NEID Reveals that The Young Warm Neptune TOI-2076 b Has a Low Obliquity

TOI-2076 b is a sub-Neptune-sized planet (R = 2.39 Eath radii) that transits a young (200Myr) bright (V = 9.2) K-dwarf hosting a system of three transiting planets. Using spectroscopic observations with the NEID spectrograph on the WIYN 3.5m Telescope we model the Rossiter-McLaughlin effect of TOI-2076 b, and derive a sky-projected obliquity of -3 (+/- 16) degrees. Using the size of the star (R = 0.775 Solar radii), and the stellar rotation period (Prot = 7.27 days), we estimate a true obliquity of 18 (+/-10) degrees, demonstrating that TOI-2076 b is on a well-aligned orbit. The RV observations exhibit a large inverted and chromatic RV slope, which we attribute to stellar activity. Simultaneous diffuser-assisted photometry from the 3.5m Telescope at Apache Point Observatory rules out flares during the transit. TOI-2076 b joins a growing sample of young planets and compact multi-planet systems with well-aligned orbits. The low obliquity of TOI-2076 b and the presence of transit timing variations in the system suggest the TOI-2076 system likely formed via convergent disk migration in an initially well-aligned disk.