Evolution and ecology of influenza A viruses.

Cosmochemistry of the rare earth elements: meteorite studies.

▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...

/pdf/luminous-infrared-galaxies-zoi3y3hutv.pdf

Luminous infrared galaxies

We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending on the interstellar environment through which the light travels. As shown by Cardelli, Clayton, and Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, RV. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for RV and bC, the C abundance in very small grains. We also find size distributions for the line of sight to HD 210121 and for sight lines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter and present model extinction curves extending beyond the Lyman limit.

https://iopscience.iop.org/article/10.1086/318651/pdf

Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

The observed spectrum of GC-IRS 7 over the waveband 2.9–13 μm can be explained on the basis of interstellar grains which are spectroscopically similar to dried-out diatomaceous organisms.

The Infrared Spectrum of Interstellar Dust

Evidence is presented for the hypothesis that the organic grains streaming from a cometary nucleus lose substantial volatile constituents within 105 s. To develop the hypothesis, we study grain properties appropriate to both the comet-probe encounters at 0.8–0.9 AU and to comas observed at 4–5 AU. While submicron-sized grains of ice contaminated by 1% or more absorptive graphite can explain the strong OH coma far from the Sun, as in comet Bowell at 4.6 AU, the dynamical lifetime of the grain coma implies mm-sized and therefore cooler grains, with weaker H2O or OH attachment than ice at about 10kcal/mole. Grains in comet Halley, if composed of similar organic material must also contain fractions of more strongly bound components. In this study we adopt kerogen as a prototype organic complex having a range of bond energies. Temperatures and evaporation rates of kerogen grains are calculated using Arrhenius relations and Mie-Guttler radiative scattering theory with complex refractive index as measured for two cases: organic material of biological origin and UV-processed methane ice (“tholin”). A time-scale of 104 s at 0.9 AU corresponds to submicron grains with rather strongly-bound organics of ~ 40 kcal/mole, identified with bridges of ether, ketone, sulphide etc., bonds. The steeply increasing strength of H and O inside 1 AU (∝ r −4), unlike OH, corresponds to increasing breakdown following rupture of the chemical bridges. The 10 µm IR feature can be explained by grains of an organo-siliceous material or organic mantle on a siliceous core, a few µm in size and about 20 kcal/mole bond strength.

Evaporating Grains in p/ Halley's Coma

Giant comets thrown into short-period, Earth-crossing orbits are a major source of mass flux into the inner planetary system. Their disintegration products may give rise to climatic cycles, ice epochs, periodic mass extinctions and other global disturbances. Comets ≳100 kilometres in diameter, in chaotic orbits beyond Jupiter, probably constitute a more substantial current hazard than stray asteroids.

Giant Comets, Evolution and Civilization

/pdf/star-formation-in-clouds-of-solid-hydrogen-grains-4uk3anz4cb.pdf

Star formation in clouds of solid hydrogen grains.

It is argued that the infrared emission including 10 and 18 μ features observed in recent comets is unlikely to be due to silicates. The vaporization temperature of the emitting material ~ 500 K is consistent with emission by crystalline polyformaldehyde.

N. C. Wickramasinghe

Papers

The Infrared Spectrum of Interstellar Dust

Evaporating Grains in p/ Halley's Coma

Giant Comets, Evolution and Civilization

Star formation in clouds of solid hydrogen grains.

Composition of cometary dust: The case against silicates