An Asymmetric Eclipse Seen toward the Pre-main-sequence Binary System V928 Tau

December 2020 • 2020AJ....160..285V

Authors • van Dam, Dirk M. • Kenworthy, Matthew A. • David, Trevor J. • Mamajek, Eric E. • Hillenbrand, Lynne A. • Cody, Ann Marie • Howard, Andrew W. • Isaacson, Howard • Ciardi, David R. • Rebull, Luisa M. • Stauffer, John R. • Patel, Rahul • Cameron + WASP Collaborators, Andrew Collier • Rodriguez, Joseph E. • Pojmański, Grzegorz • Gonzales, Erica J. • Schlieder, Joshua E. • Hambsch, Franz-Josef • Dufoer, Sjoerd • Vanmunster, Tonny • Dubois, Franky • Vanaverbeke, Siegfried • Logie, Ludwig • Rau, Steve

Abstract • K2 observations of the weak-lined T Tauri binary V928 Tau A and 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 hr, one component of the binary dims by around 60%, returning to its normal brightness about 5 hr 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 that is used to further refine the orbit of the binary, presenting a new lower bound of 67 yr, 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 and B. We also present new high-dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020AJ....160..285V
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/abc259/pdf
• PDF https://stacks.iop.org/1538-3881/160/285/pdf
• PREPRINT http://arxiv.org/abs/2010.11199
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2020AJ....160..285V
• DATA https://irsa.ipac.caltech.edu/bibdata/2020/V/2020AJ....160..285V.html
• ELECTR https://doi.org/10.3847%2F1538-3881%2Fabc259