Examinando por Autor "Mirouh, G. M."

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Acceso Abierto
Lithium and the evolution of intermediate-mass T Tauri and Herbig stars: Rotation, accretion, and planets
(EDP Sciences, 2026-05-19) Mendigutía, I.; Campbell-White, Justyn; Montesinos Comino, B.; Maldonado, J.; Fullana-García, Lucía; Mirouh, G. M.; Meeus, G.; Vioque, M.; Sicilia-Aguilar, Aurora; Zapatero Osorio, María Rosa; Villaver, E.; Kahar, Ruhee Siddiqa; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Junta de Andalucía
Context. Interior models predict that stellar envelopes change from convective to radiative during the pre-main-sequence (pre-MS) evolution of intermediate-mass stars. Although the amount of surface lithium (Li) is a direct probe of mixing in stellar interiors, analyses focused on this type of source are practically absent. Aims. We contribute to our understanding of the evolution of young intermediate-mass stars by providing a comprehensive analysis of their Li content. Methods. A sample of 71 intermediate-mass T Tauri (IMTT) and Herbig stars within the mass range 1.5–3.5 M⊙ was carefully selected for the analysis. Metallicities, rotational velocities, and accretion rates were obtained from spectra. The curves of growth for stars hotter than 8000 K were built to infer the Li abundances, which were interpreted considering standard models of stellar interiors and non-standard processes affecting Li depletion. Results. Li is generally less strongly depleted in intermediate-mass stars than in their lower-mass counterparts, as expected from standard evolution models. However, Li abundances significantly below the cosmic value are observed in 25–30% of intermediate-mass stars. It is also unexpected that the results show no significant difference between the 1.5–2.5 M⊙ and 2.5–3.5 M⊙ subsamples. Evidence is provided showing that disk-locking works in young intermediate-mass stars. This constitutes independent support for the hypothesis that magnetospheric accretion scenario operates in these sources. We found that disk-locking is effective for a timescale that is about twice shorter than for lower-mass stars, before magnetospheres reduce their sizes during the transition from the IMTT to the Herbig regime. This contraction of the magnetosphere can explain the increase in rotation by a factor of about 3 and in accretion by a factor of about 4 that is observed during this transition. We propose a complex scenario linking rotation, accretion, and the surface Li abundance. Finally, we tentatively suggest that the known relation between the presence of planets and Li depletion might also be present in intermediate-mass MS stars and might originate in the pre-MS. Conclusions. We provide the most complete Li analysis and database focused on IMTT and Herbig stars to date. However, we emphasize the need of additional observations and non-standard models such as those available for their lower-mass analogs.
Acceso Abierto
The first view of δ Scuti and γ Doradus stars with the TESS mission
(Oxford Academics: Oxford University Press, 2019-10-07) Antoci, V.; Cunha, M. S.; Bowman, D. M.; Murphy, S. J.; Kurtz, D. W.; Bedding, T. R.; Borre, C. C.; Christophe, S.; Daszyńska-Daszkiewicz, J.; Fox Machado, L.; García Hernández, A.; Ghasemi, H.; Handberg, R.; Hansen, H.; Hasanzadeh, A.; Houdek, G.; Johnston, C.; Justesen, A. B.; Kahraman Alicavus, F.; Kotysz, K.; Latham, D.; Matthews, J. M.; Monster, J.; Niemczura, E.; Paunzen, E.; Sánchez Arias, J. P.; Pigulski, A.; Pepper, J.; Richey Yowell, T.; Safari, H.; Seager, S.; Smalley, B.; Shutt, T.; Sódor, A.; Suárez, J. C.; Tkachenko, A.; Wu, T.; Zwintz, K.; Barceló Forteza, S.; Brunsden, E.; Bognár, Z.; Buzasi, D. L.; Chowdhury, S.; De Cat, P.; Evans, J. A.; Guo, Z.; Guzik, J. A.; Jetvic, N.; Lampens, P.; Lares Martiz, M.; Lovekin, C.; Li, G.; Mirouh, G. M.; Mkrtichian, D.; Monteiro, M. J. P. F. G.; Nemec, J. M.; Ouazzani, R. M.; Pascual Granado, J.; Reese, D. R.; Rieutord, M.; Rodon, J. R.; Skarka, M.; Sowicka, P.; Stateva, I.; Szabó, R.; Weiss, W. W.; Universidad Nacional Autónoma de México (UNAM); Agence Nationale de la Recherche (ANR); National Natural Science Foundation of China (NSFC); Danish National Research Foundation (DNRF); National Aeronautics and Space Administration (NASA); Fundacao para a Ciencia e a Tecnologia (FCT); National Science Centre, Poland (NCN); Hungarian Academy of Sciences (MTA); European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO); Research Foundation Flanders (FWO); BELgian federal Science Policy Office (BELSPO); Science and Technology Facilities Council (STFC); Johnston, C. [0000-0002-3054-4135]; Granado, J. P. [0000-0003-0139-6951]; Monteiro, M. J. P. F. G. [0000-0003-0513-8116]; Szabo, R. [0000-0002-3258-1909]; Browman, D. [0000-0001-7402-3852]; Safari, H. [0000-0003-2326-3201]; Simon, M. [0000-0002-5648-3107]; Houdek, G. [0000-0003-1819-810X]; Ghasemi, H. [0000-0001-9534-9763]; Handerberg, R. [0000-0001-8725-4502]; Borre, C. C. [0000-0003-1286-8512]; Cunha, M. [0000-0001-8237-7343]; Justensen, A. B. [0000-0002-0174-2466]; Antoci, V. [0000-0002-0865-3650]; Christophe, S. [0000-0002-4153-870X]; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung–Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, γ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74 per cent for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young δ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.