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Studying Infall

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

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Studying Infall

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  1. Studying Infall Neal J. Evans II

  2. Importance • Proving stars form by gravitational collapse • Testing particular theories • Determining timescales

  3. 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

  4. 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

  5. Objects in Early Stages Andre 2002

  6. Simple Collapse Models 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) C. Young

  7. Predictions of Line Profiles(Shu models) HCO+ J =3-2 HCO+ J =4-3 Gregersen et al. 1997

  8. The Infall Cartoon Andre 2002

  9. A Credible Example B335 Shu model fits line profiles of CS, H2CO (Zhou et al.1993) Improved models by Choi et al. (1995)

  10. 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

  11. 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

  12. 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

  13. Does Excess vary with Class? Based on HCO+ J = 3–2 Gregersen et al. 2000

  14. 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

  15. Inconsistency on Small Scales Observations with IRAM Array Resolution about 2.5” Dotted line shows predicted line based on standard Shu collapse. Expect higher velocities than seen. Spatial pattern also different. Wilner et al. 2000 ApJ, 544, L69

  16. Depletion Can Confuse Infall Abundance versus Radius: Different Chemical Models Line profiles resulting from different chemical models Rawling and Yates 2001 HCO+ CS

  17. 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

  18. Dust Emission Images Class –1 L1544 Class 0 B335 Class I CB230 850 micron Emission

  19. Results of Modeling Model fits to radial profiles of dust emission: Bonnor-Ebert sphere fits L1544 (–1) Power law (n ~ r–p) fits B335 (0) and CB230 (I) Dust temperature calculated self-consistently. Beam and chopping simulated. Evans et al. 2000 Shirley et al. 2002 Young et al. 2002

  20. 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

  21. 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

  22. The PPC is Invisible to Some Cut in RA: Convert to N(H2) with standard assumptions C18O does not peak C17O slight peak Optical Depth plus depletion Color: 850 micron dust continuum Contours: C18O emission

  23. Others See It Green: 850 mic. Red: N2H+ traces PPC Agrees with predictions of chemical models Nitrogen based and ions less depleted. Lee et al. 2002

  24. Evidence for Inward Motions Line profiles of HCO+ Double peaked, Blue peak stronger Signature of inward motion. Red: Model with simple dynamics, depletion model fits the data. Lee et al. 2002

  25. 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)

  26. 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

  27. Velocity Increases Inward N2H+ shows the highest velocities, probes the smallest radii. Evidence of increasing velocity inward. Bourke et al. 2002

  28. 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

  29. Inverse P-Cygni Profiles: Cartoon

  30. 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

  31. Studying the Velocity Field IRAM 04191 Shift of absorption dip to red in higher J lines indicates faster infall at smaller r. Belloche et al. 2002, preprint

  32. Velocities in IRAM 04191 Empirical Model of velocity fields in IRAM 04191 Belloche et al. 2002

  33. 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?

  34. 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

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