Evidence for planetary hypothesis for PTFO 8-8695b with five-year optical/infrared monitoring observations

TL;DR

This study presents five-year optical and infrared observations of PTFO 8-8695b, supporting the planetary hypothesis by revealing complex fading events consistent with a precessing planet and dust cloud, suggesting rapid planet formation.

Contribution

It proposes a novel scenario of a precessing planet with a dust cloud around a young star, supported by long-term observational evidence, indicating early planet formation within a few million years.

Findings

Fading events split into two components with different properties.

Wavelength dependence suggests dust cloud and precessing planet origins.

Supports planetary hypothesis despite previous negative evidence.

Abstract

PTFO 8-8695b (CVSO 30b) is a young planet candidate whose host star is a $\sim$ 2.6 Myr-old T-Tauri star, and there have been continuous discussions about the nature of this system. To unveil the mystery of this system, we observed PTFO8-8695 for around five years at optical and infrared bands simultaneously using Kanata telescope at the Higashi-Hiroshima Observatory. Through our observations, we found that the reported fading event split into two: deeper but phase-shifted "dip-A" and shallower but equiphase "dip-B". These dips disappeared at different epochs, and then, dip-B reappeared. Based on the observed wavelength dependence of dip depths, a dust clump and a precessing planet are likely origins of dip-A and B, respectively. Here we propose "a precessing planet associated with a dust cloud" scenario for this system. This scenario is consistent with the reported change in the depth of fading events, and even with the reported results, which were thought to be negative evidence to the planetary hypothesis, such as the past non-detection of the Rossiter-McLaughlin effect. If this scenario is correct, this is the third case of a young (<3 Myr) planet around a pre-main sequence star. This finding implies that a planet can be formed within a few Myr.