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Published October 10, 2015 | Published + Submitted
Journal Article Open

Tests of the planetary hypothesis for PTFO 8-8695b


The T Tauri star PTFO 8-8695 exhibits periodic fading events that have been interpreted as the transits of a giant planet on a precessing orbit. Here we present three tests of the planet hypothesis. First, we sought evidence for the secular changes in light-curve morphology that are predicted to be a consequence of orbital precession. We observed 28 fading events spread over several years and did not see the expected changes. Instead, we found that the fading events are not strictly periodic. Second, we attempted to detect the planet's radiation, based on infrared observations spanning the predicted times of occultations. We ruled out a signal of the expected amplitude. Third, we attempted to detect the Rossiter–McLaughlin effect by performing high-resolution spectroscopy throughout a fading event. No effect was seen at the expected level, ruling out most (but not all) possible orientations for the hypothetical planetary orbit. Our spectroscopy also revealed strong, time-variable, high-velocity Hα and Ca H & K emission features. All these observations cast doubt on the planetary hypothesis, and suggest instead that the fading events represent starspots, eclipses by circumstellar dust, or occultations of an accretion hotspot.

Additional Information

© 2015 The American Astronomical Society. Received 2015 July 24; accepted 2015 September 4; published 2015 October 7. We thank the referee, Jason W. Barnes, for his comments on the manuscript. We are grateful to Geoff Marcy for helping to arrange the Keck observations, to Aurélie Fumel for helping with the TRAPPIST observations, and to John Johnson and Jon Swift for attempting to perform photometric observations for this project. We thank Greg Herczeg, Hans Moritz Günther, and Nikku Madhusudhan for helpful discussions, and Julian van Eyken for providing the PTF data in a convenient format. Work by JNW was supported by the NASA Origins program (grant NNX11AG85G). M.G. and E.J. are Research Associates at the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, F.R.S-FNRS); L.D. received the support of the F.R.I.A. fund of the FNRS. TRAPPIST is a project funded by the F.R.S-FNRS under grant FRFC 2.5.594.09.F, with the participation of the Swiss National Science Foundation (SNF). B.T.M. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE1144469. The authors wish to extend special thanks to those of Hawai'ian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. Facilities: FLWO:1.2 m, Magellan:Baade, Euler1.2 m, Keck:I (HIRES), Spitzer.

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Published - Yu_2015p48.pdf

Submitted - 1509.02176v2.pdf


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