Identifying Close-in Jupiters that Arrived via Disk Migration: Evidence of Primordial Alignment, Preference of Nearby Companions and Hint of Runaway Migration

Kawai, Yugo; Fukui, Akihiko; Watanabe, Noriharu; Fukazawa, Sho; Narita, Norio
Bibliographical reference

The Astronomical Journal

Advertised on:
12
2025
Number of authors
5
IAC number of authors
2
Citations
0
Refereed citations
0
Description
Two leading hypotheses for hot Jupiter migration are disk migration and high-eccentricity migration (HEM). Stellar obliquity is commonly used to distinguish them, as high obliquity often accompanies HEM. However, low obliquity does not guarantee disk migration, due to possible spin─orbit realignment or coplanar HEM. Seeking a proxy for disk migration, we investigate the idea that when the circularization timescale of a planet on circular orbit is longer than its age (τcir > τage), HEM would not have had sufficient time to complete, favoring disk migration. We empirically calibrate the reduced planetary tidal quality factor to be Qp=4.9−2.5+3.5×105 using the eccentricity distribution of 500+ Jovian mass (0.2MJ < Mp < 13MJ) planets with measured masses and radii, a value consistent with solar system Jupiter. We then calculate τcir and identify dozens of disk migration candidates (τcir > τage, e < 0.1). These planets show three notable trends. We first find a clear cutoff of obliquity at τcir ∼ τage, suggesting the primordial alignment of protoplanetary disks. Second, we find that among hot Jupiters (a < 0.1 au), nearby companions are preferentially found around disk migration candidates, suggesting that either HEM dominates hot Jupiter formation, or disk migration also disrupts nearby companions at short separations. Finally, we find a possible dearth of disk migration candidates around mass ratio logq∼−3.2 , consistent with a similar dip suggested at longer orbits from microlensing. The lack of planets across different orbital distance, if true, could be interpreted as a hint of runaway migration.
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