Misaligned Protoplanetary Disks in a Young Binary System: Sufficient Misalignment to Drive Kozai Oscillations of Planetary Orbits
Abstract
Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our solar system. Planets' orbits may be eccentric or significantly inclined with respect to the host star's equator, and the population of giant planets orbiting very close to their host stars suggests significant orbital migration. There is currently no consensus on what causes the migration and produces inclined or eccentric orbits. Theoretical explanations often invoke interactions with a binary companion star on an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between planetary and binary star orbital planes, which until now have not been measured. Here we show that at least one of the protoplanetary disks in the young binary system HK Tau is significantly inclined to the binary orbital plane. Our ALMA observations of the molecular gas in the system show that both stars have protoplanetary disks in Keplerian rotation, the first time that disk rotation has been detected around both stars in a binary. The two disk planes are misaligned by roughly 60° from each other, so at least one of the disks is inclined 30° or more from the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits. The misalignment is present at the time of planet formation, and it is apparently a part of the binary formation process. Thus, binary companions may be important drivers of the diversity of orbits seen in extrasolar planets. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00150.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22335032J