An In-Depth Look at TOI-3884b: a Super-Neptune Transiting a M4 Dwarf with Persistent Star Spot Crossings

TL;DR

This paper provides a detailed analysis of the TOI-3884 system, revealing a super-Neptune orbiting an active M4 dwarf with star spot crossings, misalignment, and evolving spot features, offering insights into planetary and stellar activity.

Contribution

It is the first detailed characterization of TOI-3884b, including mass, radius, star spot crossing analysis, and orbital misalignment on an active M dwarf.

Findings

TOI-3884b has a mass of 32.6 Earth masses and a radius of 6.4 Earth radii.

The planet exhibits a misaligned orbit with a 75-degree angle.

Persistent star spot crossings indicate active stellar surface features.

Abstract

We perform an in-depth analysis of the recently validated TOI-3884 system, an M4 dwarf star with a transiting super-Neptune. Using high precision light curves obtained with the 3.5 m Apache Point Observatory and radial velocity observations with the Habitable-zone Planet Finder (HPF), we derive a planetary mass of 32.6 +7.3 -7.4 Earth Masses and radius of 6.4 +/- 0.2 Earth Radii. We detect a distinct star spot crossing event occurring just after ingress and spanning half the transit for every transit. We determine this spot feature to be wavelength-dependent with the amplitude and duration evolving slightly over time. Best-fit star spot models show that TOI-3884b possesses a misaligned ($\lambda$ = 75 +\- 10 degrees) orbit which crosses a giant pole-spot. This system presents a rare opportunity for studies into the nature of both a misaligned super-Neptune and spot evolution on an active mid-M dwarf.