scholarly journals Cool Star Winds – Recent Observations and Theoretical Implications

1983 ◽  
Vol 6 ◽  
pp. 549-563 ◽  
Author(s):  
L. Hartmann
Keyword(s):  
Mass Loss ◽  
Absorption Lines ◽  
Late Type ◽  
Cool Star ◽  
Circumstellar Shells ◽  
Loss Rates ◽  
Loss Mechanisms

Much of our knowledge of winds from late-type stars comes from the detection of ejected material, called circumstellar shells, as observed in absorption lines of low-excitation species such as Mg II, Ca II, Na I, and K I (cf. Reimers 1977). Observations of CS shells are difficult to translate into quantitative mass loss rates, a limitation which has not helped to test various mass loss mechanisms. The data clearly demonstrate one very important fact: shell velocities are very low. In fact, they are so much lower than surface escape velocitiesthat it was not clear that material is actually being lost until Deutsch (1956) detected the existence of the CS absorption shells ejected from α Her and α Sco in the spectra of distant companion stars. Today it is possible to demonstrate the expansion of shells out to several thousand stellar radii in K I scattering (Honeycutt et al. 1980).

scholarly journals Ice Mantle Formation in the Envelopes of OH/IR Stars

1993 ◽  
Vol 155 ◽  
pp. 329-329
Author(s):  
S.B. Charnley ◽  
R.G. Smith
Keyword(s):  
Mass Loss ◽  
Simple Theory ◽  
Late Type ◽  
Water Ice ◽  
Physical Conditions ◽  
Grain Interaction ◽  
Inner Radius ◽  
Ir Stars ◽  
Circumstellar Shells ◽  
Loss Rates

We have computed ice column densities for a sample of O-rich late-type stars.Water ice is observed in the outflows from several late-type stars (e.g. Smith et al. 1988) and it is of some observational and theoretical importance to understand how common ice mantles may be and how their formation depends upon the physical conditions in the envelope, such as the radial distributions of density and temperature. We have developed a simple theory of the gas-grain interaction in circumstellar shells (Jura & Morris 1985; Charnley et al. 1992) and used it to compute ice column densities (Nice) and mantle thicknesses (d) for a sample of well-studied OH/IR stars (Herman & Habing 1985). The models are most sensitive to the dust and gas mass loss rates, as well as to the inner radius of the envelope, Ri, which is poorly determined. Representative results are presented in the Table below where Ri was estimated according to the prescription of Herman et al. (1986).

scholarly journals FeII in the UV Spectrum of Luminous Emission Line Stars

1986 ◽  
Vol 116 ◽  
pp. 275-276
Author(s):  
G. Muratorio ◽  
M. Friedjung ◽  
R. Viotti
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Velocity ◽  
Previous Analysis ◽  
Magellanic Clouds ◽  
Absorption Lines ◽  
High Dispersion ◽  
Uv Spectrum ◽  
Loss Rates

Following the excessive mass loss rates we derived in a previous analysis of the FeII emission and absorption lines of some luminous Magellanic Clouds stars, assuming the two components formed in the same region (Muratorio et al., 1984), we again analysed the FeII data using the same method (Muratorio, 1985), but taking into account the presence of high velocity winds detected in some stars (R66, R126) by the study of the high dispersion IUE spectra (Stahl et al., 1983; Zickgraf et al., 1985).

scholarly journals Mass-Loss from Late-Type Stars: New Observational Evidence

1983 ◽  
Vol 103 ◽  
pp. 292-292
Author(s):  
P. G. Wannier ◽  
R. Sahai
Keyword(s):  
Mass Loss ◽  
Central Star ◽  
Ir Absorption ◽  
Late Type ◽  
Ir Radiation ◽  
Loss Mechanism ◽  
Continuum Source ◽  
Near Ir ◽  
Molecular Lines ◽  
Circumstellar Shells

