Radio detection of the young binary HD 160934

Abstract

Context. Precise determination of dynamical masses of pre-main-sequence (PMS) stars is essential to calibrate stellar evolution models that are widely used to derive theoretical masses of young low-mass objects. Binary stars in young, nearby loose associations are particularly good candidates for this calibration since all members share a common age. Interestingly, some of these young binaries present a persistent and compact radio emission, which makes them excellent targets for astrometric VLBI studies. Aims. We aim to monitor the orbital motion of the binary system HD 160934, a member of the AB Doradus moving group. Methods. We observed HD 160934 with the Very Large Array and the European VLBI Network at 8.4 and 5 GHz, respectively. The orbital information derived from these observations was analyzed along with previously reported orbital measurements. Results. We show that the two components of the binary, HD 160934 A and HD 160934 c, display compact radio emission at VLBI scales, providing precise information on the relative orbit. Revised orbital elements were estimated. Conclusions. Future VLBI monitoring of this pair should determine precise model-independent mass estimates for the A and c components, which will serve as calibration tests for PMS evolutionary models.

Radio Emission from Binary Stars in the AB Doradus Moving Group

“…Comparisons in H-R diagrams favor an age between 50 Myr and 100 Myr, although the Montalbán & D'Antona (2006) models predicts ages older than 100 Myr. AB Dor B is one of the systems in the AB Dor-MG whose two components are radio emitters, contributing to the evidence that many young, wide binaries are strong radio emitters (like AB Dor A and HD 160934; see Azulay et al 2014). This radio/binarity correlation may be the radio counterpart of the better established relationship between wide binaries and X-ray activity, which can be explained under the assumption that the present wide binaries were originated by dynamical interaction of hierarchical triple systems.…”

“…Introduction AB Doradus moving group (AB Dor-MG) is the most suitable to carry out the study, as it is the closest one, the estimated age is relatively accurate, and it contains stars with significant emission at radio wavelengths (Guirado et al 2006(Guirado et al , 2011Jason et al 2007;Azulay et al 2014Azulay et al , 2015. This last feature is essential because it allows the use of radio interferometry techniques to obtain astrometric information.…”

“…5.3.1, both AB Dor Ba and AB Dor Bb are strong, compact radio emitters, which contributes to the emerging perception that many radio stars reside in double or multiple systems (Melis et al 2013;Azulay et al 2014). Considering the radio/X-ray activity correlation (Güdel et al 1993), this perception finds support in other, better reported statistics which relates X-ray activity and binarity, namely, that about 79% of the X-ray emitters are in binary systems (Makarov & Eggleton 2009).…”

“…Either more accurate observations or revised models are needed. As reported in Azulay et al (2014), a VLA/VLBI program to detect binary stars with substantial emission at radio wavelengths is underway. This program focuses on stars members of the AB Doradus moving group, AB Dor-MG , which includes the already studied pairs AB Dor A/C (Guirado et al 2006) and HD 160934 A/c (Azulay et al 2014).…”

“…As reported in Azulay et al (2014), a VLA/VLBI program to detect binary stars with substantial emission at radio wavelengths is underway. This program focuses on stars members of the AB Doradus moving group, AB Dor-MG , which includes the already studied pairs AB Dor A/C (Guirado et al 2006) and HD 160934 A/c (Azulay et al 2014). Located at a distance of ∼15 pc (Guirado et al 2006), the stellar system AB Dor has a pair of binaries, AB Dor A and AB Dor B, separated by ∼9 ′′ .…”