The 10 most-cited articles in Astronomische Nachrichten, 2018

We present relative astrometric measurements of visual binaries, made in 2015, with the speckle camera PISCO of the 102‐cm Zeiss telescope of Brera Astronomical Observatory, Merate, Italy. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 196 new measurements of 173 visual binary stars, with angular separations in the range 0″.27–11″.3, and an average accuracy of 0″.019. The mean error on the position angles is 0°.6. Most of the position angles were determined without the usual 180° ambiguity with the application of triple‐correlation techniques and/or by inspection of the long integration files. We present new revised orbits for DUN 5, ADS 5958, 6276, 7294, 8211, and 13169, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. We also computed new rectilinear elements for ADS 4841 for which the physical connection is doubtful from our (and other recent) observations.

We calculate the mean density profiles for luminous and dark matter on distance scalesD ∼ 1–100 Mpc around us using recent all‐sky catalogs of galaxy groups. Within the Local Volume (D < 11 Mpc), we derived the mean stellar density Ω* = 0.44% in the critical density units and the mean total matter density Ωm = 0.17. Within a sphere of radius 40 Mpc, these quantities drop to Ω* = 0.24–0.32% and Ωm = 0.09–0.14. In a larger volume withinD ∼ 135 Mpc, the discussed densities become more uncertain: Ω* = 0.20–0.24% and Ωm = 0.05–0.16. We summarize that the major part of the cosmic dark matter is located outside the virial and collapsing zones of groups and clusters.

We present reconstructed sunspot positions based on observations reported in letters between Gottfried Kirch and other contemporary astronomers from AD 1680 to 1709, that is in the last decades of the Maunder minimum. The letters to and from Gottfried Kirch in Latin and German language were compiled and edited by Herbst ( ). The letters (and observations) from Kirch are mostly by Gottfried Kirch, but some also by his second wife Maria M. Kirch (married 1692) and their son Christfried Kirch (born 1694). Using excerpts from the letters, some with drawings, we found some 35 sunspot groups (often for several days in a row or with interruptions) by Kirch and/or his letter partners (in three cases, only the month is given: 1704 January, February, 1707 March, otherwise always the exact dates)—usually one group at a time. We also found 17 explicit spotless days, several of them new (previously without any known observations). We could constrain the heliographic latitude by Bayesian inference for 19 sunspot groups—five of them completely new (one group 1680 May 20–22 from Kirch and Ihle, one…

We have developed a new automated method intended to perform the simultaneous—and thus more consistent—measurement of both the seismic indices characterizing the oscillations and the parameters characterizing the granulation signature of red giant stars. This method, called MLEUP, takes advantage of the Maximum Likelihood Estimate (MLE) algorithm combined with the parameterized representation of red giant pulsation spectra following the universal pattern (UP). Its performances have been tested on Monte Carlo simulations for observation conditions representative of CoRoT andKeplerdata. These simulations allowed us to determine, calibrate, and propose corrections for the biases on the parameter estimates as well as on the error estimates produced with MLEUP. Finally, we applied MLEUP to CoRoT andKeplerdata. In total, MLEUP yields seismic indices for 20,122 red giant stars and granulation parameters for 17,109 of them. These data have been made available in the stellar seismic indices database ( http://ssi.lesia.obspm.fr /).

This paper shows the effect of small perturbations in the Coriolis and centrifugal forces in the restricted four‐body problem (R4BP) with variable mass. The existence, location, and stability of the libration points are investigated numerically and graphically under these perturbations. In the present problem, a fourth body with infinitesimal mass is moving under the Newtonian gravitational attraction of three primaries which are moving in a circular orbit around their common center of mass fixed at the origin of the coordinate system. Moreover, according to the solution of Lagrange, the primaries are fixed at the vertices of an equilateral triangle. The fourth body does not affect the motion of three primaries. Furthermore, the fourth body's mass varies according to Jeans' law. The equations of motion of the test particle, i.e., fourth body moving under the gravitational influence of the primaries, are derived. Throughout the paper, we consider the case where the primary body placed along the x‐axis is dominant while the other two small primaries are equal. Further, it is shown…

