The Mysterious Affair of the H${}_2$ in AU Mic

Abstract

Molecular hydrogen is the most abundant molecule in the Galaxy and plays important roles for planets, their circumstellar environments, and many of their host stars. We have confirmed the presence of molecular hydrogen in the AU Mic system using high-resolution FUV spectra from HST-STIS during both quiescence and a flare. AU Mic is a $\sim$23 Myr M dwarf which hosts a debris disk and at least two planets. We estimate the temperature of the gas at 1000 to 2000 K, consistent with previous detections. Based on the radial velocities and widths of the H${}_2$ line profiles and the response of the H${}_2$ lines to a stellar flare, the H${}_2$ line emission is likely produced in the star, rather than in the disk or the planet. However, the temperature of this gas is significantly below the temperature of the photosphere ($\sim$3650 K) and the predicted temperature of its star spots ($\gtrsim$2650 K). We discuss the possibility of colder star spots or a cold layer in the photosphere of a pre-main sequence M dwarf.

accepted to ApJ, 20 pages, many figures

References in corpus (16)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• On the age of the $\beta$ Pictoris moving group
• A planet within the debris disk around the pre-main-sequence star AU Microscopii
• Placing the spotted T Tauri star LkCa 4 on an HR diagram
• New constraints on the planetary system around the young active star AU Mic. Two transiting warm Neptunes near mean-motion resonance
• All-sky Co-moving Recovery Of Nearby Young Members. (ACRONYM) II: The Beta Pictoris Moving Group
• The Origins of Fluorescent H2 Emission From T Tauri~Stars
• The High-Energy Radiation Environment Around a 10 Gyr M Dwarf: Habitable at Last?
• SpectRes: A Fast Spectral Resampling Tool in Python
• The Mass of Stirring Bodies in the AU Mic Debris Disk Inferred from Resolved Vertical Structure
• ACRONYM III: Radial Velocities for 336 Candidate Young Low-Mass Stars in the Solar Neighborhood, Including 78 Newly Confirmed Young Moving Group Members
• A Low-Mass H2 Component to the AU Microscopii Circumstellar Disk
• Rocky Planet Formation: Quick and Neat
• FUMES. II. Ly$\alpha$ Reconstructions of Young, Active M Dwarfs
• H${}_2$ Fluorescence in M Dwarf Systems: A Stellar Origin
• Detection of H${}_2$ in the TWA 7 System: A Probable Circumstellar Origin

Cited by in corpus (3)

• AU Microscopii in the FUV: Observations in Quiescence, During Flares, and Implications for AU Mic b and c
• The Variable Detection of Atmospheric Escape around the young, Hot Neptune AU Mic b
• High CO/H2 ratios supports an exocometary origin for a CO-rich debris disk