scholarly journals Circumstellar OH Masers

1984 ◽  
Vol 110 ◽  
pp. 313-318
Author(s):  
R. S. Booth ◽  
P. J. Diamond ◽  
R. P. Norris
Keyword(s):  
Mass Loss ◽  
Stellar Mass ◽  
Important Application ◽  
Expansion Velocity ◽  
Spherical Shells ◽  
Maser Emission ◽  
Loss Rates

Synthesis maps of stellar OH maser emission have revealed that the OH lies in expanding spherical shells typically about 1016 cm in diameter. From the maps and the expansion velocity, derived from the OH spectrum, stellar mass loss rates may be determined. Typical values are 10−5 M⊙/yr. An important application of the stellar OH masers is in the estimation of stellar distances.

scholarly journals Massive star mass-loss revealed by X-ray observations of young supernovae

2018 ◽  
Vol 14 (S346) ◽  
pp. 83-87
Author(s):  
Vikram V. Dwarkadas
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Ambient Medium ◽  
Mass Loss Rate ◽  
Stellar Mass ◽  
X Rays ◽  
X Ray ◽  
The Common ◽  
Almost All ◽  
Loss Rates

AbstractMassive stars lose a considerable amount of mass during their lifetime. When the star explodes as a supernova (SN), the resulting shock wave expands in the medium created by the stellar mass-loss. Thermal X-ray emission from the SN depends on the square of the density of the ambient medium, which in turn depends on the mass-loss rate (and velocity) of the progenitor wind. The emission can therefore be used to probe the stellar mass-loss in the decades or centuries before the star’s death.We have aggregated together data available in the literature, or analysed by us, to compute the X-ray lightcurves of almost all young supernovae detectable in X-rays. We use this database to explore the mass-loss rates of massive stars that collapse to form supernovae. Mass-loss rates are lowest for the common Type IIP supernovae, but increase by several orders of magnitude for the highest luminosity X-ray SNe.

scholarly journals Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions

2011 ◽  
Vol 2011 ◽  
pp. 1-19 ◽  
Author(s):  
Douglas Rubin ◽  
Abraham Loeb
Keyword(s):  
Mass Loss ◽  
Galactic Center ◽  
Mass Loss Rate ◽  
Mass Function ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Total Mass Loss ◽  
Stellar Collisions ◽  
Mass Functions ◽  
Loss Rates

The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates>10-5M⨀yr−1in the vicinity of~1″. For present-day mass functions of the form,dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass≲7M⨀and a power-law slope≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

scholarly journals A new method to measure stellar mass-loss rates

2009 ◽  
Vol 5 (S266) ◽  
pp. 312-317
Author(s):  
Jason S. Kalirai
Keyword(s):  
Mass Loss ◽  
Galaxy Formation ◽  
Mass Loss Rate ◽  
Stellar Mass ◽  
Sequence Evolution ◽  
Nearby Star ◽  
Distant Galaxies ◽  
Galaxy Formation And Evolution ◽  
Red Giant ◽  
Loss Rates

AbstractThe total stellar mass loss that a star suffers through post-main-sequence evolution is of vital importance to understand its subsequent evolution. The mass-loss rate along the first-ascent red-giant branch alone determines the upper red-giant-branch luminosity function and horizontal-branch morphology. The distribution of stars in these phases directly affects our interpretation of the integrated colors of distant galaxies, and is therefore of fundamental importance for galaxy formation and evolution studies in the higher-redshift Universe. Yet, these mass-loss rates, especially as a function of age and metallicity, are very poorly constrained in current models. I present new constraints on this field based on imaging and spectroscopic observations of the end products from this evolution, white dwarfs. By studying the mass distribution of these dead stars in nearby star clusters with a range of (known) ages and metallicities, we can directly constrain the mass-loss rates of stars across a range of environments. These observations directly impact several fields in astrophysics, including our knowledge of the enrichment of the interstellar medium, our ability to construct population synthesis models to interpret galaxy colors and the general interpretation of the sources and processes responsible for the observed ultraviolet upturn in elliptical galaxies.

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

2010 ◽  
Vol 710 (1) ◽  
pp. 549-566 ◽  
Author(s):  
Henry A. Kobulnicky ◽  
Ian J. Gilbert ◽  
Daniel C. Kiminki
Keyword(s):  
Mass Loss ◽  
Stellar Mass ◽  
Ob Stars ◽  
Bow Shocks ◽  
Loss Rates

scholarly journals Post-AGB Variables and Stellar Mass-Loss

2000 ◽  
Vol 177 ◽  
pp. 207-216
Author(s):  
M. W. Feast
Keyword(s):  
Mass Loss ◽  
Dust Emission ◽  
Stellar Mass ◽  
Circumstellar Dust ◽  
Spherical Shells ◽  
Loss Process ◽  
Grain Formation ◽  
Term Variation

A brief review is given of the various types of star which are thought to be in the immediate post-AGB stage of evolution. The paper then concentrates on the properties of the RCB stars and particularly on the mass-loss process in these stars. It is suggested that grain formation takes place over the cool regions of giant convection cells in a super-Eddington outflow and in the form of small clouds or puffs. Attention is drawn to observations which suggest that grain formation in the outer atmospheres of Miras and other cool giants may also take place in puffs rather than in spherical shells. Evidence on the long-term variation of the circumstellar dust emission from RCB stars is summarized.

Mass Loss from Stars

1970 ◽  
Vol 39 ◽  
pp. 272-280
Author(s):  
S. R. Pottasch
Keyword(s):  
Interstellar Medium ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Stellar Mass ◽  
High Luminosity ◽  
Similar Extent ◽  
Probable Loss ◽  
Loss Rates

In this summary we shall attempt to evaluate the mass loss from several kinds of high luminosity stars, especially planetary nebulae, OB supergiants and M giants and supergiants. The purpose is to give an observational basis for the discussion of the mechanism of mass loss and of the consequences of stellar mass loss for the interstellar medium and for stellar evolution. For reasons which will presently be discussed, we are now certain that mass loss is occurring in all the objects mentioned, and probably to a similar extent in all high luminosity stars as well. The precise values of the mass loss rate are uncertain at present; for some objects the uncertainty will be large (two orders of magnitude) and have important influence on the consequences of the mass loss. Therefore we shall discuss in some detail how the different loss rates quoted in the literature have been obtained and what assumptions have been made (see also the Report by Boyarchuk, p. 281). On the basis of this discussion we will indicate the most probable loss rates and their consequences, always remembering the possible influence of the uncertainties.

scholarly journals The Structure of OH Maser Clouds Associated with Late-Type Stars

1984 ◽  
Vol 110 ◽  
pp. 327-328
Author(s):  
P. F. Bowers ◽  
K. J. Johnston ◽  
J. H. Spencer
Keyword(s):  
Spectral Line ◽  
Mass Loss ◽  
Stellar Mass ◽  
Large Array ◽  
Late Type ◽  
Very Large Array ◽  
Mira Variables ◽  
Mira Variable ◽  
The Absolute ◽  
Loss Rates

The absolute positions and the arcsec structure of OH maser clouds surrounding 20 Mira variables and late-type supergiant stars have been measured using the Very Large Array in a spectral line mode at 1612 MHz. The stars observed are listed in Table 1 which indicates that the angular radii θ of the maser clouds range up to 4″. The linear radii R range from < 100 AU for the Mira variable U Ori to 104 AU for the supergiant IRC+10420 and are correlated with the stellar mass loss rates.

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