Hot star wind mass-loss rate predictions at low metallicity

2018 ◽  
Vol 14 (S344) ◽  
pp. 208-210
Author(s):  
Jiří Krtička ◽  
Jiří Kubát
Keyword(s):  
Mass Loss ◽  
Mass Fraction ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Magnetic Line ◽  
Radiative Force ◽  
Line Profiles ◽  
Low Metallicity ◽  
Loss Rates

AbstractHot star winds are driven by the radiative force due to light absorption in lines of heavier elements. Therefore, the amount of mass lost by the star per unit of time, i.e., the mass-loss rate, is sensitive to metallicity. We provide mass-loss rate predictions for O stars with mass fraction of heavier elements 0.2 <Z/Z⊙ ≤ 1. Our predictions are based on global model atmospheres. The models allow us to predict wind terminal velocity and the mass-loss rate just from basic global stellar parameters. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as (Z/Z⊙)0.59. The predicted mass-loss rates agree with mass-loss rates derived from ultraviolet wind line profiles. At low metallicity, the rotational mixing affects the wind mass-loss rates. We study the influence of magnetic line blanketing.

scholarly journals Stellar wind models of central stars of planetary nebulae

2020 ◽  
Vol 635 ◽  
pp. A173 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Terminal Velocity ◽  
Asymptotic Giant Branch ◽  
Central Stars ◽  
Loss Rates

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

scholarly journals Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate

1995 ◽  
Vol 163 ◽  
pp. 318-319
Author(s):  
G. Meynet
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
High Mass ◽  
New Models ◽  
Theoretical Predictions ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

scholarly journals Global hot-star wind models for stars from Magellanic Clouds

2018 ◽  
Vol 612 ◽  
pp. A20 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Line Profiles ◽  
Equilibrium Equations ◽  
Theoretical Predictions ◽  
Kinetic Equilibrium ◽  
Loss Rates

We provide mass-loss rate predictions for O stars from Large and Small Magellanic Clouds. We calculate global (unified, hydrodynamic) model atmospheres of main sequence, giant, and supergiant stars for chemical composition corresponding to Magellanic Clouds. The models solve radiative transfer equation in comoving frame, kinetic equilibrium equations (also known as NLTE equations), and hydrodynamical equations from (quasi-)hydrostatic atmosphere to expanding stellar wind. The models allow us to predict wind density, velocity, and temperature (consequently also the terminal wind velocity and the mass-loss rate) just from basic global stellar parameters. As a result of their lower metallicity, the line radiative driving is weaker leading to lower wind mass-loss rates with respect to the Galactic stars. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as Ṁ ~ Z0.59. The predicted mass-loss rates are lower than mass-loss rates derived from Hα diagnostics and can be reconciled with observational results assuming clumping factor Cc = 9. On the other hand, the predicted mass-loss rates either agree or are slightly higher than the mass-loss rates derived from ultraviolet wind line profiles. The calculated P v ionization fractions also agree with values derived from observations for LMC stars with Teff ≤ 40 000 K. Taken together, our theoretical predictions provide reasonable models with consistent mass-loss rate determination, which can be used for quantitative study of stars from Magellanic Clouds.

scholarly journals The influence of inhomogeneities on hot star wind model predictions

2008 ◽  
Vol 4 (S252) ◽  
pp. 283-287 ◽  
Author(s):  
J. Krtička ◽  
L. Muijres ◽  
J. Puls ◽  
J. Kubát ◽  
A. de Koter
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
The Other ◽  
Radiative Force ◽  
Wind Model ◽  
Other Hand ◽  
Model Predictions ◽  
Line Force

AbstractWe study the effect of wind inhomogeneities (clumping) on O star wind model predictions. For this purpose we artificially include clumping into our stationary NLTE wind models. As a result of the inclusion of optically thin clumps the radiative line force is increased compared to corresponding unclumped models, with a similar effect on either the mass-loss rate or the terminal velocity. When the clumps are allowed to be optically thick in continuum, on the other hand, the radiative force and consequently the mass-loss rate decreases alternatively.

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals Mass loss and evolution of massive stars in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 480-482 ◽  
Author(s):  
Claus Leitherer ◽  
Norbert Langer
Keyword(s):  
Mass Loss ◽  
Iterative Procedure ◽  
Metal Content ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Evolutionary Models ◽  
Low Metallicity ◽  
Self Consistency

The structure and evolution of massive stars is significantly influenced by effects of chemical composition in a low-metallicity environment (as compared to the solar neighbourhood, SN), such as the Magellanic Clouds. A fundamental ingredient in evolutionary models is the stellar mass-loss rate M. Lower metal content decreases the mass-loss rates derived theoretically, which in turn affects the stellar evolution models. On the other hand, different evolutionary models predict different stellar parameters (especially L), which again influence M so that an iterative procedure is required to achieve self-consistency.

scholarly journals Jsolated Stars of Low Metallicity

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 89
Author(s):  
Efrat Sabach
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Low Mass

