Survival of fossil fields during the pre-main sequence evolution of intermediate-mass stars

Schleicher, Dominik R. G.; Hidalgo, Juan Pablo; Galli, Daniele

doi:10.1051/0004-6361/202346809

Cited by 3 publications

(1 citation statement)

References 68 publications

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“…Several scenarios have been proposed to account for the presence of strong superficial magnetic fields in intermediate-mass stars. Perhaps the most accepted possibility is a fossil origin (Schleicher et al 2023). An alternative is the generation of magnetic field through the so-called Tayler-Spruit dynamo mechanism in a rotating star (Nandal et al 2023).…”

Section: Stellar Evolution Models With Rotation For S1a and Magnetic ...mentioning

confidence: 99%

Dynamical Mass of the Ophiuchus Intermediate-mass Stellar System S1 with DYNAMO-VLBA

Ordóñez-Toro,

Dzib,

Loinard

et al. 2024

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We report dynamical mass measurements of the individual stars in the most luminous and massive stellar member of the nearby Ophiuchus star-forming region, the young tight binary system S1. We combine 28 archival data sets with seven recent proprietary Very Long Baseline Array (VLBA) observations obtained as part of the Dynamical Masses of Young Stellar Multiple Systems with the VLBA project (DYNAMO–VLBA), to constrain the astrometric and orbital parameters of the system, and recover high-accuracy dynamical masses. The primary component, S1A, is found to have a mass of 4.11 ± 0.10 M ⊙, significantly lower than the typical value ∼6 M ⊙ previously reported in the literature. We show that the spectral energy distribution (SED) of S1A can be reproduced by a reddened blackbody with a temperature between roughly 14,000 and 17,000 K. According to evolutionary models, this temperature range corresponds to stellar masses between 4 M ⊙ and 6 M ⊙, so the SED is not a priori inconsistent with the dynamical mass of S1A. The luminosity of S1 derived from SED fitting, however, is only consistent with models for stellar masses above 5 M ⊙. Thus, we cannot reconcile the evolutionary models with the dynamical mass measurement of S1A: The models consistent with the location of S1A in the Hertzsprung-Russel diagram correspond to masses higher by 25% at least than the dynamical mass. For the secondary component, S1B, a mass of 0.831 ± 0.014 M ⊙ is determined, consistent with a low-mass young star. While the radio flux of S1A remains roughly constant throughout the orbit, the flux of S1B is found to be higher near apastron.

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Section: Stellar Evolution Models With Rotation For S1a and Magnetic ...mentioning

confidence: 99%

Dynamical Mass of the Ophiuchus Intermediate-mass Stellar System S1 with DYNAMO-VLBA

Ordóñez-Toro,

Dzib,

Loinard

et al. 2024

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Chemically peculiar stars on the pre-main sequence

Kueß,

Paunzen,

Faltová

et al. 2024

A&A

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The chemically peculiar (CP) stars of the upper main sequence are defined by spectral peculiarities that indicate unusual elemental abundance patterns in the presence of diffusion in the calm, stellar atmospheres. Some of them have a stable local magnetic field of up to several kiloGauss. The pre-main-sequence evolution of these objects is still a mystery and contains many open questions. We identify CP stars on the pre-main sequence to determine possible mechanisms that lead to the occurrence of chemical peculiarities in the (very) early stages of stellar evolution. We identified likely pre-main-sequence stars by fitting the spectral energy distributions. The subsequent analysis using stellar spectra and photometric time series helped us to distinguish between CP and non-CP stars. Additionally, we compared our results to the literature to provide the best possible quality assessment. Out of 45 candidates, about 70 <!PCT!> seem to be true CP stars or CP candidates. Furthermore, 9 sources appear to be CP stars on the pre-main sequence, and all are magnetic. We finally report a possible CP2 star that is also a pre-main-sequence star and was not previously in the literature. The evolution of the peculiarities seems to be related to the (strong) magnetic fields in these CP2 stars.

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Magnetohydrodynamic simulations of A-type stars: Long-term evolution of core dynamo cycles

Hidalgo,

Käpylä,

Schleicher

et al. 2024

A&A

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Early-type stars have convective cores due to a steep temperature gradient produced by the CNO cycle. These cores can host dynamos and the generated magnetic fields may be relevant in explaining the magnetism observed in Ap/Bp stars. Our main objective is to characterise the convective core dynamos and differential rotation. We aim to carry out the first quantitative analysis of the relation between magnetic activity cycle and rotation period. We used numerical 3D star-in-a-box simulations of a $2.2 M_ A-type star with a convective core of roughly 20<!PCT!> of the stellar radius surrounded by a radiative envelope. We explored rotation rates from 8 to 20 days and used two models of the whole star, along with an additional zoom set where 50<!PCT!> of the radius was retained. The simulations produce hemispheric core dynamos with cycles and typical magnetic field strengths around $60$ kG. However, only a very small fraction of the magnetic energy is able to reach the surface. The cores have solar-like differential rotation and a substantial part of the radiative envelope has a quasi-rigid rotation. In the most rapidly rotating cases, the magnetic energy in the core is roughly 40<!PCT!> of the kinetic energy. Finally, we find that the magnetic cycle period, $P_ cyc $, increases with decreasing the rotation period, $P_ rot $, which has also been observed in many simulations of solar-type stars. Our simulations indicate that a strong hemispherical core dynamo arises routinely, but that it is not enough the explain the surface magnetism of Ap/Bp stars. Nevertheless, since the core dynamo produces dynamically relevant magnetic fields, it should not be neglected even when other mechanisms are being explored.

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Survival of fossil fields during the pre-main sequence evolution of intermediate-mass stars

Cited by 3 publications

References 68 publications

Dynamical Mass of the Ophiuchus Intermediate-mass Stellar System S1 with DYNAMO-VLBA

Dynamical Mass of the Ophiuchus Intermediate-mass Stellar System S1 with DYNAMO-VLBA

Chemically peculiar stars on the pre-main sequence

Magnetohydrodynamic simulations of A-type stars: Long-term evolution of core dynamo cycles

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