English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Cosmic-ray and X-ray heating are derived from the electron energy losscalculations of Dalgarno, Yan and Liu for hydrogen-helium gas mixtures. Theseauthors treated the heating from elastic scattering and collisionalde-excitation of rotationally excited hydrogen molecules. Here we consider theheating that can arise from all ionization and excitation processes, withparticular emphasis on the reactions of cosmic-ray and X-ray generated ionswith the heavy neutral species, which we refer to as chemical heating. Inmolecular regions, chemical heating dominates and can account for 50 per centof the energy expended in the creation of an ion pair. The heating per ion pairranges in the limit of negligible electron fraction from about 4.3 eV fordiffuse atomic gas, to about 13 eV for the moderately dense regions ofmolecular clouds and to about 18 eV for the very dense regions ofprotoplanetary disks. An important general conclusion of this study is thatcosmic-ray and X-ray heating depends on the physical properties of the medium,i.e., on the molecular and electron fractions, the total density of hydrogennuclei, and to a lesser extent on the temperature. It is also noted thatchemical heating, the dominant process for cosmic-ray and X-ray heating, playsa role in UV irradiated molecular gas.

Cosmic-ray and X-ray Heating of Interstellar Clouds and Protoplanetary Disks