We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

scholarly journals Warm CO in evolved stars from the THROES catalogue

2019 ◽  
Vol 622 ◽  
pp. A123 ◽  
Author(s):  
J. M. da Silva Santos ◽  
J. Ramos-Medina ◽  
C. Sánchez Contreras ◽  
P. García-Lario
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Strong Line ◽  
Order Estimate ◽  
Evolved Stars ◽  
Flux Variability ◽  
The Impact ◽  
Loss Rates

Context. This is the second paper of a series making use of Herschel/PACS spectroscopy of evolved stars in the THROES catalogue to study the inner warm regions of their circumstellar envelopes (CSEs). Aims. We analyse the CO emission spectra, including a large number of high-J CO lines (from J = 14–13 to J = 45–44, ν = 0), as a proxy for the warm molecular gas in the CSEs of a sample of bright carbon-rich stars spanning different evolutionary stages from the asymptotic giant branch to the young planetary nebulae phase. Methods. We used the rotational diagram (RD) technique to derive rotational temperatures (Trot) and masses (MH2) of the envelope layers where the CO transitions observed with PACS arise. Additionally, we obtained a first order estimate of the mass-loss rates and assessed the impact of the opacity correction for a range of envelope characteristic radii. We used multi-epoch spectra for the well-studied C-rich envelope IRC+10216 to investigate the impact of CO flux variability on the values of Trot and MH2. Results. The sensitivity of PACS allowed for the study of higher rotational numbers than before indicating the presence of a significant amount of warmer gas (∼200 − 900 K) that is not traceable with lower J CO observations at submillimetre/millimetre wavelengths. The masses are in the range MH2 ∼ 10−2 − 10−5 M⊙, anticorrelated with temperature. For some strong CO emitters we infer a double temperature (warm T¯rot ∼ 400 K and hot T¯rot ∼ 820 K) component. From the analysis of IRC+10216, we corroborate that the effect of line variability is perceptible on the Trot of the hot component only, and certainly insignificant on MH2 and, hence, the mass-loss rate. The agreement between our mass-loss rates and the literature across the sample is good. Therefore, the parameters derived from the RD are robust even when strong line flux variability occurs, and the major source of uncertainty in the estimate of the mass-loss rate is the size of the CO-emitting volume.

scholarly journals A new mass-loss rate prescription for red supergiants

2020 ◽  
Vol 492 (4) ◽  
pp. 5994-6006 ◽  
Author(s):  
Emma R Beasor ◽  
Ben Davies ◽  
Nathan Smith ◽  
Jacco Th van Loon ◽  
Robert D Gehrz ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Substantial Effect ◽  
Evolutionary Models ◽  
Total Mass Loss ◽  
Red Supergiants ◽  
Current Mass ◽  
The Impact ◽  
Loss Rates

ABSTRACT Evolutionary models have shown the substantial effect that strong mass-loss rates ($\dot{M}$s) can have on the fate of massive stars. Red supergiant (RSG) mass-loss is poorly understood theoretically, and so stellar models rely on purely empirical $\dot{M}$–luminosity relations to calculate evolution. Empirical prescriptions usually scale with luminosity and effective temperature, but $\dot{M}$ should also depend on the current mass and hence the surface gravity of the star, yielding more than one possible $\dot{M}$ for the same position on the Hertzsprung–Russell diagram. One can solve this degeneracy by measuring $\dot{M}$ for RSGs that reside in clusters, where age and initial mass (Minit) are known. In this paper we derive $\dot{M}$ values and luminosities for RSGs in two clusters, NGC 2004 and RSGC1. Using newly derived Minit measurements, we combine the results with those of clusters with a range of ages and derive an Minit-dependent $\dot{M}$ prescription. When comparing this new prescription to the treatment of mass-loss currently implemented in evolutionary models, we find models drastically overpredict the total mass-loss, by up to a factor of 20. Importantly, the most massive RSGs experience the largest downward revision in their mass-loss rates, drastically changing the impact of wind mass-loss on their evolution. Our results suggest that for most initial masses of RSG progenitors, quiescent mass-loss during the RSG phase is not effective at removing a significant fraction of the H-envelope prior to core-collapse, and we discuss the implications of this for stellar evolution and observations of SNe and SN progenitors.

scholarly journals Mass loss rates of Li-rich AGB/RGB stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 458-459
Author(s):  
Walter J. Macie ◽  
Roberto D. D. Costa
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Empirical Correlation ◽  
Lower Mass ◽  
Enrichment Process ◽  
Loss Rates

AbstractA sample of AGB/RGB stars with an excess of Li abundances is considered in order to estimate their mass loss rates. Our method is based on a correlation between the Li abundances and the stellar luminosity, using a modified version of the Reimers formula. We have adopted a calibration based on an empirical correlation between the mass loss rate and stellar parameters. We conclude that most Li-rich stars have lower mass loss rates compared with the majority of AGB/RGB stars, which show no evidences of Li enhancements, so that the Li enrichment process is probably not associated with an increased mass loss rate.

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