We present relative astrometric and photometric measurements of visual binaries made in 2011–2012, with PISCO2 installed at the 76-cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as binaries whose motion is still uncertain. Three different techniques have been used for obtaining those measurements: Lucky imaging, speckle interferometry,

For the first time, a direct non-local thermodynamic equilibrium (NLTE) analysis of carbon and nitrogen lines in the spectra of nine RR Lyrae stars was carried out. We have determined the abundances of these elements together with oxygen, and have shown that the nitrogen content is increased in metallicity-deficient program stars. We conclude that this is a sign of the first dredge up, which occurred

The estimation of the main parameters of star clusters is significant in astrophysical studies. The most important aspect of using the Gaia DR2 survey lies in the positions, parallax, and proper motions of cluster stars with homogeneous photometry that make the membership probability determine with high accuracy. In this respect, depending on Gaia DR2 database, an analysis of the open star cluster

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

We used two volume-limited active galactic nucleus (AGN) host galaxy samples constructed by Deng & Wen (2020, RMxAA, 56, 87), and explored the environmental dependence of the stellar mass of AGN host galaxies. In the luminous volume-limited AGN host galaxy sample, the stellar mass of AGN host galaxies apparently depends on local environments: high mass AGN host galaxies exist preferentially in the

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

We report on one of the first science observations obtained during the Calibration and Verification phase of extended ROentgen Survey with an Imaging Telescope Array (eROSITA) aboard the Spectrum-Roentgen-Gamma (SRG) mission on the famous Narrow-Line Seyfert 1 Galaxy 1H 0707-495. 1H 0707-495 is a highly variable AGN, with a complex, steep X-ray spectrum, which has been the subject of intense studies

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

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 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

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

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

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

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

A brief review on algebraic extensions of general relativity is presented. After a short summary of first attempts by Max Born and Albert Einstein, all possible algebraic extensions will be discussed, with the pseudo-complex (pc) extension left as the only viable one, because it does not contain ghost solutions. Also some metric extensions are presented, such as the non-symmetric gravitation theory

The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marked the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from the late inspiral phase of GW170817, it was possible to constrain several global properties of the equation of state of

We investigate in this work two different types of instabilities that set limits on the rotation rates of neutron (compact) stars. The first one is that caused by rotation at the Kepler frequency, at which mass shedding at the star's equator sets in. The second limit is set by instabilities driven by the growth of gravitational radiation-reaction (GRR) driven -modes of order , which are moderated by

Jets, collimated outflows of particles and fields, are observed in a wide variety of astrophysical systems, including Active Galactic Nuclei of various types, micro-quasars, gamma-ray bursts, and young stellar objects. Despite intensive efforts along several decades of observational and theoretical research, there are still many uncertainties and open questions related to how jets are produced and

This special volume includes contributions from some of the most relevant scientists who have participated in the IWARA 2020 Video Conference. The series of meetings known by the acronyms IWARA, STARS, and SMFNS,—more than a congregation of events, students and researchers which in itself would be extremely important for science—became in last years a kind of platform for scientific and academic projects

We critically discuss recent articles by S. Hoffmann and N. Vogt on historical novae and supernovae (SNe) as well as their list of “24 most promising events” “with rather high probability to be a nova” (Hoffmann et al., AN, 2020, 341, 79 (P3)). Their alleged positional accuracy of previously suggested historical nova/SN records is based on inhomogeneous datasets (Vogt et al.), but then used for the

We present a formalism for calculating the probability distribution of the most massive primordial black holes (PBHs) expected within an observational volume. We show how current observational upper bounds on the fraction of PBHs in dark matter translate to constraints on extreme masses of primordial black holes. We demonstrate the power of our formalism via a case study, and argue that our formalism

In the present paper, we investigate the dynamical behavior and motion of an infinitesimal body in the Hill problem under some perturbations. As it has been commonly noticed, this problem can be seen as a particular case of the classical restricted three-body problem. For numerical investigations, we first set the equations of motion of the infinitesimal body that we suppose having a variable mass

For nine bright K giants within 100 pc of the sun, the fundamental parameters and the non‐local thermodynamic equilibrium (LTE) abundances of three key light elements (Li, C, and O) are accurately determined. These stars are of special interest due to the planets detected around them. Their fundamental parameters are found to be typical for K giants; in particular, these stars have effective temperatures

