Search results for "Astronomy & astrophysics"
showing 8 items of 1148 documents
A photometric study of Be stars located in the seismology fields of COROT
2007
Context: In preparation for the COROT mission, an exhaustive photometric study of Be stars located in the seismology fields of the COROT mission has been performed. The very precise and long-time-spanned photometric observations gathered by the COROT satellite will give important clues of the origin of the Be phenomenon. Aims: The aim of this work is to find short-period variable Be stars located in the seismology fields of COROT and to study and characterise their pulsational properties. Methods: Light curves obtained at the Observatorio de Sierra Nevada together with data from Hipparcos and ASAS-3 of a total of 84 Be stars have been analysed in order to search for short-term variations. W…
Three-dimensional core-collapse supernovae with complex magnetic structures: I. Explosion dynamics
2021
Magnetic fields can play a major role in the dynamics of outstanding explosions associated to violent events such as GRBs and hypernovae, since they provide a natural mechanism to harness the rotational energy of the central proto-neutron star and power relativistic jets through the stellar progenitor. As the structure of such fields is quite uncertain, most numerical models of MHD-driven core-collapse supernovae consider an aligned dipole as initial magnetic field, while the field's morphology can actually be much more complex. We present three-dimensional simulations of core-collapse supernovae with more realistic magnetic structures, such as quadrupolar fields and, for the first time, an…
The impact of non-dipolar magnetic fields in core-collapse supernovae
2019
The magnetic field is believed to play an important role in at least some core-collapse supernovae if its magnitude reaches $10^{15}\,\rm{G}$, which is a typical value for a magnetar. In the presence of fast rotation, such a strong magnetic field can drive powerful jet-like explosions if it has the large-scale coherence of a dipole. The topology of the magnetic field is, however, probably much more complex with strong multipolar and small-scale components and the consequences for the explosion are so far unclear. We investigate the effects of the magnetic field topology on the dynamics of core-collapse supernovae and the properties of forming proto-neutron star (PNS) by comparing pre-collap…
Recommendations of the LHC Dark Matter Working Group: Comparing LHC searches for dark matter mediators in visible and invisible decay channels and ca…
2019
Physics of the Dark Universe 26, 100377 (2019). doi:10.1016/j.dark.2019.100377
Search for photons with energies above 1018 eV using the hybrid detector of the Pierre Auger Observatory
2017
A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1-2 EeV are found, which is compatible with the expected hadron-induced background. Upper limits on the integral flux of ultra-high energy photons of 0.027, 0.009, 0.008, 0.008 and 0.007 km-2 sr-1 yr-1 are derived at 95% C.L. for ener…
Performance analysis of Latvian zenith camera
2018
Since finalizing of design in 2016, the digital zenith camera of the University of Latvia was involved in a number of test observations as well as field observations at about 70 different sites. The paper presents analysis of observation results, estimation of instrument’s performance and accuracy. Random and systematic error sources are outlined. Impact of anomalous refraction on vertical deflection determination is discussed. Results of adaptation of GAIA reference star catalog for astrometric data reduction are reported.
The Large Observatory For x-ray Timing
2014
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m 2 effective area, 2-30 keV, 240 eV spectral resolution, 1 deg collimated field of view) and a WideFi…
High-precision measurement of a low Q value for allowed β−-decay of 131I related to neutrino mass determination
2022
The ground-state-to-ground-state β−-decay 131I (7/2+) → 131Xe (3/2+) Q value was determined with high precision utilizing the double Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The Q value of this β−-decay was found to be Q = 972.25(19) keV through a cyclotron frequency ratio measurement with a relative precision of 1.6 × 10−9. This was realized using the phase-imaging ion-cyclotron-resonance technique. The new Q value is more than 3 times more precise and 2.3σ higher (1.45 keV) than the value extracted from the Atomic Mass Evaluation 2020. Our measurement confirms that the β−-decay to the 9/2+ excited state at 971.22(13) keV in 131Xe is energetically allowed with a Q va…