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

Abridged abstract: For stars to form, material must fall inwards from corescales through the envelope towards the central protostar. The velocity profilearound protostars is poorly constrained. 6 Class 0 protostars and one Class Iprotostars observed with HIFI on board Herschel as part of the "Water instar-forming regions with Herschel" (WISH) survey show infall signatures inwater line observations. We use 1-D non-LTE RATRAN radiative transfer models ofthe observed water lines to constrain the infall velocity and chemistry in theprotostellar envelopes of these sources. We assume a free-fall velocity profileand, having found the best fit, vary the radii over which infall takes place.In the well-studied Class 0 protostar NGC1333-IRAS4A we find that infall takesplace over the whole envelope to which our observations are sensitive (r>~1000AU). For 4 sources infall takes place on core to envelope scales (i.e.~10000-3000 AU). In 2 sources the inverse P-Cygni profiles seen in theground-state lines are more likely due to larger-scale motions or foregroundclouds. Models including a simple consideration of the chemistry are consistentwith the observations, while using step abundance profiles are not. Thenon-detection of excited water in the inner envelope in 6/7 protostars isfurther evidence that water must be heavily depleted from the gas-phase atthese radii. Infall in four of the sources is supersonic and infall in allsources must take place at the outer edge of the envelope, which may beevidence that collapse is global or outside-in rather than inside-out. The massinfall rate in IRAS4A is large (>~10^-4 msol\yr), higher than the mass outflowrate and expected mass accretion rates onto the star, suggesting that anyflattened disk-like structure on small scales will be gravitationally unstable,potentially leading to rotational fragmentation and/or episodic accretion.

Waterfalls around protostars: Infall motions towards Class 0/I envelopes as probed by water