Two Rings and a Marginally Resolved, 5 AU, Disk Around LkCa 15 Identified Via Near Infrared Sparse Aperture Masking Interferometry

TL;DR

This study uses high-resolution sparse aperture masking interferometry to analyze the LkCa 15 disk, revealing extended disk structures and inner disk characteristics, but no clear planetary companions.

Contribution

First imaging detection of an elliptical Gaussian inner disk in LkCa 15, with improved modeling of extended disk emission and contrast limits for potential planets.

Findings

Detected two asymmetric rings at ~17 au and ~45 au.

Recovered an elliptical Gaussian inner disk with ~5 au FWHM.

Placed a lower limit of 1000 on the contrast for potential companions.

Abstract

Sparse aperture masking interferometry (SAM) is a high resolution observing technique that allows for imaging at and beyond a telescope's diffraction limit. The technique is ideal for searching for stellar companions at small separations from their host star; however, previous analysis of SAM observations of young stars surrounded by dusty disks have had difficulties disentangling planet and extended disk emission. We analyse VLT/SPHERE-IRDIS SAM observations of the transition disk LkCa\,15, model the extended disk emission, probe for planets at small separations, and improve contrast limits for planets. We fit geometrical models directly to the interferometric observables and recover previously observed extended disk emission. We use dynamic nested sampling to estimate uncertainties on our model parameters and to calculate evidences to perform model comparison. We compare our extended disk emission models against point source models to robustly conclude that the system is dominated by extended emission within 50 au. We report detections of two previously observed asymmetric rings at $\sim$17 au and $\sim$45 au. The peak brightness location of each model ring is consistent with the previous observations. We also, for the first time with imaging, robustly recover an elliptical Gaussian inner disk, previously inferred via SED fitting. This inner disk has a FWHM of ~5 au and a similar inclination and orientation as the outer rings. Finally, we recover no clear evidence for candidate planets. By modelling the extended disk emission, we are able to place a lower limit on the near infrared companion contrast of at least 1000.