The wind and the magnetospheric accretion onto the T Tauri star S Coronae Australis at sub-au resolution

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: rgarcia@cp.dias.ie
² Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, D02 XF86 Dublin, Ireland
³ University Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: karine.perraut@univ-grenoble-alpes.fr
⁴ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁵ Universidade do Porto – Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
⁶ CENTRA, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
⁷ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁸ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85741 Garching bei München, Germany
⁹ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC University Paris 06, University Paris Diderot, Sorbonne Paris Cité, 75005 Paris, France
¹⁰ European Southern Observatory, Casilla 19001, Santiago 19, Chile
¹¹ Max-Planck-Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹² Department of Physics, Le Conte Hall, University of California, Berkeley, CA 94720, USA
¹³ Unidad Mixta Internacional Franco-Chilena de Astronomía (CNRS UMI 3386), Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, 1058 Santiago, Chile
¹⁴ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

Received: 27 April 2017
Accepted: 5 September 2017

Abstract

Aims. To investigate the inner regions of protoplanetary discs, we performed near-infrared interferometric observations of the classical T Tauri binary system S CrA.

Methods. We present the first VLTI-GRAVITY high spectral resolution (R ~ 4000) observations of a classical T Tauri binary, S CrA (composed of S CrA N and S CrA S and separated by ~1.̋4), combining the four 8m telescopes in dual-field mode.

Results. Our observations in the near-infrared K-band continuum reveal a disc around each binary component, with similar half-flux radii of about 0.1 au at d ~ 130 pc, inclinations (i = 28 ± 3° and i = 22 ± 6°), and position angles (PA = 0°± 6° and PA = –2°± 12°), suggesting that they formed from the fragmentation of a common disc. The S CrA N spectrum shows bright He i and Brγ line emission exhibiting inverse P Cygni profiles, typically associated with infalling gas. The continuum-compensated Brγ line visibilities of S CrA N show the presence of a compact Brγ emitting region whose radius is about ~0.06 au, which is twice as big as the truncation radius. This component is mostly tracing a wind. Moreover, a slight radius change between the blue- and red-shifted Brγ line components is marginally detected.

Conclusions. The presence of an inverse P Cygni profile in the He i and Brγ lines, along with the tentative detection of a slightly larger size of the blue-shifted Brγ line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N.