A new self-consistent model of circumstellar CO emission for deriving mass-loss rates in red giants. I - The carbon-rich star U Camelopardalis

1990 ◽  
Vol 362 ◽  
pp. 652 ◽  
Author(s):  
R. Sahai
Keyword(s):  
Mass Loss ◽  
Red Giants ◽  
Consistent Model ◽  
Self Consistent ◽  
Co Emission ◽  
Loss Rates

scholarly journals Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation

2020 ◽  
Author(s):  
Jie Yu ◽  
Saskia Hekker ◽  
Timothy R Bedding ◽  
Dennis Stello ◽  
Daniel Huber ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Enrichment ◽  
Dust Mass ◽  
Red Giant ◽  
The Masses ◽  
Loss Rates

Abstract Mass loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here we investigate the relationships between mass loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 135000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and WISE and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass loss sets in at pulsation periods above ∼60 and ∼100 days, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass loss on the Red Giant Branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3%, less than the typical uncertainty on their asteroseismic masses. Thus mass loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

scholarly journals Maser emission from the CO envelope of the asymptotic giant branch star W Hydrae

2021 ◽  
Vol 654 ◽  
pp. A18
Author(s):  
W. H. T. Vlemmings ◽  
T. Khouri ◽  
D. Tafoya
Keyword(s):  
Mass Loss ◽  
Radiation Field ◽  
Asymptotic Giant Branch ◽  
Small Scale ◽  
High Angular Resolution ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Maser Emission ◽  
Co Emission ◽  
Loss Rates

Context. Observation of CO emission around asymptotic giant branch (AGB) stars is the primary method to determine gas mass-loss rates. While radiative transfer models have shown that molecular levels of CO can become mildly inverted, causing maser emission, CO maser emission has yet to be confirmed observationally. Aims. High-resolution observations of the CO emission around AGB stars now have the brightness temperature sensitivity to detect possible weak CO maser emission. Methods. We used high angular resolution observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the small-scale structure of CO J = 3−2 emission around the oxygen-rich AGB star W Hya. Results. We find CO maser emission amplifying the stellar continuum with an optical depth τ ≈−0.55. The maser predominantly amplifies the limb of the star because CO J = 3−2 absorption from the extended stellar atmosphere is strongest towards the centre of the star. Conclusions. The CO maser velocity corresponds to a previously observed variable component of high-frequency H2O masers and with the OH maser that was identified as the amplified stellar image. This implies that the maser originates beyond the acceleration region and constrains the velocity profile since we find the population inversion primarily in the inner circumstellar envelope. We find that inversion can be explained by the radiation field at 4.6 μm and that the existence of CO maser emission is consistent with the estimated mass-loss rates for W Hya. However, the pumping mechanism requires a complex interplay between absorption and emission lines in the extended atmosphere. Excess from dust in the circumstellar envelope of W Hya is not sufficient to contribute significantly to the required radiation field at 4.6 μm. The interplay between molecular lines that cause the pumping can be constrained by future multi-level CO observations.

scholarly journals The domain of radiatively driven mass loss in the H-R diagram

1979 ◽  
Vol 83 ◽  
pp. 235-240 ◽  
Author(s):  
David C. Abbott
Keyword(s):  
Steady State ◽  
Mass Loss ◽  
Radiation Pressure ◽  
Effective Temperature ◽  
Stellar Wind ◽  
Radiation Force ◽  
Theoretical Uncertainty ◽  
Line Radiation ◽  
Consistent Model ◽  
Self Consistent

Previous work by Castor, Abbott, and Klein (1975) presented a self-consistent model of a steady-state stellar wind. They also showed qualitatively that for O stars at least a static atmosphere could not exist. This paper extends that result by calculating in detail the minimum luminosity as a function of effective temperature required for the line radiation force to exceed gravity. Within the observational and theoretical uncertainty there is a one-to-one correspondence between a star's calculated ability to self-initiate a stellar wind by radiation pressure alone and the observed presence of outflowing material in the UV resonance lines.

scholarly journals Detection of rotational CO emission from the red-supergiants in the Large Magellanic Cloud

2015 ◽  
Vol 11 (A29B) ◽  
pp. 459-459
Author(s):  
Mikako Matsuura ◽  
B. Sargent ◽  
Bruce Swinyard ◽  
J.A. Yates ◽  
P. Royer ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Evolved Stars ◽  
Solar Metallicity ◽  
Red Supergiants ◽  
Low Metallicity ◽  
Co Emission ◽  
Loss Rates

AbstractIt is yet well understood how mass-loss rates from evolved stars depend on metallicities. With a half of the solar metallicity and the distance of only 50 kpc, the evolved stars of the Large Magellanic Cloud (LMC) are an ideal target for studying mass loss at low metallicity. We have obtained spectra of red-supergiants in the LMC, using the Hershel Space Observatory, detecting CO thermal lines fro J=6–5 up to 15–14 lines. Modelling CO lines with non-LTE Radiative transfer code suggests that CO lines intensities can be well explained with high gas-to-dust ratio, with no obvious reduction in mass-loss rate at the LMC. We conclude that the luminosities of the stars are primary factors on mass-loss rates, rather than the metallicity.

scholarly journals ISOGAL and 2MASS Study of the Central Regions of Our Galaxy

2001 ◽  
Vol 205 ◽  
pp. 282-283
Author(s):  
D.K. Ojha ◽  
A. Omont ◽  
S. Ganesh ◽  
Isogal Team
Keyword(s):  
Mass Loss ◽  
Interstellar Extinction ◽  
Large Mass ◽  
Red Giants ◽  
Agb Stars ◽  
Galactic Bulge ◽  
Central Regions ◽  
Loss Rates

We report the study of ISOGAL fields in the outer galactic bulge (-1.5° < l < +1.6°, −2.6° < b < + 6.0°, area ∼ 0.42 deg2). We have combined 15 μm and 7 μm ISOCAM observations with 2MASS JHKS data to determine the nature of the sources and the interstellar extinction. Most of the ISOGAL sources show evolution of mass-loss rates in the range 3×10−8 to 1 × 10−6 (M⊙/year). Most of the detected sources are red giants above the RGB tip; a few of them show an excess in J-Ks and Ks-[15] colors. These sources are AGB stars with large mass-loss rates.

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