المؤلفون: Javier Serna, Giovanni Pinzón, Jesús Hernández, Ezequiel Manzo-Martínez, Karina Mauco, Carlos G. Román-Zúñiga, Nuria Calvet, Cesar Briceño, Ricardo López-Valdivia, Marina Kounkel, Guy S. Stringfellow, Keivan G. Stassun, Marc Pinsonneault, Lucia Adame, Lyra Cao, Kevin Covey, Amelia Bayo, Alexandre Roman-Lopes, Christian Nitschelm, Richard R. Lane

المصدر: The Astrophysical Journal, Vol 968, Iss 2, p 68 (2024)

مصطلحات موضوعية: Classical T Tauri stars, Stellar evolution, Stellar magnetic fields, Stellar properties, Stellar rotation, Stellar winds, Astrophysics, QB460-466

الوصف: We developed a grid of stellar rotation models for low-mass and solar-type classical T Tauri stars (CTTS; 0.3 M _⊙ < M _* < 1.2 M _⊙ ). These models incorporate the star–disk interaction and magnetospheric ejections to investigate the evolution of the stellar rotation rate as a function of the mass of the star M _* , the magnetic field ( B _* ), and stellar wind ( ${\dot{M}}_{\mathrm{wind}}$ ). We compiled and determined stellar parameters for 208 CTTS, such as projected rotational velocity $v\sin (i)$ , mass accretion rate ${\dot{M}}_{\mathrm{acc}}$ , stellar mass M _* , ages, and estimated rotational periods using Transiting Exoplanet Survey Satellite (TESS) data. We also estimated a representative value of the mass-loss rate for our sample using the [O i ] λ 6300 spectral line. Our results confirm that $v\sin (i)$ measurements in CTTS agree with the rotation rates provided by our spin models in the accretion-powered stellar winds picture. In addition, we used the approximate Bayesian computation technique to explore the connection between the model parameters and the observational properties of CTTS. We find that the evolution of $v\sin (i)$ with age might be regulated by variations in (1) the intensity of B _* and (2) the fraction of the accretion flow ejected in magnetic winds, removing angular momentum from these systems. The youngest stars in our sample (∼1 Myr) show a median branching ratio ${\dot{M}}_{\mathrm{wind}}/{\dot{M}}_{\mathrm{acc}}\sim 0.16$ and median B _* ∼ 2000 G, in contrast to ∼0.01 and 1000 G, respectively, for stars with ages ≳3 Myr.

وصف الملف: electronic resource

Relation: https://doaj.org/toc/1538-4357

URL الوصول: https://doaj.org/article/3f2ebec67a004852aaa455cd3837a8a2

المؤلفون: Jesús Hernández, Luisa F. Zamudio, César Briceño, Nuria Calvet, Zhaohuan Zhu, Haibo Yuan, Xiaowei Liu, Ezequiel Manzo-Martínez, Carlos G. Román-Zúñiga, Javier Serna, Karina Maucó, Lucía Adame

المصدر: The Astronomical Journal, Vol 165, Iss 5, p 205 (2023)

مصطلحات موضوعية: Star forming regions, OB associations, Hertzsprung Russell diagram, Pre-main sequence, T Tauri stars, Stellar spectral types, Astronomy, QB1-991

الوصف: We present a spectroscopic analysis of T Tauri stars (TTSs) observed with the wide-field multifiber spectrograph LAMOST in the substellar associations Ori OB1a located in the Orion Star-forming Complex. Based on GAIA-DR3 data, we selected stars with proper motions and parallaxes expected for TTSs belonging to the young association. We perform a spectroscopic analysis to obtain the spectral types and measure the equivalent widths of Li i and H α to confirm the youth of the stars and estimate the accretion status. We also estimate extinctions, masses, and ages for the studied sample. Out of 342 TTSs with spectroscopic and kinematic properties indicating their membership of the subassociation, 2 are reported here for the first time. Finally, we detect four stellar kinematic groups located at different distances, two in the north fields and two in the south field. These groups also show different proper motions. This suggests that the star-forming scenario in this region is more complex than the traditional spatial-temporal scenario, in which a generation of stars triggers the formation of a new spatially differentiated generation of stars.

وصف الملف: electronic resource

Relation: https://doaj.org/toc/1538-3881

URL الوصول: https://doaj.org/article/c3dee1302ed348ac8cbd689d92050d6f

المؤلفون: Ezequiel Manzo-Martínez, Nuria Calvet, Jesús Hernández, Susana Lizano, Ramiro Franco Hernández, Christopher J. Miller, Karina Maucó, César Briceño, Paola D’Alessio

المصدر: Astrophysical Journal; 4/10/2020, Vol. 893 Issue 1, p1-1, 1p

مصطلحات موضوعية: PROTOPLANETARY disks, AGE of stars, AGE groups, BIOLOGICAL evolution, EVOLUTIONARY models, SURFACE structure, DUST

مستخلص: We present a study of the evolution of the inner few astronomical units of protoplanetary disks around low-mass stars. We consider nearby stellar groups with ages spanning from 1 to 11 Myr, distributed into four age bins. Combining PANSTARSS photometry with spectral types, we derive the reddening consistently for each star, which we use (1) to measure the excess emission above the photosphere with a new indicator of IR excess and (2) to estimate the mass accretion rate () from the equivalent width of the Hα line. Using the observed decay of as a constraint to fix the initial conditions and the viscosity parameter of viscous evolutionary models, we use approximate Bayesian modeling to infer the dust properties that produce the observed decrease of the IR excess with age, in the range between 4.5 and 24 μm. We calculate an extensive grid of irradiated disk models with a two-layered wall to emulate a curved dust inner edge and obtain the vertical structure consistent with the surface density predicted by viscous evolution. We find that the median dust depletion in the disk upper layers is at 1.5 Myr, consistent with previous studies, and it decreases to by 7.5 Myr. We include photoevaporation in a simple model of the disk evolution and find that a photoevaporative wind mass-loss rate of agrees with the decrease of the disk fraction with age reasonably well. The models show the inward evolution of the H2O and CO snowlines. [ABSTRACT FROM AUTHOR]

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المؤلفون: Hunter Campbell, Elliott Khilfeh, Kevin R. Covey, Marina Kounkel, Richard Ballantyne, Sabrina Corey, Carlos G. Román-Zúñiga, Jesús Hernández, Ezequiel Manzo Martínez, Karla Peña Ramírez, Alexandre Roman-Lopes, Keivan G. Stassun, Guy S. Stringfellow, Jura Borissova, S. Drew Chojnowski, Valeria Ramírez-Preciado, Jinyoung Serena Kim, Javier Serna, Amelia M. Stutz, Ricardo López-Valdivia, Genaro Suárez, Jason E. Ybarra, Penélope Longa-Peña, José G. Fernández-Trincado

المصدر: The Astrophysical Journal, Vol 942, Iss 1, p 22 (2022)

مصطلحات موضوعية: Accretion, Stellar accretion, Pre-main sequence stars, Be stars, Classical T Tauri stars, Emission line stars, Astrophysics, QB460-466

الوصف: Very young ( t ≲ 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11–20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of n _e = 10 ^11 –10 ^12 cm ^−3 , and excitation temperatures that are inversely correlated with electron density (from T ∼ 5000 K for n _e ∼ 10 ^12 cm ^−3 to T ∼ 12,500 K at n _e ∼ 10 ^11 cm ^−3 ). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.

وصف الملف: electronic resource

Relation: https://doaj.org/toc/1538-4357

URL الوصول: https://doaj.org/article/dcbf61c38f5742cea480a9c04b75da38