Signal artifacts due to radio frequency interference (RFI) are a common nuisance in radio astronomy. Conventionally, the RFI‐affected data are tagged by an expert data analyst in order to warrant data quality. In view of the increasing data rates obtained with interferometric radio telescope arrays, automatic data filtering procedures are mandatory. Here, we present the results from the implementation of a RFI‐detecting recurrent neural network (RNN) employing long short‐term memory (LSTM) cells. For the training of the algorithm, a discrete model was used that distinguishes RFI and non‐RFI data, based on the amplitude information from radio interferometric observations with the Giant Metre‐Wave Radio Telescope (GMRT) at 610 MHz. The performance of the RNN is evaluated by analyzing a confusion matrix. The true positive and true negative rates of the network are ∼99.9 and ∼97.9%, respectively. However, the overall efficiency of the network is ∼30% because of the fact that a large amount non‐RFI data is classified as being contaminated by RFI. Matthews correlation coefficient is 0.42,…

Small‐scale dynamo action is often held responsible for the generation of quiet Sun magnetic fields. We aim to determine the excitation conditions and saturation level of small‐scale dynamos in nonrotating turbulent convection at low magnetic Prandtl numbers. We use high‐resolution direct numerical simulations of weakly stratified turbulent convection. We find that the critical magnetic Reynolds number for dynamo excitation increases as the magnetic Prandtl number is decreased, which might suggest that small‐scale dynamo action is not automatically evident in bodies with small magnetic Prandtl numbers, such as the Sun. As a function of the magnetic Reynolds number (Rm), the growth rate of the dynamo is consistent with an Rm1/2scaling. No evidence for a logarithmic increase of the growth rate with Rm is found.

Radiation reaction acting on a charged particle moving at a stable circular orbit of a magnetized black hole (BH) can lead to the shift of the orbital radius outward from the BH. The effect causes an increase of the energy and angular momentum of the particle measured by an observer at rest at infinity. In this paper, we show that “widening” of such orbits is independent of the field configuration, but it appears only in the cases with the external Lorentz force acting outward from the BH. This condition corresponds to qLB > 0, where q and L are the charge and angular momentum of the particle, and B is intensity of the external magnetic field. As examples of the orbital widening, we consider two scenarios with an external homogeneous magnetic field and a magnetic dipole field generated by a current loop around a Schwarzschild BH. We show that the orbital widening is accompanied by quasi‐harmonic oscillations of the particle, which are considerably large in the magnetic dipole fields. We also estimate the timescales of orbital widening, from which it follows that the effect can be…

The recently reported coincidences between high‐energy neutrino events and major blazar outbursts reinforce the relevance of lepto‐hadronic emission models for blazars. We study the influence of physical parameters on the neutrino output by modeling blazar spectral energy distributions self‐consistently assuming a relativistically propagating acceleration zone surrounded by a larger cooling zone. We find that the gross features of the spectral energy distribution can readily be explained with the model. A rigorous test requires time‐resolved measurements of blazar spectral energy distributions during an outburst and high‐statistics neutrino measurements to discriminate the leptonic and hadronic emission components.

The short‐spacing problem describes the inherent inability of radio‐interferometric arrays to measure the integrated flux and structure of diffuse emission associated with extended sources. New interferometric arrays, such as Square Kilometer Array (SKA), require solutions to efficiently combine interferometer and single‐dish data. We present a new and open‐source approach for merging single‐dish and cleaned interferometric datasets, requiring a minimum of data manipulation while offering a rigid flux determination and full high‐angular resolution. Our approach combines single‐dish and cleaned interferometric data in the image domain. This approach is tested for both galactic and extragalacticHidatasets. Furthermore, a quantitative comparison of our results with commonly used methods is provided. Additionally, for the interferometric datasets of NGC 4214 and NGC 5055, we study the impact of different imaging parameters as well as their influence on the combination for NGC 4214. The approach does not require raw data (visibilities) or any additional special information, such as…