| 1. |
- Da Silva Santos, J. M., et al.
(författare)
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Subarcsecond Imaging of a Solar Active Region Filament With ALMA and IRIS
- 2022
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature (Tb) maps taken with ALMA Band 6 complemented by simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms, and SDO/AIA extreme-UV images. Some of the dark threads visible in the AIA 304 Å passband and in the core of Mg ii resonance lines have dark (Tb << 5,000 K) counterparts in the 1.25 mm maps, but their visibility significantly varies across the filament spine and in time. These opacity changes are possibly related to variations in temperature and electron density in filament fine structures. The coolest Tb values (<< 5,000 K) coincide with regions of low integrated intensity in the Mg ii h and k lines. ALMA Band 3 maps taken after the Band 6 ones do not clearly show the filament structure, contrary to the expectation that the contrast should increase at longer wavelengths based on previous observations of quiescent filaments. The ALMA maps are not consistent with isothermal conditions, but the temporal evolution of the filament may partly account for this.
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| 2. |
- Telloni, D., et al.
(författare)
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First polar observations of the fast solar wind with the Metis - Solar Orbiter coronagraph : Role of 2D turbulence energy dissipation in the wind acceleration
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 670
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Tidskriftsartikel (refereegranskat)abstract
- Context. The fast solar wind is known to emanate from polar coronal holes.Aims. This Letter reports the first estimate of the expansion rate of polar coronal flows performed by the Metis coronagraph on board Solar Orbiter.Methods. By exploiting simultaneous measurements in polarized white light and ultraviolet intensity of the neutral hydrogen Lyman-α line, it was possible to extend observations of the outflow velocity of the main component of the solar wind from polar coronal holes out to 5.5 R⊙, the limit of diagnostic applicability and observational capabilities.Results. We complement the results obtained with analogous polar observations performed with the UltraViolet Coronagraph Spectrometer on board the SOlar and Heliospheric Observatory during the previous full solar activity cycle, and find them to be satisfactorily reproduced by a magnetohydrodynamic turbulence model.Conclusions. This suggests that the dissipation of 2D turbulence energy is a viable mechanism for coronal plasma heating and the subsequent acceleration of the fast solar wind.
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| 3. |
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| 4. |
- Coughlin, M. W., et al.
(författare)
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Standardizing kilonovae and their use as standard candles to measure the Hubble constant
- 2020
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- The detection of GW170817 is revolutionizing many areas of astrophysics with the joint observation of gravitational waves and electromagnetic emissions. These multimessenger events provide a new approach to determine the Hubble constant, thus, they are a promising candidate for mitigating the tension between measurements of type-Ia supernovae via the local distance ladder and the cosmic microwave background. In addition to the "standard siren"provided by the gravitational-wave measurement, the kilonova itself has characteristics that allow one to improve existing measurements or to perform yet another, independent measurement of the Hubble constant without gravitational-wave information. Here, we employ standardization techniques borrowed from the type-Ia community and apply them to kilonovae, not using any information from the gravitational-wave signal. We use two versions of this technique, one derived from direct observables measured from the light curve, and the other based on inferred ejecta parameters, e.g., mass, velocity, and composition, for two different models. These lead to Hubble constant measurements of H0=109-35+49 km s-1 Mpc-1 for the measured analysis, and H0=85-17+22 km s-1 Mpc-1 and H0=79-15+23 km s-1 Mpc-1 for the inferred analyses. This measurement has error bars within ∼2 to the gravitational-wave measurements (H0=74-8+16 km s-1 Mpc-1), showing its promise as an independent constraint on H0.
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| 6. |
- De Groot, Natasja M.S., et al.
(författare)
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Critical appraisal of technologies to assess electrical activity during atrial fibrillation : a position paper from the European Heart Rhythm Association and European Society of Cardiology Working Group on eCardiology in collaboration with the Heart Rhythm Society, Asia Pacific Heart Rhythm Society, Latin American Heart Rhythm Society and Computing in Cardiology
- 2022
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Ingår i: Europace. - : Oxford University Press (OUP). - 1099-5129. ; 24:2, s. 313-330
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Forskningsöversikt (refereegranskat)abstract
- We aim to provide a critical appraisal of basic concepts underlying signal recording and processing technologies applied for (i) atrial fibrillation (AF) mapping to unravel AF mechanisms and/or identifying target sites for AF therapy and (ii) AF detection, to optimize usage of technologies, stimulate research aimed at closing knowledge gaps, and developing ideal AF recording and processing technologies. Recording and processing techniques for assessment of electrical activity during AF essential for diagnosis and guiding ablative therapy including body surface electrocardiograms (ECG) and endo- or epicardial electrograms (EGM) are evaluated. Discussion of (i) differences in uni-, bi-, and multi-polar (omnipolar/Laplacian) recording modes, (ii) impact of recording technologies on EGM morphology, (iii) global or local mapping using various types of EGM involving signal processing techniques including isochronal-, voltage- fractionation-, dipole density-, and rotor mapping, enabling derivation of parameters like atrial rate, entropy, conduction velocity/direction, (iv) value of epicardial and optical mapping, (v) AF detection by cardiac implantable electronic devices containing various detection algorithms applicable to stored EGMs, (vi) contribution of machine learning (ML) to further improvement of signals processing technologies. Recording and processing of EGM (or ECG) are the cornerstones of (body surface) mapping of AF. Currently available AF recording and processing technologies are mainly restricted to specific applications or have technological limitations. Improvements in AF mapping by obtaining highest fidelity source signals (e.g. catheter-electrode combinations) for signal processing (e.g. filtering, digitization, and noise elimination) is of utmost importance. Novel acquisition instruments (multi-polar catheters combined with improved physical modelling and ML techniques) will enable enhanced and automated interpretation of EGM recordings in the near future.
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| 7. |
- Heinzel, J., et al.
(författare)
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Comparing inclination-dependent analyses of kilonova transients
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 502:2, s. 3057-3065
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Tidskriftsartikel (refereegranskat)abstract
- The detection of the optical transient AT2017gfo proved that binary neutron star mergers are progenitors of kilonovae (KNe). Using a combination of numerical-relativity and radiative-transfer simulations, the community has developed sophisticated models for these transients for a wide portion of the expected parameter space. Using these simulations and surrogate models made from them, it has been possible to perform Bayesian inference of the observed signals to infer properties of the ejected matter. It has been pointed out that combining inclination constraints derived from the KN with gravitational-wave measurements increases the accuracy with which binary parameters can be estimated, in particular breaking the distance-inclination degeneracy from gravitational wave inference. To avoid bias from the unknown ejecta geometry, constraints on the inclination angle for AT2017gfo should be insensitive to the employed models. In this work, we compare different assumptions about the ejecta and radiative reprocesses used by the community and we investigate their impact on the parameter inference. While most inferred parameters agree, we find disagreement between posteriors for the inclination angle for different geometries that have been used in the current literature. According to our study, the inclusion of reprocessing of the photons between different ejecta types improves the modeling fits to AT2017gfo and, in some cases, affects the inferred constraints. Our study motivates the inclusion of large similar to 1-mag uncertainties in the KN models employed for Bayesian analysis to capture yet unknown systematics, especially when inferring inclination angles, although smaller uncertainties seem appropriate to capture model systematics for other intrinsic parameters. We can use this method to impose soft constraints on the ejecta geometry of the KN AT2017gfo.
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