arXiv subjects

A. V. Freckelton

Publications and source records attributed to A. V. Freckelton.

2 recordsLinked to original sources

arXiv2026

The Neptunian ridge planet WASP-156 b does not have a polar orbit

The population of short-period exo-Neptunes is thought to be shaped by an interplay between different dynamical mechanisms, such as orbital migration and tidal effects, and photoevaporation. We can gain insight into these processes by studying observables such as the stellar obliquity. Here we study the Rossiter-McLaughlin (RM) effect and measure the projected obliquity, $λ$, of the Neptunian ridge planet WASP-156 b. We analyse new ESPRESSO and MAROON-X spectroscopic transit observations, and new NGTS photometry simultaneous to the ESPRESSO data. Our analyses show an aligned orbit ($λ=-8\pm16^\circ$, based on the ESPRESSO observations), in contrast to a previous report of a highly misaligned orbit. We also find the star's projected rotational velocity to be $v \sin i_\mathrm{\star}\leq2$ km/s from spectral line modelling and $v \sin i_\mathrm{\star}=0.40\pm0.11$ km/s from the RM modelling. This is lower than the previously reported value of $\sim4$ km/s, which could partly explain the previously derived polar orbit. We also update the system's orbital parameters and rule out Jupiter-mass companions within 5 au using long-term radial velocity data. The planet's aligned and circular orbit ($e<0.16$ at $3σ$), and lack of nearby massive companions, are consistent with in situ formation or early disc-driven migration. Our findings move WASP-156 b from a tentative cluster of close-in Neptunes in polar orbits to the group of aligned Neptunes.

astro-ph.EP↗

arXiv2025

HD 28471: a near-resonant compact multiplanet system with a possible cold giant planet

We present radial velocity measurements of the star HD 28471, observed by HARPS at the ESO 3.6 m telescope over a baseline of $\sim19$ years. We have searched for planetary companions to HD 28471 using kima, a trans-dimensional diffusive nested sampling algorithm where the number of planetary signals is explored as a free parameter. We detect a compact system of three planets, with signals in the preferred solution corresponding to orbits of $P\sim3.16,~6.12,~\textrm{and }11.68$ d. These planets lie firmly in the super-Earth and sub-Neptune mass regime, with (minimum) masses of $3.7, 5.7, \textrm{and }4.9$ M$_{\oplus}$, respectively. A long-period ($\sim1500$ d) signal is also strongly detected. Assessment of activity indicator periodicities and RV correlations suggests that the three short-period signals are genuine planets, but casts doubt upon the nature of the long-period signal. The origin may be a short stellar magnetic cycle, though additional data are required to fully sample the periodicity without intervening offsets. HD 28471 b exhibits a more eccentric orbit than the other planets, which may be due to dynamical interaction, or a result of RV variation from an as-yet-undetected 4th planet interior to this compact system. The detected planets lie close to a resonant configuration, indicating that the system may retain features of its natal configuration, with convergent migration potentially responsible for evolving the planets onto such short-period orbits.

astro-ph.EP↗