2020/10/21 by Dirk van Dam, Matthew Kenworthy, Trevor David +21 · 1 voice
Physics and Astronomy · #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-3881/abc259
30 pages, 9 tables, 10 figures, accepted for publication in ApJ, GitHub repository for scripts and figures on https://github.com/dmvandam/v928tau
arxiv created 2020/10/21 · arxiv published 2020/10/21 · arxiv updated 2020/12/02
K2 observations of the weak-lined T Tauri binary V928 Tau A+B show the detection of a single, asymmetric eclipse which may be due to a previously unknown substellar companion eclipsing one component of the binary with an orbital period > 66 days. Over an interval of about 9 hours, one component of the binary dims by around 60%, returning to its normal brightness about 5 hours later. From modeling of the eclipse shape we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of 0.9923 ± 0.0005 R_*, with an inclination of 56.78 ± 0.03^∘, a tilt of 41.22 ± 0.05^∘, an impact parameter of -0.2506 ± 0.0002 R_* and an opacity of 1.00. The occulting disk must also move at a transverse velocity of 6.637 ± 0.002 R_* day-1, which depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 km s-1. A search in ground based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry which is used to further refine the orbit of the binary, presenting a new lower bound of 67 years, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18" (∼2250 au) from the lower mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A+B. We also present new high dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.