ISSN / EISSN : 0004-6337 / 1521-3994
Published by: Wiley (10.1002)
Total articles ≅ 48,261
Latest articles in this journal
Astronomische Nachrichten; doi:10.1002/asna.202113968
The emergence and development of a power-law tail (PLT) at the high-density end of the observed column-density distribution are thought to be indicative for advanced evolution of star-forming molecular clouds. As shown from many numerical simulations, it corresponds to a morphologically analogous evolution of the mass-density distribution (ρ-PDF). The latter may display also a second, shallower PLT at the stage of collapse of the first formed protostellar cores. It is difficult to estimate the parameters of a possible second PLT due to resolution constraints. To address the issue, we extend the method for the extraction of single PLTs from arbitrary density distributions suggested by Veltchev et al. (MNRAS, 489, 788, 2019) to detect a second PLT. The technique is elaborated through tests on an analytic ρ-PDF and applied to a set of hydrodynamical high-resolution simulations of isothermal self-gravitating clouds. In all but one case two PLTs were detected—the first slope is always steeper and the second one is typically . These results are in a good agreement with numerical and theoretical works and do suggest that the technique extracts correctly double PLTs from smooth PDFs.
Published: 7 July 2021
Astronomische Nachrichten; doi:10.1002/asna.202113987
The publisher has not yet granted permission to display this abstract.
Astronomische Nachrichten; doi:10.1002/asna.202114000
We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius diagram. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the constant-sound-speed (CSS) equation of state (EoS) and the nuclear matter phase around saturation density is varied from very soft (APR) to stiff (DD2 with excluded nucleon volume). Different construction schemes for the deconfinement transition are applied: Maxwell construction, mixed phase construction, and parabolic interpolation. We demonstrate for the first time that the SP is invariant not only against changing the nuclear matter EoS, but also against variation of the construction schemes for the phase transition. Since the SP serves as a proxy for the maximum mass and accessible radii of massive hybrid stars, we draw conclusions for the limiting masses and radii of hybrid neutron stars.
Astronomische Nachrichten; doi:10.1002/asna.202113867
This study reports a probabilistic insight into the stellar-mass and supernovae (SNe) explosion energy of five CEMP-no stars' possible progenitors. As such, a direct comparison between the abundance ratios [X/Fe] of the light-elements and the predicted nucleosynthetic yields of SN of high-mass metal-free stars has been performed. This comparison suggests that the possible progenitors have a stellar-mass range of 11 − 22 M⊙ and explosion energies of 0.3 − 1.8 × 1051 erg. In addition, we investigate the kinematic signatures, derived from Gaia DR2, to conclude that these five CEMP-no stars have halo-like kinematic and do not enter the outer-halo region. In addition, we link the abundance patterns with kinematic signatures to investigate the Gaia-Sausage and Gaia-Sequoia memberships. This chemo-dynamical analysis suggests that these CEMP-no stars are neither Gaia-Sausage nor Gaia-Sequoia remnant stars, but another accretion event might be responsible for the contribution of these stars to the Galactic Halo.
Astronomische Nachrichten; doi:10.1002/asna.202113993
In this contribution, we identify two scenarios for the evolutionary branch cut universe. In the first scenario, the universe evolves continuously from the negative complex cosmological time sector, prior to a primordial singularity, to the positive one, circumventing continuously a branch cut, and no primordial singularity occurs in the imaginary sector, only branch points. In the second scenario, the branch cut and branch point disappear after the realization of the imaginary component of the complex time by means of a Wick rotation, which is replaced by the thermal time. In the second scenario, the universe has its origin in the Big Bang, but the model contemplates simultaneously a mirrored parallel evolutionary universe going backwards in the cosmological thermal time negative sector. A quantum formulation based on the Wheeler–DeWitt equation is sketched and preliminary conclusions are drawn.
