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Examinando (CAB) Artículos por Materia "Accretion Disc"
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Publicación Restringido Detection of a possible multiphase ultra-fast outflow in IRAS 13349+2438 with NuSTAR and XMM-Newton.(Oxford Academics: Blackwell Publishing, 2020-08-25) Parker, M. L.; Matzeu, G. A.; Alston, W. N.; Fabian, A. C.; Lobban, A.; Miniutti, G.; Pinto, C.; Santos Lleó, M.; Schartel, N.; European Space Agency (ESA); 0000-0002-5635-5340; 0000-0003-1994-5322; 0000-0003-2658-6559; 0000-0001-5948-8360; 0000-0003-2532-7379; 0000-0002-9378-4072; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737We present joint NuSTAR and XMM–Newton observations of the bright, variable quasar IRAS 13349+2438. This combined data set shows two clear iron absorption lines at 8 and 9 keV, which are most likely associated with two layers of mildly relativistic blueshifted absorption, with velocities of ∼0.14c and ∼0.27c. We also find strong evidence for a series of Ly α absorption lines at intermediate energies in a stacked XMM–Newton EPIC-pn spectrum, at the same blueshift as the lower velocity iron feature. This is consistent with a scenario where an outflowing wind is radially stratified, so faster, higher ionization material is observed closer to the black hole, and cooler, slower material is seen from streamlines at larger radii.Publicación Acceso Abierto The accretion rates and mechanisms of Herbig Ae/Be stars(Oxford Academics: Oxford University Press, 2020-01-20) Wichittanakom, C.; Oudmaijer, R. D.; Fairlamb, J. R.; Mendigutía, I.; Vioque, M.; Ababakr, K. M.; Comunidad de Madrid; European Research Council (ERC); National Science Foundation (NSF); Mendigutía, I. [0000-0002-0233-5328]; Farlamb, J. [0000-0002-2833-2344]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737This work presents a spectroscopic study of 163 Herbig Ac/Be stars. Amongst these, we present new data for 30 objects. Stellar parameters such as temperature, reddening, mass, luminosity, and age are homogeneously determined. Mass accretion rates are determined from Ha emission line measurements. Our data is complemented with the X-Shooter sample from previous studies and we update results using Gain DR2 parallaxes giving a total of 78 objects with homogeneously determined stellar parameters and mass accretion rates. In addition, mass accretion rates of an additional 85 HAeBes are determined. We confirm previous findings that the mass accretion rate increases as a function of stellar mass, and the existence of a different slope for lower and higher mass stars, respectively. The mass where the slope changes is determined to be 3.98(-0.94)(+1.37) M-circle dot. We discuss this break in the context of different modes of disc accretion for low- and high-mass stars. Because of their similarities with T Tauri stars, we identify the accretion mechanism for the late-type Herbig stars with the Magnetospheric Accretion. The possibilities for the earlier-type stars are still open, we suggest the Boundary Layer accretion model may be a viable alternative. Finally, we investigated the mass accretion age relationship. Even using the superior Gaia based data, it proved hard to select a large enough sub-sample to remove the mass dependence in this relationship, Yet, it would appear that the mass accretion does decline with age as expected from basic theoretical considerations.
