Kavli Affiliate: Andrew Vanderburg
| First 5 Authors: Rayna Rampalli, Melissa K. Ness, Elisabeth R. Newton, Andrew Vanderburg, Tobias Buck
| Summary:
We explore how the correlation between host star metallicity and giant
planets shapes hot Jupiter occurrence as a function of Galactic birth radius
(rbirth) and phase-space density in the Milky Way disk. Using the GALAH and
APOGEE surveys and a galaxy from the NIHAO simulation suite, we inject hot
Jupiters around stars based on metallicity power laws, reflecting the trend
that giant planets preferentially form around metal-rich stars. For rbirth
$geq 5$ kpc, hot Jupiter occurrence decreases with rbirth by $sim -0.1%$
per kpc; this is driven by the Galaxy’s chemical evolution, where the inner
regions of the disk are more metal-rich. Differences in GALAH occurrence rates
versus APOGEE’s and the simulation’s at rbirth $< 5$ kpc arise from survey
selection effects. APOGEE and the NIHAO simulation have more high-$alpha$
sequence stars than GALAH, resulting in average differences in metallicity
(0.2–0.4 dex), $alpha$-process element enrichment (0.2 dex), and vertical
velocities (7–14 km/s) at each rbirth bin. Additionally, we replicate the
result of cite{Winter20}, which showed that over 92% of hot Jupiters are
associated with stars in phase-space overdensities, or "clustered
environments." However, our findings suggest that this clustering effect is
primarily driven by chemical and kinematic differences between low and
high-$alpha$ sequence star properties. Our results support stellar
characteristics, particularly metallicity, being the primary drivers of hot
Jupiter formation, which serves as the "null hypothesis" for interpreting
planet demographics. This underscores the need to disentangle planetary and
stellar properties from Galactic-scale effects in future planet demographics
studies.
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