Evidence for He i 10830 Å Absorption during the Transit of a Warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder

Joe P. Ninan, Gudmundur Stefansson, Suvrath Mahadevan, Chad Bender, Paul Robertson, Lawrence Ramsey, Ryan Terrien, Jason Wright, Scott A. Diddams, Shubham Kanodia, William Cochran, Michael Endl, Eric B. Ford, Connor Fredrick, Samuel Halverson, Fred Hearty, Jeff Jennings, Kyle Kaplan, Emily Lubar, Andrew J. MetcalfAndrew Monson, Colin Nitroy, Arpita Roy, Christian Schwab

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


Understanding the dynamics and kinematics of outflowing atmospheres of hot and warm exoplanets is crucial to understanding the origins and evolutionary history of the exoplanets near the evaporation desert. Recently, ground-based measurements of the meta-stable helium atom's resonant absorption at 10830 Å has become a powerful probe of the base environment which is driving the outflow of exoplanet atmospheres. We report evidence for the He i 10830 Å in absorption (equivalent width ∼0.012 ± 0.002 Å) in the exosphere of a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the Habitable Zone Planet Finder near-infrared spectrograph. This marks the first reported evidence for He i 10830 Å atmospheric absorption for a planet orbiting an M-dwarf. Our detected absorption is broad and its blueshifted wing extends to-36 km s-1, the largest reported in the literature to date. We modeled the state of helium atoms in the exosphere of GJ3470b based on assumptions on the UV and X-ray flux of GJ 3470, and found our measurement of flux-weighted column density of meta-stable state helium {equation presented}, derived from our transit observations, to be consistent with the model, within its uncertainties. The methodology developed here will be useful to study and constrain the atmospheric outflow models of other exoplanets like GJ 3470b, which are near the edge of the evaporation desert.

Original languageEnglish (US)
Article number97
JournalAstrophysical Journal
Issue number2
StatePublished - May 10 2020

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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