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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

[[abstract]]The DR 21 massive star-forming region contains two cometary H II regions, aligned nearly perpendicular to each other on the sky. This others a unique opportunity to discriminate among models of cometary H II regions. We present hydrogen recombination and ammonia line observations of DR 21 made with the Very Large Array. The velocity of the molecular gas, measured from NH3 emission and absorption lines, is constant to within +/-1 km s(-1) across the region. However, the radial velocity of the ionized material, measured from hydrogen recombination lines, differs by approximate to9 km s(-1) between the "heads'' of the two cometary H II regions and by up to similar to7 km s(-1) from that of the molecular gas. These findings indicate a supersonic velocity difference between the compact heads of the cometary regions and between each head and the ambient molecular material. This suggests that the observed cometary morphologies are created largely by the motion of wind-blowing, ionizing stars through the molecular cloud, as in a bow shock model.[[fileno]]2010504010005[[department]]天文

Dual Cometary HiiRegions in DR 21: Bow Shocks or Champagne Flows?