The Enigmatic Young Low-Mass Variable TWA 30
  TWA 30 is a remarkable young (7+/-3 Myr), low-mass (0.12+/-0.04 Msun),
late-type star (M5+/-1) residing 42+/-2 pc away from the sun in the TW Hydrae
Association. It shows strong outflow spectral signatures such as [S II], [O I],
[O II], [O III], and Mg I], while exhibiting weak Halpha emission (-6.8+/-1.2
Angstroms). Emission lines of [S II] and [O I] are common to T Tauri stars
still residing in their natal molecular clouds, while [O III] and Mg I]
emission lines are incredibly rare in this same population; in the case of TWA
30, these latter lines may arise from new outflow material colliding into older
outflow fronts. The weak Halpha emission and small radial velocity shifts of
line emission relative to the stellar frame of rest (generally <=10 km/s)
suggest that the disk is viewed close to edge-on and that the stellar axis may
be inclined to the disk, similar to the AA Tau system, based on its temporal
changes in emission/absorption line strengths/profiles and variable reddening
(A_V=1.5-9.0). The strong Li absorption (0.61+/-0.13 Angstroms) and common
kinematics with members of the TWA confirm its age and membership to the
association. Given the properties of this system such as its proximity, low
mass, remarkable outflow signatures, variability, and edge-on configuration,
this system is a unique case study at a critical time in disk evolution and
planet-building processes.
