The 10 most-cited articles in Astronomische Nachrichten, 2017

Observations of the X‐ray sky after the next decade will most likely be dominated by Athena (Advanced Telescope for HighENergyAstrophysics), the second large mission ofESA's Cosmic Vision 2015–2035 programme. Athena has been conceived to address the “Hot and Energetic Universe” science theme, which focuses on the assembly and evolution of hot baryons in cosmic structures as well as the physics and energetic output generated by accreting super‐massive black holes, along with the relationship between the two processes, dubbed cosmic feedback. Thanks to its transformational capabilities, Athena will enable bringing all of today'sXMM‐Newton'shot science topics to a new stage. In this paper, we summarize the Athena science case, science requirements, as well as the expected mission performance, mission concept, and its status.

Galaxy clusters are thought to grow hierarchically through the continuous merging and accretion of smaller structures across cosmic time. In the local universe, these phenomena are still active in the outer regions of massive clusters (R > R500), where the matter distribution is expected to become clumpy and asymmetric because of the presence of accreting structures. We present the XMM‐Newton cluster outskirts project (X‐COP), which targets the outer regions of a sample of 13 massive clusters (M500 > 3 × 1014M⊙) in the redshift range 0.04–0.1 at uniform depth. The sample was selected based on the signal‐to‐noise ratio in the Planck Sunyaev–Zeldovich (SZ) survey with the aim of combining high‐quality X‐ray and SZ constraints throughout the entire cluster volume. Our observing strategy allows us to reach a sensitivity of 3 × 10− 16 ergs cm− 1 s− 1 arcmin− 2 in the 0.5–2.0 keV range thanks to a good control of systematic uncertainties. The combination of depth and field of view achieved in X‐COP will allow us to pursue the following main goals: (a) measure the distribution of entropy…

Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high‐resolution chrono‐chemo‐kinematical maps of the Galaxy. Data from large‐scale astrometric and spectroscopic surveys will soon provide us with a well‐defined view of the current chemo‐kinematical structure of the Milky Way, but it will only enable a blurred view on the temporal sequence that led to the present‐day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler , and K2, asteroseismology provides the way forward: solar‐like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age–initial mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar…

In this article, we first review the past decade of efforts in detecting the missing baryons in the warm hot intergalactic medium and summarize the current state of the art by updating the baryon census and physical state of the detected baryons in the local Universe. We then describe observational strategies that should enable a significant step forward in the next decade, while waiting for the step‐up in quality offered by future missions. In particular, we design a multi‐megasecond and multiple cycleXMM‐Newtonlegacy' program(which we name the Ultimate Roaming Baryon Exploration, orURBE), aimed at securing detections of the peaks in the density distribution of the Universe of missing baryons over their entire predicted range of temperatures.

From our sample of spotted late‐type stars showing surface differential rotation, we find that the relationship between the rotation period and the surface shear coefficientα= ΔΩ/Ωeqis significantly different for single stars compared to members in close binaries. Single stars follow a general trend thatαincreases with the rotation period. However, differential rotation of stars in close binary systems shows much weaker dependence on the rotation, if any, suggesting that in such systems, tidal forces operate as a controlling mechanism of differential rotation.

Background Several recent studies indicated possible long‐term variations of physical properties of sunspots. Materials and Methods Using observations of sunspot magnetic field strengths ( H ) from the Crimean Astrophysical Observatory and area ( S ) of sunspots from the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory, we investigate the changes in the relation between H and S over the period of about two solar cycles (1994– 2013). The data were fitted by H = A + B log S , where A = (778 ± 46) and B = (778 ± 25). Results We show that the correlation between H and S varies with the phase of solar cycle, and A coefficient decreases significantly after year 2001, while B coefficient does not change significantly. Furthermore, our data confirm the presence of two distinct populations in the distribution of sunspots (small sunspots with weaker field strength and large sunspots with stronger field). We show that the relative contribution of each component to the distribution of sunspots by their area changes with the phase of solar cycle and on longer‐than‐cycle periods.…

Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterization is notoriously difficult, requiring high‐quality observations and advanced analysis techniques. Significant progress has been recently achieved by several types of direct magnetic field studies on the surfaces of cool, active stars. In particular, complementary techniques of field topology mapping with polarization data and total magnetic flux measurements from intensity spectra have been systematically applied to different classes of active stars, leading to interesting and occasionally controversial results. In this paper, we summarize the current status of direct magnetic field studies of cool stars and investigations of surface inhomogeneities caused by the field, based on the material presented at the Cool Stars 19 splinter session.

The nonlinear relation between X‐ray and UV luminosity in quasars can be used to estimate their distance. Recently, we have shown that, despite the large dispersion of the relation, a Hubble diagram made of large samples of quasars can provide unique constraints on cosmology at high redshift. Furthermore, the dispersion of the relation is heavily affected by measurement errors: until now we have used serendipitous X‐ray observations, but dedicated observations would significantly increase the precision of the distance estimates. We discuss the future role of XMM in this new field, showing (a) the fundamental contribution of the Serendipitous Source Catalog and of large surveys and (b) the breakthrough advancements we may achieve with the observation of a large number of Sloan Digital Sky Survey (SDSS) quasars at high redshift: every ∼10 quasars observed at z∼3 would be equivalent to discovering a supernova at that redshift.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian–German Spectrum‐Roentgen‐Gamma (SRG) mission, which is currently scheduled for launch in late 2017. eROSITA will perform a deep survey of the entire X‐ray sky. In the soft band (0.5–2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2–8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters up to redshifts z > 1 in order to study the large‐scale structure in the universe and test cosmological models including dark energy. In addition, eROSITA is expected to yield a sample of a few million active galactic nuclei, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X‐ray binaries, active stars, and diffuse emission within the galaxy. The eROSITA flight model has passed calibration and integration and is currently…

This article reviews the current knowledge and status of investigations on the variable magnetic activity of cool stars. We discuss the Sun in the context of solar‐type stars, highlighting peculiarities and common features in terms of its magnetic activity and variability over different time scales. We examine how both theory and observations are providing new clues about the main physical processes that generate magnetic fields in the interior of cool stars, as well as about those that lead to evolving stellar surface magnetism and varying chromospheric and coronal phenomena. We then proceed to discuss the relations between stellar age, rotation, and activity throughout the evolution of cool stars. Finally, we touch upon the importance of understanding stellar magnetism also in view of its effect on planetary environments.