A5002053477- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Geophysics and Gravity Measurements
- Geomagnetism and Paleomagnetism Studies
- Atmospheric Ozone and Climate
- Planetary Science and Exploration
- Mechanics and Biomechanics Studies
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Ionosphere and magnetosphere dynamics
- Calibration and Measurement Techniques
- High-pressure geophysics and materials
- History and Developments in Astronomy
- Advanced Thermodynamics and Statistical Mechanics
- Solar Radiation and Photovoltaics
- Spectroscopy and Laser Applications
- Advanced Chemical Physics Studies
- Atomic and Subatomic Physics Research
- Geophysics and Sensor Technology
Università della Svizzera italiana
2022-2024
Istituto Ricerche Solari Locarno
2022-2024
Institut für Sonnenphysik
2014-2023
University of Freiburg
2010-2022
University of Hawaii System
2013-2020
Kavli Institute for Particle Astrophysics and Cosmology
2019
University of California, Santa Barbara
2019
University of Hawaii Maui College
2019
École Normale Supérieure de Lyon
2018
Centre de Recherche Astrophysique de Lyon
2018
Magnetic activity similar to that of the Sun is observed on a variety cool stars with external convection envelopes. Stellar rotation coupled convective motions generate strong magnetic fields in stellar interior and produce multitude phenomena including starspots photosphere, chromospheric plages, coronal loops, UV, X-ray, radio emission flares. Here I review phenomenon different types stars, observational tools diagnostic techniques for studying as well starspot properties their...
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto hole, which heats the sufficiently to emit x-rays. We report polarimetric observation of XRB Cygnus X-1 using Imaging Polarimetry Explorer. The electric field position angle aligns with outflowing jet, indicating that jet launched inner emitting region. polarization degree (4.01+-0.20)% at 2 8 kiloelectronvolts, implying accretion disk viewed closer edge-on than orbit. observations reveal...
Abstract Study Analysis Group 21 (SAG21) of NASA’s Exoplanet Exploration Program was organized to study the effect stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring wavelength-dependent radius planet as it transits its star. Transmission spectroscopy relies precise understanding spectrum star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and...
A novel analysis of sunspot group data for the past 120 years reveals that sunspots in both northern and southern hemispheres are formed preferably two persistent active longitudes separated by 180°. In Carrington reference frame, continuously migrate phase with respect to meridian a variable rate. They remain however quasi-rigid structure. We find migration is determined changes mean latitude differential rotation. The rotation rate calculated from agreement SOHO/MDI measurements. longitude...
We report first multicolor polarimetric measurements (UBV bands) for the hot Jupiters HD189733b and confirm our previously reported detection of polarization in B band (Berdyugina et al. 2008). The wavelength dependence indicates dominance Rayleigh scattering with a peak blue U bands ~10^-4+/-10^-5 at least factor two lower signal V band. Rayleigh-like dependence, detected also transmitted light during transits, implies rapid decrease toward longer wavelengths. Therefore, nondetection by...
The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of solar atmosphere, from deep photosphere to upper chromosphere. Its design combines knowledge and expertise gathered by physics community during construction operation state-of-the-art telescopes operating in visible near-infrared wavelengths: Swedish 1m (SST), German Vacuum Tower (VTT) GREGOR, French T\'elescope H\'eliographique pour l'\'Etude du Magn\'etisme et des Instabilit\'es Solaires...
We present the results of an extensive time series analysis longitudinally-averaged synoptic maps, recorded at National Solar Observatory (NSO/Kitt Peak) from 1975 to 2003, and provide evidence for a multitude quasi-periodic oscillations in photospheric magnetic field Sun. In low frequency range, we have located sources , periodicities that were previously detected north-south asymmetry unsigned flux (Knaack et al. 2004, A&A, 418, L17). addition, quasi-periodicities around been found. The...
Context. A small fraction of upper main sequence stars have strong, highly structured magnetic fields. The origin and evolution these fields are not adequately understood.
The observational signatures of black holes in x-ray binary systems depend on their masses, spins, accretion rate, and the misalignment angle between hole spin orbital angular momentum. We present optical polarimetric observations MAXI J1820+070, from which we constrain position orbital. Combining this with previous determinations relativistic jet orientation, traces spin, inclination orbit, determine a lower limit 40° spin-orbit angle. must originate either evolution or formation stages. If...
We present the first evidence that a single active dwarf of solar type can show long-lived, non axi symmetric spot distribution – longitudes on opposite hemispheres, similar to evolved, rapidly rotating RS CVn-type binary stars. analyse new as well published photometric observations young LQ Hya, spanning almost 20 years. find activity star has three cycles: 5.2-yr "flip-flop" cycle, 7.7-yr period in amplitude modulation brightness and an approximately 15-yr variations mean brightness. The...
Using realistic ab initio simulations of radiative magnetoconvection, we show that the bright structures in images taken "G band," a spectral band dominated by lines CH molecule, precisely outline small-scale concentrations strong magnetic fields on visible solar surface. The brightening is caused depletion molecules hot and tenuous structures, thus confirming model radiatively heated flux concentrations. These results provide firm basis for observational studies evolution dynamics field...
