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 Space Distribution of Red Giants and the Galactic Structure

1984 ◽  
Vol 78 ◽  
pp. 257-260
Author(s):  
K. Ishida
Keyword(s):  
Galactic Structure ◽  
Space Distribution ◽  
Red Giants ◽  
Stellar Content ◽  
Late Type ◽  
Ir Radiation ◽  
Near Ir ◽  
The Galaxy ◽  
K Band

AbstractStellar content contributing to near IR radiation do not show radial differentiation in the Galaxy. Late-type giants and supergiants supply about 70% of the total volume emissivity at the K band, in the solar vicinity within 1 kpc, and also at the distance of several kpc in the Scutum region.

scholarly journals Infrared Observations of Be Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 219-236
Author(s):  
Henny J.G.L.M. Lamers
Keyword(s):  
Dust Emission ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Ir Radiation ◽  
Infrared Observations ◽  
Near Ir ◽  
Circumstellar Shells ◽  
Early Type Stars ◽  
Ir Emission ◽  
Rule Out

The first indication that Be stars have an excess near-IR radiation, compared to normal stars of the same spectral type was found by Johnson et al. (1966). Johnson (1967) noticed that in his sample of 85 early type stars all the Be stars and shell stars had an excess in K-L and he concluded that this is due to IR emission from circumstellar shells. Woolf et al. (1970) suggested that the IR excess of Be stars might be due to free-free emission in the ionized circumstellar envelope which also produces the Balmer emission lines, but their observations at 5 and 10 µ could not rule out the possibility that circumstellar dust contributed to the excess. The observations by Allen (1973) of a large number of Be stars up to a wavelength of 3.5 µ could not make the distiction between free-free or dust emission either.

scholarly journals Extended Dust Shells around Carbon Stars in the Infrared and in Optical Light

2000 ◽  
Vol 177 ◽  
pp. 425-432
Author(s):  
Hideyuki Izumiura ◽  
L.B.F.M. Waters ◽  
T. De Jong ◽  
C. Loup ◽  
O. Hashimoto
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Scattered Light ◽  
Far Infrared ◽  
Central Star ◽  
Carbon Stars ◽  
Core Mass ◽  
Dust Shells ◽  
Circumstellar Shells ◽  
Thermal Pulses

We investigate the structure of extended dust shells around optical carbon stars in the far-infrared and in optical light. In the optical we have discovered that R Scl and U Ant are associated with circularly extended emission, the radii of which are about 20″ and 58″, respectively. The emission is probably scattered light of the central star by dust grains in their circumstellar shells. In the far-infrared we have discovered a double shell structure surrounding U Ant in high resolution IRAS images, which is direct evidence of a periodic change of mass-loss on a time-scale of the order of 104 years in the AGB evolution. Relating the two shells to two consecutive thermal pulses allows for a self-consistent determination of the interpulse period, core-mass, luminosity, and distance. Direct mapping of Y CVn at 90 and 160 μm with ISOPHOT on board ISO has revealed a very extended detached dust shell around this star. The mass-loss rate is found to have decreased drastically by two orders of magnitude 1.4×104 years ago, which should be an important clue to the understanding of J-type stars.

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 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 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 Infrared Spectroscopy and Molecules in Circumstellar Envelopes

1994 ◽  
Vol 146 ◽  
pp. 98-112
Author(s):  
Kenneth H. Hinkle
Keyword(s):  
Mass Loss ◽  
Central Star ◽  
Circumstellar Envelopes ◽  
Interstellar Gas ◽  
Spectral Techniques ◽  
Loss Process ◽  
Circumstellar Gas ◽  
Circumstellar Shells ◽  
Circumstellar Shell ◽  
Circumstellar Environment

During the last two decades there has been a tremendous renewal of interest in the circumstellar environment of evolved stars. This renewal has been mainly driven by sensitive microwave observing techniques. Microwave spectroscopy has resulted in a number of fundamental discoveries in circumstellar shells, including the discovery of maser lines and complex circumstellar chemistry. Historically, interest in circumstellar shells originates from a desire to understand the mass-loss process. It has been known for at least 50 years that circumstellar gas is the origin of interstellar gas and dust. As such the circumstellar shell becomes the pathway through which elements created in the interior of the central star enrich galactic abundances. High resolution spatial and spectral techniques and an ever improving knowledge of stellar evolution has resulted in an increased but still incomplete understanding of the mass-loss process.

