Search results for "Cosmology"

Accretion in young stars: measure of the stream velocity of TW Hya from the X-ray Doppler shift

2015

High-resolution X-ray spectra are a unique tool to investigate the accretion process in young stars. In fact X-rays allow to investigate the accretion-shock region, where the infalling material is heated by strong shocks due to the impact with the denser stellar atmosphere. Here we show for the first time that it is possible to constrain the velocity of the accretion stream by measuring the Doppler shift of the emitted X-rays. To this aim we analyzed the deep Chandra/HETGS observation of the accreting young star TW Hya. We selected a sample of emission lines free from significant blends, fitted them with gaussian profiles, computed the radial velocity corresponding to each line, and average…

Modelling and Simulation in Science, Proceedings of the 6th International Workshop on Data Analysis in Astronomy >

2007

Could Themis be the Deity who «Steers» Parmenides’ Cosmos?

2021

In this paper I will investigate the identity of the daímōn introduced by Parmenides in B12, 3 DK, the deity “who steers all things”. The importance of this deity is not adequately reflected in ancient doxography but in recent decades many scholars have reconsidered its role. I argue that in Parmenides’ poem this daímōn may play a relevant role in connecting the theological, ontological and cosmological planes. My purpose is to provide enough arguments for the hypothesis that the daímōn may be the same goddess, Themis, who in the proem (B1, 28) is paired with Dike as a guide for Parmenides to the theá who will reveal to him the truth of tò eón, and in the part of the poem called alḗtheia (B…

THE INFLUENCE OF TEXTURE SYMMETRY IN MARKER POINTING: EXPERIMENTING WITH HUMANS AND ALGORITHMS

2011

Symmetry plays a fundamental role in aiding the visual system, to organize its environmental stimuli and to detect visual patterns of natural and artificial objects. Various kinds of symmetry exist, and we will discuss how internal symmetry due to textures influences the choice of direction in visual tasks. Two experiments are presented: the first, with human subjects, deals with the effect of textures on preferences for a pointing direction. The second emulates the performances obtained in the first through the use of an algorithm based on a physic metaphor. Results from both experiments are shown and comment.

Hochschild Cohomology Theories in White Noise Analysis

2008

We show that the continuous Hochschild cohomology and the differential Hochschild cohomology of the Hida test algebra endowed with the normalized Wick product are the same.

AE Aurigae: First detection of non-thermal X-ray emission from a bow shock produced by a runaway star

2012

Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace due to the encounter of two massive binary systems and now is passing through the dense nebula IC 405…

Catching the radio flare in CTA 102. III. Core-shift and spectral analysis

2013

The temporal and spatial spectral evolution of the jets of AGN can be studied with multi-frequency, multi-epoch VLBI observations. The combination of both, morphological and spectral parameters can be used to derive source intrinsic physical properties such as the magnetic field and the non-thermal particle density. In the first two papers of this series, we analyzed the single-dish light curves and the VLBI kinematics of the blazar CTA 102 and suggested a shock-shock interaction between a traveling and a standing shock wave as a possible scenario to explain the observed evolution of the component associated to the 2006 flare. In this paper we investigate the core-shift and spectral evoluti…

Origin of asymmetries in X-ray emission lines from the blast wave of the 2014 outburst of nova V745 Sco

2016

The symbiotic nova V745 Sco was observed in outburst on 2014 February 6. Its observations by the Chandra X-ray Observatory at days 16 and 17 have revealed a spectrum characterized by asymmetric and blue-shifted emission lines. Here we investigate the origin of these asymmetries through three-dimensional hydrodynamic simulations describing the outburst during the first 20 days of evolution. The model takes into account thermal conduction and radiative cooling and assumes a blast wave propagates through an equatorial density enhancement. From the simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra. We find that both the blast wave and th…

Modeling the remnants of core-collapse supernovae from luminous blue variable stars

2021

LBVs are massive evolved stars that suffer sporadic and violent mass-loss events. They have been proposed as the progenitors of some core-collapse SNe, but this idea is still debated due to the lack of direct evidence. Since SNRs can carry in their morphology the fingerprints of the progenitor stars as well as of the inhomogeneous CSM sculpted by the progenitors, the study of SNRs from LBVs could help to place core-collapse SNe in context with the evolution of massive stars. We investigate the physical, chemical and morphological properties of the remnants of SNe originating from LBVs, in order to search for signatures, revealing the nature of the progenitors, in the ejecta distribution and…

Cosmological shock waves: clues to the formation history of haloes

2012

Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal w…