An Aligned Orbit for the Young Planet V1298 Tau b

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+7−10 deg. By combining the spectroscopically measured vsini⋆ and the photometrically measured rotation period of the host star we also find that the orbit is aligned in 3D, ψ=8+4−7 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°.

Doppler tomographic data from PEPSI (top three panels) and HIRES (bottom). All plots show the time-series line profile residuals, i.e., each horizontal line shows the deviation of the line profile from the average line profile at that time. Time increases from bottom to top; units are such that ingress = 0 and egress = 1. The vertical dotted lines show v = 0, ±$v sin i_star, the horizontal dotted line the time of mid-transit, and the two small plus signs first and second contact. In the HIRES plot we also show two slanted dotted lines to guide the eye along the spot signatures, which are less obvious than in the PEPSI data.

Read more:  Johnson et al. 2022, AJ, 163, 247