High-Energy Processes in Young Stellar Objects

Feigelson, E. D.; Montmerle, T.

doi:10.1146/annurev.astro.37.1.363

Cited by 698 publications

(727 citation statements)

References 210 publications

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“…Angular momentum conservation during the initial contraction of a proto-stellar cloud eventually leads to a central pre-main sequence star surrounded by a disk. As angular momentum is transported outward through the disk, material must move from the disk, either onto the star or into a wind (see, e.g., Feigelson & Montmerle 1999). Theoretical studies on star formation suggest that a substantial portion of a star's final mass is accreted through such a disk.…”

Section: Discussionmentioning

confidence: 99%

A spectroscopic study of the close eclipsing binary HS Herculis

Çakırlı

İbanoǧlu

Frasca³

2007

A&A

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Aims. New high-resolution spectroscopic observations of the eclipsing binary HS Herculis are presented. The main aims were to determine the stellar parameters of the two components, their evolutionary stage, and to search for spectroscopic evidence for a possible third body. Methods. Using the cross-correlation technique, we detect spectroscopically the faint secondary component of HS Herculis, and for the firts time measure its radial velocity. The primary and secondary radial velocity curves are analyzed simultaneously and the results of the orbital solution are combined with those derived from multiband light curve analysis to derive orbital and stellar parameters. Results. We find the masses to be M 1 = 4.49± 0.16 and M 2 = 1.75± 0.09 M , the radii to be R 1 = 2.83± 0.04 and R 2 = 1.61± 0.02 R , and the effective temperatures to be T 1 = 15 200 ± 750 K and T 2 = 7600 ± 400 K for the primary and secondary stars, respectively. We also derive projected rotational velocities of the components as v 1 sin i = 81 ± 3 and v 2 sin i = 24 ± 6. Conclusions. While a synchronous rotation for the primary star is indicated by the broadening of the spectral lines, the secondary component appears to rotate more slowly, nearly one half the synchronous rotation velocity. This discrepancy indicates that the less massive secondary component could have not yet attained tidal synchronization. Although the presence of a third body physically bound to the eclipsing pair has been suggested by many investigators, we find no sign of its presence in our CCD spectra. The evolutionary stage of the system's components is briefly discussed by comparing their physical parameters with those of theoretical models. We find that the two components are located near the zero-age main sequence, with an age of about 32 Myr.

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Section: Discussionmentioning

confidence: 99%

A spectroscopic study of the close eclipsing binary HS Herculis

Çakırlı

İbanoǧlu

Frasca³

2007

A&A

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“…We then consider a separate X-ray illuminated model in which the gas is solely exposed to X-rays, but not FUV photons, aiming at evaluating the influence of these two energy sources on the chemistry. There is evidence for X-ray emission in protoplanetary disks (Feigelson & Montmerle 1999). The main effect of X-rays on the chemistry is the ionization of the gas producing high-energy photoelectrons (ph-e − ), which further ionize and dissociate the species.…”

Section: Chemical Modelmentioning

confidence: 99%

Formation of simple organic molecules in inner T Tauri disks

Agúndez¹,

Cernicharo²,

Goicoechea³

2008

A&A

155

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Aims. We present time dependent chemical models for a dense and warm O-rich gas exposed to a strong, far ultraviolet (FUV) field aimed at exploring the formation of simple organic molecules in the inner regions of protoplanetary disks around T Tauri stars.Methods. An up-to-date chemical network is used to compute the evolution of molecular abundances. Reactions of H 2 with small organic radicals such as C 2 and C 2 H, which are not included in current astrochemical databases, overcome their moderate activation energies at warm temperatures and become very important for the gas phase synthesis of C-bearing molecules.Results. The photodissociation of CO and release of C triggers the formation of simple organic species such as C 2 H 2 , HCN, and CH 4 . In timescales between 1 and 10 4 years, depending on the density and FUV field, a steady state is reached in the model in which molecules are continuously photodissociated, but also formed, mainly through gas phase chemical reactions involving H 2 . Conclusions. The application of the model to the upper layers of inner protoplanetary disks predicts large gas phase abundances of C 2 H 2 and HCN. The implied vertical column densities are as large as several 10 16 cm −2 in the very inner disk (<1 AU), in good agreement with the recent infrared observations of warm C 2 H 2 and HCN in the inner regions of IRS 46 and GV Tau disks. We also compare our results with previous chemical models studying the photoprocessing in the outer disk regions, and find that the gas phase chemical composition in the upper layers of the inner terrestrial zone (a few AU) is predicted to be substantially different from that in the upper layers of the outer disk (>50 AU).

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“…Using such proxy it has been shown that magnetic activity increases with rotation rate and that above a given rotation rate (that depends on the stellar spectral type but is around Ros ∼ 0.1), stellar magnetic activity first saturates (Pizzolato et al 2003;Wright et al 2011) and then possibly "over-saturates" for extremely fast rotation rate such as the ones found in young solar-like T-Tauri stars (Feigelson and Montmerle 1999). One can thus simply seek to characterize how the saturation of the dynamo generated field can be linked to the saturation of solar-like star X-ray emissivity.…”

Section: Nonlinear Dynamo Effect Magnetic Activity and Cyclesmentioning

confidence: 99%

The Solar-Stellar Connection

Brun¹,

García²,

Houdek³

et al. 2017

Space Sciences Series of ISSI

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We discuss how recent advances in observations, theory and numerical simulations have allowed the stellar community to progress in its understanding of stellar convection, rotation and magnetism and to assess the degree to which the Sun and other stars share similar dynamical properties. Ensemble asteroseismology has become a reality with the advent of large time domain studies, especially from space missions. This new capability has provided improved constraints on stellar rotation and activity, over and above that obtained via traditional techniques such as spectropolarimetry or CaII H&K observations. New data and surveys covering large mass and age ranges have provided a wide parameter space to confront theories of stellar magnetism. These new empirical databases are complemented by theoretical advances and improved multi-D simulations of stellar dynamos. We trace these pathways through which a lucid and more detailed picture of magnetohydrodynamics of solar-like stars is beginning to emerge and discuss future prospects.

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High-Energy Processes in Young Stellar Objects

Cited by 698 publications

References 210 publications

A spectroscopic study of the close eclipsing binary HS Herculis

A spectroscopic study of the close eclipsing binary HS Herculis

Formation of simple organic molecules in inner T Tauri disks

The Solar-Stellar Connection

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