Systematic Multiepoch Monitoring of LkCa 15: Dynamic Dust Structures on Solar System Scales

Abstract

We present the highest-angular-resolution infrared monitoring of LkCa 15, a young solar analog hosting a transition disk. This system has been the subject of a number of direct-imaging studies from the millimeter through the optical, which have revealed multiple protoplanetary disk rings as well as three orbiting protoplanet candidates detected in infrared continuum emission (one of which was simultaneously seen at Hα). We use high-angular-resolution infrared imaging from 2014 to 2020 to systematically monitor these infrared signals and determine their physical origin. We find that three self-luminous protoplanets cannot explain the positional evolution of the infrared sources since the longer time baseline images lack the coherent orbital motion that would be expected for companions. However, the data still strongly prefer a time-variable morphology that cannot be reproduced by static scattered-light disk models. The multiepoch observations suggest the presence of complex and dynamic substructures moving through the forward-scattering side of the disk at ∼20 au or quickly varying shadowing by closer-in material. We explore whether the previous Hα detection of one candidate would be inconsistent with this scenario and in the process develop an analytical signal-to-noise penalty for Hα excesses detected near forward-scattered light. Under these new noise considerations, the Hα detection is not strongly inconsistent with forward scattering, making the dynamic LkCa 15 disk a natural explanation for both the infrared and Hα data.

Deep Paβ Imaging of the Candidate Accreting Protoplanet AB Aur b

“…Alternatively, if the companion's emission source is a compact protoplanetary disk feature seen in scattered starlight, one or both of the following may be possible. The localized dynamics in the disk material could have changed the effective light-scattering area of the disk substructure (e.g., LkCa 15 Thalmann et al 2016;Currie et al 2019;Sallum et al 2023). Alternatively, there could have been enhanced Paβ emission caused by accretion onto the central star, but the delay in light travel time to reach the companion may have prevented the observation of enhanced emission at the location of AB Aur b within the observing window.…”

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. IV. NIRISS Aperture Masking Interferometry Performance and Lessons Learned

“…By blocking the majority of the light, AMI enables the calculation of self-calibrating observables that provide sensitivity to asymmetries close to and even within the classical diffraction limit. This technique has been thoroughly demonstrated from the ground via observations of stellar and substellar companions (e.g., Ireland & Kraus 2008;Biller et al 2012;Hinkley et al 2015), circumstellar disks (e.g., Tuthill et al 2001;Sallum et al , 2023 and more.…”

Searching for Protoplanets around MWC 758 and MWC 480 in Br-γ Using Kernel Phase and SCExAO/CHARIS

“…For example λ/D in K band at 150 pc corresponds to ∼10 au for current 8 m class telescopes, twice the orbital separation of Jupiter. Finally, identifying protoplanets around a young star presents its own challenges; for example, extinction from the ample dust in the environment may limit sensitivity, and the complex structure of the circumstellar disk itself may make it difficult to unambiguously identify a planet (e.g., LkCa 15; Sallum et al 2023).…”