Rapid mass-loss is observed in many late-type stars, yet the mass-loss mechanisms operating are not well understood. A survey of molecular emission from circumstellar shells has been carried out using millimeterwave molecular lines and suggests that radiation pressure alone may be inadequate to explain the observed mass-loss, especially in the case of carbon-rich objects which may display rates in excess of 10−5 M⊙/yr. Recent near-IR molecular line observations provide evidence for ejected material at several different velocities along the line-of-sight and may indicate the additional mass-loss mechanism at work. Resonantly scattered IR radiation spatially displaced from the central IR continuum source has now been observed for the first time and sheds new light on the IR absorption-line results, providing information about material within 1016 cm of the central star. These results are discussed along with recent high-resolution millimeterwave observations.

scholarly journals Swift UVOT near-UV transit observations of WASP-121 b

2019 ◽  
Vol 623 ◽  
pp. A57 ◽  
Author(s):  
M. Salz ◽  
P. C. Schneider ◽  
L. Fossati ◽  
S. Czesla ◽  
K. France ◽  
...  
Keyword(s):  
Mass Loss ◽  
Spectral Range ◽  
Relative Accuracy ◽  
Uv Absorption ◽  
Absorption Lines ◽  
Optical Telescope ◽  
Hot Jupiters ◽  
Excess Absorption ◽  
Loss Rates ◽  
Gas Planets

Close-in gas planets are subject to continuous photoevaporation that can erode their volatile envelopes. Today, ongoing mass loss has been confirmed in a few individual systems via transit observations in the ultraviolet spectral range. We demonstrate that the Ultraviolet/Optical Telescope (UVOT) onboard the Neil Gehrels Swift Observatory enables photometry to a relative accuracy of about 0.5% and present the first near-UV (200–270 nm, NUV) transit observations of WASP-121 b, a hot Jupiter with one of the highest predicted mass-loss rates. The data cover the orbital phases 0.85–1.15 with three visits. We measure a broadband NUV transit depth of 2.10 ± 0.29%. While still consistent with the optical value of 1.55%, the NUV data indicate excess absorption of 0.55% at a 1.9σ level. Such excess absorption is known from the WASP-12 system, and both of these hot Jupiters are expected to undergo mass loss at extremely high rates. With a Cloudy simulation, we show that absorption lines of Fe II in a dense extended atmosphere can cause broadband near-UV absorption at the 0.5% level. Given the numerous lines of low-ionization metals, the NUV range is a promising tracer of photoevaporation in the hottest gas planets.

scholarly journals Infrared Observations of Late Type Stars

1977 ◽  
Vol 42 ◽  
pp. 446-494 ◽  
Author(s):  
K.M. Merrill
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Particulate Material ◽  
High Mass ◽  
Circumstellar Dust ◽  
Late Type ◽  
Infrared Band ◽  
Significant Information ◽  
Cool Star ◽  
High Mass Loss

AbstractSubstantative mass-loss resulting in appreciable circumstellar dust envelopes is common in late-type stars. The evolutionary history and physical state of a cool star determine the chemistry within the outer stellar atmosphere mirrored by the molecular and particulate material present in the envelope. The observational consequences of this debri determined by moderate spectral resolution (λ/Δλ ~ 50-100) infrared spectrophotometry are reviewed. Significant information is provided by observations of the emergent energy flux of both the cool stellar photosphere and of the circumstellar dust envelope. While most of the infrared features observed in late-type stars can be plausibly identified, an as yet unknown emission mechanism marked by strong infrared band structure is known to be operative in a variety of infrared sources. The observed range in shell optical depth in both M and C stars suggests that mass-loss occurs to some degree throughout late stellar evolutionary phases and that occasional periods of high mass-loss are not uncommon.

scholarly journals Infrared Observations of Circumstellar Molecules

1987 ◽  
Vol 120 ◽  
pp. 327-338 ◽  
Author(s):  
Albert Betz
Keyword(s):  
Infrared Spectroscopy ◽  
Mass Loss ◽  
Abundant Species ◽  
High Resolution Spectroscopy ◽  
Late Type ◽  
Infrared Observations ◽  
Negative Results ◽  
Circumstellar Gas ◽  
Circumstellar Shells ◽  
Vantage Points

