Untangling the Near-IR Spectral Features in the Protoplanetary Environment of KH 15D

TL;DR

This study uses Gemini/GNIRS spectra of KH 15D to analyze its complex environment, revealing details about its stars, jet, scattering dust, and potential planetary companion, with implications for planet formation zones.

Contribution

First detailed near-IR spectral analysis of KH 15D disentangling multiple components and suggesting possible presence of a young planet based on excess emission.

Findings

Confirmed star B as early-K subgiant

Detected variable He I emission indicating accretion

Identified excess IR emission consistent with a 10 M_J planet

Abstract

We report on Gemini/GNIRS observations of the binary T Tauri system V582 Mon (KH 15D) at three orbital phases. These spectra allow us to untangle five components of the system: the photosphere and magnetosphere of star B, the jet, scattering properties of the ring material, and excess near-IR radiation previously attributed to a possible self-luminous planet. We confirm an early-K subgiant classification for star B and show that the magnetospheric He I emission line is variable, possibly indicating increased mass accretion at certain times. As expected, the H$_2$ emission features associated with the inner part of the jet show no variation with orbital phase. We show that the reflectance spectrum for the scattered light has a distinctive blue slope and spectral features consistent with scattering and absorption by a mixture of water and methane ice grains in the 1-50 $\mu$m size range. This suggests that the methane frost line is closer than $\sim$5 AU in this system, requiring that the grains be shielded from direct radiation. After correcting for features from the scattered light, jet, magnetosphere, and photosphere, we confirm the presence of leftover near-IR light from an additional source, detectable near minimum brightness. A spectral emission feature matching the model spectrum of a 10 M$_{J}$, 1 Myr old planet is found in the excess flux, but other expected features from this model are not seen. Our observations, therefore, tentatively support the picture that a luminous planet is present within the system, although they cannot yet be considered definitive.