Research Note

The magnetically-active, low-mass, triple system WDS 19312+3607

¹ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain e-mail: caballero@astrax.fis.ucm.es
² Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, 28040 Madrid, Spain
³ Observatorio de Tacande, La Palma, Spain
⁴ Observatori Astronòmic del Garraf, Barcelona, Spain
⁵ Centro Astronómico Hispano Alemán de Calar Alto (CSIC-MPG), c/ Jesús Durbán Remón 2–2, 04004 Almería, Spain

Received: 12 March 2010
Accepted: 7 June 2010

Abstract

Aims. We investigated in detail the system WDS 19312+3607, whose primary is an active M4.5Ve star previously inferred to be young (τ ~ 300–500 Ma) based on its high X-ray luminosity.

Methods. We collected intermediate- and low-resolution optical spectra taken with 2 m-class telescopes, photometric data from the B to 8 μm bands, and data for eleven astrometric epochs with a time baseline of over 56 years for the two components in the system, G 125–15 and G 125–14.

Results. We derived the M4.5V spectral types of both stars, confirmed their common proper motion, estimated their heliocentric distance and projected physical separation, determined their Galactocentric space velocities, and deduced a most-probable age of older than 600 Ma. We discovered that the primary, G 125–15, is an inflated, double-lined, spectroscopic binary with a short period of photometric variability of 1.6 d, which we associated with orbital synchronisation. The observed X-ray and Hα emissions, photometric variability, and abnormal radius and effective temperature of G 125–15 AB are indicative of strong magnetic activity, possibly because of the rapid rotation. In addition, the estimated projected physical separation between G 125–15 AB and G 125–14 of about 1200 AU ensures that WDS 19312+3607 is one of the widest systems with intermediate M-type primaries.

Conclusions. G 125–15 AB is a nearby (d ≈ 26 pc), bright (J ≈ 9.6 mag), active spectroscopic binary with a single proper-motion companion of the same spectral type at a wide separation. They are thus ideal targets for specific follow-ups to investigate wide and close multiplicity or stellar expansion and surface cooling because of the lower convective efficiency.