The ambipolar diffusion time scale and the location of star formation in magnetic interstellar gas clouds

1983 ◽  
Vol 275 ◽  
pp. 836 ◽  
Author(s):  
E. H. Scott
Keyword(s):  
Star Formation ◽  
Time Scale ◽  
Ambipolar Diffusion ◽  
Diffusion Time ◽  
Interstellar Gas

scholarly journals Connecting the Interstellar Gas and Dust Properties in Distant Galaxies Using Quasar Absorption Systems

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Monique C. Aller ◽  
Varsha P. Kulkarni ◽  
Donald G. York ◽  
Daniel E. Welty ◽  
Giovanni Vladilo ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Absorption Feature ◽  
Dust Grains ◽  
Interstellar Gas ◽  
Chemical Enrichment ◽  
Normal Galaxies ◽  
History Of ◽  
Dust Grain ◽  
Grain Properties

AbstractGas and dust grains are fundamental components of the interstellar medium and significantly impact many of the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of the interstellar material. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous quasars, provide a valuable tool to directly study the properties of the interstellar gas and dust in distant, normal galaxies. We have established the presence of silicate dust grains in at least some gas-rich QASs, and find that they exist at higher optical depths than expected for diffuse gas in the Milky Way. Differences in the absorption feature shapes additionally suggest variations in the silicate dust grain properties, such as in the level of grain crystallinity, from system-to-system. We present results from a study of the gas and dust properties of QASs with adequate archival IR data to probe the silicate dust grain properties. We discuss our measurements of the strengths of the 10 and 18 μm silicate dust absorption features in the QASs, and constraints on the grain properties (e.g., composition, shape, crystallinity) based on fitted silicate profile templates. We investigate correlations between silicate dust abundance, reddening, and gas metallicity, which will yield valuable insights into the history of star formation and chemical enrichment in galaxies.

Dynamical imprint of interstellar gas on persistence of spiral structure in galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 296-297
Author(s):  
Soumavo Ghosh ◽  
Chanda J. Jog
Keyword(s):  
Time Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Disk Galaxies ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
Pattern Speed

AbstractThe persistence of the spiral structure in disk galaxies has long been debated. In this work, we investigate the dynamical influence of interstellar gas on the persistence of the spiral arms in disk galaxies. We show that the gas helps the spiral arms to survive for longer time-scale (~ a few Gyr). Also, we show that the addition of gas in calculation is necessary for getting a stable density wave corresponding to the observed pattern speed of the spiral arms.

3. Stars

2016 ◽  
pp. 22-49
Author(s):  
James Binney
Keyword(s):  
Star Formation ◽  
20Th Century ◽  
Binary Stars ◽  
Star Clusters ◽  
Solar Neutrinos ◽  
Interstellar Gas ◽  
Stellar Seismology ◽  
Stellar Masses ◽  
Century Science ◽  
The Universe

Most of what we know about the Universe has been gleaned from the study of stars, and a major achievement of 20th-century science was to understand how stars work and their lifecycles from birth to death. ‘Stars’ describes this lifecycle beginning with star formation when a cloud of interstellar gas suffers a runaway of its central density. It then considers nuclear fusion, key stellar masses, and life after the main sequence when the star burns its core helium. The surfaces of stars are described along with stellar coronae and exploding stars—both core-collapse and deflagration supernovae. Finally, globular star clusters, solar neutrinos, stellar seismology, and binary stars are discussed.

Estimation of formation temperature from bottom‐hole temperature measurements: COST ♯1 well, Norton Sound, Alaska

Geophysics ◽  
1988 ◽  
Vol 53 (12) ◽  
pp. 1619-1621 ◽  
Author(s):  
S. Cao ◽  
C. Hermanrud ◽  
I. Lerche
Keyword(s):  
Thermal Conductivity ◽  
Numerical Method ◽  
Time Scale ◽  
Efficiency Factor ◽  
Diffusion Time ◽  
Formation Temperature ◽  
Temperature Estimation ◽  
Bottom Hole ◽  
Free Parameters ◽  
Borehole Temperature