Astronomische Nachrichten; doi:10.1002/asna.202113998
The recent discovery of binary neutron star mergers has opened a new and exciting venue of research into hot and dense strongly interacting matter. For the first time, this elusive state of matter, described by the theory of quantum chromo dynamics, can be studied in two very different environments. On the macroscopic scale, in the collisions of neutron stars; and on the microscopic scale, in collisions of heavy ions at particle collider facilities. We will discuss the conditions that are created in these mergers and the corresponding high energy nuclear collisions. This includes the properties of quantum chromo dynamics matter, that is, the expected equation of state as well as expected chemical and thermodynamic properties of this exotic matter. To explore this matter in the laboratory, a new research prospect is available at the Facility for Antiproton and Ion Research, FAIR. The new facility is being constructed adjacent to the existing accelerator complex of the GSI Helmholtz Centre for Heavy Ion Research at Darmstadt/Germany, expanding the research goals and technical possibilities substantially. The worldwide unique accelerator and experimental facilities of FAIR will open the way for a broad spectrum of unprecedented research supplying a variety of experiments in hadron, nuclear, atomic, and plasma physics as well as biomedical and material science, which will be briefly described.
Astronomische Nachrichten; doi:10.1002/asna.202113988
We review the properties of the strongly interacting quark-gluon plasma (QGP) at finite temperature and baryon chemical potential as created in heavy-ion collisions at ultrarelativistic energies. The description of the strongly interacting (non-perturbative) QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature from lattice QCD. Based on a microscopic transport description of heavy-ion collisions, we discuss which observables are sensitive to the QGP creation and its properties.
Astronomische Nachrichten; doi:10.1002/asna.202113972
We present the latest results of our ongoing multiplicity study of (Community) TESS Objects of Interest, using astro- and photometric data from the ESA-Gaia mission, to detect stellar companions of these stars and to characterize their properties. In total, 107 binary, 5 hierarchical triple star systems, as well as one quadruple system were detected among 585 targets surveyed, which are all located at distances closer than about 500 pc around the Sun. As proven with their accurate Gaia EDR3 astrometry, the companions and the targets are located at the same distance and share a common proper motion, as it is expected for components of gravitationally bound stellar systems. The companions exhibit masses in the range between about 0.09 M⊙ and 4.5 M⊙ and are most frequently found in the mass range between 0.15 and 0.6 M⊙. The companions are separated from the targets by about 120 up to 9,500 au and their frequency is the highest and constant within about 500 au while it continually decreases for larger separations. Beside mainly early to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature was revealed by their photometric properties.
Astronomische Nachrichten; doi:10.1002/asna.202113992
In this article, we follow a previously developed theoretical approach, based on the tools of the singular semi-Riemannian geometry, to push the limits of time beyond the primordial spacetime singularity. By complexifying the Friedmann–Lemaître–Robertson–Walker (FLRW) metric and Friedmann's equations, we model a branch cut universe, in which the cosmic FLRW metric scale factor is analytically continued to the complex plane, and becomes equivalent from a conceptual point of view of describing a hypothetical general metric of maximally symmetric and homogeneous superposed multiple universes.
Astronomische Nachrichten; doi:10.1002/asna.202113961
We present spectroscopy of the coma center of comet C/2020 F3 (NEOWISE), carried out at the end of July 2020 with the Échelle spectrograph FLECHAS at the University Observatory Jena. The comet was observed in five nights and many prominent emission features were detected between 4,685 and 7,376 Å. Beside the C2 Swan emission bands also several emission features of the amidogen radical, as well as two forbidden lines of oxygen were identified in the FLECHAS spectra of the comet in all observing epochs. In contrast, strong sodium emission was detected only in the spectra of the comet, taken on 21 and July 23, 2020, which significantly faded between these two nights, and was no longer present in the spectra as of July 29, 2020. In this paper, we present and characterize the most prominent emission features, detected in the FLECHAS spectra of the comet, discuss their variability throughout our spectroscopic monitoring campaign, and use them to derive the radial velocity of the comet in all observing nights.