Grain Growth in Protoplanetary Disks: the (Sub)Millimeter

1. Grain Growth in Protoplanetary Disks: the (Sub)Millimeter David J. Wilner Harvard-Smithsonian Center for Astrophysics Sep 11, 2006 From Dust to Planetesimals, Ringberg

2. Relevance of (Sub)Millimeter • “vibrational” dust emission is dominant mechanism (thermal fluctuations in charge distribution) • longest observable ’s for dust: 0.35 to 35 mm • sensitive to cold dust, T<10’s of K • low opacity, sample emission at all disk depths •  dependence of opacity diagnostic of dust properties (e.g. growth to millimeter size) • no contrast issue with stellar photosphere • major new facilities under construction: ALMA, eVLA PPV: Natta, Testi, Calvet, Henning, Waters & Wilner, astro-ph/0602041

3. Williams, Andrews, Wilner 2005 ISM  Protoplanetary Disks 0.85 mm Johnstone & Bally 1999

4. (Sub)Millimeter Observables • T Tauri, Herbig Ae disks (d≤150 pc, 1-10 Myr) • integrated flux vs.  (single dish bolometer) • observe power law form, F ~ -, 2 <  < 3 • spatially resolved brightness (interferometer) SMA Raman et al. 2006 star dust F~-2.5 HD169142 Dent et al. 2006 300 AU

5. Basics of “” • mass opacity ( > 0.1 mm) power law form • normalization, power law index , depend on dust properties: • composition • size distribution • geometry • … (see Draine 2006) ~-2 Adams et al. 1988, following Draine & Lee 1984

6. From  to  • flux density emitted by an element dA • if <<1 and h<<kT, then and  simply related to  F ~-(2+)

7. Disk Dust appears Different • early (sub)mm obs: disk <>~1 vs. ISM ~1.7 (e.g Weintraub et al. 1989, Adams et al. 1990, Beckwith et al. 1990, Beckwith & Sargent 1991, Mannings & Emerson 1994) Beckwith & Sargent (1991) d=(-2)(1+) 0 1 2 

8. ~1 Interpretations Pollack et al. 1994 mixture, compact, segregated spheres, n(a) ~ a-q, q=3.5 1. changes in dust properties: • grain growth small, a << /2=2 large, a >> /2  =0 mm size, ~1 •  ~ -1 due to dust composition particle geometry 2. optically thick emission: • F ~ -2 (in part)   > ( - 2) amax=1 mm amax=10 cm Calvet & D’Alessio 2001

9. Dust Properties or Optical Depth? • e.g. Herbig Ae stars UX Ori, CQ Tau: • 1.1-7mm~ 2.0±0.3, 2.65±0.1 •  ~ 0 and large disk? any  and small disk? Testi et al. (2001)

10. Resolve Ambiguity • observe spatial distribution of sub(mm) brightness • arcsecond scales require interferometry • 1.3, 3 mm: BIMA, OVRO, PdBI, NMA; ATCA, SMA • 7 mm: VLA (thanks to CONACyT, MPIfR, NSF) longer : lever minimizes  uncertainty, probes larger dust; more concern about ionized gas

11. combine fluxes, images, improved disk models: TW Hya CQ Tau 7 (2) Herbig Ae stars 14 (10) Taurus PMS stars 10 (5) southern PMS stars 24 (20) Taurus/Oph PMS stars Calvet et al. 2002 Testi et al. 2003 Natta et al. 2004 Rodmann et al. 2006 Lommen et al. 2006 Andrews & Williams 2007 Interferometer Studies TBvs. disk radius at 0.4, 3, and 7 mm, from two dust models of D’Alessio et al. 2001 Calvet & D’Alessio 2001

12. Grain Growth in TW Hya • irradiated accretion disk model matches SED and VLA (and SMA) intensities from 10’s to Rout~ 200 AU • shallow (sub)mm slope requires amax >> 1 mm • observed 7 mm low brightness requires  << 1 =0.70.1 Calvet et al. 2002

13. Many (Barely) Resolved Disks ATCA 3mm Lommen et al. 2006 SMA 0.87/1.3mm Andrews & Williams VLA/PdBI/OVRO Natta et al. 2004 VLA 7mm Rodmann et al. 2006

14. Many More  Determinations • ≤1 for many/most resolved disks solid: Lommen et al. 2006 dashed: Rodmann et al. 2006 dotted: Natta et al. 2004

15. b1-7mm 2 1 0 k1mm Limitations/Complexity of  •  is an average, for any dust model • cannot disentangle all properties • <1: hard to avoid substantial mass fraction a~O() amax Natta & Testi 2004 Natta & Testi 2004

16. TW Hya at 3.5 cm? • disk model underpredicts 3.5 cm emission • emission mechanism? • ionized protostellar wind • if FcmdMacc/dt, low by 103x • spinning dust (Rafikov 2006) • requires high (unrealistic) C fraction in nanoparticles/PAHs • synchrotron • X-rays not stellar activity: dense, cool, and depleted accretion (Stelzer & Schmitt 2004) • thermal dust,   const F ~ -2.60.1

17. Grain Size Evolution • theory: growth, settling, destruction, … • depart from simple power law size distribution • create midplane population of ~cm size (timescale?) Weidenschilling 1997 Dullemond & Dominik 2005

18. TW Hya: Pebble Population Wilner et al. 2005 • 3.5 cm disk dust emission 1. not variable: weeks to years 2. resolved at arcsec scale, brightness only ~10 K 3. steep spectrum to 6 cm toy model: small + ~cm size grains

19. Any  Correlations? • no trend of  with stellar luminosity, mass, age • tantalizing trends of  with mid-ir growth, settling indicators   Acke et al. 2004  Lommen et al. 2006 PPV: Natta et al. 2006

20. Remarks • (sub)mm <1: compelling evidence for growth • most of original dust mass in mm size particles • no clear trends with stellar properties • mm/cm sizes persist for Myrs • competition between agglomeration and collisions • are the disks we can study in the (sub)mm the ones that will never form planets? • probably not: transition disks

21. Transition Disks: Inner Holes Spitzer IRS implies r~24 AU hole “... we remain skeptical of the existence of such a large central gap [5 AU] devoid of dust.” - Chiang & Goldreich (1999) Calvet et al. 2005 Wilner et al. 2006

22. Transition Disks: Inner Holes mid-ir implies r~4 AU hole Calvet et al. 2002 Hughes et al., in prep

23. at the limits of ALMA Wolf & D’Angelo 2005 Next Generation (Sub)mm Facilities • 10 to 100x better sensitivity, resolution, image quality • dust emission structure at 0.1 to 0.01 arcsec • precision (sub)mm spectral index maps

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