Numerical search for a potential planet sculpting the young disc of HD 115600

Abstract

Radial and azimuthal features (such as disc offsets and eccentric rings) seen in high resolution images of debris discs, provide us with the unique opportunity of finding potential planetary companions which betray their presence by gravitationally sculpting such asymmetric features. The young debris disc around HD 115600, imaged recently by the Gemini Planet Imager, is such a disc with an eccentricity e ∼ 0.1 − 0.2 and a projected offset from the star of ∼ 4 AU. Using our modified N-body code which incorporates radiation forces, we firstly aim to determine the orbit of a hidden planetary companion potentially responsible for shaping the disc. We run a suite of simulations covering a broad range of planetary parameters using a Monte Carlo Markov Chain sampling method and create synthetic images from which we extract the geometric disc parameters to be compared with the observed and model-derived quantities. We then repeat the study using a traditional grid to explore the planetary parameter space and aim secondly to compare the efficiency of both sampling methods. We find a planet of 7.8 Jupiter mass orbiting at 30 AU with an eccentricity of e = 0.2 to be the best fit to the observations of HD 115600. Technically, such planet has a contrast detectable by direct imaging, however the system's orientation does not favour such detection. In this study, at equal number of explored planetary configurations, the Monte Carlo Markov Chain not only converges faster but provides a better fit than a traditional grid.

VLT/SPHERE Multiwavelength High-contrast Imaging of the HD 115600 Debris Disk: New Constraints on the Dust Geometry and the Presence of Young Giant Planets

“…Our dataset improves characterization of the surrounding debris disk and upper limits on possible exoplanets embedded in the disk. We model the debris disk to investigate structure that could indicate unseen exoplanet(s), as suggested by Currie et al (2015b) and Thilliez & Maddison (2017). We determine disk geometry by two methods, using the code ZODIPIC (Kuchner 2012) to inject and subtract a grid of disk models into the raw data, and by a 'maximum merit' ellipse fitting method on the ADI images, as described in Thalmann et al (2011).…”

“…The sharp ring-like structure of the disk may suggest sculpting by a planet (or planets) and the measured offset of the disk further implies that this planet could be massive. Numerical modeling by Thilliez & Maddison (2017) determined that disk structures driven by a ∼ 8M J planet located at ∼30 au are the best fit to observed morphology. While the predicted contrast (4 × 10 −5 in H band) of this hypothetical planet is within the theoretical performance capabilities of current extreme adaptive optics (hereafter extreme AO) instruments such as SPHERE and GPI (Mesa et al 2015;Bailey et al 2016), the orientation of the disk (i = 79 • ) makes the detection very challenging.…”

“…Our results on the disk eccentricity imply that any unseen exoplanets are likely less massive than previously estimated. Using the projected disk offset estimated by Currie et al (2015b), Thilliez & Maddison (2017) showed that a 7.8 M J planet could be present in the system at 30 au with an eccentricity of e = 0.2, which could be detected by SPHERE or GPI. Due to the inclination of the system, however, there is a high probability that the planet would lie within the inner working angle of both instruments, and thus undetected.…”

“…Sco-Cen includes many of the currently known directly-imaged planetary companions (e.g. Rameau et al 2013;Quanz et al 2013;Bailey et al 2014;Currie et al 2015a;Chauvin et al 2017;Keppler et al 2018) and numerous debris disks resolved in scattered light (e.g Thalmann et al 2013;Currie et al 2015b;Lagrange et al 2016;Matthews et al 2017;Bonnefoy et al 2017).…”