An Aligned Orbit for the Young Planet V1298 Tau b

Abstract

The alignment of planetary orbits with respect to the stellar rotation preserves information on their dynamical histories. Measuring this angle for young planets helps illuminate the mechanisms that create misaligned orbits for older planets, as different processes could operate over timescales ranging from a few megayears to a gigayear. We present spectroscopic transit observations of the young exoplanet V1298 Tau b; we update the age of V1298 Tau to be 28 ± 4 Myr based on Gaia EDR3 measurements. We observed a partial transit with Keck/HIRES and LBT/PEPSI, and detected the radial velocity anomaly due to the Rossiter–McLaughlin effect. V1298 Tau b has a prograde, well-aligned orbit, with λ = 4 − 10 + 7 deg. By combining the spectroscopically measured v sin i ⋆ and the photometrically measured rotation period of the host star we also find that the orbit is aligned in 3D, ψ = 8 − 7 + 4 deg. Finally, we combine our obliquity constraints with a previous measurement for the interior planet V1298 Tau c to constrain the mutual inclination between the two planets to be i mut = 0° ± 19°. This measurements adds to the growing number of well-aligned planets at young ages, hinting that misalignments may be generated over timescales of longer than tens of megayears. The number of measurements, however, is still small, and this population may not be representative of the older planets that have been observed to date. We also present the derivation of the relationship between i mut, λ, and i for the two planets.

A Tendency Toward Alignment in Single-star Warm-Jupiter Systems

“…Our choice to focus on only single-star systems excludes some highly misaligned warm Jupiters in systems with more than one star (e.g., K2-290 c, Hjorth et al 2021;Kepler-420 b, Santerne et al 2014;and WASP-8 b Queloz et al 2010;Bourrier et al 2017). However, other warm Jupiters in binary or multistar systems have instead been observed in or near alignment (e.g., V1298 Tau b, Gaidos et al 2022 andJohnson et al 2022;and WASP-11 b, Mancini et al 2015). The set of obliquity constraints in binary star systems so far appears to be more heterogeneous than in the sample of single-star systems, and further measurements are required to delineate the dominant trends in this population.…”

“…However, other warm Jupiters in binary or multi-star systems have instead been observed in or near alignment (e.g. V1298 Tau b (Gaidos et al 2022;Johnson et al 2022) and WASP-11 b (Mancini et al 2015)). The set of obliquity constraints in binary star systems so far appears to be more heterogeneous than in the sample of single-star systems, and further measurements are required to delineate the dominant trends in this population.…”

Overfitting Affects the Reliability of Radial Velocity Mass Estimates of the V1298 Tau Planets

“…All HIRES RVs used in this study are given in Table 1. Some of these RVs were previously published in Johnson et al (2022), and the processing is identical in that paper and this. The same stellar template, constructed from two stellar spectra taken on 2019 October 24 UT without the iodine in the light path, was used to derive RVs in both studies.…”

A sub-Neptune transiting the young field star HD 18599 at 40 pc

“…Obliquity measurements were conducted for a growing number of young planets (e.g. Johnson et al 2022;Wirth et al 2021;Gaidos et al 2020). These planets were found to have well-aligned orbits which indicates that misalignments may be generated over timescales of longer than tens of Myr.…”