Search results for "TAU"
showing 10 items of 4585 documents
X-ray emission from stellar jets by collision against high-density molecular clouds: an application to HH 248
2015
We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts against a dense molecular cloud. This scenario may be usual for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10 MK, consistent with producti…
Mu-tau neutrino refraction and collective three-flavor transformations in supernovae
2008
9 pages, 6 figures.-- PACS nrs.: 14.60.Pq; 97.60.Bw.-- ArXiv pre-print available at: http://arxiv.org/abs/0712.1137
Zvaigžņotā Debess: 2009/10, Ziema (206)
2009
Contents: TASS and Soviet Press materials. Flight of the Group of Three Soviet Spaceships ; Soviet and Foreign Press materials. Second Expedition on the Moon ; Č.Šklennik. Excursion to an Ancient Laboratory ; M.Gills. Opening Address ; Conference “Astronomy in Latvia” Programme ; From Presentation Abstracts ; I.Pundure. First Enterprise of this Kind ; N.Cimahoviča. Astronomical Contribution to Culture ; A.Alksnis. First Findings of Space Mission CoRoT ; I.Pundure. Ten Years of Chandra Hot Universe Exploration ; M.Gills. The Beginning of Autumn with Astronomy ; Buying Stars and Star Names (translation from IAU) ; I.Pundure. Arturs Balklavs and Astronomy of Latvia (1990-1997) ; J.Jaunbergs. A…
The Close T Tauri Binary System V4046 Sgr: Rotationally Modulated X-Ray Emission from Accretion Shocks
2012
We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotatio…
Predicting the time variation of radio emission from MHD simulations of a flaring T-Tauri star
2020
ABSTRACT We model the time-dependent radio emission from a disc accretion event in a T-Tauri star using 3D, ideal magnetohydrodynamic simulations combined with a gyrosynchrotron emission and radiative transfer model. We predict for the first time, the multifrequency (1–1000 GHz) intensity and circular polarization from a flaring T-Tauri star. A flux tube, connecting the star with its circumstellar disc, is populated with a distribution of non-thermal electrons that is allowed to decay exponentially after a heating event in the disc and the system is allowed to evolve. The energy distribution of the electrons, as well as the non-thermal power-law index and loss rate, are varied to see their …
Effects of radiation in accretion regions of classical T Tauri stars
2019
Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the su…
Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
2013
(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic f…
CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and acc…
2017
Pre-main sequence stars are variable sources. In stars with disks, this variability is related to the morphology of the inner circumstellar region (<0.1 AU) and that of the photosphere and corona, all impossible to be spatially resolved with present day techniques. This has been the main motivation for the Coordinated Synoptic Investigation of NGC 2264. In this paper, we focus on the stars with disks. We analyze the X-ray spectral properties extracted during optical bursts and dips in order to unveil the nature of these phenomena. We analyze simultaneous CoRoT and Chandra/ACIS-I observations to search for coherent optical and X-ray flux variability in stars with disks. Then, stars are an…
"Table 2" of "Measurement and Interpretation of Fermion-Pair Production at LEP Energies of 183 and 189 GeV"
2003
No description provided.
Sociāli vājākās grupas (atraitnes, bāreņi, sveštautieši, vergi) Senās Izraēlas sabiedrībā 1207-1010.g.p.m.ē.
2017
Darba tēma ir “Sociāli vājākās grupas (atraitnes, bāreņi, sveštautieši, vergi) Senās Izraēlas sabiedrībā 1207. – 1010. g.p.m.ē.” Šī tēma tika izvēlēta, jo sociālā vēsture Senajā Izraēlā ir nepietiekami izpētīta tēma, kurai pēdējās desmitgadēs pavērušās jaunas pētījumu iespējas un metodes. Tika pētīts, kā veidojās un funkcionēja Izraēlas sabiedrība laikā pirms monarhijas un kādā stāvoklī atradās tās sociāli vājākās grupas, kuras kā tādas apraksta Vecā Derība – atraitnes, bāreņi, sveštautieši un vergi. Tika secināts, ka šīs grupas nonāk sociāli marginalizētā stāvoklī, zaudējot klana aizsardzību – nomirstot ģimenes galvam, nabadzības dēļ vai indivīdiem pametot kalnu kopīgi apdzīvotās teritorij…