Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758

TL;DR

This paper reports the direct imaging and spectroscopic detection of a cold, young giant protoplanet in the MWC 758 system, providing evidence that such planets can drive spiral arms in protoplanetary disks.

Contribution

First direct detection of a protoplanet in a disk with spiral arms, revealing its properties and confirming its role in shaping the disk structure.

Findings

Detected a giant protoplanet at ~100 au in MWC 758

Protoplanet has a temperature around 500 K or higher with extinction

Supports the hypothesis that giant planets drive spiral arms in disks

Abstract

Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present new thermal infrared observations that are uniquely sensitive to redder (i.e., colder or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of ~100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with Teff = 500 +/- 100 K for a low level of extinction (AV<30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and also as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.