Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): A close low-mass companion to ET Cha^⋆

¹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
e-mail: c.ginski@uva.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ Jet Propulsion Laboratory, California Institute of Technology, M/S 321-100, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁶ Department of Physics & Astronomy, University of Rochester, 500 Wilson Blvd., Rochester, NY 14627, USA
⁷ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁸ Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS, UMI 3386 and Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹² University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
¹³ Exzellenzcluster ORIGINS, Boltzmannstr. 2, 85748 Garching, Germany
¹⁴ INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹⁵ INAF-Osservatorio Astronomico di Padova, Vicolodell’Osservatorio 5, 35122 Padova, Italy
¹⁶ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
¹⁷ CRAL, UMR 5574, CNRS, Université de Lyon, École Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
¹⁸ School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
¹⁹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
²⁰ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
²¹ Institute for Astronomy, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
²² Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile

Received: 8 May 2020
Accepted: 9 July 2020

Abstract

Context. To understand the formation of planetary systems, it is important to understand the initial conditions of planet formation, that is, the young gas-rich planet forming disks. Spatially resolved, high-contrast observations are of particular interest since substructures in disks that are linked to planet formation can be detected. In addition, we have the opportunity to reveal close companions or even planets in formation that are embedded in the disk.

Aims. In this study, we present the first results of the Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS), an ESO/SPHERE large program that is aimed at studying disk evolution in scattered light, mainly focusing on a sample of low-mass stars (< 1 M_⊙) in nearby (∼200 pc) star-forming regions. In this particular study, we present observations of the ET Cha (RECX 15) system, a nearby “old” classical T Tauri star (5−8 Myr, ∼100 pc), which is still strongly accreting.

Methods. We used SPHERE/IRDIS in the H-band polarimetric imaging mode to obtain high spatial resolution and high-contrast images of the ET Cha system to search for scattered light from the circumstellar disk as well as thermal emission from close companions. We additionally employed VLT/NACO total intensity archival data of the system taken in 2003.

Results. Here, we report the discovery, using SPHERE/IRDIS, of a low-mass (sub)stellar companion to the η Cha cluster member ET Cha. We estimate the mass of this new companion based on photometry. Depending on the system age, it is either a 5 Myr, 50 M_Jup brown dwarf or an 8 Myr, 0.10 M_⊙ M-type, pre-main-sequence star. We explore possible orbital solutions and discuss the recent dynamic history of the system.

Conclusions. Independent of the precise companion mass, we find that the presence of the companion likely explains the small size of the disk around ET Cha. The small separation of the binary pair indicates that the disk around the primary component is likely clearing from the outside in, which explains the high accretion rate of the system.