Journal
ASTRONOMICAL JOURNAL
Volume 140, Issue 5, Pages 1486-1499Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/140/5/1486
Keywords
brown dwarfs; circumstellar matter; open clusters and associations: individual (TW Hydrae Association); stars: evolution; stars: individual (2MASS J11321822-3018316, TWA 30A, TWA 30B), stars: low-mass; stars: pre-main sequence
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Funding
- Canadian Space Agency
- National Aeronautics and Space Administration
- National Science Foundation
- Science and Technology Facilities Council [ST/H00307X/1] Funding Source: researchfish
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0909463] Funding Source: National Science Foundation
- STFC [ST/H00307X/1] Funding Source: UKRI
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We report the discovery of TWA 30B, a wide (similar to 3400 AU), co-moving M dwarf companion to the nearby (similar to 42 pc) young star TWA 30. Companionship is confirmed from their statistically consistent proper motions and radial velocities (RVs), 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 (Hi 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 RV shifts in the emission lines relative to the stellar frame of rest (Delta V less than or similar to 30 km s(-1)) 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 mag 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 black body 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 similar to 3-5 R-circle dot. As the second and third closest actively accreting and outflowing stars to the Sun (after TWA 3), TWA 30AB presents an ideal system for a detailed study of star and planetary formation processes at the low-mass end of the hydrogen-burning spectrum.
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