Dynamical Constraints on the HR 8799 Planets with GPI

Abstract

2 Wang et al. The HR 8799 system uniquely harbors four young super-Jupiters whose orbits can provide insights into the system's dynamical history and constrain the masses of the planets themselves. Using the Gemini Planet Imager (GPI), we obtained down to one milliarcsecond precision on the astrometry of these planets. We assessed four-planet orbit models with different levels of constraints and found that assuming the planets are near 1:2:4:8 period commensurabilities, or are coplanar, does not worsen the fit. We added the prior that the planets must have been stable for the age of the system (40 Myr) by running orbit configurations from our posteriors through N -body simulations and varying the masses of the planets. We found that only assuming the planets are both coplanar and near 1:2:4:8 period commensurabilities produces dynamically stable orbits in large quantities. Our posterior of stable coplanar orbits tightly constrains the planets' orbits, and we discuss implications for the outermost planet b shaping the debris disk. A four-planet resonance lock is not necessary for stability up to now. However, planet pairs d and e, and c and d, are each likely locked in two-body resonances for stability if their component masses are above 6 M Jup and 7 M Jup , respectively. Combining the dynamical and luminosity constraints on the masses using hot-start evolutionary models and a system age of 42 ± 5 Myr, we found the mass of planet b to be 5.8 ± 0.5 M Jup , and the masses of planets c, d, and e to be 7.2 +0.6 −0.7 M Jup each.

The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au

“…The campaign observations resulted in the detection of three of the four planets, HR 8799 cde, with HR 8799 b outside the field of view of GPI in our nominal search mode. Astrometry obtained with GPI was also used in conjunction with measurements obtained with Keck/NIRC2 to investigate the dynamical properties and long-term stability of the system (Wang et al 2018a). By utilizing N-body simulations, the combination of astrometry and dynamical limits placed tighter constraints on the orbital parameters and the masses of the individual planets, which when combined with evolutionary models give a mass for HR 8799 b of 5.8±0.5 M Jup , and 7.2 0.7 0.6 -+ M Jup for planets c, d, and e.…”

Revised astrometric calibration of the Gemini Planet Imager

“…The changes to the pipeline described in Section 3 and the revised astrometric calibration of the instrument described in Section 6 both necessitate a revision of previously-published relative astrometry of substellar companions measured using GPI observations. Revisions for β Pictoris b Here, we present corrections to the astrometry for the exoplanets in the HR 8799 5 and HD 95086 7 systems, and the brown dwarfs HR 2562 B 34 and HD 984 B, 35 that correct for the changes to the pipeline and the revised astrometric calibration of the instrument. We reduced the same images used in the previous studies with the latest version of the GPI DRP.…”

“…One of the objectives of the large Gemini Planet Imager Exoplanet Survey 3 (GPIES) was to characterize via relative astrometry the orbits of the brown dwarfs and exoplanets imaged as a part of the campaign. 4 These measurements have been used to investigate the dynamical stability of the multi-planet HR 8799 system, 5 the interactions between substellar companions and circumstellar debris disks, 6,7 and to directly measure the mass of β Pictoris b (Nielsen et al 2019, submitted). Improved accuracy in orbit determination benefits comparisons to or joint fits with observations from other facilities.…”

Multi-epoch Direct Imaging and Time-variable Scattered Light Morphology of the HD 163296 Protoplanetary Disk

“…Pic b, HR 8799 bcde(Lagrange et al 2010;Marois et al 2010;Currie et al 2011;Snellen and Brown 2018;Wang et al 2018;Dupuy et al 2019) -are inconsistent with a cold-start evolutionary model. At the candidate's location in each data cube, we injected a planet whose temperature matches that expected for a 4 M J , 5 M yr planet according to these models.…”