We report on significant periodic variations of the magnetic activity between north and south hemisphere Sun. For this purpose, we have investigated north–south asymmetry two solar data sets, namely Kitt Peak synoptic Carrington rotation maps photospheric field (1975–2003) monthly averaged sunspot areas (1874–2003). Using Fourier wavelet analysis, found a regular pattern pronounced oscillations with periods 1.50 ± , 1.79 3.6 in flux asymmetry. The former are related to process which leads...
Bright points (BPs) in the solar photosphere are thought to be radiative signatures (small-scale brightness enhancements) of magnetic elements described by slender flux tubes or sheets located darker intergranular lanes photosphere. They contribute ultraviolet (UV) variations over cycle and hence may play a role influencing Earth's climate. Here we aim obtain better insight into their properties combining high-resolution UV spectro-polarimetric observations BPs Sunrise Observatory with 3D...
We have built a new broad-band polarimeter (DIPOL-2), capable of measuring polarization with the precision at 10<sup>-5</sup> level. Two dichroic beam-splitters are used to split light into three passbands (BVR), simultaneously recorded CCDs. A rotatable superachromatic λ/2 (or λ/4) plate is as modulator and plane parallel calcite analyzer. Simple yet effective design small number optical elements moving mechanical parts makes DIPOL-2 highly versatile reliable instrument...
Fresh inner solar system material preserved in the Oort cloud may hold key to understanding our formation.
Abstract We develop a polarimetry-based remote-sensing method for detecting and identifying life forms in distant worlds distinguishing them from non-biological species. To achieve this we have designed built bio-polarimetric laboratory experiment BioPol measuring optical polarized spectra of various biological samples. Here focus on pigments, which are common plants bacteria that employ either photosynthesis or protection against reactive oxygen Photosynthesis, provides organisms with the...
Abstract We present a photometric detection of the first brightness dips unique variable star KIC 8462852 since end Kepler space mission in 2013 May. Our regular surveillance started 2015 October, and sequence dipping began 2017 May continuing on through 2017, when was no longer visible from Earth. distinguish four main 1%–2.5% dips, named “ Elsie ,” Celeste Skara Brae Angkor which persist timescales several days to weeks. results so far are as follows: (i) there apparent changes stellar...
Realistic simulations of radiative magneto-convection in the solar (sub)photosphere are used for a spectral synthesis Fraunhofer's G band, which is dominated by lines from CH molecule. It found that spatial pattern integrated G-band brightness closely matches structure magnetic flux concentrations convective downflow regions. The contrast mainly caused weakening due to reduced abundance and resulting shift optical depth scale hot tenuous concentrations. Various properties synthetic images...
The magnetic, thermal and velocity structure of a regular sunspot, observed close to solar disk center is presented. Spectropolarimetric data obtained with the Tenerife Infrared Polarimeter (TIP) in two infrared Fe I lines at 15 648.5 Åand 652.8 Åare inverted employing technique based on response functions retrieve atmospheric stratification every point sunspot. In order improve results for umbra, profiles Zeeman split OH blending also consistently fit. Thus we obtain maps temperature,...
An overview of the theory Zeeman effect in diatomic molecules for limiting Hund's cases (a) and (b) is given a numerical approach intermediate coupling case (a–b) developed. In contrast to earlier derivations, which were limited doublets, this valid terms any multiplicity. General properties various are deduced. Finally, calculated Landé factors prominent molecular bands sunspot cool-star spectra employed predict general behaviour these presence magnetic field below Paschen-Back limit. The...
Recent advances in the computation of Zeeman splitting molecular lines have paved way for their use as diagnostics solar and stellar magnetic fields. A systematic study diagnostic capabilities had not been carried out so far, however. Here we investigate how can be used to deduce thermal structure sunspots, starspots cool stars. First, briefly describe Stokes radiative transfer Zeeman-split lines. Then, compute spectra TiO, OH, CH FeH capabilities. We also compare synthetic profiles with...
We report the first direct detection of an exoplanet in visible polarized light. The transiting planet HD189733b is one very hot Jupiters with shortest periods and, thus, smallest orbits, which makes them ideal candidates for polarimetric detections. obtained measurements HD189733 $B$ band well distributed over orbital period and detected two polarization maxima near planetary elongations a peak amplitude $\sim2\cdot10^{-4}$. Assuming Rayleigh scattering, we estimated effective size...
Abstract We report the first direct detection of a strong, 5 kG magnetic field on surface an active brown dwarf. LSR J1835+3259 is M8.5 dwarf exhibiting transient radio and optical emission bursts modulated by fast rotation. have detected as circularly polarized signatures in 819 nm sodium lines when region faced Earth. Modeling Stokes profiles these reveals effective temperature 2800 K log gravity acceleration 4.5. These parameters place evolutionary tracks young with mass <?CDATA $55\pm...
We investigate the linear polarization produced by interstellar dust aligned magnetic field in solar neighborhood (d< 50 pc). also look for intrinsic effects from circumstellar processes, specifically terms of variability and wavelength dependence. aim to detect map clouds which give rise statistically significant amounts starlight passing through cloud, determine direction position angle observed polarization. High-precision broad-band (BVR) observations are made 361 stars spectral classes...