Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
Currently Skimming:
10. Astrophysical Dust Grains in Stars, the Interstellar Medium, and the Solar System
10. Astrophysical Dust Grains in Stars, the Interstellar Medium, and the Solar System
Pages 126-142
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 126... ...
Grain materials identified in sources external to the solar system include silicates, silicon carbide, amorphous carbon, and possibly hydrocarbon compounds. The nucleation and growth of astrophysical carbon grains has been documented by infrared observations of classical novae.
|
From page 127... ...
THE CYCLING OF DUST IN STELLAR EVOLUTION AND THE FORMATION OF PLANETARY SYSTEMS Small refractory dust grains are present in circumstellar shells around many different classes of stars, in the interstellar medium (ISM) , and in comets and the zodiacal cloud in the solar system.
|
From page 128... ...
ASTROPHYSICAL DUST GRAINS IN CIRCUMSTELLAR ENVIRONMENTS Infrared observations made more than two decades ago provided the first convincing evidence that dust grains are present in the winds of latetype giant and supergiant stars. Most of this circumstellar dust is refractory material.
|
From page 129... ...
often show a 11.3pm emission feature caused by SiC and a near infrared thermal continuum due to amorphous carbon (Gehrz et al.
|
From page 130... ...
The existing data are not spatially or spectrally detailed enough to lead to definitive conclusions about the mineral composition and size distribution of these fossil remnants of star/planetary system formation. There are large amounts of dust present in the circumstellar regions of many young stellar objects (YSO's)
|
From page 131... ...
It is broad and without structure, suggesting that the grains are amorphous with a wide range of grain sizes. The feature appears in absorption in compact sources deeply embedded in molecular cloud cores such as the BN (Becklin-Neugebauer)
|
From page 132... ...
CIRCUMSTELLAR GRAIN FORMATION ANI) MASS LOSS The observations described above suggest that many classes of evolved stellar objects are undergoing steady-state mass loss that injects stardust of various compositions into the interstellar medium.
|
From page 133... ...
· .. IRS 7 ·— in, ~ 1 3.0 3.2 3.4 3.6 3.8 WAVELENGTH IN MICRONS FIGURE 3 High-resolution infrared spectra of the 3.3-3.4p hydrocarbon emission and absorption bands in three extra-solar-systems sources and Comet Halley.
|
From page 134... ...
have reported possible hydrocarbon emission from a recent nova, and Gerbault and Goebel (1989) have argued that hydrocarbons may produce anomalous infrared emission from some carbon stars, there is currently no compelling evidence that hydrocarbon grains are an abundant constituent of the dust that is expelled into the ISM in stellar outflows (Gehrz 1989~.
|
From page 135... ...
, and several other ~`unidentified', infrared emission features that are seen in the ~14pm thermal infrared spectra of some HII regions, molecular cloud cores, and young stellar objects (Allamandola 1984; Allamandola et al.
|
From page 136... ...
show the characteristic near infrared continuum dust emission that is probably caused by small iron or carbon grains, and prominent 10 and 20m emission features characteristic of silicate grains (Ney 1974; Gehrz and Ney 1986~. The cometary silicate features, first discovered in Comet Bennett by Maas et al.
|
From page 137... ...
THE SURVIVAL OF DUST GRAINS DURING STELLAR EVOLUTION An intriguing question is whether significant numbers of stardust grains can survive from the time that they condense in circumstellar outflows until they are accreted into the cold solid bodies in primitive planetary systems. While there is evidence that grains are rapidly destroyed in the ISM by supernova shocks (Scab 1987)
|
From page 139... ...
Infrared satellite experiments to measure the spectrum of the cloud can provide significant diagnostic information. Near infrared reflectance spectroscopy can reveal the presence, mineral composition, and size distribution of various types of silicate grains.
|
From page 140... ...
1988. The infrared temporal development of classical novae.
|
From page 141... ...
1984. The formation of stellar systems from interstellar molecular clouds.
|
From page 142... ...
1987. Companson of laboratory determined properties of interplanetary dust with those of Comet Halley particles.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.