H$\alpha$ Emission From Active Equal-mass, Wide M Dwarf Binaries

TL;DR

This study investigates chromospheric activity via Hα emission in equal-mass wide M dwarf binaries, revealing variability and activity patterns that challenge simple age-activity relations.

Contribution

It provides the first detailed spectroscopic analysis of Hα activity and variability in a sample of coeval, equal-mass wide M dwarf binaries, highlighting the complexity of stellar activity.

Findings

Most binary components show low or no Hα activity.

Active components often exhibit higher activity levels than their companions.

Hα variability is common and independent of spectral type or activity strength.

Abstract

We identify a sample of near-equal mass wide binary M dwarf systems from the SLoWPoKES catalog of common proper-motion binaries and obtain follow-up observations of their chromospheric activity as measured by the H$\alpha$ emission line. We present optical spectra for both components of 48 candidate M dwarf binaries, confirming their mid-M spectral types. Of those 48 coeval pairs, we find eight with H$\alpha$ emission from both components, three with weak emission in one component and no emission in the other, and 37 with two inactive components. We find that of the eleven pairs with at least one active component, only three follow the net trend of decreasing activity strength $L_{\rm H\alpha}/L_{\rm bol}$ with later spectral type. The difference in quiescent activity strength between the A and B components is larger than what would be expected based on the small differences in color (mass). For five binaries with two active components, we present 47 hours of time-resolved spectroscopy, observed on the ARC 3.5-m over twelve different nights. For four of the five pairs, the slightly redder (B) component exhibits a higher level of H$\alpha$ emission during the majority of the observations and the redder objects are the only components to flare. The full range of H$\alpha$ emission observed on these variable mid-M dwarfs is comparable to the scatter in H$\alpha$ emission found in single-epoch surveys of mid-M dwarfs, indicating that variability could be a major factor in the spread of observed activity strengths. We also find that variability is independent of both activity strength and spectral type.