Calculations of periodicity from H{\alpha} profiles of Proxima Centauri

TL;DR

This study uses high-resolution spectra and photometry over 13 years to determine Proxima Centauri's rotation period, confirming an 82.6-day cycle and highlighting the potential of spectroscopic Hα measurements for stellar rotation analysis.

Contribution

Introduces a new symmetry-based Peak Ratio method for period detection and compares spectroscopic and photometric approaches, emphasizing the need for 3D chromospheric models.

Findings

Confirmed Proxima Centauri's rotation period as 82.6 days

Spectroscopic Hα can recover rotation periods but photometry is more reliable

3D models are necessary to reproduce observed line shape variations

Abstract

We investigate retrieval of the stellar rotation signal for Proxima Centauri. We make use of high-resolution spectra taken with uves and harps of Proxima Centauri over a 13-year period as well as photometric observations of Proxima Centauri from asas and hst. We measure the H{\alpha} equivalent width and H{\alpha} index, skewness and kurtosis and introduce a method that investigates the symmetry of the line, the Peak Ratio, which appears to return better results than the other measurements. Our investigations return a most significant period of 82.6 $\pm$ 0.1 days, confirming earlier photometric results and ruling out a more recent result of 116.6 days which we conclude to be an alias induced by the specific harps observation times. We conclude that whilst spectroscopic H{\alpha} measurements can be used for period recovery, in the case of Proxima Centauri the available photometric measurements are more reliable. We make 2D models of Proxima Centauri to generate simulated H{\alpha}, finding that reasonable distributions of plage and chromospheric features are able to reproduce the equivalent width variations in observed data and recover the rotation period, including after the addition of simulated noise and flares. However the 2D models used fail to generate the observed variety of line shapes measured by the peak ratio. We conclude that only 3D models which incorporate vertical motions in the chromosphere can achieve this.