Exploring Brown Dwarf Origins Ray Jayawardhana (University of Michigan -> University of Toronto) Subhanjoy Mohanty, Gibor Basri, Beate Stelzer, David Ardila,

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Exploring Brown Dwarf Origins Ray Jayawardhana (University of Michigan -> University of Toronto) Subhanjoy Mohanty, Gibor Basri, Beate Stelzer, David Ardila, Karl Haisch, David Barrado y Navascus Slide 2 Context and Motivation * Sub-stellar objects appear to be common in the field and in star- forming regions (e.g., review by Chabrier 2003) * Overlap between stellar and planetary mass distributions? (e.g., Lucas & Roche 2000; Zapatero Osorio et al. 2000, 2002; Mohanty et al. 2004a; Mohanty, Jayawardhana & Basri 2004b) * Understanding BD origins is important for theories on the formation of stars and planets - embryos ejected from multiple proto-stellar systems (Reipurth & Clarke 2001; Bate et al. 2002, 2003) - turbulent fragmentation (Padoan & Nordlund 2002) * Studies of young sub-stellar objects could provide clues to their formation mechanism(s) Zinneckers talk Slide 3 Investigating Young Brown Dwarfs: A Multi-Faceted Approach * Measurements of Disk Excess * Search for Spectroscopic Signatures of Accretion * Disk Mass Estimates from mm Fluxes * Determination of Sub-Stellar Physical Properties * Studies of Angular Momentum Evolution (v sin i, photometric periods) * Probes of Activity (X-rays, H ) Slide 4 Key Observational Question: Do Young Sub-Stellar Objects undergo a T Tauri-like Phase? Jets/Outflows Fig. Courtesy L. Hartmann Slide 5 Disk Excess Measurements Sample Objects with known spectral types later than M5 in nearby star-forming regions Total: 50+ Observations JHKL photometry at VLT, Keck and IRTF Supplemented with 2MASS JHK K-L is a more reliable measure of disk fractions (Haisch et al. 2001): less susceptible to geometric effects, smaller extinction corrections, easily measurable above photospheric emission Slide 6 Jayawardhana, Ardila, Stelzer & Haisch (2003) Slide 7 Disk Fractions by Region RegionFractionEst. Age Oph6/7< 1 Myr IC 3483/6~2 Myr Taurus5/9~1-3 Myr Cha I8/15~1-3 Myr Upper Sco4/8~3-5 Myr Ori2/6~5-7 Myr TW Hya0/2 ~10 Myr Jayawardhana, Ardila, Stelzer & Haisch (2003) Slide 8 ISO Measurements of Disk Excess at 7 m & 14 m: Chamaeleon I and Oph Comeron et al. (1998); Natta & Testi (2001); Natta et al. (2002) Slide 9 Ground-based Mid-IR Observations I: Cha H 2 Apai et al. (2002) Flat disk with no silicate feature Slide 10 Mohanty, Jayawardhana et al. (2004) Flared disks in GY 310 and GY 11 Inner disk holes of a few sub-stellar radii in all three Possible silicate feature in GY 310 Ground-based Mid-IR Observations II Slide 11 2MASS1207-3932 Cha H 1 Luhmans talk Sterzik et al. (2004) Flared disk in ChaH 1 Mid-IR excess in TW Hya BD 2MASS1207-3932 Ground-based Mid-IR Observations III Slide 12 Millimeter Observations of Cold Dust (CFHT BD-Tau 4 and IC 348 613) A few Earth masses of dust (assuming dust opacities similar to TTS disks) Assuming gas-to-dust ratio of 100, disk mass ~a few % of BD mass Pascucci et al. (2003); Klein et al. (2003) Slide 13 Spectroscopic Signatures of Accretion Sample Objects with known spectral types later than M5 in Upper Scorpius, Ophiuchus, IC 348, Taurus, Chamaeleon I, and TW Hydrae Total ~ 70 Observations High-resolution optical spectra at Keck and Magellan R~33,000 (HIRES), R~20,000 (MIKE) H line profiles in high-resolution spectra is a good diagnostic of accretion (also OI, HeI, CaII in some cases) Slide 14 H Criterion for Accretion * H EW > 10A are usually categorized as CTTS * But this threshold value varies with spectral type * H line width at 10% of the peak may be a better indicator * Nearly free-falling flow between disk inner edge and star * For brown dwarfs at a few Myr, adopted accretion threshold: ~200 km/s (+ other diagnostics) (Jayawardhana, Mohanty, & Basri 2003) Slide 15 Natta et al. (2004) Accretion Rate vs. H 10% Width Slide 16 Jayawardhana, Mohanty & Basri (2003); Jayawardhana et al, in prep.; also see White & Basri (2003); Muzerolle et al. (2003) H line profiles for IC 348 and Taurus Slide 17 Jayawardhana, Mohanty & Basri (2003) OI (8446A) and CaII (8662A) line profiles for three accretors in IC 348 Broad HeI (6678A) line also seen in IC 348-165 Slide 18 Jayawardhana, Mohanty & Basri (2002) H line profiles for Upper Sco (~5 Myr) Slide 19 Mohanty, Jayawardhana, & Barrado y Navascus (2003) H and He I line profiles of 2MASS 1207-3932 in the TW Hydrae Association (~10 Myr) (comparison to flaring field dwarf LHS 2243) Slide 20 Fraction of Accretors RegionFractionEst. Age Oph(need IR)< 1 Myr IC 3487/13~2 Myr Taurus8/27~1-3 Myr Cha I2/13~1-3 Myr Upper Sco2/19~3-5 Myr TW Hya1/3 ?~10 Myr In Taurus, Cha I and Upper Sco, several objects with K-L excess do not show accretion-like H profiles Disks persist after accretion rates have dropped? 2MASS1207-3932 in TWA: accretion and mid-IR excess, no L excess Slide 21 Natta et al. (2004) Accretion Rate vs. (Sub-)Stellar Mass Slide 22 Rotation-Disk Connection? Basri, Mohanty & Jayawardhana, in prep. talks by Mohanty & Scholz Slide 23 Barrado y Navascus, Mohanty & Jayawardhana (2004) Accretion and outflow in the sub-stellar domain? The case of LS RCrA 1 (Fernandez & Comeron 2001) Slide 24 Slide 25 Slide 26 Conclusions * A large fraction of young sub-stellar objects harbor K-L excess consistent with optically thick disks * Mid-IR and mm observations suggest a range of disk geometries and dust properties similar to those of TTS * Many brown dwarfs show signs of accretion at very young ages * Disks appear to persist after accretion rates have dropped below measurable levels (e.g., Upper Sco) * Inner disk lifetimes of brown dwarfs do not appear to be vastly different from those of T Tauri stars * Tantalizing hint of outflows in at least one object? Compelling Evidence for a T Tauri Phase in Young Sub-Stellar Objects Slide 27 Implication Does this imply a common formation mechanism for isolated sub-stellar objects and low-mass stars? Likely. (Even some `planemos may form the same way as stars do D-burning limit shouldnt affect formation: Chabrier 2003) But, it may be too early to rule out the ejection scenario and other models for the origin of at least some brown dwarfs. Slide 28 Future Prospects * High-resolution near-infrared spectroscopy of embedded proto-brown dwarfs (Keck) * Mid-infrared and far-infrared measurements of disk excess and silicate feature (Spitzer) * Disk dust mass estimates from mm observations (IRAM, JCMT) * Scattered-light imaging of disks and narrow-band imaging of jets? * Studies of angular momentum evolution and activity