scholarly journals 3.20. OH/IR stars as signposts for ancient starburst activity in the Galactic center

1998 ◽  
Vol 184 ◽  
pp. 129-130 ◽  
Author(s):  
L.O. Sjouwerman ◽  
H.J. Habing ◽  
H.J. van Langevelde ◽  
M. Lindqvist ◽  
A. Winnberg
Keyword(s):  
Mass Loss ◽  
Galactic Center ◽  
Expansion Velocity ◽  
Late Type ◽  
Considerable Fraction ◽  
Ir Stars ◽  
Circumstellar Shells

We have surveyed the Galactic center (GC) for OH/IR stars, evolved late-type stars of different masses - and thus ages - in a short-lived stage of heavy mass-loss. By observing the 1612 MHz OH masers generated in their circumstellar shells, it is found that a considerable fraction of these OH/IR stars has the same high-valued shell expansion velocity of 19 km s−1.

Near IR Absorption in Heavily Doped Silicon – An Empirical Approach

2000 ◽  
Author(s):  
R. Aaron Falk
Keyword(s):  
Near Infrared ◽  
Empirical Approach ◽  
Ir Absorption ◽  
Free Carrier Absorption ◽  
Ir Radiation ◽  
Laser Probing ◽  
Near Ir ◽  
Carrier Absorption ◽  
Heavily Doped ◽  
Heavy Doping

Abstract Backside failure analysis techniques rely heavily on transmission of near infrared (IR) radiation through the silicon substrate. This statement applies both to emission techniques and active laser probing. Heavy doping of substrates causes them to become highly absorptive in the near IR due to band gap shifts, which effects phonon-assisted absorption, and to free-carrier absorption. Substrate thinning is often required to allow adequate optical transmission. This paper describes an empirical approach to determining the absorption coefficient in a heavily doped substrate and use of the coefficient in determining the amount of substrate thinning required.

Plasmon-assisted interaction of Si with light, for cancer hyperthermia and electromagnetic energy harvest

2020 ◽  
Vol 92 (2) ◽  
pp. 20101
Author(s):  
Behnam Kheyraddini Mousavi ◽  
Morteza Rezaei Talarposhti ◽  
Farshid Karbassian ◽  
Arash Kheyraddini Mousavi
Keyword(s):  
Silicon Nanowires ◽  
Metallic Nanoparticles ◽  
Near Infrared ◽  
Optical Transition ◽  
Electromagnetic Energy ◽  
Energy Harvest ◽  
Absorption Enhancement ◽  
Ir Absorption ◽  
Absorption Mechanism ◽  
Near Ir

Metal-assisted chemical etching (MACE) is applied for fabrication of silicon nanowires (SiNWs). We have shown the effect of amorphous sheath of SiNWs by treating the nanowires with SF6 and the resulting reduction of absorption bandwidth, i.e. making SiNWs semi-transparent in near-infrared (IR). For the first time, by treating the fabricated SiNWs with copper containing HF∕H2O2∕H2O solution, we have generated crystalline nanowires with broader light absorption spectrum, up to λ = 1 μm. Both the absorption and photo-luminescence (PL) of the SiNWs are observed from visible to IR wavelengths. It is found that the SiNWs have PL at visible and near Infrared wavelengths, which may infer presence of mechanisms such as forbidden gap transitions other can involvement of plasmonic resonances. Non-radiative recombination of excitons is one of the reasons behind absorption of SiNWs. Also, on the dielectric metal interface, the absorption mechanism can be due to plasmonic dissipation or plasmon-assisted generation of excitons in the indirect band-gap material. Comparison between nanowires with and without metallic nanoparticles has revealed the effect of nanoparticles on absorption enhancement. The broader near IR absorption, paves the way for applications like hyperthermia of cancer while the optical transition in near IR also facilitates harvesting electromagnetic energy at a broad spectrum from visible to IR.

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