Neal J Evans II The University of Texas at Austin A Brief History of Collapse 19689 Al Cheung Townes discover ammonia water 1970 Molecular Clouds studied Lines much broader than thermal ID: 632696
Download Presentation The PPT/PDF document "Yes, Stars DO form by Gravitational C..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Yes, Stars DO form by Gravitational Collapse
Neal J. Evans
II
The University of Texas at AustinSlide2
A Brief History of Collapse1968-9 Al Cheung, Townes, … discover ammonia, water~1970 Molecular Clouds studied
Lines much broader than thermal
1974
Goldreich
and Kwan
Linewidths
caused by collapse
1974 Zuckerman and Evans
Linewidths
caused by turbulenceSlide3
A Brief History of Collapse1980s Myers et al.
etc
Dense cores within clouds
1977
Shu
Collapse of a singular isothermal sphere
Inside-out collapse
1982 Wynn-Williams
“Protostars are the Holy Grail of infrared astronomy.”
Collapsing
protostar
: the “holy grail”Slide4
A Brief History of B335Barnard (1905)Small round cloud, totally isolated
“[...] a very small black spot, B335, which looks like a defect, but is not. It is probably of the same nature as the larger ones just mentioned. It can hardly be a hole through the star cloud.’’ - E. E. Barnard, from his comments on Plate 41, August 27,
1905Slide5
B335: The Theorists’ DreamSlide6
More Recent DevelopmentsB335 moved closer (100 pc instead of 250)Stutz 2008,
Oloffson
2009
Spitzer, Herschel detected source at much shorter IR wavelengths
Now have a full SEDSlide7
Detected now from 3.6 to 1300 micron.
Spectrophotometry over much of that range.
Closer distance plus better photometry:
L = 0.72
L
sunSlide8
Observing Infall with ALMA
A key observation is to observe the infalling gas in
redshifted
absorption
against the background
protostar
Very high spectral resolution (<0.1 km/s) is required
High sensitivity to observe in absorption against disk
.
(Slide from talks in mid 2000s about what we could do with ALMA)Slide9
ALMA Exists!
66 Antennas at 5000 m altitude in the Atacama of ChileSlide10
ALMA ObservationsRe-assembled folks who worked on infall in late 90sProposed for Cycle 1
Eventually observed
Continuum and four lines
CS 7-6, HCO
+
4-3, HCN 4-3, H
13
CN 4-3
Resolution ~ 0.5” and 0.1 km/sSlide11
Continuum at 860 microns
Fit by 2D Gaussian
Size 0.53” by 0.47”
(0.5” = 50 AU)
Could be disk or inner part of envelope.
Mass ~ 10
–3
M
sun
Also see arc structure; probably edge of outflow cavitySlide12
Channel Maps of HCNSlide13
Channel Maps of HCNSlide14
Channel Maps of HCNSlide15
Channel Maps of HCNSlide16
Channel Maps of HCNSlide17
Channel Maps of HCNSlide18
Channel Maps of HCNSlide19
Channel Maps of HCNSlide20
Channel Maps of HCNSlide21
The four lines towardcontinuum peak.
Continuum has been subtracted, so T
R
< 0 means absorbing continuum.
Blue line marks systemic velocity.
We do see
redshifted
absorption in two lines.Slide22
Updating the ModelMove closer (100 pc)r
inf
= 0.012 pc (~2500 AU)
Age is 5 x 10
4
yr
r
in
= 3 x 10
–5
pc (= 6 AU)
Still spherical, still
Shu
model
Add continuum source as observed
Try simple abundance models for nowStep functions or “drop” functionsSlide23
Model in red
For two lines with absorption against the continuum.
Can reproduce the red-shifted dips reasonably well. Also the line wings from very inner part of infall; no need for outflow contribution.Slide24
SummaryClouds don’t collapse, cores doUnless the cloud IS a core (e.g., B335)
Evidence for collapse of cores has accumulated
ALMA can provide “smoking gun” evidence
B335 provides cleanest test
Data are qualitatively supportive of infall
But puzzles remain