Exoplanets & Exomoons

A Larger Sample Confirms Small Planets Around Hot Stars Are Misaligned

By Keith Cowing
Status Report
July 1, 2024
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A Larger Sample Confirms Small Planets Around Hot Stars Are Misaligned
Planetary properties for the combined sample used for analysis and probability density distribution split by planet radius or period. Left: Planetary radius and orbital period for all the known transiting planets associated with the 153 planet hosts in Louden et al. (2021) and the 20 planet hosts in the 2022 sample are shown on top of the full KOI sample. The planets outlined in black have hosts with Teff > 6250 K. Right: We divided the planets into subsets based on radius and period and fit the sub-samples. The dashed lines on the left panel show the locations of the cuts over the planet sample in period-radius space. After performing each of the two cuts, the resulting distributions of ⟨sin i⟩ are labeled according to the half they represent. — astro-ph.EP

The distribution of stellar obliquities provides critical insight into the formation and evolution pathways of exoplanets. In the past decade, it was found that hot stars hosting hot Jupiters are more likely to have high obliquities than cool stars, but it is not clear whether this trend exists only for hot Jupiters or holds for other types of planets.

In this work, we extend the study of the obliquities of hot (6250-7000K) stars with transiting super-Earth and sub-Neptune-sized planets. We constrain the obliquity distribution based on measurements of the stars’ projected rotation velocities. Our sample consists of 170 TESS and Kepler planet-hosting stars and 180 control stars chosen to have indistinguishable spectroscopic characteristics. In our analysis, we find evidence suggesting that the planet hosts have a systematically higher ⟨sini⟩ compared to the control sample.

This result implies that the planet hosts tend to have lower obliquities. However, the observed difference in ⟨sini⟩ is not significant enough to confirm spin-orbit alignment, as it is 3.8σ away from perfect alignment. We also find evidence that within the planet-hosting stars there is a trend of higher obliquity (lower ⟨sini⟩) for the hotter stars (teff > 6250 K) than for the cooler stars in the sample. This suggests that hot stars hosting smaller planets exhibit a broader obliquity distribution(⟨sini⟩=0.79±0.053) than cooler planet-hosting stars, indicating that high obliquities are not exclusive to hot Jupiters and instead are more broadly tied to hot stars.

Emma M. Louden, Songhu Wang, Joshua N. Winn, Erik A. Petigura, Howard Isaacson, Luke Handley, Samuel W. Yee, Corey Beard, Joseph M. Akana Murphy, Gregory Laughlin

Comments: Accepted for publication in ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.20035 [astro-ph.EP] (or arXiv:2405.20035v1 [astro-ph.EP] for this version)
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Submission history
From: Emma Louden
[v1] Thu, 30 May 2024 13:18:18 UTC (1,310 KB)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