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

Abstract

TOI-2076 b is a sub-Neptune-sized planet ($R=2.39\pm 0.10R_{\oplus }$) that transits a young ($204\pm 50MYr$) bright ($V=9.2$) K-dwarf hosting a system of three transiting planets. Using spectroscopic observations with the NEID spectrograph on the WIYN 3.5 m Telescope, we model the Rossiter-McLaughlin effect of TOI-2076 b, and derive a sky-projected obliquity of $\hat{I}»=-3_{-15}^{+16\circ }$. Using the size of the star ($R=0.775\pm 0.015R_{\odot }$), and the stellar rotation period ($P_{\mathrm{rot}}=7.27\pm 0.23$ days), we estimate an obliquity of $\ddot{I}ˆ=18_{-9}^{+10\circ }$ ($\ddot{I}ˆ<34^{\circ }$ at 95\% confidence), demonstrating that TOI-2076 b is on a well-aligned orbit. Simultaneous diffuser-assisted photometry from the 3.5 m Telescope at Apache Point Observatory rules out flares during the transit. TOI-2076 b joins a small but growing sample of young planets in compact multi-planet systems with well-aligned orbits, and is the fourth planet with an age $\lesssim 300$ Myr in a multi-transiting system with an obliquity measurement. 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.

Published in ApJL, 11 pages, 4 figures, 3 tables