The T Tauri phase down to nearly planetary masses: Echelle spectra of 82 very low mass stars and brown dwarfs
Feb, 2005
64 pages
Published in:
- Astrophys.J. 626 (2005) 498-522
e-Print:
- astro-ph/0502155 [astro-ph]
DOI:
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Abstract: (arXiv)
Using the largest high-resolution spectroscopic sample to date of young, very low mass stars (VLMS) and brown dwarfs (BDs), we investigate disk accretion in objects ranging from just above the hydrogen-burning limit all the way to nearly planetary masses. Our 82 targets span spectral types from M5 to M9.5, or masses from 0.15 Msun down to ~15 Jupiters. They are confirmed members of the rho Oph, Taurus, Cha I, IC 348, R CrA, Upper Sco and TW Hydrae regions, with ages <1 to ~10 Myr. The sample contains 41 BDs (spectral types >= M6.5). We find that: (1) classical T Tauri-like disk-accretion persists in the BD domain down to nearly the deuterium-burning limit/ (2) in addition to H-alpha, permitted emission lines of CaII, OI and HeI are also good accretion indicators, as in CTTs/ (3) the CaII 8662A flux is an excellent quantitative measure of the accretion rate (Mdot) in VLMS and BDs(as in CTTs)/ (4) Mdot diminishes as M^2 -- our measurements support previous findings of this correlation, and extend it to the entire range of sub-stellar masses/ (5) the accretor fraction among VLMS and BDs decreases substantially with age, as in higher-mass stars/ (6) at any given age, the VLMS and BD accretor fraction is comparable to that in higher-mass stars/ and (7) a number of sources with IR disk excesses do not evince measurable accretion, with the incidence of such a mismatch increasing with age: this implies that disks in the low mass regime can persist beyond the main accretion phase, and parallels the transition from the classical to post-T Tauri stage in more massive stars. These strong similarities at young ages, between higher-mass stars and low-mass bodies close to and below the hydrogen-burning limit, are consistent with a common formation mechanism in the two mass regimes. (abridged)- circumstellar matter
- planetary systems
- stars: formation
- stars: low-mass, brown dwarfs
- stars: pre
- main-sequence
- techniques: spectroscopic
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