The 10 most-cited articles in Astronomische Nachrichten, 2021

Abstract 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…

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 null energy condition (NEC), and the dominant energy condition (DEC) under the simplest non‐minimal matter geometry coupling with a perfect fluid distribution. The model parameter is constrained by energy conditions and a single‐parameter proposed equation of state (EoS), resulting in the compatibility of the f(R, T) models with the accelerated expansion of the universe. It is seen that the EoS parameter illustrates the quintessence phase in a dominated accelerated phase, pinpoint to the cosmological constant yields as a prediction the phantom era. Also, the present values of the cosmological constant and the acceleration of the universe are used to check the viability of our linear f(R,…

Abstract In this paper, we attribute high braking indicesn > 3of two magnetars SGR 0501+4516 and 1E 2259+586 to the decrease in their inclination angles using the double magnetic‐dipole model proposed by Hamil et al. (2016). In this model, there are two magnetic moments inside a neutron star—one is generated by the rotation effect of a charged sphere,M1, and the other is generated by the magnetization of ferromagnetically ordered material,M2. Our calculations indicate that the magnetic momentM2would evolve toward alignment with the spin axis of the two magnetars and cause their magnetic inclination angles to decrease. We also define a ratioη = M2/M1, which reflects the magnetization degree, and find that the values ofηof the two magnetars are about two orders of magnitude higher than that of rotationally powered pulsar PSR J1640‐4631 withn = 3.15(3), assuming that they have the same rate of decrease in their inclination angles.

Abstract With the first multi‐messenger observation of a binary neutron star merger (GW170817), new constraints became available for masses and radii of neutron stars. We introduce a class of hybrid EoS that fulfills all these constraints and predicts a region in the mass‐radius diagram that could be populated only by hybrid neutron stars with quark matter cores. A confirmation of this conjecture would be provided when the NICER radius measurement for the high‐mass pulsar PSR J0740 + 6620 yields a radius significantly less than 11 km. Would this radius measurement yield a result in excess of 12 km, this would allow for both, a purely hadronic and a hybrid nature of this star. In the latter case, the maximum mass could reach 2.6 M⊙ so that the lighter object in the asymmetric binary merger GW190814 could have been a hybrid star. We demonstrate that this high mass can be compatible with an early onset of deconfinement for stars with masses below 1 M⊙ and the occurrence of low‐mass twin stars. In such a case, the remnant of GW170817 could be a long‐lived hypermassive pulsar.

Abstract 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.

Abstract 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 communication. There is, however, no astrophysically motivated standard color palette for illustrative representations of stars, and some stars are actually represented in misleading colors. We use precomputed PHOENIX and TLUSTY stellar model spectra and convolve them with the three standard color‐matching functions for human color perception between 360 and 830 nm. The color‐matching functions represent the three sets of receptors in the eye that respond to red, green, and blue light. For a grid of main‐sequence stars with effective temperatures between 2,300 and 55,000 K of different metallicities, we present the red–blue–green and hexadecimal color codes that can be used for…

Abstract Magnetars are a kind of pulsars powered mainly by superhigh magnetic fields. They are popular sources with many unsolved issues in themselves but are also linked to various high‐energy phenomena, such as quasi periodic oscillations (QPOs), giant flares, fast radio bursts, and superluminous supernovae. In this work, we first review our recent works on the dissipation of toroidal magnetic fields in magnetars and rotationally powered pulsars and then review the spin‐down evolution of young and strongly magnetized pulsars, especially of magnetars. We present an interesting and important relation between the magnetization parameter and magnetic field in the magnetar crust. Finally, we introduce our two works in progress: to explain the magnetar “antiglitch” events in the thermal plastic flow model and to revisit the expression of braking index n, which is independent of the second derivative of spin frequency of a pulsar, and give some proposals for our future work.

Abstract 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 according to Jeans' law. We get an effective and perceptible variation due to parameters in both the locations of lagrangian points, regions of motion, and basins of attraction. Finally, we examine the stability for the lagrangian points using Meshcherskii's space–time inverse transformations.

Abstract Relativistic jets can interact with the ambient gas distribution of the host galaxy, before breaking out to larger scales. In the past decade, several studies have simulated jet‐driven outflows to understand how they affect the nearby environment, and over what spatial and temporal scales such interactions occur. The simulations are able to capture the interaction of the jets with the turbulent clumpy interstellar medium and the resultant energetics of the gas. In this review, we summarize the results of such recent studies and discuss their implications on the evolution of the dynamics of the gas distribution and the star formation rate.

Abstract Rapid advance has been made recently in accurate distance measurements for nearby ( Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way‐like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass‐to‐K‐band luminosity ratio is for the luminous galaxies, increasing up to toward dwarfs. The bulge‐dominated luminous galaxies are characterized with , while the disk‐dominated spirals have . We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km s−1 and a poor dark matter halo with . We note that a fraction of quenched (dSph, dE) companions around Milky Way‐like…