studying infall
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Studying Infall. Neal J. Evans II. Importance. Proving stars form by gravitational collapse Testing particular theories Determining timescales. Why is it so hard?. Troubled history early claims and sharp criticism Velocities low v inf = 1 km/s [(M * /M sun )/(r/1000AU)] 0.5 - PowerPoint PPT PresentationTRANSCRIPT
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Studying Infall
Neal J. Evans II
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Importance
• Proving stars form by gravitational collapse
• Testing particular theories
• Determining timescales
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Why is it so hard?
• Troubled history– early claims and sharp criticism
• Velocities low – vinf = 1 km/s [(M*/Msun)/(r/1000AU)]0.5
• Compared to – turbulence vturb ~ r0.5
– rotation on small scales vrot ~ r–1
– outflows vflow ~ 1 to 100 km/s
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Renaissance
• Discovery of objects in very early stages– Class 0– Class –1 or Pre-Protostellar Cores (PPCs)
• Simple models for collapse– Shu 1977 and variations
• Systematic predictions of line profiles– Zhou 1992
• A credible example: B335– Zhou et al. 1993
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Objects in Early Stages
Andre 2002
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Simple Collapse Models
C. Young
Time Evolution of a Shu, inside-out collapse model.Initially a 10 K SIS. OH5 dust.t = 104 to 7 x 105 in 70 steps, dM/dt = 2 x 10-6 Msun/yr, R* = 3Rsun.Dust temperature computed with DUSTY (Ivezic and Elitzur 1997)
QuickTime™ and aGIF decompressor
are needed to see this picture.
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Predictions of Line Profiles(Shu models)
HCO+
J =3-2
HCO+
J =4-3
Gregersen et al.1997
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The Infall Cartoon
Andre 2002
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A Credible Example
B335 Shu model fits line profiles of CS, H2CO(Zhou et al.1993)Improved models byChoi et al. (1995)
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Surveys for Infall Signatures
• Globules C18O, H2CO 3/12– Wang et al. 1995
• Class 0 Cores HCO+ , H13CO+ 6/18– Gregersen et al. 1997
• Class 0/I Cores CS, H2CO, N2H+
– 14/37 CS, 15/47 H2CO– Mardones et al. 1997
• Class I Cores HCO+ 8/16– Gregersen et al. 2000
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Inward Motions in Class –1
• Class –1 CS, N2H+ 17/70
– Lee et al. 1999
• Class –1 HCO+ , H13CO+ 6/17– Gregersen and Evans 2000
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Getting Quantitative
• A variety of line profiles– Some blue, some red, some neither– Define BLUE: delta v < –0.25
– delta v = (vthick – vthin)/Delta vthin
• For a sample, define excess of blue over red
• Excess: E = (Nblue – Nred)/Ntot
– Surveys: Positive Excess– Systematic tendency for inward motion
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Does Excess vary with Class?
–1 0 I
0.35 0.31 0.31
Based on HCO+ J = 3–2 Gregersen et al. 2000
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Storm Clouds
• Interferometers find deviations– Line profiles on small scales not as predicted
• Choi et al. (1999)
• Wilner et al. (2000)
• Chemical Effects– Depletion can remove infall signature
• Rawlings and Yates
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Inconsistency on Small Scales
Wilner et al. 2000ApJ, 544, L69
Observations with IRAM ArrayResolution about 2.5”Dotted line shows predicted linebased on standard Shu collapse.Expect higher velocities than seen.Spatial pattern also different.
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Depletion Can Confuse Infall
Abundance versusRadius: Different Chemical Models
HCO+ CS
Rawling and Yates 2001
Line profiles resulting from different chemical models
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Back to Basics
• Use dust continuum emission – More robust tracer of n(r)
– Modeling with RT yields TD(r)
• Gas–Dust energetics yields TK(r)
• Use these as constraints
• Derive empirical abundances X(r)
• Eventually model chemistry/dynamics
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Dust Emission Images
Class –1L1544
Class 0B335
Class ICB230
850 micron Emission
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Results of Modeling
Evans et al. 2000
Shirley et al. 2002
Young et al. 2002
Model fits to radial profiles of dust emission: Bonnor-Ebert sphere fits L1544 (–1)Power law (n ~ r–p) fitsB335 (0) and CB230 (I)
Dust temperature calculated self-consistently.Beam and chopping simulated.
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Conclusions for Class –1
• Bonnor-Ebert spheres are good fit– Central densities of 105 to 106 cm–3
– Unstable if only thermal support
• Weather Report for Class –1– Very cold (TD(K) ~ 7 K in center)
– Calm (very low turbulence)– Precipitation is expected
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Molecular Line Studies
• Study of PPCs with dust emission models– L1512, L1544, L1689B
• Maps of species to probe specific things– C18O, C17O, HCO+, H13CO+, DCO+, N2H+, CCS
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The PPC is Invisible to Some
Color: 850 micron dust continuumContours: C18O emission
Cut in RA: Convert to N(H2) with standard assumptions
C18O does not peak C17O slight peakOptical Depth plus depletion
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Others See It
Green: 850 mic.Red: N2H+
traces PPC
Agrees withpredictions ofchemical models
Nitrogen basedand ions lessdepleted.
Lee et al. 2002
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Evidence for Inward Motions
Lee et al. 2002
Line profiles of HCO+
Double peaked,Blue peak strongerSignature of inwardmotion.
Red: Model withsimple dynamics,depletion modelfits the data.
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Results from Molecular Lines
• Cold, dense interior causes heavy depletion• Molecular emission affected by
– Opacity, depletion, low temperature
• Evidence of inward motions – Before central source forms– Plummer model provides reasonable fit
• Other models can fit too– Two-layer model (Myers)
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Two-layer Model for L1544
N2H+ Spectra toward L1544 Spectrum from 30-m shows infall asymmetry. Model fit with inward motions at constant velocity (v~0.15 km/s)
Bourke et al. 2002
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Velocity Increases Inward
N2H+ shows the highest velocities, probes the smallest radii. Evidence of increasing velocity inward.
Bourke et al. 2002
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The Smoking Gun
• Absorption against a central continuum – Redshifted absorption implies infall– Disk as central source– Seen toward NGC 1333 IRAS 4A
• Choi et al. 1999
• Di Francesco et al. 2001
– Will be easy with ALMA– May be possible in NIR/MIR with high R
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Inverse P-Cygni Profiles: Cartoon
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Inverse P-Cygni Profiles: Observed
Inverse P-Cygni profile: absorption against continuum from disk redshifted due to infall. Di Francesco et al.
2001 Ap. J. 562,770
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Studying the Velocity Field
IRAM 04191Shift of absorption dipto red in higher J lines indicates faster infall at smaller r.
Belloche et al. 2002, preprint
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Velocities in IRAM 04191
Belloche et al. 2002
Empirical Model of velocity fields in IRAM 04191
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Future Prospects
• Combined dust and gas analysis – Class –1 and 0, esp. early Class 0
• Studies of redshifted absorption– CARMA, ALMA
• Detailed studies of velocity fields– On a range of spatial scales– 2D, 3D radiative transfer, include rotation
• Tests of theoretical models• Infall in regions forming massive stars?
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Blue Profile in a Massive Region
A Blue profile in HCO+
toward a region with L = 104 to 105 Lsun.
G. Fuller, hot off the 30 m
HCO+ 1–0