The 10 most-cited articles in Astronomische Nachrichten, 2020

Abstract The properties (temperature, density, chemical composition, velocity) of hot astrophysical plasma and the physical processes affecting them (heating/cooling, turbulence, shocks, acceleration) can be probed by high‐resolution X‐ray spectroscopy, to be complemented by high‐spatial‐resolution imaging. The paper presents the status of the European Space Agency's Advanced Telescope for High Energy Astrophysics (Athena) mission, particularly focusing on the science performance of its two focal‐plane instruments for studies of extended X‐ray sources: the wide‐field imager and the X‐ray integral field unit. This paper then provides a brief summary of the breakthroughs expected with Athena on the astrophysics of hot plasma, building on the vast heritage of the discoveries and revolutionary results obtained by Chandra and XMM‐Newton in this field. As of November 12, 2019, Athena successfully concluded its feasibility study, and has since then moved into the definition phase, with a launch date scheduled in the early 2030s.

The first results of a new survey, which explores the second data release of the ESA‐Gaia mission, are reported in order to search for stellar companions of (Community) TESS Objects of Interest and to characterize their properties. In total, 193 binary and 15 hierarchical triple star systems are presented, detected among 1,391 target stars, which are located at distances closer than about 500 pc around the Sun. The companions and the targets are equidistant and share a common proper motion, as is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.08 M⊙ and 3M⊙ and are most frequently found in the mass range between 0.13 and 0.6M⊙. The companions are separated from the targets by about 40 up to 9,900 au, and their frequency continually decreases with increasing separation. While most of the detected companions are late K to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature is revealed by their photometric properties.

Abstract Guided by the working hypothesis that the Schwabe cycle of solar activity is synchronized by the 11.07‐year alignment cycle of the tidally dominant planets Venus, Earth, and Jupiter, we reconsider the phase diagrams of sediment accumulation rates in Lake Holzmaar and of methanesulfonate data in the Greenland ice core Greenland Ice Sheet Project 2 (GISP2), which are available for the period 10000–9000 cal. BP. As some half‐cycle phase jumps appearing in the output signals are, very likely, artifacts of applying a biologically substantiated transfer function, the underlying solar input signal with a dominant 11.04‐year periodicity can be considered to be mainly phase‐coherent over the 1,000‐year period in the early Holocene. For more recent times, we show that the reintroduction of a hypothesized “lost cycle” at the beginning of the Dalton minimum would lead to a real phase jump. Similarly, by analyzing various series of 14C and 10Be data and comparing them with Schove's historical cycle maxima, we support the existence of another “lost cycle” around 1565, also connected with…

Abstract The Next Generation Transit Survey (NGTS) is a photometric survey for transiting exoplanets, consisting of 12 identical 0.2‐m telescopes. We report a measurement of the transit of HD 106315 c using a novel observing mode in which multiple NGTS telescopes observed the same target, with the aim of increasing the signal‐to‐noise ratio. Combining the data allows the robust detection of the transit, which has a depth less than 0.1%, rivaling the performance of much larger telescopes. We demonstrate the capability of NGTS to contribute to the follow‐up of K2 and Transiting Exoplanet Survey Satellite discoveries using this observing mode. In particular, NGTS is well‐suited to the measurement of shallow transits of bright targets. This is particularly important to improve orbital ephemerides of relatively long‐period planets, where only a small number of transits are observed from space.

Abstract Blazars represent the dominant population of the extragalactic γ‐ray sources in the universe. These sources exhibit some characteristic properties such as strong and nonthermal continuum emission over the entire electromagnetic spectrum, from radio to Tera electron Volts (TeV) γ‐rays, with rapid variability on all timescales. The emission at radio and optical wavelengths is highly polarized with significant variation. The fastest variability in the blazar emission is observed during the flaring activity, which is an important observational property of blazars. In this paper, we describe various methods to characterize the temporal variability in the multiwavelength light curves of blazars. We also provide a detailed description of the set of statistical parameters that are used to quantify the level of variability present in the time series. Implications of the information derived from the variability study to probe the physics of blazars using multiwavelength observations are also discussed.

