Sparse aperture masking interferometry survey of transitional discs^⋆

Search for substellar-mass companions and asymmetries in their parent discs

¹ University of Exeter, Astrophysics Group, School of Physics, Stocker Road, Exeter EX4 4QL, UK
e-mail: mwillson@astro.ex.ac.uk
² Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Ave, Ann Arbor, MI 48109, USA
³ Research School of Astronomy & Astrophysics, Mount Stromlo Observatory Cotter Road, Weston Creek, ACT 2611, Australia
⁴ Department of Physics, University of Cincinnati, Cincinnati, OH 45221, USA
⁵ Space Science Institute, 475 Walnut St., Suite 205, Boulder, CO 80301, USA
⁶ Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138, USA

Received: 4 May 2016
Accepted: 14 July 2016

Abstract

Context. Transitional discs are a class of circumstellar discs around young stars with extensive clearing of dusty material within their inner regions on 10s of au scales. One of the primary candidates for this kind of clearing is the formation of planet(s) within the disc that then accrete or clear their immediate area as they migrate through the disc.

Aims. The goal of this survey was to search for asymmetries in the brightness distribution around a selection of transitional disc targets. We then aimed to determine whether these asymmetries trace dynamically-induced structures in the disc or the gap-opening planets themselves.

Methods. Our sample included eight transitional discs. Using the Keck/NIRC2 instrument we utilised the Sparse Aperture Masking (SAM) interferometry technique to search for asymmetries indicative of ongoing planet formation. We searched for close-in companions using both model fitting and interferometric image reconstruction techniques. Using simulated data, we derived diagnostics that helped us to distinguish between point sources and extended asymmetric disc emission. In addition, we investigated the degeneracy between the contrast and separation that appear for marginally resolved companions.

Results. We found FP Tau to contain a previously unseen disc wall, and DM Tau, LkHα330, and TW Hya to contain an asymmetric signal indicative of point source-like emission. We placed upper limits on the contrast of a companion in RXJ 1842.9-3532 and V2246 Oph. We ruled the asymmetry signal in RXJ 1615.3-3255 and V2062 Oph to be false positives. In the cases where our data indicated a potential companion we computed estimates for the value of M_cṀ_c and found values in the range of 10⁻⁵−10⁻³ M²_J yr⁻¹.

Conclusions. We found significant asymmetries in four targets. Of these, three were consistent with companions. We resolved a previously unseen gap in the disc of FP Tau extending inwards from approximately 10 au.