http://arxiv.org/abs/2006.13243
We obtained spectra of the pre-main sequence star AU Microscopii during a transit of its Neptune-sized planet to investigate its orbit and atmosphere. We used the high-dispersion near-infrared spectrograph IRD on the Subaru telescope to detect the Doppler “shadow” from the planet and constrain the projected stellar obliquity; we find that the stellar spin and orbit are aligned ($\lambda=-4.7_{-6.4}^{+6.8}$ degrees), suggesting that the planet formed and possibly migrated within the protoplanetary disk. We use both the IRD data and spectra obtained with NIRSPEC on Keck-2 to search for absorption in the 1083\,nm line of metastable triplet He\,I by the planet’s atmosphere and place an upper limit for the equivalent width of 3.7 m\AA{} at 99\,\% confidence. From this limit, we constrain the mass loss rate of the planetary atmosphere to $<0.15-0.45$ \mearth\,Gyr$^{-1}$, comparable to the rate predicted by an energy-limited escape calculation and in the range required to test models of XUV-driven atmospheric escape from close-in young “Neptunes”.
T. Hirano, V. Krishnamurthy, E. Gaidos, et. al.
Thu, 25 Jun 20
44/78
Comments: 10 pages, 5 figures, submitted to AAS Journals
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