Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No evidence for Temporal Variation of the Spin-Orbit Angle

TL;DR

This study refines the orbital parameters of the XO-3 exoplanet system, confirms its unusual configuration, and finds no evidence for changes in the spin-orbit angle over time, suggesting previous discrepancies were due to noise.

Contribution

The paper provides updated measurements and models of the XO-3 system, clarifying its orbital and spin characteristics and addressing previous conflicting results on the spin-orbit angle.

Findings

Confirmed the eccentric orbit of XO-3b.

Found no significant temporal variation in the spin-orbit angle.

Resolved previous measurement discrepancies likely caused by systematic noise.

Abstract

We present 12 new transit light curves and 16 new out-of-transit radial velocity measurements for the XO-3 system. By modelling our newly collected measurements together with archival photometric and Doppler velocimetric data, we confirmed the unusual configuration of the XO-3 system, which contains a massive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric ($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \pm 0.00145\,$day) orbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\odot}$). Furthermore, we find no strong evidence for a temporal change of either $V\sin i_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit profile (and thus orbital angular momentum vector of XO-3b). We conclude that the discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\circ} \pm 15.0^{\circ}$ (Hebrard et al. 2008); $37.3^{\circ} \pm 3.7^{\circ}$ (Winn et al. 2009); $37.3^{\circ} \pm 3.0^{\circ}$ (Hirano et al. 2011)) may have stemmed from systematic noise sources.