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SUMMARY:The Most Rapidly Collapsing Molecular Clumps [IIA Colloquium]
DTSTART:20260623T100000Z
DTEND:20260623T110000Z
DTSTAMP:20260623T115200Z
UID:indico-event-443@events.iiap.res.in
CONTACT:colloqm@iiap.res.in
DESCRIPTION:Speakers: James Jackson (NRAO)\n\nAbstractAn analysis of the M
 illimetre Astronomy Legacy Team 90 GHz (MALT90) survey has produced a samp
 le of 27 candidate dense molecular clumps with large collapse motions\, as
  revealed by large "blue" asymmetrical line profiles of the optically thic
 k HCO+ (1–0) line. New\, more sensitive molecular line observations of t
 his sample\, conducted with the Mopra 22-m telescope\, confirm the blue as
 ymmetries in the HCO+(1–0) line profiles\, with large\, positive values 
 of the asymmetry parameter A (HCO+) = 0.69±0.01\, and decreasing values o
 f A for lines with smaller optical depths\, as expected for collapsing clu
 mps. The hyperfine ratios for N2H+(1–0) are in their optically thin\, LT
 E\, values\, but for HCN (1–0) they are not\; the F = 1 → 1 hyperfine 
 line shows abnormally weak intensities. A simple two-component model shows
  that self-absorption of the background F = 1 → 1 hyperfine line by the 
 main F = 2 → 1 hyperfine line of a cold\, foreground\, redshifted cloud 
 can reproduce the observed HCN (1–0) hyperfine intensities and match bot
 h the HCN (1–0) and HCO+(1–0) line profiles. All of these results are 
 consistent with self-absorption of the optically thick lines on the red si
 de of the profile\, as expected for collapsing clumps. A simple two-cloud 
 model suggests that this sample represents dense clumps with extreme colla
 pse velocities\, V_inf ∼ 2.4 km s−1\, the highest known. \n\nhttps://
 events.iiap.res.in/event/443/
LOCATION:Auditorium
URL:https://events.iiap.res.in/event/443/
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