We recently developed a numerical method, the Formation Temperature Estimation (FTE) model, to determine formation temperatures by inversion of borehole temperature (BHT) measurements (Cao et al., 1988a). For more than two BHT measurements, the FTE model can estimate (1) true formation temperature [Formula: see text], (2) mud temperature [Formula: see text] at the time the mud circulation stops, (3) thermal invasion distance R into the formation before the formation is at the true formation temperature, (4) formation thermal conductivity K perpendicular to the borehole, and (5) efficiency factor F for mud heating in the borehole after mud circulation has stopped. The method optimizes three free parameters: τ (diffusion time‐scale), ε (scaling parameter related to the thermal invasion distance R), and [Formula: see text] (normalized efficiency factor for mud heating.

scholarly journals How to Model the Chemical Evolution of Galaxies

1993 ◽  
Vol 155 ◽  
pp. 557-566
Author(s):  
Joachim Köppen
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Time Scale ◽  
Life Time ◽  
Magellanic Clouds ◽  
Formation Time ◽  
List Type ◽  
The Galaxy ◽  
H Ii Region ◽  
Magellanic Stream

For a first interpretation of the comparison of observational data, the crude “Simple Model” of chemical evolution is quite useful. Since it has well been described in the literature (e.g. Pagel and Patchett 1975, Tinsley 1980), let us here just review the assumptions and whether they are satisfied: 1.The galaxy is a closed system, with no exchange of matter with its surroundings: For the solar neighbourhood this probably is not true (the infamous Gdwarf-“problem”, Pagel 1989b). For the Magellanic Clouds this is most certainly wrong, because of the presence of the Inter-Cloud Region and the Magellanic Stream, and evidence for interaction with each other and the Galaxy as well (cf. e.g. Westerlund 1990).2.It initially consists entirely of gas (without loss of generality of primordial composition): This is good approximation also for models with gas infall, as long as the infall occurs with a time scale shorter than the star formation time scale.3.The metal production of the average stellar generation (the yield y) is constant with time: Initially, it is reasonable to make this assumption. For tables of the oxygen yield see Koppen and Arimoto (1991).4.The metal rich gas ejected by the stars is completely mixed with the ambient gas. To neglect the finite stellar life times (“instantaneous recycling approximation”) is appropriate for elements synthesized in stars whose life time is much shorter than the star formation time scale, such as oxygen, neon, sulphur, and argon.5.The gas is well mixed at all times: We don't know. The dispersion of H II region abundances may give an indication. In the Magellanic Clouds Dufour (1984) finds quite a low value (±0.08 dex for oyxgen).

scholarly journals Derivation of the initial luminosity function and the past rate of star formation

1959 ◽  
Vol 10 ◽  
pp. 99-104
Author(s):  
M. Schmidt
Keyword(s):  
Star Formation ◽  
Luminosity Function ◽  
Main Sequence ◽  
Life Time ◽  
Interstellar Gas ◽  
The Past ◽  
Constant Rate

The initial luminosity function ψ(Mv) was introduced by Salpeter. He assumed uniform formation of stars and derived the initial luminosity function from the observed main-sequence luminosity function and the life time of a star of magnitude Mvon the main sequence. Recently van den Bergh considered the depletion of the interstellar gas by star formation. He found that at a constant rate of star formation the gas in the solar vicinity will be exhausted about 7 × 108years from now.

scholarly journals Supershells

1988 ◽  
Vol 101 ◽  
pp. 447-459
Author(s):  
Richard McCray
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Interstellar Medium ◽  
Milky Way ◽  
Disk Galaxy ◽  
Interstellar Gas ◽  
Irregular Galaxies ◽  
Nearby Galaxies ◽  
Gas Layer

AbstractRepeated supernovae from an OB association will, in a few ×107 yr, create a cavity of coronal gas in the interstellar medium, with radius > 100 pc, surrounded by a dense expanding shell of cool interstellar gas. Such a cavity will likely burst through the gas layer of a disk galaxy. Such holes and “supershells” have been observed in optical and H I radio emission maps of the Milky Way and other nearby galaxies. The gas swept up in the supershell is likely to become gravitationally unstable, providing a mechanism for propagating star formation that may be particularly effective in irregular galaxies.

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