Differences in radio emission from similar M dwarfs in the binary system Ross 867-8

Abstract

Serendipitously, we have rediscovered radio emission from the binary system Ross 867 (M4.5V) and Ross 868 (M3.5V) while inspecting archival Giant Metrewave Radio Telescope (GMRT) observations. The binary system consists of two M-dwarf stars that share common characteristics such as spectral type, astrometric parameters, age and emission at infrared, optical and X-rays frequencies. The GMRT data at 610 MHz taken on July 2011 shows that the radio emission from Ross 867 is polarized and highly variable on hour time scales with a peak flux of 10.4 $\pm$ 0.7 mJy/beam. Additionally, after reviewing archival data from several observatories (VLA, GMRT, JVLA and LOFAR), we confirm that although both stars are likely coeval, only Ross 867 has been detected, while Ross 868 remains undetected at radio wavelengths. As they have a a large orbital separation, this binary stellar system provides a coeval laboratory to examine and constrain the stellar properties linked to radio activity in M dwarfs. We speculate that the observed difference in radio activity between the dwarfs could be due to vastly different magnetic field topologies or that Ross 867 has an intrinsically different dynamo.

Accepted for publication in A&A. Language edition included

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