Search results for "Astronomi"

Surface and Atmospheric Structure on the T Tauri Star V2129 Oph

2011

We provide an overview of a multi-wavelength observing campaign focusing on the accretion and coronal processes in the young star V2129 Oph. V2129 Oph is a classical T Tauri star with a 6.5 day rotation period in the ρ Oph star forming region. On 27-29 June 2009 we obtained two 100 ksec Chandra HETG exposures, aiming at opposite hemispheres of the star. We discuss the X-ray data elsewhere. In order to place the coronal X-ray emission in context, we obtained contemporaneous optical and near-IR photometry and high dispersion optical spectroscopy. The photometry shows the existence of dark photospheric spots. The Hα line profiles show a modulation of the mean Hα velocity and the presence of re…

Spin caloric transport from density-functional theory

2019

Spin caloric transport refers to the coupling of heat with spin transport. Its applications primarily concern the generation of spin currents and control of magnetisation by temperature gradients for information technology, known by the synonym spin caloritronics. Within the framework of ab initio theory, new tools are being developed to provide an additional understanding of these phenomena in realistic materials, accounting for the complexity of the electronic structure without adjustable parameters. Here, we review this progress, summarising the principles of the density-functional-based approaches in the field and presenting a number of application highlights. Our discussion includes th…

Coronal properties of active G-type stars in different evolutionary phases

2005

We report on the analysis of XMM-Newton observations of three G-type stars in very different evolutionary phases: the "weak-line" T Tauri star HD 283572, the Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Corn. The X-ray luminosities of the three stars are all in the range 10(30) - 10(31) erg/s. We compare the Emission Measure Distributions of these bright sources, derived from high-resolution X-ray spectra, as well as the pattern of elemental abundances vs. First Ionization Potential (FIP). The results of our analysis suggest that the coronae of these stars are very similar in terms of dominant coronal magnetic structures, in spite of differences in their evolutio…

High Energy Emission and its Variability in Young Stellar Objects

2019

Young stars show a variety of highly energetic phenomena, from accretion and outflow processes to hot coronal plasmas confined in their outer atmosphere, all regulated by the intense stellar magnetic fields. Many aspects on each of these phenomena are debated, but, most notably, their complex mutual interaction remains obscure. In this work I report how these phenomena are simultaneously responsible for the high-energy emission from young stars, with a special focus on the expected and observed variability in the X-ray band. Investigating variations in the X-ray emission from young stars allows us to pose constraints on flare and coronal plasma properties, coronal heating, accretion stream …

The Gaia-ESO Survey: impact of extra mixing on C and N abundances of giant stars

2018

The GES survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements C and N at their surface. The surface abundances of these chemical species are well-known to change in stars during their evolution on the red giant branch after the first dredge-up episod, as a result of extra-mixing phenomena. We investigate the effects of thermohaline mixing on C and N abundances using the first comparison between the GES [C/N] determinations with simulations of the observed fields using a model of stellar population synthesis. We explore the effects of thermohaline mixing on the chemic…

Activity-rotation relation in the young cluster h Per

2015

The activity-rotation relation in PMS stars is still an open issue. To bridge the gap between the well constrained case of MS stars and the puzzling case of very young PMS stars, we studied the activity-rotation relation in the young cluster h Persei. Because of its age (˜13 Myr) h Per contains both fast and slow rotators, allowing us therefore to test the different regimes of stellar dynamo. We analyzed a deep Chandra/ACIS-I observation to constrain the activity level of h Per members. Rotational periods were derived by tet{MorauxArtemenko2013}. From the comparison of the 1002 detected X-ray sources, and the 586 h Per members with measured rotational period, we obtained a final catalog of …

Simbol-X capability of detecting the non-thermal emission of stellar flares.

2008

We investigate the capability of detecting, with Simbol-X, non-thermal emission during stellar flares, and distinguishing it from hot thermal emission. We find that flare non-thermal emission is detectable when at least ~20 cts are detected with the CZT detector in the 20-80 keV band. Therefore Simbol-X will detect the non-thermal emission from some of the X-ray brightest nearby stars, whether the thermal vs. non-thermal relation, derived for solar flares, holds.

X-ray emission from the old CTTS MP Muscae

2007

We study the properties of X-ray emitting plasma of MP Mus, an old classical T Tauri star. XMM-Newton/RGS spectra allow us to measure the plasma electron density, which probes whether X-ray emission is produced in the accretion process. X-ray emission from MP Mus originates from high density cool plasma but a hot flaring component is also present, suggesting that both coronal magnetic activity and accretion contribute to the observed X-ray emission. From the soft part of the X-ray emission from MP Mus, mostly produced by plasma heated in the accretion shock, we derive the accretion parameters and the characteristics of the shock-heated plasma.

X-ray emission from an adolescent classical T Tauri star

2007

CSI 2264: Simultaneous optical and X-ray variability in the pre-main sequence stars of NGC 2264

2019

Context. Pre-main sequence stars are variable sources. In diskless stars this variability is mainly due to the rotational modulation of dark photospheric spots and active regions, as in main sequence stars even if associated with a stronger magnetic activity.Aims. We aim at analyzing the simultaneous optical and X-ray variability in these stars to unveil how the activity in the photosphere is connected with that in the corona, to identify the dominant surface magnetic activity, and to correlate our results with stellar properties, such as rotation and mass.Methods. We analyzed the simultaneous optical and X-ray variability in stars without inner disks (e.g., class III objects and stars with…