PTFO 8-8695: Two Stars, Two Signals, No Planet

TL;DR

This study investigates PTFO 8-8695, revealing it as a binary star system with complex variability, and suggests the observed dips are due to circumstellar material around young, rapidly rotating M dwarfs, not a planet.

Contribution

The paper provides new insights by analyzing TESS and Gaia data, demonstrating PTFO 8-8695 is a binary star with transient dips caused by circumstellar material, challenging the planetary hypothesis.

Findings

PTFO 8-8695 is a binary star system.

Observed dips are inconsistent with planetary transits.

Dips likely caused by circumstellar material around young M dwarfs.

Abstract

PTFO 8-8695 (CVSO 30) is a star in the 7-10 million year old Orion-OB1a cluster that shows brightness dips that resemble planetary transits. Although strong evidence against the planet hypothesis has been presented, the possibility remains debated in the literature. To obtain further clues, we inspected data from the NASA Transiting Exoplanet Survey Satellite (TESS) and the ESA Gaia mission. The Gaia data suggest that PTFO 8-8695 is a binary: the photometric data show it to be overluminous with respect to members of its kinematic group, and the astrometric data are inconsistent with a single star. The TESS light curve shows two different photometric periods. The variability is dominated by a sinusoidal signal with a period of 11.98 hr, presumably caused by stellar rotation. Also present is a 10.76 hr signal consisting of a not-quite sinusoid interrupted by hour-long dips, the type of signal previously interpreted as planetary transits. The phase of the dips is nearly 180$^\circ$ away from the phase of the originally reported dips. As noted previously, this makes them difficult to explain as planetary transits. Instead, we believe that PTFO 8-8695 is a pair of young and rapidly rotating M dwarfs, one of which shows the same "transient-dipper" behavior that has been seen in at least 5 other cases. The origin of these transient dips is still unknown but likely involves circumstellar material.