Unveiling the β Pictoris system, coupling high contrast imaging, interferometric, and radial velocity data

Abstract

Context. The nearby and young β Pictoris system hosts a well resolved disk, a directly imaged massive giant planet orbiting at ≃9 au, as well as an inner planet orbiting at ≃2.7 au, which was recently detected through radial velocity (RV). As such, it offers several unique opportunities for detailed studies of planetary system formation and early evolution. Aims. We aim to further constrain the orbital and physical properties of β Pictoris b and c using a combination of high contrast imaging, long base-line interferometry, and RV data. We also predict the closest approaches or the transit times of both planets, and we constrain the presence of additional planets in the system. Methods. We obtained six additional epochs of SPHERE data, six additional epochs of GRAVITY data, and five additional epochs of RV data. We combined these various types of data in a single Markov-chain Monte Carlo analysis to constrain the orbital parameters and masses of the two planets simultaneously. The analysis takes into account the gravitational influence of both planets on the star and hence their relative astrometry. Secondly, we used the RV and high contrast imaging data to derive the probabilities of presence of additional planets throughout the disk, and we tested the impact of absolute astrometry. Results. The orbital properties of both planets are constrained with a semi-major axis of 9.8 ± 0.4 au and 2.7 ± 0.02 au for b and c, respectively, and eccentricities of 0.09 ± 0.1 and 0.27 ± 0.07, assuming the HIPPARCOS distance. We note that despite these low fitting error bars, the eccentricity of β Pictoris c might still be over-estimated. If no prior is provided on the mass of β Pictoris b, we obtain a very low value that is inconsistent with what is derived from brightness-mass models. When we set an evolutionary model motivated prior to the mass of β Pictoris b, we find a solution in the 10–11 MJup range. Conversely, β Pictoris c’s mass is well constrained, at 7.8 ± 0.4 MJup, assuming both planets are on coplanar orbits. These values depend on the assumptions on the distance of the β Pictoris system. The absolute astrometry HIPPARCOS-Gaia data are consistent with the solutions presented here at the 2σ level, but these solutions are fully driven by the relative astrometry plus RV data. Finally, we derive unprecedented limits on the presence of additional planets in the disk. We can now exclude the presence of planets that are more massive than about 2.5 MJup closer than 3 au, and more massive than 3.5 MJup between 3 and 7.5 au. Beyond 7.5 au, we exclude the presence of planets that are more massive than 1–2 MJup. Conclusions. Combining relative astrometry and RVs allows one to precisely constrain the orbital parameters of both planets and to give lower limits to potential additional planets throughout the disk. The mass of β Pictoris c is also well constrained, while additional RV data with appropriate observing strategies are required to properly constrain the mass of β Pictoris b.

SCExAO/CHARIS Direct Imaging of A Low-mass Companion At A Saturn-like Separation from an Accelerating Young A7 Star

“…Direct imaging and two indirect methods-radial-velocity (RV) and astrometry-provide ways to detect and characterize young exoplanets, brown dwarfs, and low-mass stellar companions at Jupiter or greater separations around nearby stars (Nakajima et al 1995;Marois et al 2008;Zimmerman et al 2010;Brandt 2018;Borgniet et al 2019;Brandt et al 2019;Currie et al 2020;Lagrange et al 2020). Each method in isolation has its strengths and weaknesses.…”

First Doppler Limits on Binary Planets and Exomoons in the HR 8799 System

“…Another promising way to detect exomoons around directly imaged planets is by measuring the astrometric wobble of the planet due to an orbiting satellite (Agol et al 2015). Recently, the GRAVITY instrument on the Very Large Telescope Interferometer (VLTI) has achieved extremely precise astrometric measurements (uncertainties ranging from 20-150 microarcseconds) of directly imaged planets (Gravity Collaboration et al 2020;Lagrange et al 2020;Lacour et al 2021), including HR 8799 e (Gravity Collaboration et al 2019). The astrometric signal induced by a Jupiter-mass companion in a 10 day orbit around one of the HR 8799 planets would be about 60 microarcseconds, roughly 3 times larger than the smallest single-point GRAVITY astrometric uncertainties.…”

Dynamical Mass of the Exoplanet Host Star HR 8799

“…Dynamical mass measurements, on the other hand, are "gold standards" because they rely only on Kepler's laws (e.g., Hillenbrand & White 2004, see also review by Serenelli et al 2021). While host star dynamical masses have been measured in other systems with a directly imaged substellar companion (e.g., β Pic, Nielsen et al 2014;Wang et al 2016;Dupuy et al 2019;Gravity Collaboration et al 2020;Nielsen et al 2020;Lagrange et al 2020;Vandal et al 2020;Brandt et al 2021a), it is more often the case that the modest orbital coverage from long-period planets cannot admit a well constrained dynamical mass (e.g., Bowler et al 2020).…”