Measuring the Obliquities of the TRAPPIST-1 Planets with MAROON-X

TL;DR

This study uses the MAROON-X spectrograph to measure the obliquity of the TRAPPIST-1 system, providing insights into its formation, with a low obliquity and slow stellar rotation, demonstrating the instrument's high-precision capabilities.

Contribution

First measurement of TRAPPIST-1's obliquity using MAROON-X, showcasing its effectiveness for late M dwarf systems and advancing understanding of their system architectures.

Findings

TRAPPIST-1 has a low obliquity of approximately 0 degrees.

The star is a slow rotator with a velocity of 2.1 km/s.

No significant differential rotation or planetary Doppler signals detected.

Abstract

A star's obliquity with respect to its planetary system can provide us with insight into the system's formation and evolution, as well as hinting at the presence of additional objects in the system. However, M dwarfs, which are the most promising targets for atmospheric follow-up, are underrepresented in terms of obliquity characterization surveys due to the challenges associated with making precise measurements. In this paper, we use the extreme-precision radial velocity spectrograph MAROON-X to measure the obliquity of the late M dwarf TRAPPIST-1. With the Rossiter-McLaughlin effect, we measure a system obliquity of $-2^{+17}_{-19}$ degrees and a stellar rotational velocity of 2.1 $\pm$ 0.3 km s$^{-1}$. We were unable to detect stellar surface differential rotation, and we found that a model in which all planets share the same obliquity was favored by our current data. We were unable to make a detection of the signatures of the planets using Doppler tomography, which is likely a result of the both the slow rotation of the star and the low SNR of the data. Overall, TRAPPIST-1 appears to have a low obliquity, which could imply that the system has a low primordial obliquity. It also appears to be a slow rotator, which is consistent with past characterizations of the system and estimates of the star's rotation period. The MAROON-X data allow for a precise measurement of the stellar obliquity through the Rossiter-McLaughlin effect, highlighting the capabilities of MAROON-X and its ability to make high-precision RV measurements around late, dim stars.