A5069592382- Stellar, planetary, and galactic studies
- Solar and Space Plasma Dynamics
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Geomagnetism and Paleomagnetism Studies
- Ionosphere and magnetosphere dynamics
- Gamma-ray bursts and supernovae
- Geophysics and Gravity Measurements
- Astronomical Observations and Instrumentation
- History and Developments in Astronomy
- Complex Systems and Time Series Analysis
- Computational Drug Discovery Methods
- Magnetic confinement fusion research
- Fluid Dynamics and Turbulent Flows
- Nonlinear Dynamics and Pattern Formation
- Fractal and DNA sequence analysis
- Molecular spectroscopy and chirality
- Quantum chaos and dynamical systems
- Scientific Research and Discoveries
- Calibration and Measurement Techniques
- Historical Astronomy and Related Studies
- Chaos control and synchronization
- African Studies and Geopolitics
- Inertial Sensor and Navigation
Osservatorio Astrofisico di Catania
2022-2024
Institut d'Estudis Espacials de Catalunya
2022-2024
Institute of Space Sciences
2022-2024
National Institute for Astrophysics
2023
Institute of Space Science - INFLPR Subsidiary
2022
University of Crete
2018-2020
Foundation for Research and Technology Hellas
2019-2020
Stockholm University
2009-2017
Yale University
2015-2017
KTH Royal Institute of Technology
2012-2017
Proxima could host a planet on ∼5-year orbit, which Gaia can confirm in the near future providing its exact mass.
Context. Detecting a planetary companion in short-period orbit through radio emission from the interaction with its host star is new prospect exoplanet science. Recently, tantalising signal was found close to low-mass stellar system GJ 1151 using LOFAR observations. Aims. We studied spectroscopic time-series data of order search for companions, investigate possible signatures magnetic activity, and find explanations signal. Methods. used combined radial velocities measured spectra acquired...
Context. Current exoplanet surveys are focused on detecting small exoplanets orbiting in the liquid-water habitable zones of their host stars. Despite recent significant advancements instrumentation, main limitation these is intrinsic variability star itself. Aims. Our aim to investigate wavelength dependence high-precision radial velocities (RV), as stellar activity induced RVs should exhibit a while RV variation due an planet will be independent. Methods. We used chromatic index (CRX)...
Many astrophysical bodies harbor magnetic fields that are thought to be sustained by a dynamo process. However, it has been argued the production of large-scale mean-field action is strongly suppressed at large Reynolds numbers owing conservation helicity. This phenomenon known as {\it catastrophic quenching}. Advection stellar and galactic winds toward outer boundaries away from expected alleviate such quenching. Here we explore relative roles played advective turbulent--diffusive fluxes...
Owing to technological advances, the number of exoplanets discovered has risen dramatically in last few years. However, when trying observe Earth analogs, it is often difficult test veracity detection. We have developed a new approach analysis exoplanetary spectral observations based on temporal multifractality, which identifies time scales that characterize planetary orbital motion around host star, and those arise from stellar features such as spots. Without fitting models data, we show...
In the absence of rotation and shear, under assumption constant temperature or specific entropy, purely potential forcing by localized expansion waves is known to produce irrotational flows that have no vorticity. Here we study production vorticity idealized conditions when there rotation, baroclinicity, address problem generation in interstellar medium a systematic fashion. We use three-dimensional periodic box numerical simulations investigate various effects isolation. find for slow an...
Magnetic fields have been observed in massive Ap/Bp stars and presumably are also present the radiative zone of solar-like stars. Yet, to date there is no clear understanding dynamics magnetic field stably stratified layers. A purely toroidal configuration known be unstable, developing mainly non-axisymmetric modes. Rotation a small poloidal component may lead stable configuration. Here we perform global MHD simulations with EULAG-MHD code explore evolution located layer whose stratification...
The resistive decay of chains three interlocked magnetic flux rings is considered. Depending on the relative orientation field in rings, late-time can be either fast or slow. Thus, qualitative degree tangledness less important than actual value linking number or, equivalently, net helicity. Our results do not suggest that invariants higher order helicity need to considered characterize field.
The detection and characterisation of Earth-like planets with Doppler signals the order 1 m/s currently represent one greatest challenge for extrasolar-planet hunters. As results such findings are often controversial, it is desirable to provide independent confirmations discoveries. Testing different models suppression non-Keplerian stellar usually plaguing radial velocity data essential ensuring robust reproducible. Using an alternative treatment noise that discussed in discovery paper, we...
Estimates for the non-linear α effect in helical turbulence with an applied magnetic field are presented using two different approaches: imposed-field method where electromotive force owing to is used, and test-field separate evolution equations solved a set of test fields. Both approaches agree stronger fields, but there apparent discrepancies weaker fields that can be explained by influence dynamo-generated on scale domain referred as meso-scale Examples discussed these lead both...
