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

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 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 ∼17 and ∼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.

Gap Opening and Inner Disk Structure in the Strongly Accreting Transition Disk of DM Tau

“…The tentative detection of a companion at ∼6 au using SAM observations of Willson et al (2016) was interpreted using the accreting circumplanetary disk models of Zhu (2015) as a planet and disk with  M M M 10 yr p J 5 2 1 = --, which for an average circumplanetary disk accretion rate sufficient to form a 1 M J planet in 1 Myr of 10 −9 M e yr −1 is equivalent to a planet mass of 10 M J . However, the detected emission may also be from the bright inner disk of DM Tau, as SAM can result in extended emission being confused for point sources (Currie et al 2019;Blakely et al 2022). Overall, the presence of giant planets within the 21 au dust gap of DM Tau is not ruled out at the sensitivity limits of observations to date.…”

“…Previous searches for planets toward DM Tau have not resulted in a robust detection. A Keck/NIRC2 sparse aperture masking (SAM) search identified a K-band point source at 6 au at 11.0 ± 0.3 mag with 4.27σ significance (Willson et al 2016); however, emission from the inner disk can be spuriously identified as planets in SAM observations (Currie et al 2019;Blakely et al 2022). Uyama et al (2017) observed DM Tau in the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey with Subaru, and did not detect any companions down to an H-band 5σ contrast limit at 0 25 of 14.76 mag.…”

ALMA Detection of Dust Trapping around Lagrangian Points in the LkCa 15 Disk

“…10 − 0. 13 (16-21 au; Kraus & Ireland 2012;Sallum et al 2015), which however have been later interpreted as inner disk emission (Thalmann et al 2016;Currie et al 2019;Blakely et al 2022). No CPDs associated to these candidates were detected in 7 mm continuum (Isella et al 2014).…”

“…With high-resolution (68 × 47 mas) Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3 mm, Facchini et al (2020) showed that the disk has three dust rings exterior to the cavity and suggested that a planet is forming around the bright middle ring. Three giant planet candidates have also been claimed through optical and IR imaging techniques at radial distances of 0 10−0 13 (16-21 au; Kraus & Ireland 2012;Sallum et al 2015), which, however, have been later interpreted as inner disk emission (Thalmann et al 2016;Currie et al 2019;Blakely et al 2022). No CPDs associated with these candidates were detected in 7 mm continuum (Isella et al 2014).…”

Deep Orbital Search for Additional Planets in the HR 8799 System

“…In any case, the use of nested sampling may allow one to reliably calculate the Bayes factor between these two models for such significant detections. For an example of using nested sampling and a Bayes factor to evaluate the presence of an exoplanet from aperture masking interferometry data, see Blakely et al (2022).…”