. Their mass loss rates are of the same order of magnitude (10−9 M⊙/yr) as those of normal stars. Four helium rich sdO stars are identified as possible descendants of the B-type extreme helium stars.

The Influence of the Ratio of Total to Selective Extinction on the Determination of the Mass Loss Rate of Wolf Rayet Stars from Infrared Excess Measurements

10.1017/s0074180900028862 ◽

1982 ◽

Vol 99 ◽

pp. 197-201

Author(s):

P.S. The ◽

K.A. van der Hucht ◽

M. Arens

Keyword(s):

Mass Loss ◽

Loss Rate ◽

Near Infrared ◽

Mass Loss Rate ◽

Infrared Excess ◽

Photometric Observations ◽

Order Of Magnitude ◽

Selective Extinction ◽

It is shown that the mass loss rate of the WN7 star HD 93162 decreases with larger values of the ratio of total to selective extinction R. for HD 93162 the mass loss rate will change one order of magnitude, only if ΔR ∼ 2. Mass loss rates are derived for nine other WR stars of which visual, red and near-infrared photometric observations were obtained.

Helium-star Mass Loss and Its Implications for Black Hole Formation and Supernova Progenitors

Publications of the Astronomical Society of Australia ◽

10.1071/as01121 ◽

2002 ◽

Vol 19 (2) ◽

pp. 233-237 ◽

Cited By ~ 26

Author(s):

Onno R. Pols ◽

Jasinta D. M. Dewi

Keyword(s):

Black Hole ◽

Mass Loss ◽

High Mass ◽

Binary Interaction ◽

Compact Binary ◽

Helium Stars ◽

High Mass Loss ◽

Helium Star ◽

Black Hole Masses ◽

AbstractRecently the observationally derived stellar-wind mass-loss rates for Wolf-Rayet stars, or massive naked helium stars, have been revised downwards by a substantial amount. We present evolutionary calculations of helium stars incorporating such revised mass-loss rates, as well as mass transfer to a close compact binary companion. Our models reach final masses well in excess of 10 M⊙, consistent with the observed masses of black holes in X-ray binaries. This resolves the discrepancy found with previously assumed high mass-loss rates between the final masses of stars which spend most of their helium-burning lifetime as Wolf-Rayet stars (˜3 M⊙) and the minimum observed black hole masses (6 M⊙). Our calculations also suggest that there are two distinct classes of progenitors for Type Ic supernovae: one with very large initial masses (35 M⊙), which are still massive when they explode and leave black hole remnants, and one with moderate initial masses (˜12–20 M⊙) undergoing binary interaction, which end up with small pre-explosion masses and leave neutron star remnants.

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.

The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037900 ◽

2020 ◽

Vol 641 ◽

pp. A57

Author(s):

S. Massalkhi ◽

M. Agúndez ◽

J. Cernicharo ◽

L. Velilla-Prieto

Keyword(s):

Mass Loss ◽

Mass Loss Rate ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Circumstellar Envelopes ◽

Fractional Abundance ◽

Wide Range ◽

Order Of Magnitude ◽

Large Velocity Gradient ◽

Aims. We aim to determine the abundances of SiO, CS, SiS, SO, and SO2 in a large sample of oxygen-rich asymptotic giant branch (AGB) envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in these environments. Methods. We surveyed a sample of 30 oxygen-rich AGB stars in the λ 2 mm band using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. Results. We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO, and SO2 in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10−6 M⊙ yr−1, whereas it is detected in all envelopes with mass loss rates above that threshold. From a comparison with a previous, similar study on C-rich sources, it becomes evident that the fractional abundances of CS and SiS show a marked differentiation between C-rich and O-rich sources, being two orders of magnitude and one order of magnitude more abundant in C-rich sources, respectively, while the fractional abundance of SiO turns out to be insensitive to the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly to C-rich sources, that is, the denser the envelope the lower its abundance. A similar trend, albeit less clear than for SiO, is observed for SO in O-rich sources. Conclusions. The marked dependence of CS and SiS abundances on the C/O ratio indicates that these two molecules form more efficiently in C- than O-rich envelopes. The decline in the abundance of SiO with increasing envelope density and the tentative one for SO indicate that SiO and possibly SO act as gas-phase precursors of dust in circumstellar envelopes around O-rich AGB stars.

