WASP-12b and HAT-P-8b are Members of Triple Star Systems

TL;DR

This study reveals that the hot Jupiters WASP-12b and HAT-P-8b are part of hierarchical triple star systems, with detailed imaging confirming their companions and enabling future dynamical mass measurements.

Contribution

The paper provides high-resolution imaging evidence that hot Jupiter hosts are often in triple star systems, highlighting the potential for complex dynamics and new methods for mass determination.

Findings

WASP-12b and HAT-P-8b are in triple star systems with distant M dwarf companions.

The secondary around WASP-12 was resolved into two sources separated by 84.3 mas.

HAT-P-8's companion is composed of two stars separated by 65.3 mas.

Abstract

We present high spatial resolution images that demonstrate the hot Jupiters WASP-12b and HAT-P-8b orbit the primary star of hierarchical triple star systems. In each case, two distant companions with colors and brightness consistent with M dwarfs co-orbit the planet host as well as one another. Our adaptive optics images spatially resolve the secondary around WASP-12, previously identified by Bergfors et al. 2011 and Crossfield et al. 2012, into two distinct sources separated by 84.3+/-0.6 mas (21 +/- 3 AU). We find that the secondary to HAT-P-8, also identified by Bergfors et al. 2011, is in fact composed of two stars separated by 65.3+/-0.5 mas (15+/-1 AU). Our follow-up observations demonstrate physical association through common proper-motion. HAT-P-8 C has a particularly low mass, which we estimate to be 0.18+/-0.02Msun using photometry. Due to their hierarchy, WASP-12 BC and HAT-P-8 BC will enable the first dynamical mass determination for hot Jupiter stellar companions. These previously well-studied planet hosts now represent higher-order multi-star systems with potentially complex dynamics, underscoring the importance of diffraction-limited imaging and providing additional context for understanding the migrant population of transiting hot Jupiters.