Searching for close-in planets around TWA 7 with SPIRou

TL;DR

This study used the SPIRou spectropolarimeter to analyze TWA 7's magnetic field and radial velocities, tentatively detecting a close-in planet and star-planet interaction signatures in a young star with a debris disk.

Contribution

First detailed magnetic field modeling of TWA 7 over two years and tentative detection of a close-in planet using near-infrared spectropolarimetry.

Findings

TWA 7 hosts a evolving poloidal magnetic field with increasing dipole strength.

A tentative 15.2-day planet signature suggests a possible 0.17 Mjup planet at 0.09 au.

Modulation of specific spectral lines indicates potential star-planet interactions.

Abstract

We outline in this paper observations of the young pre-main-sequence low-mass star TWA 7, hosting a debris disk and a distant planet. Using data collected with the near-infrared SPIRou spectropolarimeter / precision velocimeter at the Canada-France-Hawaii Telescope from early 2019 to mid 2021, we detected the magnetic field of TWA 7 from the circularly polarized Zeeman signatures and Zeeman broadening of atomic spectral lines, and the rotational modulation of its longitudinal component at the known stellar rotation period (of 5.012+-0.007 d). We then modeled the large-scale and small-scale magnetic properties of TWA 7 using Zeeman-Doppler imaging. We found that TWA 7 hosted a mainly poloidal field that significantly evolved from 2019 to 2021, the dipole component getting stronger (increasing from 0.5 kG in 2019 to 0.7 kG in 2021) and less inclined to the stellar rotation axis (from 22{\deg} in 2019 to 15{\deg} in 2021). We also analyzed the radial velocities of TWA 7 derived from the SPIRou data, and found a tentative planet signature at a period of 15.2 d (with aliases at 20.8 and 30.4 d), very close to the detection limit of our data and that would correspond to a 0.17 Mjup planet at a distance of 0.09 au if confirmed. We finally report modulation of the 1083 nm He I and 1282 nm Pa-beta lines of TWA 7 with a period of 6.6 d, different from the rotation period and potentially hinting at the presence of a close-in planet triggering star-planet interactions.