A multiwavelength study of the M dwarf binary YY Geminorum

BUTLER C. J., ERKAN N., BUDDING E., DOYLE J. G., Foing B., Bromage G. E., ...More

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.446, no.4, pp.4205-4219, 2015 (SCI-Expanded) identifier identifier


We review the results of the 1988 multiwavelength campaign on the late-type eclipsing binary YY Geminorum. Observations include: broad-band optical and near-infrared photometry, simultaneous optical and ultraviolet (IUE) spectroscopy, X-ray (Ginga) and radio (VLA) data. From models fitted to the optical light curves, fundamental physical parameters have been determined together with evidence for transient maculations (spots) located near quadrature longitudes and intermediate latitudes. Eclipses were observed at optical, ultraviolet and radio wavelengths. Significant drops in 6 cm radio emission near the phases of both primary and secondary eclipse indicate relatively compact radio emitting volumes that may lie between the binary components. IUE observations during secondary eclipse are indicative of a uniform chromosphere saturated with Mg II emission and an extended volume of Ly alpha emission. Profile fitting of high-dispersion Ha spectra confirms the chromospheric saturation and indicates significant Ha opacity to heights of a few per cent of the photospheric radius. There is evidence for an enhanced Ha emission region visible near phase 0.25-0.35 which may be associated with a large spot on the primary and with two small optical flares which were also observed at other wavelengths: one in microwave radiation and the other in X-rays. For both flares, L-X/L-opt is consistent with energy release in closed magnetic structures.