# # Program information file # PROGRAM_ID 2021A027 PROGRAM_TITLE The Helium Exosphere of a TESS-Discovered Warm Neptune PROGRAM_INV1 Ian Crossfield PROGRAM_INV2 Jonathan Brande PROGRAM_INV3 Alex Polanski PROGRAM_INV4 David Coria PROGRAM_INV5 Molly Kosiarek PROGRAM_SCICAT extra-solar planets PROGRAM_ABSTRACT_BEG Our understanding of outflowing exoplanet atmospheres [first observed during transit via the Lyman-alpha line] is being revolutionize by the metastable 10833 Angstrom helium line. Unlike Ly-alpha, the He line is unaffected by the ISM or the geocorona, and it can be observed using ground-based spectrographs since this wavelength region is mostly free of telluric emission and absorption, allowing the entire line shape [not just the wings] can be precisely measured. An emerging trend shows that the extent of the He exosphere depends on both the incident EUV irradiation and on the overall H/He mass fraction of the targeted planet: all observed planets with high H/He mass fractions and high EUV have detected He exospheres, while smaller and less-irradiated planets result in non-detections. We request 12~hrs on IRTF/iSHELL to measure the exosphere and mass loss from warm Neptune TOI~674b [a confirmed planet with a measured mass, orbiting an M dwarf] via transmission spectroscopy during three transits. PROGRAM_ABSTRACT_END