Spectroscopic determinations of rubidium abundances were made by applying the spectrum‐fitting method to the Rb(i) 7800 line for an extensive sample of ∼500 late‐type dwarfs as well as giants (including Hyades cluster stars) belonging to the galactic disk population, with the aim of establishing the behavior of [Rb/Fe] ratio for disk stars in the metallicity range of −0.6 ≲ [Fe/H] ≲ +0.3. An inspection

Using TESS photometry and Rozhen spectra of the Be/γ‐ray binaries MWC 148 and MWC 656, we estimate the projected rotational velocity (v sin i), rotational period (Prot), radius (R1), and inclination (i) of the mass donor. For MWC 148, we derive Prot = 1.10 ± 0.03 day, R1 = 9.2 ± 0.05 Rsun, i = 40° ± 2°, and v sin i = 272 ± 5 km s−1. For MWC 656, we obtain Prot = 1.12 ± 0.03 day, R1= 8.8 ± 0.5 Rsun

Nowadays, publications in astrophysics are mainly published and read in digitized formats. Astrophysical publications in both research and in popular outreach often use colorful representations of stars to indicate various stellar types, that is, different spectral types or effective temperatures. Computer‐generated and computer‐displayed imagery has become an integral part of stellar astrophysics

Some properties of the Lemaitre regularization in the planar three‐body problem are considered. Application of these properties to the degenerate case of a rectilinear problem in the space of forms is studied. A number of the collinear orbits are obtained using suitable parametrization. Properties of such orbits are analyzed.

In this study, we develop an analytic treatment, which would allow us to model magnetic deformation of neutron stars in the quasi-Newtonian framework. We assume non-magnetic, spherical relativistic stars as backgrounds and regard the magnetic fields as the perturbation. We analyze the problem by taking density profiles from various analytic approaches. The first density profile is the n = 1 solution

We present the results of a search for the magnetic field inhomogeneity for the red giant ϵ Tau. This research is based on observations obtained over 10 nights in 2008–2010 with the ESPaDOnS CFHT spectropolarimeter. We found a previously undescribed instrumental effect in the ESPaDOnS spectra, consisting of random polarization outliers. Therefore, to measure the magnetic field from the unblended individual

We outline our experience in organizing the 9th edition of the International Workshop on Astronomy and Relativistic Astrophysics: from Quarks to Cosmos, in virtual format, denominated IWARA2020 Video Conference, held from 6 to 12 September, 2020. The IWARA 2020 Video Conference aimed to bring together leading academic scientists, professors, students, and research scholars for exchanging experiences

The discovery of an elite burial in Tlailotlacan, a neighborhood of Teotihuacan, gave us a unique opportunity not only to put together a group of multidisciplinary specialists, but to revive this remarkable woman who inhabited, ate, drank, and traveled through most of Mesoamerican. The different analysis carried out provided us with a unique opportunity to reconstruct part of the relations between

In this contribution, we seek to identify points of contact between the conceptions about space, time, and Cosmos, carried out by thinkers and scientists throughout history, and the corresponding cosmogonic view of the Inka culture. We conclude that a proper understanding and interpretation of the Inka legacy in the fields of astronomy and archeoastronomy can only be carried out properly when inserted

In this paper, we discuss the astronomical orientations in the city plans of Teotihuacan and Tenochtitlan. Mesoamerica exhibits much archaeoastronomy and these two sites are rich examples. Both exhibit alignments for solar horizon events that are integral in deliberate calendrical systems. The logic of these systems is shown, and this demonstrates that these cities were carefully planned with astronomical

The hypothesis that one or more biodiversity drops in the Phanerozoic eon, evident in the geological record, might have been caused by the most powerful kind of stellar explosion so far, known Gamma Ray Bursts (GRBs), has been discussed in several works. These stellar explosions could have left an imprint in the biological evolution on Earth and in other habitable planets. In this work, we calculate

Based on quantum mechanical framework for the minimal length uncertainty, we demonstrate that the generalized uncertainty principle (GUP) parameter could be best constrained by recent gravitational waves observations on one hand. On the other hand, this suggests modified dispersion relations (MDRs) enabling an estimation for the difference between the group velocity of gravitons and that of photons

