Examining the rotation of the planet-hosting M dwarf GJ 3942

TL;DR

This study re-analyzes multiple datasets to clarify the rotation period of the M dwarf GJ 3942, finding ambiguous evidence for a 16-day or 32-day rotation period due to observational limitations and harmonic signals.

Contribution

It provides a comprehensive multi-instrument analysis revealing the challenges in precisely determining stellar rotation periods from photometric and spectroscopic data.

Findings

No significant periodicities in SuperWASP data.

Hipparcos data is insufficient for definitive period detection.

TESS data suggests possible 16- or 32-day rotation period, but resolution limits prevent confirmation.

Abstract

Based on radial velocities, EXORAP photometry, and activity indicators, the HADES team reported a 16.3-day rotation period for the M dwarf GJ 3942. However, an RV--H$\alpha$ magnitude-squared coherence estimate has significant peaks at frequencies 1/16 cycles/day and 1/32 cycles/day. We re-analyze HADES data plus Hipparcos, SuperWASP, and TESS photometry to see whether the rotation period could be 32 days with 16-day harmonic. SuperWASP shows no significant periodicities, while the Hipparcos observing cadence is suboptimal for detecting 16- and 32-day periodicities. Although the average TESS periodogram has peaks at harmonics of 1/16 cycles/day, the harmonic sequence is not fully resolved according to the Rayleigh criterion. The TESS observations suggest a 1/16 cycles/day rotation frequency and a 1/32 cycles/day subharmonic, though resolution makes the TESS rotation detection ambiguous.