  We report the discovery of TWA 30B, a wide (~3400 AU), co-moving M dwarf
companion to the nearby (~42 pc) young star TWA 30. Companionship is confirmed
from their statistically consistent proper motions and radial velocities, as
well as a chance alignment probability of only 0.08%. Like TWA 30A, the
spectrum of TWA 30B shows signatures of an actively accreting disk (H I and
alkali line emission) and forbidden emission lines tracing outflowing material
([O I], [O II], [O III], [S II], and [N II]). We have also detected [C I]
emission in the optical data, marking the first such detection of this line in
a pre-main sequence star. Negligible radial velocity shifts in the emission
lines relative to the stellar frame of rest (Delta V < 30 km/s) indicate that
the outflows are viewed in the plane of the sky and that the corresponding
circumstellar disk is viewed edge-on. Indeed, TWA 30B appears to be heavily
obscured by its disk, given that it is 5 magnitudes fainter than TWA 30A at
K-band despite having a slightly earlier spectral type (M4 versus M5). The
near-infrared spectrum of TWA 30B also evinces an excess that varies on day
timescales, with colors that follow classical T Tauri tracks as opposed to
variable reddening (as is the case for TWA 30A). Multi-epoch data show this
excess to be well-modeled by a blackbody component with temperatures ranging
from 630 to 880 K and emitting areas that scale inversely with the temperature.
The variable excess may arise from disk structure such as a rim or a warp at
the inner disk edge located at a radial distance of ~3-5 R_sun. As the second
and third closest actively accreting and outflowing stars to the Sun (after TWA
3), TWA 30AB presents an ideal system for detailed study of star and planetary
formation processes at the low-mass end of the hydrogen-burning spectrum.

Solar and Stellar Astrophysics;Earth and Planetary Astrophysics;Astrophysics of Galaxies