When minimal length uncertainty emerging from a generalized uncertainty principle (GUP) is thoughtfully implemented, it is of great interest to consider its impacts on gravitational Einstein field equations (gEFEs) and to try to assess consequential modifications in metric manifesting properties of quantum geometry due to quantum gravity. GUP takes into account the gravitational impacts on the noncommutation

We outline the modifications in the numerical Boltzmann code Cosmic Linear Anisotropy Solving System (CLASS) in order to include extra inflationary fields. The functioning of the code is first described, how and where modifications are meant to be done are later explained. In the present study, we focus on the modifications needed for the implementation of a two‐field inflationary model, with canonical

We determine the causal structure of the McVittie spacetime for a cosmological model with an asymmetric bounce. The analysis includes the computation of trapping horizons; regular, trapped, and antitrapped regions; and the integration of the trajectories of radial null geodesics before, during, and after the bounce. We find a trapped region since the beginning of the contracting phase up to shortly

We present the results of General Relativistic Magnetohydrodynamic simulations utilizing initial conditions from both the Electroweak and Quantum Chromodynamic (QCD) phase transitions in order to determine if seed magnetic fields may be generated via the Biermann Battery Mechanism of Magnetogenesis. These simulations occur in a simulated early universe between 10−11 s and 103 s after the Big Bang.

In today's scenario, going beyond Einstein's theory of gravity leads us to some more complete and modified gravity theories. One of them is the f(R, T) gravity in which R is the Ricci scalar, and T is the trace of the energy‐momentum tensor. Using a well‐motivated linear f(R, T) gravity model with a single parameter, we studied the strong energy condition (SEC), the weak energy condition (WEC), the

The present study reports a reconstruction scheme for f(T) gravity under the assumption that the density due to the torsion T evolves like the variable‐generalized Chaplygin gas (VGCG), a phenomenological candidate of dark energy. This reconstruction has been demonstrated in viscous as well as non‐viscous cases. The state‐finder trajectory {r − s} has been found to attain the ΛCDM fixed point under

We study the magnetic properties of a relativistic neutral vector bosons gas under the action of a constant and uniform magnetic field. An analytical expression for the magnetization at any temperature is obtained, and a discussion of the influence of the antiparticles, the vacuum, and the Bose‐Einstein condensation over this magnitude is presented. We analyze the validity of the non‐relativistic and

In 2015, the first direct detection of gravitational waves was reported. Data analysis indicated that the waves had originated from the violent collision of two black holes, which scattered them through space–time as Einstein predicted. That detection was made possible by many advances in measurement technology, mainly vibration isolation of the detector optics, since, at 10 Hz, the motion of the

In this work, a methodology to design two‐mode mechanical transducers for the spherical resonant‐mass gravitational wave detector SCHENBERG is presented. This detector uses microwave multiparametric sensors and has 17 mechanical modes together with 6 electromagnetic modes for the microwave cavities. These transducers, when placed on the spherical surface of the detector, must have an effective mass

An outlook of different aspects of the incidence of magnetic fields on early universe events is presented. The events we will focus on include inflation and the electroweak phase transition. The guideline of the study is mainly the effect of the magnetic field on the effective potential of phase transitions and the decay process of the field leading the phase transition. We will consider both weak

We calculate the axial ring‐down frequencies of the merger of two black holes, using a modified version of the pseudo‐complex General Relativity (pc‐GR) and comparing it with the standard General Relativity (GR). The path, on how to determine the axial modes, serve as a starting point for more general extensions of GR, involving additions of r‐dependent functions to g00.