Ring nebulae: what they tell us about Wolf-Rayet stars

10.1017/s0074180900205573 ◽

1999 ◽

Vol 193 ◽

pp. 306-315 ◽

Cited By ~ 1

Author(s):

Anthony P. Marston

Keyword(s):

Mass Loss ◽

Total Mass ◽

Massive Stars ◽

Gas Kinematics ◽

Total Mass Loss ◽

Neutral Gas ◽

History Of ◽

Complex Forms ◽

Ring Nebulae ◽

The environments of evolved massive stars provide an opportunity of obtaining information on the past, as well as current, condition of the stars themselves. In this review we will look at the incidence of ring nebulae around Wolf-Rayet stars, their differing morphologies at various wavelengths and the existence of multiple, concentric shells. We use this information to show that WRs are indeed evolved stars and that the various phases of evolution for a WR star are evidenced in their environments. Abundance measurements and kinematics show that complex forms of mass ejection are likely to have occurred in the evolution of WR stars providing clumpy structures of dust, and both ionized and neutral gas. Gas kinematics also provide estimates to the time-scales of each of the evolutionary phases of WR stars, which can be combined with estimates of nebular masses to provide the approximate values for such crucial parameters as total mass-loss and historical mass-loss rates. Overall, it is illustrated that studies of the environments of WR stars have the potential to provide important information about the mass-loss history of very massive stars, including estimates of the time period of each mass-loss phase, typical mass loss rates, total mass lost and likely evolutionary path. Some of the remaining problems relating to the use of ring nebulae as probes to the evolutionary history of WR stars are also discussed.

Helium stars: Towards an understanding of Wolf–Rayet evolution

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317003404 ◽

2016 ◽

Vol 12 (S329) ◽

pp. 255-259

Author(s):

Liam A. S. McClelland ◽

J. J. Eldridge

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Convection Zone ◽

Star Models ◽

Surface Temperatures ◽

Helium Stars ◽

Pure Helium ◽

Helium Star ◽

Large Grid ◽

AbstractRecent observational modelling of the atmospheres of hydrogen-free Wolf–Rayet stars have indicated that their stellar surfaces are cooler than those predicted by the latest stellar evolution models. We have created a large grid of pure helium star models to investigate the dependence of the surface temperatures on factors such as the rate of mass loss and the amount of clumping in the outer convection zone. Upon comparing our results with Galactic and LMC WR observations, we find that the outer convection zones should be clumped and that the mass-loss rates need to be slightly reduced. We discuss the implications of these findings in terms of the detectability of Type Ibc supernovae progenitors, and in terms of refining the Conti scenario.

Observations of Wolf-Rayet Mass Loss

10.1017/s0074180900045320 ◽

1991 ◽

Vol 143 ◽

pp. 265-280 ◽

Cited By ~ 1

Author(s):

Allan J Willis

Keyword(s):