This review presents an updated listing of infrared observations of circumstellar molecules. The compendium is restricted to the more abundant species with infrared spectra accessible to groundbased observations. No analysis is offered on the chemical importance of a particular species, and no attempt is made to correlate the infrared work with the much larger body of data available from radio frequency observations. Some discussions of these topics may be found in the more comprehensive reviews listed below. The observations described here include both the successful and the unrewarded efforts. Often the negative results from attempted observations are not widely disseminated, even though such results can sometimes be of significant theoretical value. Discussions of infrared stellar and circumstellar spectroscopy from other vantage points may be found in the following reviews. in 1979 Merrill and Ridgway surveyed the contributions of infrared spectroscopy to studies of stellar photospheres and the near circumstellar environment. The following year Zuckerman (1980) summarized the current state of knowledge on circumstellar molecular clouds with attention given to both infrared and microwave observations. Ridgway and Keady (1981) subsequently noted the importance of infrared spectroscopy for studies of circumstellar gas and dust in the star IRC + 10216. in 1983 Hinkle reviewed the high-resolution spectroscopy of late-type circumstellar shells in general but emphasized chemistry and kinematics. Finally, in the proceedings of the 1984 UCLA meeting on mass-loss, Omont (1985) reviewed the physical and chemical structure of circumstellar envelopes and IRC + 10216 in particular, and Wannier (1985) discussed the significance of infrared spectroscopy for studies of mass-loss in late-type stars.

scholarly journals What is the essential physics of mass loss from late-type stars?

1987 ◽  
Vol 122 ◽  
pp. 271-287
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
Mass Loss ◽  
Solar Atmosphere ◽  
Critical Role ◽  
Large Mass ◽  
Late Type ◽  
Atmospheric Structure ◽  
Cool Stars ◽  
Thermally Driven ◽  
Molecular Condensation ◽  
Loss Rates

In this review I consider what clues the data are providing us concerning the mass loss from late-type stars. I consider in turn the major classes of mass-loss mechanisms (thermally-driven winds, radiatively-driven winds, and wave-driven winds), and consider whether the empirical mass loss rates and other data are consistent with any of these mechanisms acting alone. It is likely that several mechanisms act together to produce the large mass loss rates in the Mira and non-pulsating M supergiants. Studies of the solar atmosphere suggest that thermal bifurcation driven by molecular condensation instabilities may play a critical role in cooling the atmospheres of luminous cool stars and forming silicate dust. It is possible that several metastable modes of atmospheric structure may exist for a given set of stellar parameters.

scholarly journals What do binaries teach us about mass-loss from late-type stars?

1987 ◽  
Vol 122 ◽  
pp. 307-318
Author(s):  
Dieter Reimers
Keyword(s):  
Mass Loss ◽  
Light Source ◽  
Stellar Evolution ◽  
Binary Systems ◽  
Late Type ◽  
Stellar Radius ◽  
Hydrogen Ionization ◽  
Wind Velocities ◽  
Red Giant ◽  
Loss Rates

It is shown that the binary technique - a B star companion is used as a light source which probes the wind of the red giant primary - has yielded accurate mass-loss rates and wind velocities for 8 G to M (super) giants and (in some cases) estimates of wind temperature.Eclipsing binary systems have in addition revealed that G and K supergiants possess extended chromospheres which could be detected outwards to ∼ 1 R* stellar radius) above the photospheres. Electron temperatures Te and hydrogen ionization ne/nH seem to increase with height up to at least 0.5 R* (ne/nH= 10−2, Te = 104 K at 0.5 R*), and the winds start to be accelerated at heights above ∼ 0.5 R*.Mass-loss rates appear to increase steeper than linearly with L/g · R. It is shown that the observed mass-loss rates are consistent with stellar evolution constraints for both Pop. II and Pop I stars.

scholarly journals Angular Momentum Loss in Polars

2009 ◽  
Vol 5 (S262) ◽  
pp. 362-363
Author(s):  
Belinda Kalomeni
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Cataclysmic Variables ◽  
Physical Parameters ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Loss Rates ◽  
Loss Mechanisms

AbstractWe discuss the possible angular momentum loss mechanisms in AM Her type cataclysmic variables and their corresponding mass loss rates using the observed physical parameters of them.

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