The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs

By S. Mohanty, R. Jayawardhana, G. Basri. 2005

262 citations recorded by the source corpus.

Using the largest high-resolution spectroscopic sample to date of young, very low mass stars and brown dwarfs, 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 M☉ down to about 15 jupiters. They are confirmed members of the ρ Ophiuchus, Taurus, Chamaeleon I, IC 348, R Coronae Australis, Upper Scorpius, and TW Hydrae star-forming regions and young clusters, with ages from <1 to ~10 Myr. The sample contains 41 brown dwarfs (spectral types ≥M6.5). We have previously presented high-resolution optical spectra for roughly half the sample; the rest are new. This is a close to complete survey of all confirmed brown dwarfs known so far in the regions examined, except in ρ Oph and IC 348 (where we are limited by a combination of extinction and distance). We find that (1) classical T Tauri-like disk accretion persists in the substellar domain down to nearly the deuterium-burning limit; (2) while an Hα 10% width ≳200 km s-1 is our prime accretion diagnostic (following our previous work), permitted emission lines of Ca II, O I, and He I are also good accretion indicators, just as in classical T Tauri stars (we caution against a blind use of Hα width alone, since inclination and rotation effects on the line are especially important at the low accretion rates in very low mass objects); (3) the Ca II λ8662 line flux is an excellent quantitative measure of the accretion rate in very low mass stars and brown dwarfs (as in higher mass classical T Tauri Stars), correlating remarkably well with the obtained from veiling and Hα modeling; (4) the accretion rate diminishes rapidly with mass—our measurements support previous suggestions that ∝ ℳ (albeit with considerable scatter) and extend this correlation to the entire range of substellar masses; (5) the fraction of very low mass stellar and substellar accretors decreases substantially with age, as in higher mass stars; (6) at any given age, the fraction of very low mass stellar and substellar accretors is comparable to the accretor fraction in higher mass stars; and (7) a number of our sources with infrared excesses arising from dusty disks do not evince measurable accretion signatures, 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 on the one hand and low-mass bodies close to and below the hydrogen-burning limit on the other, are consistent with a common formation mechanism in the two mass regimes.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a16e63eb21c8b3590fe73f1a74b5cbe1b17cddb0

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In Astronomy and Astrophysics

1. K. Luhman
2. L. Hillenbrand
3. Eric Mamajek
4. G. Herczeg
5. Ralf Klessen
6. L. Hartmann
7. Michael C. Liu
8. N. Calvet

In Instrumentation

1. K. Luhman
2. Michael C. Liu
3. L. Hillenbrand
4. Eric Mamajek
5. G. Herczeg
6. A. Reiners
7. Kelle Cruz
8. T. Dupuy

Citations in the corpus

• Accretion onto Pre-Main-Sequence Stars (2016, background): “…lines as secondary accretion rate measurements, where a line luminosity or shape is converted to an accretion luminosity on the basis of correlations from stars where both are measured (e.g., Muzerolle et al. 1998, Natta et al. 2004, Mohanty et al. 2005, Dahm 2008, Herczeg & Hillenbrand 2008).”
• A Moving Cluster Distance to the Exoplanet 2M1207b in the TW Hydrae Association (2005, background): “While astrophysically interesting in its own right as a representative of the new class of young, accreting brown dwarfs (e.g. Muzerolle et al. 2005; Mohanty et al. 2005), it appears that 2M1207 may become most famous for being the host “Sun” for the first imaged extrasolar planet – if indeed…”
• UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs (2008, methodology): “…the Hα line profile (Muzerolle et al. 2000, 2003, 2005), by extending relationships between Ṁ and line luminosities established at higher masses to brown dwarf masses (Natta et al. 2004, 2006; Mohanty et al. 2005), or in a few cases from measurements of the Paschen continuum (White & Basri 2003).”
• TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR (2009, background): “…correlation is unknown and many theories have been proposed in explanation, such as mass-dependent stellar properties (e.g., Muzerolle et al. 2003; Mohanty et al. 2005; Natta et al. 2006b), initial core properties (Dullemond et al. 2006), Bondi-Hoyle accretion (Padoan et al. (2005) and scatter…”
• Star and Protoplanetary Disk Properties in Orion's Suburbs (2009, background): “Power law fits of the formṀacc∝Mα∗ have yielded values in the range 1.0−2.1 for the exponentα (White & Basri 2003; Muzerolle et al. 2003; Calvet et al. 2004; Muzerolle et al. 2005; Mohanty et al. 2005; Natta et al. 2006; Garcia Lopez et al. 2006; Herczeg & Hillenbrand 2008; Gatti et al. 2008).”
• The Disk Population of the Chamaeleon I Star-forming Region (2008, background): “Because of the relatively low extinction, optical wavelengths are accessible for the spectral classification of the stellar population (Comerón et al. 2004; Luhman 2004a, references therein) and for measuring diagnostics of accretion (Mohanty et al. 2005; Muzerolle et al. 2005).”
• Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, result): “We compare it with data from Calvet et al. (2004), Mohanty et al. (2005), Muzerolle et al. (2005), and Natta et al. (2006) as displayed in Fig.”
• AN INFRARED/X-RAY SURVEY FOR NEW MEMBERS OF THE TAURUS STAR-FORMING REGION (2009, background): “Because young stars and brown dwarfs that lack IRAC excesses rarely exhibit evidence of accretion in Hα (Mohanty et al. 2005; Muzerolle et al. 2003, 2005; Hartmann et al. 2005b; Guieu et al. 2007; Luhman et al. 2006, 2008), the Hα emission in the spectrum of 2M 0437+2331 probably arises from the…”
• EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H–R DIAGRAMS? (2009, background): “We have considered (1) constant rates, (2) exponentially time-decreasing rates and (3) rates obeying the empirical mass dependence Ṁ ∝ M2 observed in young clusters (Mohanty et al. 2005, Herczeg & Hillenbrand 2008).”
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs (2008, methodology): “All our test objects start with rotation velocities of 10 km s−1, which is motivated by the projected rotation velocities in low-mass stars and brown dwarfs observed during their T Tauri phase (Mohanty et al. (2005), see also Basri (2002)).”
• Accretion Rates in Herbig Ae stars (2006, methodology): “Results can be found, e.g., in Gullbring et al. 1998, Muzerolle et al. (1998, 2003, 2005), White and Ghez (2001), Natta et al. (2004, 2006), Mohanty et al. (2005).”
• IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 PC. I. SPECTROSCOPIC OBSERVATIONS (2009, methodology): “Mohanty et al. (2005) use He i λ6678 emission as yet another accretion indicator, though several of the objects they determined to be accreting do not exhibit He i emission, while others with He i emission show no signs of accretion.”
• Timescale of mass accretion in pre-main-sequence stars (2009, background): “In the case of Upper Sco Mohanty et al. (2005)e.g., found an increase from 7% (± 2”