Research Note

Close-in planets around giant stars

Lack of hot-Jupiters and prevalence of multiplanetary systems

¹ European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
e-mail: jlillobox@eso.org
² Depto. de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus 28691 Villanueva de la Cañada ( Madrid), Spain
³ CIDMA, Departamento de Física, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
⁴ ASD, IMCCE-CNRS UMR 8028, Observatoire de Paris, 77 Av. Denfert-Rochereau, 75014 Paris, France

Received: 2 November 2015
Accepted: 11 March 2016

Abstract

Extrasolar planets abound in almost any possible configuration. However, until five years ago, there was a lack of planets orbiting closer than 0.5 au to giant or subgiant stars. Since then, recent detections have started to populated this regime by confirming 13 planetary systems. We discuss the properties of these systems in terms of their formation and evolution off the main sequence. Interestingly, we find that 70.0 ± 6.6% of the planets in this regime are inner components of multiplanetary systems. This value is 4.2σ higher than for main-sequence hosts, which we find to be 42.4 ± 0.1%. The properties of the known planets seem to indicate that the closest-in planets (a< 0.06 au) to main-sequence stars are massive (i.e., hot Jupiters) and isolated and that they are subsequently engulfed by their host as it evolves to the red giant branch, leaving only the predominant population of multiplanetary systems in orbits 0.06 <a< 0.5 au. We discuss the implications of this emerging observational trend in the context of formation and evolution of hot Jupiters.