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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-1146
DTSTART:20080422T204500Z
DURATION:PT1H0M0S
DTSTAMP:20260423T041113Z
LAST-MODIFIED:20080331T173827Z
LOCATION:6515 Sterling Hall
SUMMARY:Outflows from massive (proto) stars and evidence for an 'impro
 ved' evolutionary sequence\, Astronomy Colloquium\, Debra Shepherd\, N
 RAO
DESCRIPTION:Stars of all masses form in dense clouds of molecular gas.
  They begin life as a protostar\; a warm ball of gas and dust heated b
 y thermal	pressure. For more than a million years\, the protostar gain
 s material	through an accretion disk which regulates the accretion rat
 e onto the	star and directs high angular momentum material into specta
 cular molecular and ionized outflows. Disks and molecular outflows in 
 the form of wide-angle winds and/or well-collimated jets are associate
 dwith protostars of all luminosities. Because outflows provide record 
 of the mass-loss history of the system\, they can be useful tools to h
 elp understand the underlying formation processes of young stars. Ther
 e is reasonable evidence that accretion-related processes are responsi
 ble for generating massive molecular flows from protostars up to spect
 ral type B0 (10-15 Msun). Above a luminosity of 10\,000 L sun\, O star
 s generate powerful wide-angle\, ionized winds that dramatically affec
 t outflow morphology and even call into question the relationship betw
 een outflow and accretion. Recently Beuther & Shepherd proposed an evo
 lutionary scenario in which massive protostellar flows begin collimate
 d. Once the star reaches the Main Sequence\, the ionizing radiation af
 fects the balance between magnetic and plasma pressure\, inducing chan
 ges in the flow morphology	and energetics. I will review the known pro
 perties of outflows  from young\, massive OB stars\, discuss implicati
 ons and observational tests of this proposed evolutionary scenario\, a
 nd examine differences between low-mass and massive star formation.
URL:https://www.physics.wisc.edu/events/?id=1146
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