Abstract The aim of this paper is to analyze and shed light on the potential relations between two bodies of finite dimensions and different shapes. After explaining the properties of different shaped bodies, we analyze the gravitational potential between an irregular body and a point mass, followed by the potential relation between two irregular bodies with discussion of its different properties. We also explore the potential relation between two solid cylinders, which can be degraded to 16 potential relations; one of these relations is the potential relation between two finite straight segments. With a new development for the potential relation, we evaluate the gravitational potential between a heterogeneous irregular body and a point mass followed by the potential between two heterogeneous irregular bodies with N−layers, which also can be reduced to the potential between two oblate or prolate heterogeneous bodies. We demonstrate that this relation can be degraded to many potential relations between two bodies, because it depends on the moments of inertia of the body's shape.…

Abstract Accurate chemical abundance measurements of X‐ray‐emitting atmospheres pervading massive galaxies, galaxy groups, and clusters provide essential information on the star formation and chemical enrichment histories of these large‐scale structures. Although the collisionally ionized nature of the intracluster medium (ICM) makes these abundance measurements relatively easy, the underlying spectral models can rely on different atomic codes, which brings additional uncertainties on the inferred abundances. Here we provide a simple, yet comprehensive comparison between the codes SPEXACT v3.0.5 (ciemodel) and AtomDB v3.0.9 (vapecmodel) in the case of moderate, charged‐coupled device‐like resolution spectroscopy. We show that in cool plasmas (kT ≲ 2 keV), systematic differences up to ∼20% for the Fe abundance and ∼45% for the O/Fe, Mg/Fe, Si/Fe, and S/Fe ratios may still occur. Importantly, these discrepancies are also found to be instrument‐dependent, at least for the absolute Fe abundance. Future improvements in these two codes will be necessary to better address questions on ICM…

Abstract In the present paper, an effort to generalize the restricted problem of 2 + 2 bodies has been made by considering the primary bodies m1 and m2 to be a point mass and straight segment of length 2l, respectively. The motion of the two infinitesimal bodies mi, i = 3, 4 has been investigated, in which each mi, i = 3, 4 is moving in the gravitational field of mj, j = 1, 2, 3, 4 with i ≠ j. For the present problem, 14 equilibrium points are obtained, of which 6 are collinear and the rest are noncollinear. The length parameter l has a subsequent effect on the location of all the equilibrium points. Systematic stability analysis has been carried out by using the theory of perturbation. All the equilibrium points are found to be unstable.

Abstract We have reanalyzed the data used by Bessel, von Struve, and Henderson in the 1830s to measure the first parallax distances to stars. We can generally reproduce their results, although we find that von Struve and Henderson have underestimated some of their measurement errors, leading to optimistic parallax uncertainties. We find that temperature corrections for Bessel's measured positions are larger than anticipated, explaining some systematics apparent in his data. It has long been a mystery as to why von Struve first announced a parallax for Vega of 0.″125 only to later revise it to double that value using more data. We resolve this mystery by finding that von Struve's early result used two dimensions of position data, which independently give significantly different parallaxes but, when combined, only fortuitously give the correct result. With later data, von Struve excluded the “problematic” dimension, leading to the larger parallax value. Allowing for likely temperature corrections and using his data from both dimensions reduce von Struve's parallax for Vega to a value…

Abstract Disentangling techniques are often needed to obtain the spectra of the individual components of binary or multiple systems. A thorough analysis of the shift‐and‐add algorithm of Marchenko et al, PASP, 1999;110:1416 reveals that, in many cases, the line fluxes are poorly reproduced, and spurious wings appear. The causes of these discrepancies are discussed, and a new disentangling package, QER20, is presented, which significantly reduces these errors and vastly increases the performance. When applied to the massive binary 9 Sgr, our new code yields line fluxes that are notably different from those previously published and lead us to revise the spectral classification to slightly earlier subtypes: O 3 V ((f +)) for the primary and O 5 V ((f)) for the secondary. We show that, with the MME98 algorithm, the classification of massive stars in binaries can be off by several subtypes, while there are no such errors when the QER20 package is used.