Accretion and outflow in the substellar domain: Magellan spectroscopy of LS-RCrA 1

We present low-, medium-, and high-resolution optical spectra, obtained with the Magellan Baade 6.5 m telescope, of LS-RCrA 1, a late-type object identified recently by Fernandez & Comeron in the R Coronae Australis star-forming region. We confirm both pre-main-sequence status and membership in the R CrA region for this object, through the detection of Li I, presence of narrow K I indicative of low gravity, and measurement of radial velocity. The Halpha emission profile is very broad, with a 10% full width of 316 km s(-1) at high resolution, implying the presence of ongoing accretion. Our spectra also exhibit many forbidden emission lines indicative of mass outflow, in agreement with the Fernandez & Comeron results. We derive a spectral type, independent of extinction, of M6.5 +/- 0.5 IV. Using new Two Micron All Sky Survey (2MASS) near-infrared photometry, no significant near-infrared (NIR) excess is found. Our optical veiling measurements yield a mass accretion rate of 10(-10) less than or similar to M less than or similar to 10(-9) M-. yr(-1). The presence of prominent outflow signatures at these low accretion rates is initially puzzling. We consider, and discard as improbable, the possibility that these signatures arise in a line-of-sight Herbig-Haro knot unassociated with LS-RCrA 1 itself. However, if LS-RCrA 1 possesses a nearly edge-on disk, a natural outcome would be the enhancement of any outflow signatures relative to the photosphere; we favor this view. A low accretion/outflow rate, combined with an edge-on orientation, is further supported by the absence of high-velocity components and any significant asymmetries in the forbidden lines. An edge-on geometry is also consistent with the lack of NIR excess in spite of ongoing accretion and explains the relatively large Halpha 10% width compared to other low- mass objects with similar accretion rates. Through comparison with the latest synthetic spectra, we infer T-eff approximate to 2700 +/- 100 K, somewhat lower than the previous estimate (2900 +/- 200 K). Theoretical evolutionary tracks then imply an age of similar to 20 Myr (as derived from T-eff and luminosity) or similar to 8 Myr (T-eff vs. gravity) for LS-RCrA 1. This last value is consistent with the estimated age of other T Tauri stars in R CrA (less than or similar to10 Myr), and it is substantially less than the similar to50 Myr derived previously. Therefore, LS-RCrA 1 indeed appears subluminous relative to expectations for an R CrA member. By comparing its position on the H-R diagram with that of other similarly accreting low-mass objects, we show that accretion-induced effects are unlikely to account for its faintness. We suggest instead that LS-RCrA 1 possesses a nearly edge-on disk and its photosphere is seen predominantly in scattered light, making it appear much fainter (and older) than it really is. The ease with which such a disk simultaneously explains all the puzzling aspects of LS-RCrA 1 - subluminosity, unusually prominent outflow signatures without high-velocity components or asymmetries, very broad Halpha, lack of NIR excess combined with accretion - makes its presence a strong possibility. Finally, the surface gravity and T-eff estimates, combined with the latest evolutionary tracks, indicates a mass of similar to 0.06 or 0.035 +/- 0.010 M-. (depending on the T-eff scale), i.e., at or below the substellar boundary. Our results, together with those of Fernandez & Comeron, imply that young brown dwarfs can not only harbor accretion disks but also generate jets/outflows analogous to those in higer mass classical T Tauri stars. This is further evidence of a common formation mechanism for stars and brown dwarfs.