Mass Loss ◽

Current Knowledge ◽

Mass Loss Rate ◽

Intrinsic Variability ◽

Order Of Magnitude ◽

Wind Velocities ◽

Optical Line ◽

Thermal Sources ◽

Line P ◽

Current knowledge of the stellar winds and mass loss rates for WR stars is reviewed. Recent IR spectroscopy and reassessments of UV resonance line P Cygni profiles have led to revisions of terminal velocities, with v∞ ≃ 0.75 × previous estimates. Radio and IR (10μm) free-free emission for well-established thermal sources, coupled with recent considerations of the wind ionisation balance and chemistry, leads to WR mass loss rates lying in the range 10-5 − 10-4 M⊙ yr–1. This scale is confirmed by independent analyses of optical polarisation modulation in WR+O binaries. No significant differences are apparent between the mean mass loss rates of: (a) single and binary WR stars; (b) WN and WC stars, and (c) the WN and WC subclasses. The overall mean WR mass loss rate is ~ 5 × 10-5 M⊙ yr–1. Although WR radiative luminosities are uncertain, there may be a rough scaling of MWR with L∗, with a spread of up to an order of magnitude at a given L∗. WR winds have the highest momenta of the hot luminous stars, with values of M v∞ c/L∗ in the range 1-30 (WN7,8 and WC9 stars may lie near the lower bound). An additional mechanism to radiation pressure may be required to initiate the high WR mass loss, although thereafter the winds may be radiatively accelerated. Intrinsic variability in optical light, polarisation and emission lines, and in UV P Cygni profiles, indicate significant instability in the WR winds. For extragalactic WR stars in the Local Group, optical line strengths and widths do not suggest substantial differences in wind velocities and mass loss rates of subtypes compared to galactic counterparts.

Prediction model based on chemical composition change for the mechanical degradation of Korean pine (Pinus koraiensis) after brown-rot fungi (Gloeophyllum trabeum) invasion

Holzforschung ◽

10.1515/hf-2021-0082 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Lipeng Zhang ◽

Qifang Xie ◽

Liujie Yang ◽

Yajie Wu ◽

Xingxia Ma

Keyword(s):

Chemical Composition ◽

Mass Loss ◽

Decay Time ◽

Brown Rot ◽

Strength Loss ◽

Gloeophyllum Trabeum ◽

Korean Pine ◽

Composition Change ◽

Brown Rot Decay ◽

Abstract In order to predict the mechanical properties of Korean pine after brown-rot decay based on its chemical composition change, 252 samples were prepared and exposed to a 14-week accelerated laboratory decay test using the brown-rot fungus Gloeophyllum trabeum. The mass loss, parallel-to-grain compressive strength, parallel-to-grain tensile strength and bending strengths were tested. Then chemical components and scanning electron micrograph analysis were conducted every two weeks. Results indicated that the mass loss rates of the samples increased with the increasing decay time and were negatively correlated with the sample volume. The strength loss rates were positively correlated with the decay time and mass loss rates. After 14 weeks the average strength loss rates of the parallel-to-grain compressive, tensile and bending samples reached 32%, 41% and 41%, respectively. Strengths degradation was found sensitive to the change of cellulose and hemicellulose contents. Further, mathematical regression models were proposed based on the content changes of the cellulose and hemicellulose to quantitatively predict the degradation of the strengths of Korean pine after brown-rot decay.

An extensive grid of DARWIN models for M-type AGB stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935366 ◽

2019 ◽

Vol 626 ◽

pp. A100 ◽

Cited By ~ 10

Author(s):

S. Bladh ◽

S. Liljegren ◽

S. Höfner ◽

B. Aringer ◽

P. Marigo

Keyword(s):

