Time-lapse Very Long Baseline Interferometry Imaging of the Close Active Binary HR 1099

Abstract

We report multiepoch astrometric very long baseline interferometry observations of the chromospherically active binary HR 1099 (V711 Tau, HD 22468) at six epochs over 63 days using the Very Long Baseline Array at 22.2 GHz. We determined hourly radio positions at each epoch with a positional uncertainty significantly smaller than the component separation. The aggregate radio positions at all epochs define an ellipse in the comoving reference frame with an inclination = $39.5_{-3.5}^{+3.6}°$ and longitude of ascending node $\Omega =212°\pm 22°$. The ellipse center is offset from the Third Gaia Celestial Reference Frame position by $\Delta \alpha =-0.81_{-0.25}^{+0.37}$, $\Delta \delta =0.45_{-0.23}^{+0.25}$ mas. All radio centroids are well displaced from the binary center of mass at all epochs, ruling out emission from the interbinary region. We examined the motion of the radio centroids within each epoch by comparing hourly positions over several hours. The measured speeds were not statistically significant for five of the six epochs, with $2\sigma$ upper limits in the range 200-1000 km/sec. However, for one flaring epoch, there was a $3\sigma$ detection $v_{\perp }=228\pm 85$ km/sec. This speed is comparable to the mean speed of observed coronal mass ejections on the Sun.

15 pages, 6 figures, ApJ accepted version

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• XRISM view of a stellar flare: High-resolution Fe K spectra of HR 1099, an RS CVn-type star