scholarly journals Envelope Distention and Mass Loss IN W VIR Pulsating Variables

1989 ◽  
Vol 111 ◽  
pp. 262-262
Author(s):  
Yu. A. Fadeyev ◽  
H. Muthsam
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Stellar Atmosphere ◽  
Scale Height ◽  
The Other ◽  
Escape Velocity ◽  
Hydrodynamic Calculations ◽  
The Mean ◽  
Radial Pulsations

AbstractThe hydrodynamic calculations of nonlinear self-excited radial pulsations were done for the models of W Vir stars with mass 0.6 M⊙ and luminosities from 794L⊙ to 3981L⊙. The periods of the models are longer than 10 days. The pulsations are shown to be accompanied by periodic shocks that change the density distribution in the pulsating stellar atmosphere. At radii less than 5 Rph, where Rph is the radius of the photosphere, the mean dynamic scale height is nearly five times the static scale height. In this region of the atmosphere the mean radii of outer mass zones do not change perceptably. On the other hand, at radii larger than 5 Rph the scale height is of the order of Rph so that the outermost layers ultimately expand with a velocity exceeding the local escape velocity. The mass flux in the atmosphere increases with decreasing mass to radius ratio and mass loss rate in W Vir type variables is in the range from 2 X 10−6M⊙·yr−1 to 10−5M⊙·yr−1.

scholarly journals Radio observations and the mass flow rate of α Cyg (A2Ia)

1981 ◽  
Vol 59 ◽  
pp. 61-64
Author(s):  
B. Wolf ◽  
O. Stahl ◽  
W.J. Altenhoff
Keyword(s):  
Mass Loss ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Growth Analysis ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
The Other ◽  
Radio Flux ◽  
Radio Observations ◽  
Lower Mass

From the free-free excess at 10μ. Barlow and Cohen (1977) (hereafter referred to as BC) derived a mass loss rate of 6.9 10-7 M⊙ yr-1 for α Cyg. They predicted a 10 GHz radio flux of 2.2 mJy. On the other hand Praderie et al. (1980) derived a considerable lower mass loss rate of 1.1 10 -8 ≤Ṁ ≤ 7 10-8 M ⊙ yr-1 from a curve of growth analysis of the envelope ultraviolet Fell-lines of α Cyg. Radio observations are desirable to make a decision about these discrepant results. Therefore we observed α Cyg at 15 GHz with the 100 m telescope of the MPIfR at Effelsberg. The observations are discussed together with recent VLA data of Abbott et al. (1980).

scholarly journals Spectral analysis of LBV stars in M31: AF And and Var 15

2014 ◽  
Vol 9 (S307) ◽  
pp. 146-147
Author(s):  
A. F. Valeev ◽  
O. Sholukhova ◽  
S. Fabrika
Keyword(s):  
Spectral Analysis ◽  
Mass Loss ◽  
Hydrogen Content ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Time Interval ◽  
Escape Velocity ◽  
Bona Fide

AbstractWe study spectra of two bona fide LBV stars in M31: AF And and Var 15. The spectra were obtained with the 6-m telescope (Russia) from 2005 to 2012. The model spectra were calculated with the CMFGEN code. We have not found strong changes in the spectra of the LBV stars in that time interval, however a certain variability has been detected. We estimate the star and wind parameters, such as luminosity, temperature, raduis, mass loss rate, escape velocity, hydrogen content, and reddening. We study the stars on the Hertzsprung-Russell diagram and find their initial masses using evolutionary tracks by Meynet et al. (1994).

scholarly journals Spectroscopic Study of Pleione in 1977–1979

1982 ◽  
Vol 98 ◽  
pp. 161-165 ◽  
Author(s):  
Ryuko Hirata ◽  
Jun'ichi Katahira ◽  
Jun Jugaku
Keyword(s):  
Mass Loss ◽  
Spectroscopic Study ◽  
Shell Structure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Radial Velocities ◽  
The Other

Shell spectra of Pleione in 1977–1979 are characterized by further increase in their strengths and by the development of the blue-winged profiles without noticeable variation of their radial velocities. The MgII resonance lines at λ2800A have the blue-shifted components with a velocity of-35 km/s relative to the other shell lines. The development of the shell structure is derived. The mass loss rate was 7×10−11 M⊙/yr.

