Radio Astrometry of the Close Active Binary Hr 5110

Abstract

The close active binary HR 5110 was observed at six epochs over 26 days using a global VLBI array at 15.4 GHz. We used phase-referencing to determine the position of the radio centroid at each epoch with an uncertainty significantly smaller than the component separation. After correcting for proper motion and parallax, we find that the centroid locations of all six epochs have barycenter separations consistent with an emission source located on the KIV secondary, and not in an interaction region between the stars or on the F primary. We used a homogeneous power-law gyrosynchrotron emission model to reproduce the observed flux densities and fractional circular polarization. The resulting ranges of mean magnetic field strength and relativistic electron densities are of order 10 G and 10 5 cm −3 respectively in the source region.

A circular polarisation survey for radio stars with the Australian SKA Pathfinder

“…7) is an F2IV/K2IV binary known to demonstrate large X-ray flares (Graffagnino et al 1995), and is one of the most radio active RS CVn systems. VLBI observations at 15.4 GHz show radio emission originating from the K-type secondary (Abbuhl et al 2015), which is typically unpolarised at 1.5 GHz and consistently right handed at higher frequencies (White & Franciosini 1995). Non-eclipsing RS CVn systems such as this typically demonstrate a reversal in the polarisation sense between 1.4 to 5 GHz (Mutel et al 1987), which is consistent with our left handed detection at 887.5 MHz.…”

“…RS CVn and Algol binaries are known to possess strong magnetic fields generated by rapid, tidally-induced rotation periods. The radio emission associated with these stars is generally non-thermal with moderate circular polarisation, with both quiescent gyrosynchrotron emission (Jones et al 1994;Abbuhl et al 2015) HR 1099 / V711 Tau (see Fig. 6) is a K2:Vnk/K4 RS CVn binary with extensive study at radio frequencies, and is known to exhibit both strong radio flaring and periods of quiescent emission.…”

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

“…Whether enhanced radio emission (and other enhanced activity indicators) arises from an interbinary region in CABs is still an open question. While most radio astrometric studies have concluded that the emission originates at the subgiant (Lestrade et al 1993;Ransom et al 2012;Abbuhl et al 2015), several studies (e.g., Graffagnino et al 1995;Siarkowski et al 1996) argue that X-ray emission could arise in the interbinary region. Unfortunately, since there is only a modest correlation between X-ray and radio flares (at least for HR 1099; Osten et al 2004), inferring the location of the radio emission from X-ray data is problematic.…”

“…Nonthermal radio emission from active stars is a unique probe of the highest-energy (∼MeV) particle populations in the coronal magnetoactive plasma. The physical properties and extent of the emitting plasma can be inferred both by modeling the observed spectra (e.g., Falla et al 1994;Jones et al 1994;Trigilio et al 2001;Golay et al 2023) and by directly measuring the spatial distribution in the binary system using very long baseline interferometry (VLBI; e.g., Mutel et al 1985;Massi et al 1988;Lestrade et al 1993;Lebach et al 1999Lebach et al , 2012Ransom et al 2002Ransom et al , 2005Peterson et al 2010Peterson et al , 2011Abbuhl et al 2015;Climent et al 2020). The dominant radiation mechanism at centimeter wavelengths is often interpreted as gyrosynchrotron emission from mildly relativistic electrons filling a region comparable in size to the active star radius, with a modest (∼10-100 G) magnetic field (Dulk 1985;Hewitt & Melrose 1986;Mutel et al 1998;Güdel 2002).…”

Parameters of the Link between the Optical and Radio Frames from Gaia DR2 Data and VLBI Measurements

“…To construct the histogram in Fig. 2b, we used 49 stars that were selected under constraints on the error in the differences (see (1) and the table): σ ∆π < 0.25 mas. The parameters of the Gaussian found (an expectation value of −0.35 mas and a dispersion of 0.18 mas) are now in excellent agreement with the result (6).…”