ISPY – NaCo Imaging Survey for Planets around Young stars

Discovery of an M dwarf in the gap between HD 193571 and its debris ring^{⋆ ,⋆⋆}

¹ Max Planck Institute for Astronomy (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
e-mail: musso@mpia.de
² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³ Lakeside Labs, Lakeside Park B04b, 9020 Klagenfurt, Austria
⁴ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁵ Observatoire Astronomique de l’Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
⁶ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
⁷ European Southern Observatory (ESO), Karl-Schwazschild-Str. 2, 85748 Garching, Germany
⁸ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
e-mail: johan.olofsson@uv.cl
⁹ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
¹⁰ The University of Western Ontario, Dept. of Physics and Astronomy, 1151 Richmond Avenue, London, ON N6A 3K7, Canada

Received: 28 January 2019
Accepted: 20 May 2019

Abstract

Context. The interaction between low-mass companions and the debris discs they reside in is still not fully understood. A debris disc can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive collisions. In addition, the presence of a companion could further stir the disc (companion-stirring). Additional information is necessary to understand this fundamental step in the formation and evolution of a planetary system, and at the moment of writing only a handful of systems are known where a companion and a debris disc have both been detected and studied at the same time.

Aims. Our primary goal is to augment the sample of these systems and to understand the relative importance between self-stirring and companion-stirring.

Methods. In the course of the VLT/NaCo Imaging Survey for Planets around Young stars (ISPY), we observed HD 193571, an A0 debris disc hosting star at a distance of 68 pc with an age between ∼60 and 170 Myr. We obtained two sets of observations in L′ band and a third epoch in H band using the GPI instrument at Gemini-South.

Results. A companion was detected in all three epochs at a projected separation of ∼11 au (∼0.17″), and co-motion was confirmed through proper motion analysis. Given the inferred disc size of 120 au, the companion appears to reside within the gap between the host star and the disc. Comparison between the L′ and H band magnitude and evolutionary tracks suggests a mass of ∼0.31 − 0.39 M_⊙.

Conclusions. We discovered a previously unknown M-dwarf companion around HD 193571, making it the third low-mass stellar object discovered within a debris disc. A comparison to self- and companion-stirring models suggests that the companion is likely responsible for the stirring of the disc.