This content originally appeared on HackerNoon and was authored by EScholar: Electronic Academic Papers for Scholars
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:::info Authors:
(1) I. Mendigutía, Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Madrid, Spain;
(2) J. Lillo-Box, Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Madrid, Spain;
(3) M. Vioque, European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany and Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355, Chile;
(4) J. Maldonado, INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo, Italy;
(8) B. Montesinos, Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Madrid, Spain;
(6) N. Huélamo, Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Madrid, Spain;
(7) J. Wang, Departamento de Física Teórica, Módulo 15, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
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ABSTRACT
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 (. 5R∗). 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 (& 5R∗). 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.
\ Conclusions. Our results suggest that the inner gas (and 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.
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1. Introduction
Short-period (< 10 days) planets orbiting close (< 0.1 au) to their host, main sequence (MS) stars are relatively uncommon (Kunimoto & Matthews 2020). However, their role in shaping our understanding of planet formation has been recognized since the first detection of 51 Peg b (Mayor & Queloz 1995), especially with respect to the gas giants known as "hot Jupiters." Without neglecting the role that interactions with other stars and planets may play in explaining hot Jupiters around some systems, in this work we assume that their orbits are primarily fixed by the physical conditions of the protoplanetary disks that surround young stars during the pre-MS (see below and e.g., Mulders et al. 2015; Benkendorff et al. 2024).
\ Protoplanetary disks are limited by two main barriers that prevent them from extending up to the stellar surfaces (e.g., Romanova et al. 2019). Solid particles cannot survive close to the stars because dust sublimates at temperatures above ∼ 1500 K. The size of such a dust barrier scales with the square root of the stellar luminosity (Tuthill et al. 2001; Monnier & Millan-Gabet 2002). Gas in disks is also truncated close to the central sources, where it is channeled by the star’s magnetic field until it accretes at high stellar latitudes. The size of this magnetospheric barrier for the gas decreases for smaller stellar magnetic fields and stronger mass accretion rates (Koenigl 1991).
\ Regardless of whether planets form in situ or migrate, the limits established by both the inner dust and gas radii have been invoked to explain the presence of short-period planets and its abrupt decline at smaller orbits (e.g., Lee & Chiang 2017; Flock et al. 2019; Romanova et al. 2019). In particular, the role that the magnetospheric truncation radius may play as a nearly universal explanation for close orbits in widely different systems was recently pointed out (Batygin et al. 2023). However, previous analyses focused on low-mass FGK stars, making hard to observationally disentangle which of the two barriers, dust or gas,
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\ actually determines the innermost planetary orbits. Indeed, the magnetospheric truncation radii in solar type and lower-mass, T Tauri stars are typically similar to their dust-destruction radii (5-10 R∗ or ∼ 0.05 au; Pinte et al. 2008; Bouvier et al. 2007; Gravity Collaboration et al. 2023), both associated with comparable orbital periods.
\ On the other hand, from the study of stellar interiors it is well settled that convective envelopes necessary to sustain strong, ordered magnetic fields are small or absent in MS stars with spectral type A and earlier (e.g. Simon et al. 2002, and references therein). For this reason (and because mass accretion rates increase with the stellar mass), the magnetospheric radius tends to significantly reduce or even disappear (< 5R∗) in their younger precursors, the Herbig stars (see, e.g., the reviews in Mendigutía 2020; Brittain et al. 2023, and references therein). In addition, the inner dust disk sizes of Herbig stars are well constrained from interferometric observations, being at least one order of magnitude larger than in T Tauri stars (e.g., Marcos-Arenal et al. 2021). Because the difference between the spatial location of the inner gas and dust disks is generally much larger in Herbig stars than in T Tauri stars, the best way to address which one fixes the minimum planetary orbits is by including in the analysis short-period planets around MS stars with intermediate masses. In this work, we follow the classical boundary of 1.5 M⊙ to divide between low- and intermediate-mass MS stars with and without convective sub-photospheric regions (however, also see Sect. 4), for which statistical differences at a population level are expected. In particular, if the dust barrier controls the innermost planetary orbits, then the minimum star-planet separations should scale with the square root of the stellar luminosity and, thus, be typically larger for intermediate-mass stars than for less luminous, low-mass stars. On the contrary, if the gas barrier dominates then intermediate-mass stars should host planets with orbits generally closer to the stellar surfaces than those around lower mass stars (see Fig. 1 and e.g., Lee & Chiang 2017; Batygin et al. 2023, for a supplementary discussion).
\ Nevertheless, the number of confirmed, short-period planets around intermediate-mass MS stars is still very scarce (Sect. 2). A major issue is that the confirmation of planetary candidates, commonly identified through the transit method, usually requires additional detections through radial velocity analyses based on Doppler shifts. However, intermediate-mass stars show a limited amount of (rotationally broadened) absorption lines, for which radial velocity analyses are generally not applicable. Alternatively, statistical validation algorithms make use of light curves and ancillary observations to rule out false positives (e.g., Giacalone et al. 2021, and references therein). Because of the large photometric apertures used by the Kepler mission (Borucki et al. 2010), and especially by the Transiting Exoplanet Survey Satellite (TESS, Ricker et al. 2015), the key task of the previous validation algorithms is to discard the presence of eclipsing binaries in the field that may mimic a planetary transit around the target star. For this purpose, the binarity information that Gaia provides for hundreds of thousands of sources (Gaia Collaboration et al. 2016, 2023b,a) constitutes an alternative way to detect false positives (e.g., Tarrants & Mendes 2023). Moreover, Gaia DR3 provides stellar characterization for more than a billion sources (Creevey et al. 2023; Fouesneau et al. 2023), which constitutes a great tool to homogeneously analyze populations.
\ We follow the latter approach to study the influence of the protoplanetary disk barriers on the location of short-period planets. TESS has targeted stars brighter than those observed by Kepler, covering a significant number of A stars with a cadence and sensitivity that is ideal for detecting short-period, giant planets (e.g., Zhou et al. 2019). In this work, we combine TESS and Gaia DR3 data to analyze a sample of hot Jupiters around MS, intermediate-mass stars. Section 2 describes the sample selection and its properties. Section 3 explores the trends shown by short-period planets around intermediate-mass stars, compared with the rough location of the dust and gas barriers and with an analogous sample of hot Jupiters around low-mass stars. Section 4 discusses the previous results and Sect. 5 offers a summary of our conclusions.
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:::info This paper is available on arxiv under CC BY-SA 4.0 DEED license.
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This content originally appeared on HackerNoon and was authored by EScholar: Electronic Academic Papers for Scholars
EScholar: Electronic Academic Papers for Scholars | Sciencx (2025-10-06T19:40:50+00:00) Magnetospheric Truncation as the Limiting Factor for Hot Jupiter Orbits Across Stellar Masses. Retrieved from https://www.scien.cx/2025/10/06/magnetospheric-truncation-as-the-limiting-factor-for-hot-jupiter-orbits-across-stellar-masses/
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