2024A&A...686L...1M

Context. The presence of short-period (< 10 days) planets around main sequence (MS) stars has been associated either with the dust-destruction region or with the magnetospheric gas-truncation radius in the protoplanetary disks that surround them during the pre-MS phase. However, previous analyses have only considered low-mass FGK stars, making it difficult to disentangle the two scenarios.
Aims. This exploratory study is aimed at testing whether it is the inner dust or gas disk driving the location of short-period, giant planets.
Methods. By combining TESS and Gaia DR3 data, we identified a sample of 47 intermediate-mass (1.5-3 M_⊙) MS stars hosting confirmed and firm candidate hot Jupiters. We compared their orbits with the rough position of the inner dust and gas disks, which are well separated around their Herbig stars precursors. We also made a comparison with the orbits of confirmed hot Jupiters around a similarly extracted TESS/Gaia sample of low-mass sources (0.5-1.5 M_⊙).
Results. The orbits of hot Jupiters around intermediate-mass stars tend to be closer to the central sources than the inner dust disk, most generally consistent with the small magnetospheric truncation radii typical of Herbig stars (≲5 R_*). A similar study considering the low-mass stars alone has been less conclusive due to the similar spatial scales of their inner dust and gas disks (≳5 R_*). However, considering the whole sample, we do not find the correlation between orbit sizes and stellar luminosities that is otherwise expected if the dust-destruction radius limits the hot Jupiters' orbits. On the contrary, the comparative analysis reveals that such orbits tend to be closer to the stellar surface for intermediate-mass stars than for low-mass stars, with both being mostly consistent with the rough sizes of the corresponding magnetospheres.
Conclusion. Our results suggest that the inner gas (ad not the dust) disk limits the innermost orbits of hot Jupiters around intermediate-mass stars. These findings also provide tentative support to previous works that have claimed this is indeed the case for low-mass sources. We propose that hot Jupiters could be explained via a combination of the core-accretion paradigm and migration up to the gas-truncation radius, which may be responsible for halting inward migration regardless of the stellar mass regime. Larger samples of intermediate-mass stars with hot Jupiters are necessary to confirm our hypothesis, which implies that massive Herbig stars without magnetospheres (> 3-4 M_⊙) may be the most efficient in swallowing their newborn planets.