We study spontaneous breakdown of chiral symmetry during the nonlinear evolution Tayler instability. start with an initial steady state zero helicity. Within linearized perturbation calculations, helical perturbations this have same growth rate for either sign Direct numerical simulations (DNS) fully equations, however, show that infinitesimal excess one helicity in gives rise to a saturated state. further breaking can be described by weakly finite--amplitude equations undetermined...
The magnetic fields of spiral galaxies are so strong that they cannot be primordial. Their typical values over one billion times higher than any value predicted for the early Universe. Explaining this immense growth and incorporating it in galaxy evolution theories is long-standing challenges astrophysics. So far, most successful theory sustained galactic field alpha-omega dynamo. This predicts a characteristic dipolar or quadrupolar morphology field, which has been observed external...
The full-sky Planck polarization data at 850um revealed unexpected properties of the E and B mode power spectra dust emission in interstellar medium (ISM). positive cross-correlation between total intensity, T, with modes has raised new questions about physical mechanisms that affect polarization, such as Galactic magnetic-field structure. This is key both to better understanding ISM dynamics accurately describing foregrounds Cosmic Microwave Background (CMB). In this theoretical paper we...
A comprehensive multi-wavelength campaign has been carried out to probe stellar activity and variability in the young Sun-like star $\iota$-Horologii. We present results from long-term spectropolarimetric monitoring of system by using ultra-stable spectropolarimeter/velocimeter HARPS at ESO 3.6-m telescope. Additionally, we included high-precision photometry NASA Transiting Exoplanet Survey Satellite (TESS) observations far- near-ultraviolet spectral regions STIS instrument on NASA/ESA...
We study the role of viscosity and effects a magnetic field on rotating, self-gravitating fluid, using Newtonian theory adopting ideal magnetohydrodynamic approximation. Our results confirm that can generate vorticity in inhomogeneous environments, while tension produce even absence fluid pressure density gradients. Linearizing our equations around an Einstein-de Sitter cosmology, we find adds to diluting effect universal expansion. Typically, however, dissipative viscous are confined...
Certain aspects of the mean-field theory turbulent passive scalar transport and electrodynamics are considered with particular emphasis on compressible fluids. It is demonstrated that total diffusivity for in a flow may well be smaller than molecular diffusivity. This full analogy to an old finding regarding magnetic electrically conducting turbulently moving fluid. These phenomena occur if irrotational part motion dominates vortical part, P\'eclet or Reynolds number not too large, and,...
Unveiling the evolution of toroidal field instability, known as Tayler is essential to understand strength and topology magnetic fields observed in early-type stars, core red giants, or any stellar radiative zone. We want study non-linear instability a stored stably stratified layer, spherical symmetry absence rotation. In particular, we intend quantify suppression function Brunt-V\"ais\"ala ($\omega_{\rm BV}$) Alfv\'en A}$) frequencies. use MHD equations implemented anelastic approximation...
Proxima Centauri is known to host an earth-like planet in its habitable zone; very recently a second candidate was proposed based on radial velocities. At quadrature, the expected projected separation of this new larger than 1 arcsec, making it potentially interesting target for direct imaging. While difficult, identification optical counterpart would allow detailed characterization closest planetary system. We searched SPHERE images acquired during four years through SHINE survey. In order...
Context. Gliese 832 (GJ 832) is an M2V star hosting a massive planet on decade-long orbit, GJ 832b, discovered by radial velocity (RV). Later, super Earth or mini-Neptune orbiting within the stellar habitable zone was reported 832c). The recently determined rotation period (45.7 $\pm$ 9.3 days) close to orbital of putative c (35.68 0.03 days). Aims. We aim confirm dismiss planetary nature RV signature attributed 832c, adding 119 new data points, photometric data, and analysis spectroscopic...
Context . The estimation of rotation periods stars is a key challenge in stellar astrophysics. Given the large amount data available from ground-based and space-based telescopes, there growing interest finding reliable methods to quickly automatically estimate with high level accuracy precision. Aims This work aims develop computationally inexpensive approach, based on machine learning techniques, accurately predict thousands periods. Methods innovation our approach use XGBoost algorithm...
The predictive power of mean-field theory is emphasized by comparing with simulations under controlled conditions. recently developed test-field method used to extract turbulent transport coefficients both in the kinematic and nonlinear or quasi-kinematic cases. A striking example provided magnetic buoyancy-driven flows that produce an α effect diffusion.
During their main sequence evolution, massive stars can develop convective regions very close to surface. These are caused by an opacity peak associated with iron ionization. Cantiello et al. (2009) found a possible connection between the presence of sub-photospheric motions and small scale stochastic velocities in photosphere early-type stars. This supports physical mechanism where microturbulence is waves that triggered subsurface convection zones. They further suggest clumping inner parts...
We investigate the effect of magnetic helicity on stability buoyant cavities as found in intergalactic medium. In these cavities, we insert helical fields and test whether or not can increase their to shredding through Kelvin-Helmholtz instability and, with that, lifetime. This is compared case an external vertical field which known reduce growth rate instability. By comparing a low-helicity configuration high one same energy find that internal stabilizes cavity. increases content....