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

Aims: Hydrogen deficient white dwarfs are characterized by very dense,fluid-like atmospheres of complex physics and chemistry that are still poorlyunderstood. The incomplete description of these atmospheres by the modelsresults in serious problems with the description of spectra of these stars andsubsequent difficulties in derivation of their surface parameters. Here, weaddress the problem of infrared (IR) opacities in the atmospheres of cool whitedwarfs by direct $ab$ $initio$ simulations of IR absorption of dense helium.  Methods: We applied state-of-the-art density functional theory-based quantummolecular dynamics simulations to obtain the time evolution of the induceddipole moment. The IR absorption coefficients were obtained by the Fouriertransform of the dipole moment time autocorrelation function.  Results: We found that a dipole moment is induced due to three- and more-bodysimultaneous collisions between helium atoms in highly compressed helium. Thisresults in a significant IR absorption that is directly proportional to $\rm\rho_{\rm He}^3$, where $\rho_{\rm He}$ is the density of helium. To ourknowledge, this absorption mechanism has never been measured or computed beforeand is therefore not accounted for in the current atmosphere models. It shoulddominate the other collisionally induced absorptions (CIA), arising from $\rmH-He$ and $\rm H_2-He$ pair collisions, and therefore shape the IR spectra ofhelium-dominated and pure helium atmosphere cool white dwarfs for $\rmHe/H>10^4$.  Conclusions: Our work shows that there exists an unaccounted IR absorptionmechanism arising from the multi-collisions between He atoms in the helium-richatmospheres of cool white dwarfs, including pure helium atmospheres. Thisabsorption may be responsible for a yet unexplained frequency dependence ofnear- and mid- IR spectra of helium-rich stars.

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs