NEID Rossiter-McLaughlin Measurement of TOI-1268b: A Young Warm Saturn Aligned with Its Cool Host Star

Abstract

Close-in gas giants present a surprising range of stellar obliquity, the angle between a planet's orbital axis and its host star's spin axis. It is unclear whether the obliquities reflect the planets' dynamical history (e.g., aligned for in situ formation or disk migration versus misaligned for high-eccentricity tidal migration) or whether other mechanisms (e.g., primordial misalignment or planet-star interactions) are more important in sculpting the obliquity distribution. Here we present the stellar obliquity measurement of TOI-1268 (TIC-142394656, $V_{\mathrm{mag}}\sim 10.9$), a young K-type dwarf hosting an 8.2-day period, Saturn-sized planet. TOI-1268's lithium abundance and rotation period suggest the system age between the ages of Pleiades cluster ($\sim 120$ Myr) and Praesepe cluster ($\sim 670$ Myr). Using the newly commissioned NEID spectrograph, we constrain the stellar obliquity of TOI-1268 via the Rossiter-McLaughlin (RM) effect from both radial velocity (RV) and Doppler Tomography (DT) signals. The 3$\sigma$ upper bounds of the projected stellar obliquity $|\lambda |$ from both models are below 60${}^{\circ }$. The large host star separation ($a/R_{\star }\sim 17$), combined with the system's young age, makes it unlikely that the planet has realigned its host star. The stellar obliquity measurement of TOI-1268 probes the architecture of a young gas giant beyond the reach of tidal realignment ($a/R_{\star }\gtrsim 10$) and reveals an aligned or slightly misaligned system.

arXiv comment14 pages, 6 figures, 1 table, accepted for publication in ApJL; see independent work by Subjak et al. for RV follow-up of TOI-1268

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