A recurrent 70-100 minute quasi-periodic pulsation in the intermediate-aged mid-M dwarf GJ 3512

TL;DR

The study reports the first sustained quasi-periodic pulsation in a late-M dwarf, GJ 3512, with a period of ~70–100 minutes persisting across multiple TESS sectors over ~2–3 years. Using two-minute cadence light curves and Morlet wavelet analysis, the authors establish a robust QPP signal with amplitudes of ~1–2 mmag, incompatible with stellar pulsations or star–planet interactions. The most plausible interpretation is coronal MHD oscillations or periodic magnetic reconnection in long-lived active regions, implying stable coronal loop dynamics in fully convective stars. This finding expands the landscape of stellar magnetic activity and motivates coordinated multiwavelength follow-up to elucidate the underlying physical mechanisms.

Abstract

We report the discovery of a {recurrent} quasi-periodic pulsation (QPP) in the late-M dwarf GJ 3512 (M5.5V) using multiple TESS datasets. A strong signal with a period of 70-100 minutes was detected in wavelet analyses of the two-minute cadence light curve from Sector 20. This signal was detected also in observations from Sectors 47 and 60. The QPP persisted for weeks in sector 20 and spanned nearly three years of TESS coverage. There was no significant damping between major flares. This behavior contrasts with that of previously reported stellar QPPs, which are confined to individual flares and decay on timescales of minutes to hours. The oscillation amplitude is at the milli-magnitude level. A pulsation origin is discarded since theoretical instability strips for 100-minute pulsations are restricted to pre-main sequence stars, while GJ 3512 is an intermediate age (2-8 Gyr) main-sequence dwarf. The persistence across independent TESS sectors discards an instrumental artifact origin and points to a likely coronal origin instead, such as oscillatory reconnection or thermal non-equilibrium cycles in large active regions. This represents the first detection of a likely sustained QPP with these characteristics in a late-type star, highlighting the need for further investigation into physical mechanisms behind such variability.

Figures (4)

• Figure 1: TESS PDCSAP light curves from Sectors 20, 47, and 60 for the star GJ 3512. The right axis refers to magnitudes in the TESS band (https://tess.mit.edu/public/tesstransients/pages/readme.html#flux-calibration), which is close to the Cousin $I_C$ filter. The orbital phase of GJ 3512b (assuming $\phi = 0$ at the time of periastron passage) is given in each panel.
• Figure 2: Top: Scalogram for the first $\sim13$ days of the TESS observation from December 24, 2019, to January 29, 2020. The dashed red lines in the scalogram indicate the frequency range selected for filtering. The red continuous line in the top panel is the filtered light curve. Bottom: Zoom of the figure in the left panel. Two days of observations are shown. Here, the QPP is clearly visible.
• Figure 3: Wavelet scalogram ($|S|$) per 99.9% confidence threshold ($|S|$/threshold), for GJ 3512. The dashed red lines in the scalogram indicate the frequency range selected for filtering, which correspond to periods 70--120 minutes. The black continuous lines correspond to the 99.9% confidence threshold.
• Figure 4: Wavelet scalogram ($|S|$) per 99.9% significance threshold ($|S|$/threshold), for TYC 3804-1138-1. The dashed red lines in the scalogram indicate the frequency range selected for filtering, which correspond to periods 70--120 minutes. The black continuous lines correspond to the 99.9% significance threshold.