Measurement of spin-orbit misalignment and nodal precession for the planet around pre-main-sequence star PTFO 8-8695 from gravity darkening
Article
Article Title | Measurement of spin-orbit misalignment and nodal precession for the planet around pre-main-sequence star PTFO 8-8695 from gravity darkening |
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ERA Journal ID | 1057 |
Article Category | Article |
Authors | Barnes, Jason W. (Author), van Eyken, Julian C. (Author), Jackson, Brian K. (Author), Ciardi, David R. (Author) and Fortney, Jonathan J. (Author) |
Journal Title | The Astrophysical Journal: an international review of astronomy and astronomical physics |
Journal Citation | 774 (1), pp. 53-67 |
Article Number | 53 |
Number of Pages | 15 |
Year | 2013 |
Publisher | IOP Publishing |
Place of Publication | United States |
ISSN | 0004-637X |
1538-4357 | |
Digital Object Identifier (DOI) | https://doi.org/10.1088/0004-637X/774/1/53 |
Web Address (URL) | http://iopscience.iop.org/article/10.1088/0004-637X/774/1/53 |
Abstract | PTFO 8-8695b represents the first transiting exoplanet candidate orbiting a pre-main-sequence star (van Eyken et al. 2012, ApJ, 755, 42). We find that the unusual lightcurve shapes of PTFO 8-8695 can be explained by transits of a planet across an oblate, gravity-darkened stellar disk. We develop a theoretical framework for understanding precession of a planetary orbit's ascending node for the case when the stellar rotational angular momentum and the planetary orbital angular momentum are comparable in magnitude. We then implement those ideas to simultaneously and self-consistently fit two separate lightcurves observed in 2009 December and 2010 December. Our two self-consistent fits yield Mp = 3.0 M Jup and Mp = 3.6 M Jup for assumed stellar masses of M * = 0.34 MȮ and M * = 0.44 MȮ respectively. The two fits have precession periods of 293 days and 581 days. These mass determinations (consistent with previous upper limits) along with the strength of the gravity-darkened precessing model together validate PTFO 8-8695b as just the second hot Jupiter known to orbit an M-dwarf. Our fits show a high degree of spin-orbit misalignment in the PTFO 8-8695 system: 69° ± 2°or 73.°1 ± 0.°5, in the two cases. The large misalignment is consistent with the hypothesis that planets become hot Jupiters with random orbital plane alignments early in a system's lifetime. We predict that as a result of the highly misaligned, precessing system, the transits should disappear for months at a time over the course of the system's precession period. The precessing, gravity-darkened model also predicts other observable effects: changing orbit inclination that could be detected by radial velocity observations, changing stellar inclination that would manifest as varying vsin i, changing projected spin-orbit alignment that could be seen by the Rossiter-McLaughlin effect, changing transit shapes over the course of the precession, and differing lightcurves as a function of wavelength. Our measured planet radii of 1.64 R Jup and 1.68 R Jup in each case are consistent with a young, hydrogen-dominated planet that results from a 'hot-start' formation mechanism. |
Keywords | eclipses; planetary systems; stars: individual (PTFO 8-8695); techniques: photometric; |
Contains Sensitive Content | Does not contain sensitive content |
ANZSRC Field of Research 2020 | 510109. Stellar astronomy and planetary systems |
Public Notes | For access to this article, please click on the URL link provided. |
Institution of Origin | University of Southern Queensland |
Byline Affiliations | University of Idaho, United States |
University of California, United States | |
Carnegie Institution of Washington, United States | |
National Aeronautics and Space Administration (NASA), United States |
https://research.usq.edu.au/item/q4310/measurement-of-spin-orbit-misalignment-and-nodal-precession-for-the-planet-around-pre-main-sequence-star-ptfo-8-8695-from-gravity-darkening
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