Accretion and Outflow in the Substellar Domain: Magellan Spectroscopy of LS-RCrA 1

Abstract

We present low-, medium-, and high-resolution optical spectra of LS-RCrA~1. We confirm both pre-main sequence status and membership, through the detection of lithium, presence of narrow potassium 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, implying the presence of ongoing accretion. Our spectra also exhibit many forbidden emission lines indicative of mass outflow. Using new 2MASS near-infrared photometry, no significant NIR excess is found. Our optical veiling measurements yield a mass accretion rate of 10^-10 / 10^{-9} M(sun)/yr. Through comparison with the latest synthetic spectra, we infer Teff~2700+-100K. Theoretical tracks imply an age of ~20 Myr (as derived from luminosity) or ~8 Myr (Teff vs. gravity) for LS-RCrA~1. Therefore, LS-RCrA~1 indeed appears sub-luminous 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 posesses 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. Finally, the surface gravity and Teff estimates, combined with the latest evolutionary tracks, indicate a mass of ~0.07 or 0.035+-0.010 M(sun) (depending on the Teff scale).