Search results for "STELLA"

The mass determination challenge for exoplanetary science

2023

The mass of an exoplanet is a key parameter for the characterisation of the internal structure of a planet, as well as the study of the formation and the evolution of the planet, and its atmosphere. The radial velocity technique allows for measuring the planetary mass from the radial velocity variation of its parent star. However, limitations in the property determination of exoplanets, particularly in their masses, can arise from various sources especially from astrophysical noise due to stellar variability, caused by magnetic activity, which affects the detection and characterisation of exoplanets. This PhD thesis aims to understand the impact of our knowledge of the planetary mass in the…

Modeling X-ray Emission From The Coronae Of Low Mass Stars

2009

By extrapolating from observationally derived surface magnetograms of low-mass stars we construct models of their coronal magnetic fields and compare the 3D field geometries with axial multipoles. AB Dor, which has a radiative core, has a very complex field, whereas V374 Peg, which is completely convective, has a simple dipolar field. We calculate global X-ray emission measures assuming that the plasma trapped along the coronal loops is in hydrostatic equilibrium and compare the differences between assuming isothermal coronae, or by considering loop temperature profiles. Our preliminary results suggest that the non-isothermal model works well for the complex field of AB Dor, but not for the…

Analysis of the XMM-Newton observations of IC443

2017

We analyze for the first time the full set of archive XMM-Newton EPIC observations of the Galactic Supernova Remnant IC 443. We aim at identifying the contribution of the shocked ejecta and interstellar medium and at the describing the physical and chemical properties of the shocked plasma. We also aim at addressing the presence of overionized plasma and its physical origin. We trace the morphology of Si- and S-rich ejecta with unprecedented spatial resolution, by adopting a novel method to produce maps of equivalent width. We describe in detail the method adopted and the results obtained and present preliminary results of a spatially resolved spectral analysis performed on selected regions…

THE INTERACTION OF THE STELLAR HIGH ENERGY RADIATION WITH THE CIRCUMSTELLAR MEDIUM

The purpose of this Thesis is to study how stellar high energy radiation affects exo- planetary atmospheres. High level of stellar high energy, X-rays and (vacuum end extreme) ultraviolet radiation may prevent planets’ habitability and limit the width of the habitability zone. Such radiation may ionize a star surrounding, affecting the chemistry and thermal bal- ance. The effects of X-rays can be wide ranging or relatively local. Soft X-rays are absorbed closer to the source than X-rays with energy greater than 1 keV. The absorption cross-section of hard X-rays are generally very small, so that such radiation may affect a whole galaxy to some extent. The product of photo-ionization is a cas…

Multiwavelength diagnostics of accretion in an X-ray selected sample of CTTSs

2011

Context. High resolution X-ray spectroscopy has revealed soft X-rays from high density plasma in classical T Tauri stars (CTTSs), probably arising from the accretion shock region. However, the mass accretion rates derived from the X-ray observations are consistently lower than those derived from UV/optical/NIR studies. Aims: We aim to test the hypothesis that the high density soft X-ray emission originates from accretion by analysing, in a homogeneous manner, optical accretion indicators for an X-ray selected sample of CTTSs. Methods: We analyse optical spectra of the X-ray selected sample of CTTSs and calculate the accretion rates based on measuring the Hα, Hβ, Hγ, He ii 4686 Å, He i 5016 …

High Resolution X-ray Spectroscopy of Pre-Main-Sequence Stars: TWA 5 and PZ Tel

2004

We report on the analysis of high resolution X-ray spectra of two pre-main-sequence stars: TWA 5 (observed with XMM-Newton) and PZ Telescopii (observed with Chandra/HETGS). TWA 5 is a classical T Tauri star in the TW Hydrae association while PZ Tel is a rapidly rotating weak-lined T Tauri star in the beta-Pictoris moving group. For both stars we have reconstructed the emission measure distribution and derived the coronal abundances to check for possible patterns of the abundances related to the first ionization potential of the various elements. We have also derived estimates of the plasma density from the analysis of the He-like triplets. We compare the characteristics of our targets with …

Testing the Ability of Field Extrapolation Models to Predict the X-ray Emission Properties of Pre-Main Sequence Stars

2010

By extrapolating from observationally derived magnetic surface maps, obtained through Zeeman-Doppler imaging, models of stellar magnetospheres can be constructed. By assuming that the plasma trapped along the closed field lines is in hydrostatic equilibrium, coronal X-ray emission properties, such as the global X-ray emission measure and the amount of rotational modulation of X-ray emission, can be predicted. For pre-main sequence magnetospheres the analysis can be extended to incorporate accretion flows, and predict the amount of softer X-ray emission from accretion spots that would be observed. I will detail the preliminary results of an ambitious multi-wavelength, multi-observing site, a…

Dialettica e trasformazione in Th. W. Adorno

2020

La dialettica può svolgere un’effettiva funzione critico-conoscitiva in quanto, pur irretita nelle maglie del pensare identico, di esso è capace di ridisegnare la struttura concettuale, rendendola permeabile a quel che le sue rigide procedure classificatorie tendono inevitabilmente ad opprimere e occultare. Se la dialettica non è logica manifestativa del vero, se anzi rivela una compromissione inevitabile con il sapere illusorio prodotto dal pensiero identificante, del pensiero identificante rappresenta però l’unica chance di trasformazione Dialectics can play an effective critical-cognitive function in that, although caught in the mesh of «identity thinking», it is capable of redesigning t…

Episodios caballerescos del Espejo de príncipes y cavalleros en La tempestad de Shakespeare: posibles transferencias

2013

El artículo pretende profundizar en el tema de las posibles influencias que Espejo de príncipes y caballeros, un popular libro de caballerías, traducido al inglés, pudo haber ejercido en el dramaturgo William Shakespeare en el proceso creativo de La tempestad. Se estudian en especial los paralelos entre los episodios marítimos, los personajes de Artidón y Calibán, los sabios y magos (Artemidoro, Polisteo y Próspero), la maga Artimaga y la bruja Artimaga y la bruja Sycorax.

XMM-Newton large programme on SN1006 - II. Thermal emission

2016

Based on the XMM-Newton large program on SN1006 and our newly developed spatially resolved spectroscopy tools (Paper~I), we study the thermal emission from ISM and ejecta of SN1006 by analyzing the spectra extracted from 583 tessellated regions dominated by thermal emission. With some key improvements in spectral analysis as compared to Paper~I, we obtain much better spectral fitting results with less residuals. The spatial distributions of the thermal and ionization states of the ISM and ejecta show different features, which are consistent with a scenario that the ISM (ejecta) is heated and ionized by the forward (reverse) shock propagating outward (inward). Different elements have differe…