Two Rings and a Marginally Resolved, 5 au Disk around LkCa 15 Identified via Near-infrared Sparse Aperture Masking Interferometry

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 analyses of SAM observations of young stars surrounded by dusty disks have had difficulties disentangling planet and extended disk emission. We analyze 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 similar to 17 and similar to 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 an FWHM of 5 au and a similar inclination and orientation to the outer rings. Finally, we recover no clear evidence for candidate planets. By modeling the extended disk emission, we are able to place a lower limit on the near-infrared companion contrast of at least 1000.

Automated summary

Sparse aperture masking interferometry (SAM) is a high-resolution observing technique that allows for imaging at and beyond a telescope's diffraction limit. This study analyzed VLT/SPHERE-IRDIS SAM observations of the transition disk LkCa 15, modeled the extended disk emission, and improved contrast limits for planets. The study detected two previously observed asymmetric rings and for the first time, robustly recovered an elliptical Gaussian inner disk.