Dusty disk winds at the sublimation rim of the highly inclined, low mass young stellar object SU Aurigae

¹ School of Physics and Astronomy, Astrophysics Group, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK
e-mail: al612@exeter.ac.uk
² Department of Astronomy, University of Michigan, S University Ave, Ann Arbor, MI 48109, USA
³ Mount Wilson Observatory, The CHARA Array of Georgia State University, Mount Wilson, CA 91023, USA
⁴ Department of Physics and Astronomy, Georgia State University, Atlanta, GA, USA
⁵ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Steward Observatory, University of Arizona, Tucson, AZ 85721, USA

Received: 21 February 2019
Accepted: 28 May 2019

Abstract

Context. T Tauri stars are low-mass young stars whose disks provide the setting for planet formation. Despite this, their structure is poorly understood. We present new infrared interferometric observations of the SU Aurigae circumstellar environment that offer resolution that is three times higher and a better baseline position angle coverage than previous observations.

Aims. We aim to investigate the characteristics of the circumstellar material around SU Aur, constrain the disk geometry, composition and inner dust rim structure.

Methods. The CHARA array offers unique opportunities for long baseline observations, with baselines up to 331 m. Using the CLIMB three-telescope combiner in the K-band allows us to measure visibilities as well as closure phase. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrain the physical parameters of the disk. For the first time, a dusty disk wind is introduced to the radiative transfer code TORUS to model protoplanetary disks. Our implementation is motivated by theoretical models of dusty disk winds, where magnetic field lines drive dust above the disk plane close to the sublimation zone.

Results. Image reconstruction reveals an inclined disk with slight asymmetry along its minor-axis, likely due to inclination effects obscuring the inner disk rim through absorption of incident star light on the near-side and thermal re-emission and scattering of the far-side. Geometric modelling of a skewed ring finds the inner rim at 0.17 ± 0.02 au with an inclination of 50.9 ± 1.0° and minor axis position angle 60.8 ± 1.2°. Radiative transfer modelling shows a flared disk with an inner radius at 0.18 au which implies a grain size of 0.4 μm assuming astronomical silicates and a scale height of 15.0 at 100 au. Among the tested radiative transfer models, only the dusty disk wind successfully accounts for the K-band excess by introducing dust above the mid-plane.