Surveys have shown radio‐loud (RL) quasars constitute 10–15% of the total quasar population. However, it is unknown if the radio‐loud fraction (RL quasars/Total quasars) remains consistent among different parameter spaces. This study shows that radio‐loud fraction increases for increasing full width half maximum (FWHM) velocity of the Hβ and MgII broad emission line. Our data have been obtained from

Properties of galaxies, such as color, age, and star formation activity, appear to be associated with the environment in which they are immersed. To investigate how the environment‐galaxy relation is established, we study protoclusters, which are numerically dense environments of galaxies in the early Universe, and which give rise to galaxy clusters today. In this work, we use submillimeter galaxies

The stellar Initial Mass Function (IMF) seems to be close to universal in the local star‐forming regions. However, this quantity of a newborn stellar population responds differently at gas metallicities Z ∼ Z⊙ than Z = 0. A view on the cosmic star formation history suggests that the cooling agents in the gas vary both in their types and molecular abundances. For instance, in the primordial gas environment

To investigate the effect of feedback from active galactic nuclei (AGN) on their surrounding medium, we study the diffuse X‐ray emission from galaxy groups and clusters by coupling the Astrophysical Plasma Emission Code (APEC) with the cosmological hydrodynamic simulation involving AGN feedback. We construct a statistical sample of synthetic Chandra X‐ray photon maps to observationally characterize

We present a new approach to improve the forward modeling of reconstruction method for the Baryonic Acoustic Oscillations study. We use probability information from the Halo Occupation Distribution (HOD) function of a given type of galaxies in order to enhance the estimation of the local density field of the dark matter. We couple the HOD information to the Conditional Luminosity Function of red type

The results of 20‐year observations of the Perseus cluster centering on the NGC 1275 including IC 310 radio galaxy and extragalactic supernova SN 2006gy at energies 800 GeV to 45 TeV by the SHALON telescope are presented. Also, the emission from the galactic source of non‐thermal radio and X‐ray emission GK Per (Nova 1901) of classical nova type was found as it accompanied to the observations. For

The process of stationary acceleration of protons by an electric field in the electromagnetic field of active galactic nuclei, including the regions of the magnetosphere of a supermassive black hole and a relativistic jet, is considered. The process of collisionless acceleration of the proton as a component of ultrahigh‐energy cosmic rays is assumed. It is shown that during acceleration to the maximum

Infrared luminous galaxies are rare locally but dominate the star formation activity at z ≥ 1. The study of these objects is difficult at optical wavelengths especially on account of the abundant dust. At the smallest scales, dust becomes micron‐sized molecules known as PAHs that are excited by UV photons and whose emission can be used to reveal physical properties of obscured regions that otherwise

In this work, we construct a sample of black hole X‐ray binaries (BH XRBs), low‐luminosity active galactic nuclei (LLAGNs), and FR Is with wider distribution of Eddington ratios and re‐explore their fundamental plane of BH activities, that is, . We find that the quiescent BH sources follow a similar fundamental plane (ξX ∼ 0.6) with sub‐Eddington BH sources very well, while the strong radio sources

We derive closed formulas for the mass M and spin a parameters of a Kerr black hole in terms of a minimal quantity of observational data: the red‐/blue‐shifts of photons emitted by massive particles (stars) moving on geodesics around the black hole and their respective orbital radius. It turns out that for a single star orbiting the black hole, we need a minimal set of four observational measurements

In spite of its key role in compact star physics, the surface tension of quark matter is not well comprehended yet. In this work, we analyze the behavior of the surface tension of three‐flavor quark matter in the outer and inner core of cold deleptonized magnetars, proto magnetars born in core collapse supernovae, and hot magnetars produced in binary neutron stars mergers. We explore the role of temperature

We study the neutrino chirality flip during the birth of a neutron star, produced in a core made of strange quark matter. This mechanism is applied to the neutron star kick velocity problem and we show that it is efficient when the neutrino magnetic moment is not smaller than 4.7 × 10−15μB, where μB is the Bohr magneton. When this lower bound is combined with the most stringent upper bound, our results

The role of magnetic field decay in normal radio pulsars is still debated. In this paper, we present results which demonstrate that an episode of magnetic field decay in hot young neutron stars can explain anomalous values of braking indices recently measured for more than a dozen of sources. It is enough to have few tens of per cent of such hot neutron stars in the total population to explain observables

Pulsars are stars whose electromagnetic radiation is observed to pulsate in well‐defined time intervals while they rotate as long as the electromagnetic signal is not emitted in the direction of the rotation axis. The frequencies of the pulses decay with time as quantified by the braking index (n). In the canonical model, n = 3 for all pulsars, but observational data yield n < 3. In this work, this