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




  • 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., Pojmanski, Grzegorz, Gonzales, Erica J., Schlieder, Joshua E., Hambsch, Franz-Josef, Dufoer, Sjoerd, Vanmunster, Tonny, Dubois, Franky, Vanaverbeke, Siegfried, Logie, Ludwig and Rau, Steve


  • 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.

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  • 2020



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