Kavli Affiliate: David Charbonneau
| First 5 Authors: Samuel W. Yee, Samuel W. Yee, , ,
| Summary:
The “Neptunian ridge” is a recently identified peak in the frequency of
planets with sizes between that of Neptune and Saturn orbiting their host stars
with periods between 3 and 6 days (A. Castro-Gonz’alez et al. 2024). These
planets may have formed similarly to their larger, hot Jupiter counterparts in
the “three-day pile-up”, through a dynamically excited migration pathway. The
distribution of stellar obliquities in hot Neptune systems may therefore
provide a vital clue as to their origin. We report a new stellar obliquity
measurement for TOI-2374,b, a planet in the Neptunian ridge ($P = 4.31$ days,
$R_p = 7.5 R_oplus$). We observed a spectroscopic transit of TOI-2374 b with
the Keck Planet Finder, detecting the Rossiter-McLaughlin (RM) anomaly with an
amplitude of 3 m/s, and measured a sky-projected obliquity of $lambda =
81^circ^+23^circ_-22^circ$, indicating an orbit significantly
misaligned with the spin axis of its host star. A reloaded RM analysis of the
cross-correlation functions confirms this misalignment, measuring $lambda =
65^circ^+32^circ_-24^circ$. Additionally, we measured a stellar
rotation period of $P_mathrmrot = 26.4^+0.9_-0.8$ days with photometry
from the Tierras observatory, allowing us to deduce the three-dimensional
stellar obliquity of $psi = 85.9^circ^+8.6^circ_-9.2^circ$. TOI-2374
b joins a growing number of hot Neptunes on polar orbits. The high frequency of
misaligned orbits for Neptunian ridge and desert planets, compared with their
longer period counterparts, is reminiscent of patterns seen for the giant
planets and may suggest a similar formation mechanism.
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