Evidence for a T Tauri Phase in Young Brown Dwarfs

By R. Jayawardhana, S. Mohanty, G. Basri. 2003

146 citations recorded by the source corpus.

As part of a multifaceted program to investigate the origin and early evolution of substellar objects, we present high-resolution Keck optical spectra of 14 very low mass sources in the IC 348 young cluster and the Taurus star-forming cloud. All of our targets, which span a range of spectral types from M5 to M8, exhibit moderate to very strong Hα emission. In half of the IC 348 objects, the Hα profiles are broad and asymmetric, indicative of ongoing accretion. Of these, IC 348-355 (M8) is the lowest mass object to date to show accretion-like Hα. Three of our ~M6 IC 348 targets with broad Hα also harbor broad O I (8446 Å) and Ca II (8662 Å) emission, and one shows broad He I (6678 Å) emission; these features are usually seen in strongly accreting classical T Tauri stars. We find that in very low mass accretors, the Hα profile may be somewhat narrower than that in higher mass stars. We propose that low accretion rates combined with small infall velocities at very low masses can conspire to produce this effect. In the nonaccretors in our sample, Hα emission is commensurate with, or higher than, saturated levels in field M dwarfs of similar spectral type. Our results constitute the most compelling evidence to date that young brown dwarfs undergo a T Tauri-like accretion phase similar to that in stars. This is consistent with a common origin for most low-mass stars, brown dwarfs, and isolated planetary mass objects.

View Paper: https://www.semanticscholar.org/paper/21c449f2808ba0875506205373e7193a02be1d93

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1. K. Luhman
2. G. Herczeg
3. L. Hartmann
4. L. Hillenbrand
5. A. Natta
6. L. Testi
7. S. Andrews
8. R. Jayawardhana

Citations in the corpus

• The “Mysterious” Origin of Brown Dwarfs (2002, background): “One problem with this model is that protostellar disks are frequently found around BDs (Natta & Testi 2001; Natta et al. 2002; Liu 2003; Jayawardhana et al. 2003a, 2003b; Klein et al. 2003; Martı́n et al. 2004; López Martı́ et al. 2004; Mohanty et al. 2004).”
• On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga (2004, background): “The emission lines of IRAS 04158+2805 and IRAS 04248+2612 are also marginal, consistent with an edge-on orientation, but the narrow profiles of these two stars may simply result from the lower infall /outflow velocities expected in substellar objects (e.g., Jayawardhana et al. 2003).”
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation (2008, methodology): “Hence they can sustain accretion and outflows as observed (Jayawardhana et al. 2003; Muzerolle et al. 2005; Mohanty et al. 2005; Whelan et al. 2005).”
• Accretion in brown dwarfs: An infrared view (2004, background): “A disk with mass of only 10−4 M⊙will live about 3 × 10 5 years, much less than a typical disk of TTSs, and also much less than the age of many BDs with infrared excess in star-forming regions (e.g., Jayawardhana et al. 2003a).”
• An Empirical Criterion to Classify T Tauri Stars and Substellar Analogs Using Low-Resolution Optical Spectroscopy (2003, unknown): “They were selected from Natta & Testi (2001), Natta et al. (2002), Testi et al. (2002), Comerón et al. (1998), and Jayawardhana et al. (2002b, 2003b).”
• The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs (2005, background): “So do spectroscopic signatures of disk accretion, such as broad, asymmetric H lines (Jayawardhana et al. 2002, 2003b, hereafter JMB02, JMB03; Muzerolle et al. 2003, hereafter M03; Natta et al. 2004, hereafter N04).”
• Measuring Accretion in Young Substellar Objects: Approaching the Planetary Mass Regime (2005, background): “The former type of emission is likely due to chromospheric activity on the substellar surface, while the latter is probably produced in accretion flows channeled from a circumstellar disk by the substellar magnetic field (Muzerolle et al. 2000; M03; WB03).”
• UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs (2008, background): “Excess IR emission indicates the presence of disks around some of these very low-mass objects2 (e.g. Muzerolle et al. 2003; 1 Caltech, MC105-24, 1200 E. California Blvd., Pasadena, CA 91125 Jayawardhana et al. 2003; Natta et al. 2004).”