scholarly journals The dichotomy of atmospheric escape in AU Mic b

2020 ◽  
Vol 498 (1) ◽  
pp. L53-L57
Author(s):  
S Carolan ◽  
A A Vidotto ◽  
P Plavchan ◽  
C Villarreal D’Angelo ◽  
G Hazra
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Evaporation Rate ◽  
Loss Rate ◽  
Extreme Ultraviolet ◽  
Mass Loss Rate ◽  
Young Star ◽  
Planetary Atmosphere ◽  
The Other ◽  
Atmospheric Escape

ABSTRACT Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Microscopii (AU Mic) b. On one hand, the high extreme-ultraviolet stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planet’s atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate ($\dot{\mathrm{ M}}_\odot$). To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind–planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly α transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a ‘no wind’ scenario to up to a stellar wind with a mass-loss rate of $1000~\dot{\mathrm{ M}}_\odot$. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from 6.5 × 1010  g s−1 to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly α absorption drops from $\sim 20{{\ \rm per\ cent}}$ in the case of ‘no wind’ to barely any Ly α absorption in the extreme stellar wind scenario. Future Ly α transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.

scholarly journals The fraction of O-type supergiants in our galaxy in the LMC and in the SMC: an evidence of the correlation between mass loss rate and chemical abundance

1981 ◽  
Vol 59 ◽  
pp. 255-259
Author(s):  
G.F. Bisiacchi ◽  
C. Firmani
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Galactic Center ◽  
Mass Loss Rate ◽  
Relative Number ◽  
The Other ◽  
Be Stars ◽  
Chemical Abundance ◽  
Low Gravity ◽  
Hydrogen Burning

The distribution of the spectral types of the WR stars in our galaxy is different at different distances from the galactic center. This distribution is also different in all three galaxies, in our, in the LMC and in the SMC. These results have been interpreted as due to the dependence of the mass loss rate from the original chemical abundace which is known to be different in these objects.On the other hand it has been proposed by Chiosi et al. (1974) and confirmed by Bisiacchi et al. (1978) that most of the 0 supergiants should be stars in the hydrogen burning phase. These authors also find evidence that the large relative number of supergiants among th 0 and early B type stars must be related to the longer time spent by the evolutionary tracks with mass loss at the low gravity region. Recently, a new empirical formula has been proposed by Chiosi (1980) for the mass loss rate as function of the luminosity and temperature of the stars.

scholarly journals Hot subdwarf wind models with accurate abundances

2019 ◽  
Vol 631 ◽  
pp. A75 ◽  
Author(s):  
J. Krtička ◽  
J. Janík ◽  
I. Krtičková ◽  
S. Mereghetti ◽  
F. Pintore ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Chemical Separation ◽  
The Other ◽  
Strong Wind ◽  
Radiative Force ◽  
Other Hand ◽  
Radiative Diffusion

Context. Hot subdwarfs are helium burning objects in late stages of their evolution. These subluminous stars can develop winds driven by light absorption in the lines of heavier elements. The wind strength depends on chemical composition which can significantly vary from star to star. Aims. We aim to understand the influence of metallicity on the strength of the winds of the hot hydrogen-rich subdwarfs HD 49798 and BD+18° 2647. Methods. We used high-resolution UV and optical spectra to derive stellar parameters and abundances using the TLUSTY and SYNSPEC codes. For derived stellar parameters, we predicted wind structure (including mass-loss rates and terminal velocities) with our METUJE code. Results. We derived effective temperature Teff = 45 900 K and mass M = 1.46 M⊙ for HD 49798 and Teff = 73 000 K and M = 0.38 M⊙ for BD+18° 2647. The derived surface abundances can be interpreted as a result of interplay between stellar evolution and diffusion. The subdwarf HD 49798 has a strong wind that does not allow for chemical separation and consequently the star shows solar chemical composition modified by hydrogen burning. On the other hand, we did not find any wind in BD+18° 2647 and its abundances are therefore most likely affected by radiative diffusion. Accurate abundances do not lead to a significant modification of wind mass-loss rate for HD 49798, because the increase of the contribution of iron and nickel to the radiative force is compensated by the decrease of the radiative force due to other elements. The resulting wind mass-loss rate Ṁ = 2.1 × 10−9 M⊙ yr−1 predicts an X-ray light curve during the eclipse which closely agrees with observations. On the other hand, the absence of the wind in BD+18° 2647 for accurate abundances is a result of its peculiar chemical composition. Conclusions. Wind models with accurate abundances provide more reliable wind parameters, but the influence of abundances on the wind parameters is limited in many cases.

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.

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