Far-ultraviolet flares and variability of the young M dwarf AU Mic: a non-detection of planet c in transit at Lyman-alpha

Abstract

Atmospheric escape's potential to shape the exoplanet population motivates detailed observations of systems actively undergoing escape. AU Mic is a young and active M dwarf hosting two close-in transiting sub- to Neptune-sized planets. Atmospheric escape was previously detected on the inner planet b, with radially-blown neutral hydrogen producing ~30% blue-shifted absorption in Lyman-alpha. We obtained one HST/STIS transit of the outer planet c, to search for the planet's escaping atmosphere in transmission at Lyman-alpha and compare with AU Mic b. We detected 6 short-duration flares in Si IV and C IV, of which only one corresponded to a Lyman-alpha flare. We identified longer-duration stellar variability at the tens of percent level for lines less sensitive to stellar activity, including O I, C II and Lyman-alpha, which inhibits detection of an exosphere. We do not report absorption associated with an exosphere containing neutral hydrogen or any metals detectable in the far-ultraviolet, and discuss the implications of the non-detection. This work highlights the importance of 1) careful consideration of stellar variability in atmospheric escape observations, and 2) the dual-influence of photoionization and stellar wind when interpreting and modeling atmospheric escape.

22 pages, 12 figures, 5 tables

References in corpus (26)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Atmospheric Escape from Hot Jupiters
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• On the age of the $\beta$ Pictoris moving group
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• A planet within the debris disk around the pre-main-sequence star AU Microscopii
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• XUV-driven mass loss from extrasolar giant planets orbiting active stars
• The long egress of GJ~436b's giant exosphere
• Investigating the young AU~Mic system with SPIRou: large-scale stellar magnetic field and close-in planet mass
• The magnetic field and multiple planets of the young dwarf AU~Mic
• Limits on the Spin-Orbit Angle and Atmospheric Escape for the 22 Myr-old Planet AU Mic b
• DREAM I. Orbital architecture orrery
• p-winds: an open-source Python code to model planetary outflows and upper atmospheres
• Signatures of Strong Magnetization and Metal-Poor Atmosphere for a Neptune-Size Exoplanet
• Global 3D hydrodynamic modeling of in-transit Lyα absorption of GJ436b
• HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Star
• A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c
• One year of AU Mic with HARPS: I -- measuring the masses of the two transiting planets
• The dichotomy of atmospheric escape in AU Mic b
• H-alpha and Ca II Infrared Triplet Variations During a Transit of the 23 Myr Planet V1298 Tau c
• A Lyman-alpha transit left undetected: the environment and atmospheric behavior of K2-25b
• The Variable Detection of Atmospheric Escape around the young, Hot Neptune AU Mic b