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

Reflection nebulae--dense cores--illuminated by surrounding stars offer aunique opportunity to directly test our quantitative model of grain alignmentbased on radiative torques (RATs) and to explore new effects arising fromadditional torques. In this paper, we first perform detailed modeling of grainalignment by RATs for the IC 63 reflection nebula illuminated both by a nearby$\gamma$ Cas star and the diffuse interstellar radiation field. We calculatelinear polarization $p_{\lambda}$ of background stars by radiatively alignedgrains and explore the variation of fractional polarization ($p_{\lambda}/A_V$)with visual extinction $A_{V}$ across the cloud. Our results show that thevariation of $p_{V}/A_{V}$ versus $A_{V}$ from the dayside of IC 63 to itscenter can be represented by a power-law ($p_{V}/A_{V}\propto A_{V}^{\eta}$)with different slopes depending on $A_{V}$. We find a shallow slope $\eta \sim-0.1$ for $A_{V}< 3$ and a very steep slope $\eta\sim -2$ for $A_{V}> 4$. Wethen consider the effects of additional torques due to H$_{2}$ formation andmodel grain alignment by joint action of RATs and H$_2$ torques. We find that$p_{V}/A_{V}$ tends to increase with an increasing magnitude of H$_{2}$torques. In particular, the theoretical predictions obtained for $p_{V}/A_{V}$and peak wavelength $\lambda_{\max}$ in this case show an improved agreementwith the observational data. Our results reinforce the predictive power of theRAT alignment mechanism in a broad range of environmental conditions and showthe effect of pinwheel torques in environments with efficient H$_2$ formation.Physical parameters involved in H$_2$ formation may be constrained usingdetailed modeling of grain alignment combined with observational data. Inaddition, we discuss implications of our modeling for interpreting latestobservational data by {\it Planck} and other ground-based instruments.

Modeling Grain Alignment by Radiative Torques and Hydrogen Formation Torques in Reflection Nebula