Searching for Protoplanets around MWC 758 and MWC 480 in Br-$\gamma$ using Kernel Phase and SCExAO/CHARIS

TL;DR

This study employs kernel phase interferometry with SCExAO/CHARIS to search for actively accreting protoplanets around young stars, setting new limits on their presence at small orbital separations.

Contribution

It demonstrates the effectiveness of KPI combined with high-resolution spectroscopy to detect or constrain protoplanets at closer distances than previous methods.

Findings

Set limits on protoplanets between 4 and 16 au

Achieved contrast sensitivity to detect companions with 6-8 mag contrast

Demonstrated KPI with SCExAO/CHARIS as a promising technique for small-separation planet searches

Abstract

Discovering new actively-accreting protoplanets is crucial to answering open questions about planet formation. However, identifying such planets at orbital distances where they are expected to be abundant is extremely challenging, both due to the technical requirements and large distances to star-forming regions. Here we use the kernel phase interferometry (KPI) technique to search for companions around the $\sim$6 and $\sim$8 Myr old Herbig Ae stars MWC 758 and MWC 480. KPI is a data analysis technique which is sensitive to moderate asymmetries, arising from eg. a circumstellar disk or companions with contrasts of up to 6-8 mags, at separations down to and even below the classical Rayleigh diffraction limit ($\sim 1.2\lambda / D$). Using the high spectral resolution K-band mode of the SCExAO/CHARIS integral field spectrograph, we search for both excess Br-$\gamma$ line emission and continuum emission from companions around MWC 480 and MWC 758. We are able to set limits on the presence of rapidly accreting protoplanets and brown dwarfs between 4 and 16 au, well interior to those of previous studies. In Br-$\gamma$, we set limits on excess line emission equivalent to accretion rates ranging from $10^{-5} M_{j}^{2}.yr^{-1}$ to $10^{-6}M_{j}^{2}.yr^{-1}$. Our achievable contrasts demonstrate that KPI using SCExAO/CHARIS is a promising technique to search for giant accreting protoplanets at smaller separations compared to conventional imaging.