On hot Jupiters and stellar clustering: the role of host star demographics

ABSTRACT The variation in hot Jupiter (HJ) occurrence across stellar environments holds clues as to the dominant formation channels of these extreme planets. Recent studies suggest HJ hosts preferentially reside in regions of high-phase space density, possibly reflecting natal environmental conditions. These regions are kinematically cold (|v| 40\: km\: s^{-1}), prompting the alternative hypothesis that the correlation reflects an age bias: planetary systems in overdensities are systematically younger and therefore less likely to have undergone tidal inspiral and destruction. We test whether the apparent excess of HJs in phase space overdensities arises from differences in intrinsic host properties – mass, metallicity, and age – which may correlate with phase space density or whether there is evidence for an additional environmental effect. We derive homogeneous estimates for the mass, metallicity, and age of planet-hosting stars using Two Micron All-Sky Survey (2MASS) and Gaia DR3 photometry, parallaxes, and self-consistent spectroscopic and spectrophotometric observables. In a sample of 2265 confirmed exoplanet hosts, we find a significant relative excess of HJs orbiting stars in overdense regions. However, we also find that overdensities preferentially host younger, more massive, and more metal-rich stars compared to underdensities. After correcting for these differences, either by detrending the phase space density against age or by matching host properties across subsamples, we find no significant differences in the HJ populations between over- and underdense regions. Our results suggest that the previously reported correlation between HJ occurrence and phase space density is driven by underlying differences in host star demographics rather than an intrinsic environmental effect.