HR 10: a main-sequence binary with circumstellar envelopes around both components

Discovery and analysis^★

¹ Departmento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: bmm@cab.inta-csic.es
² Departamento Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain
³ Observatorio Astrónomico de Calar Alto, CAHA, 04550 Gérgal, Almería, Spain
⁴ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁵ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Santa Cruz de Tenerife, Spain
⁶ Space sciences, Technologies, and Astrophysics Research (STAR) Institute, University of Liège, Belgium
⁷ Large Binocular Telescope Observatory, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁸ Steward Observatory, Department of Astronomy, University of Arizona, 993 N. Cherry Avenue, Tucson, AZ 85721, USA
⁹ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, 20014 Finland
¹⁰ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
¹¹ Department of Astronomy, University of California, Berkeley, CA, USA
¹² ESA–ESAC, Operations Department, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹³ Aurora Technology B.V. for ESA, ESA–ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁴ Observatorio Astronómico Nacional (OAN-IGN) – Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
¹⁵ INAF – Osservatorio Astronomico di Palermo Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received: 26 June 2019
Accepted: 13 July 2019

Abstract

Context. This paper is framed within a large project devoted to studying the presence of circumstellar material around main sequence stars, and looking for exocometary events. The work concentrates on HR 10 (A2 IV/V), known for its conspicuous variability in the circumstellar narrow absorption features of Ca II K and other lines, so far interpreted as β Pic-like phenomena, within the falling evaporating body scenario.

Aims. The main goal of this paper is to carry out a thorough study of HR 10 to find the origin of the observed variability, determine the nature of the star, its absolute parameters, and evolutionary status.

Methods. Interferometric near-infrared (NIR) observations, multi-epoch high-resolution optical spectra spanning a time baseline of more than 32 yr, and optical and NIR photometry, together with theoretical modelling, were used to tackle the above objectives.

Results. Our results reveal that HR 10 is a binary. The narrow circumstellar absorption features superimposed on the photospheric Ca II K lines – and lines of other species – can be decomposed into two or more components, the two deep ones tracing the radial velocity of the individual stars, which implies that their origin cannot be ascribed to transient exocometary events, their variability being fully explained by the binarity of the object. There does not appear to be transient events associated with potential exocomets. Each individual star holds its own circumstellar shell and there are no traces of a circumbinary envelope. Finally, the combined use of the interferometric and radial velocity data leads to a complete spectrometric and orbital solution for the binary, the main parameters being: an orbital period of 747.6 days, eccentricities of the orbits around the centre of mass 0.25 (HR 10-A), 0.21 (HR 10-B) and a mass ratio of q = M_B∕M_A = 0.72–0.84. The stars are slightly off the main sequence, the binary being ~530 Myr old.