Mass Loss ◽

Mass Loss Rate ◽

Stellar Atmospheres ◽

Asymptotic Giant Branch ◽

Driving Mechanism ◽

Agb Stars ◽

Wide Range ◽

Order Of Magnitude ◽

Dynamical Properties ◽

Context. The stellar winds of asymptotic giant branch (AGB) stars are commonly attributed to radiation pressure on dust grains, formed in the wake of shock waves that arise in the stellar atmospheres. The mass loss due to these outflows is substantial, and modelling the dynamical properties of the winds is essential both for studies of individual stars and for understanding the evolution of stellar populations with low to intermediate mass. Aims. The purpose of this work is to present an extensive grid of dynamical atmosphere and wind models for M-type AGB stars, covering a wide range of relevant stellar parameters. Methods. We used the DARWIN code, which includes frequency-dependent radiation-hydrodynamics and a time-dependent description of dust condensation and evaporation, to simulate the dynamical atmosphere. The wind-driving mechanism is photon scattering on submicron-sized Mg2SiO4 grains. The grid consists of ~4000 models, with luminosities from L⋆ = 890 L⊙ to L⋆ = 40 000 L⊙ and effective temperatures from 2200 to 3400 K. For the first time different current stellar masses are explored with M-type DARWIN models, ranging from 0.75 M⊙ to 3 M⊙. The modelling results are radial atmospheric structures, dynamical properties such as mass-loss rates and wind velocities, and dust properties (e.g. grain sizes, dust-to-gas ratios, and degree of condensed Si). Results. We find that the mass-loss rates of the models correlate strongly with luminosity. They also correlate with the ratio L*∕M*: increasing L*∕M* by an order of magnitude increases the mass-loss rates by about three orders of magnitude, which may naturally create a superwind regime in evolution models. There is, however, no discernible trend of mass-loss rate with effective temperature, in contrast to what is found for C-type AGB stars. We also find that the mass-loss rates level off at luminosities higher than ~14 000 L⊙, and consequently at pulsation periods longer than ~800 days. The final grain radii range from 0.25 to 0.6 μm. The amount of condensed Si is typically between 10 and 40%, with gas-to-dust mass ratios between 500 and 4000.

Sulphur-bearing molecules in AGB stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833317 ◽

2018 ◽

Vol 617 ◽

pp. A132 ◽

Cited By ~ 13

Author(s):

T. Danilovich ◽

S. Ramstedt ◽

D. Gobrecht ◽

L. Decin ◽

E. De Beck ◽

...

Keyword(s):

Chemical Composition ◽

Mass Loss ◽

Loss Rate ◽

Mass Loss Rate ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Circumstellar Envelopes ◽

Carbon Stars ◽

Order Of Magnitude ◽

Transfer Modelling

Context. Sulphur has long been known to form different molecules depending on the chemical composition of its environment. More recently, the sulphur-bearing molecules SO and H2S have been shown to behave differently in oxygen-rich asymptotic giant branch (AGB) circumstellar envelopes of different densities. Aims. By surveying a diverse sample of AGB stars for CS and SiS emission, we aim to determine in which environments these sulphur-bearing molecules most readily occur. We include sources with a range of mass-loss rates and carbon-rich, oxygen-rich, and mixed S-type chemistries. Where these molecules are detected, we aim to determine their CS and SiS abundances. Methods. We surveyed 20 AGB stars of different chemical types using the APEX telescope, and combined this with an IRAM 30 m and APEX survey of CS and SiS emission towards over 30 S-type stars. For those stars with detections, we performed radiative transfer modelling to determine abundances and abundance distributions. Results. We detect CS towards all the surveyed carbon stars, some S-type stars, and the highest mass-loss rate oxygen-rich stars, (Ṁ ≥ 5 × 10−6 M⊙ yr−1). SiS is detected towards the highest mass-loss rate sources of all chemical types (Ṁ ≥ 8 × 10−7 M⊙ yr−1). We find CS peak fractional abundances ranging from ~4 × 10−7 to ~2 × 10−5 for the carbon stars, from ~3 × 10−8 to ~1 × 10−7 for the oxygen-rich stars, and from ~1 × 10−7 to ~8 × 10−6 for the S-type stars. We find SiS peak fractional abundances ranging from ~9 × 10−6 to ~2 × 10−5 for the carbon stars, from ~5 × 10−7 to ~2 × 10−6 for the oxygen-rich stars, and from ~2 × 10−7 to ~2 × 10−6 for the S-type stars. Conclusions. Overall, we find that wind density plays an important role in determining the chemical composition of AGB circumstellar envelopes. It is seen that for oxygen-rich AGB stars both CS and SiS are detected only in the highest density circumstellar envelopes and their abundances are generally lower than for carbon-rich AGB stars by around an order of magnitude. For carbon-rich and S-type stars SiS was also only detected in the highest density circumstellar envelopes, while CS was detected consistently in all surveyed carbon stars and sporadically among the S-type stars.