Weak lensing in the second post-Newtonian approximation: gravitomagnetic potentials and the integrated Sachs–Wolfe effect

Dark matter currents in the large-scale structure give rise to gravitomagnetic terms in the metric, which affect the light propagation. Corrections to the weak-lensing power spectrum due to these gravitomagnetic potentials are evaluated by perturbation theory. A connection between gravitomagnetic lensing and the integrated Sachs–Wolfe (iSW) effect is drawn, which can be described by a line-of-sight integration over the divergence of the gravitomagnetic vector potential. This allows the power spectrum of the iSW-effect to be derived within the framework of the same formalism as derived for gravitomagnetic lensing and reduces the iSW-effect to a second-order lensing phenomenon. The three-dimensional power spectra are projected by means of a generalized Limber-equation to yield the angular power spectra. Gravitomagnetic corrections to the weak-lensing spectrum are negligible at currently accessible scales, and cosmic-variance considerations suggest that the detection of the iSW-effect's contribution to the cosmic microwave background angular power spectrum is too small to be detectable at multipoles probed by the Planck satellite.     

Spectroscopy of the Candidate Pre-CV LTT 560

We present preliminary results on spectroscopic data of the candidate pre-cataclysmic variable LTT 560. A fit to the flux-calibrated spectrum reveals the temperature of the white-dwarf primary to be T _eff=7000–7500 K, and confirms the result of previous studies on the detection of an M5V secondary star. The analysis of radial velocity data from spectral features attributed to the primary and the secondary star show evidence for low-level accretion.     

Rosat observations of pleiades flare stars

The X-ray data of a sample of 104 flare stars (FSs) in the Pleiades cluster region obtained by Stauffer et al. [1] on the basis of deep ROSAT PSPC observations are analyzed. If we divide the X-ray emission detected in late-type stars of the Pleiades cluster into FSs and non-FSs, we find that X-ray luminosities of stars of both groups can be considered as coming from the same parent population. Moreover, in order to classify stars in a sample of 23 late-type Pleiades stars of unknown nature discriminant analysis in a four-dimensional parameter space (log (L_x, log (L_x/L_bol), and ROSAT hardness ratios HR1 and HR2) has been used. It can be shown that the majority of these stars (16) are very likely FSs rather than non-FSs. Published in Astrofizika, Vol. 40, No. 4, pp. 545–557, October-December, 1997.     

“Terrae motus factus est”: earthquakes in Switzerland before A.D. 1000. A critical approach

We focus on Swiss earthquakes in antiquity and the early medieval period before A.D. 1000. We have information on less than half a dozen earthquakes within this era, since written records for the first half of the first millennium A.D. are minimal, and there is little hope of finding more written evidence for earthquakes. Furthermore, interpreting the documents at hand is somewhat complex. For the 6th century Gregory of Tours in Historia Francorum gives hints of a rockslide near the castle Tauredunum (Le Grammont) in the Swiss canton Valais, an event that has been considered in the literature as caused by an earthquake. The Carolingian period (ca. 750–950) included the rise of some very important cultural centers in various parts of today’s Switzerland. For instance, the ecclesiastical culture in St. Gallen generated a remarkable number of written records, which survived for our use in a unique manner. From the 9th and 10th centuries, we have evidence for earthquakes in the years 849, 867, 902, and 944. However, information on them remains so scarce that their location and intensity are generally difficult to assess. Nevertheless, the finding of a new document - a memoir written by the abbot of Reichenau - offers some insight into the A.D. 849 event and its reportedly aftershocks.

The Pseudobrookite Group: Crystal Chemical Features of the Armalcolite Fe2+ Analogue

Doklady Earth Sciences - The crystal structure of a potentially new mineral, the Fe2+-dominant analogue of armalcolite with the idealized formula Fe2+Ti2O5 has been solved. The sample studied...     

Co-location of space geodetic techniques carried out at the Geodetic Observatory Wettzell using a closure in time and a multi-technique reference target

The quality of the links between the different space geodetic techniques (VLBI, SLR, GNSS and DORIS) is still one of the major limiting factors for the realization of a unique global terrestrial reference frame that is accurate enough to allow the monitoring of the Earth system, i.e., of processes like sea level change, postglacial rebound and silent earthquakes. According to the specifications of the global geodetic observing system of the International Association of Geodesy, such a reference frame should be accurate to 1 mm over decades, with rates of change stable at the level of 0.1 mm/year. The deficiencies arise from inaccurate or incomplete local ties at many fundamental sites as well as from systematic instrumental biases in the individual space geodetic techniques. Frequently repeated surveys, the continuous monitoring of antenna heights and the geometrical mount stability (Lösler et al. in J Geod 90:467–486, 2016.  https://doi.org/10.1007/s00190-016-0887-8) have not provided evidence for insufficient antenna stability. Therefore, we have investigated variations in the respective system delays caused by electronic circuits, which is not adequately captured by the calibration process, either because of subtle differences in the circuitry between geodetic measurement and calibration, high temporal variability or because of lacking resolving bandwidth. The measured system delay variations in the electric chain of both VLBI- and SLR systems reach the order of 100 ps, which is equivalent to 3 cm of path length. Most of this variability is usually removed by the calibrations but by far not all. This paper focuses on the development of new technologies and procedures for co-located geodetic instrumentation in order to identify and remove systematic measurement biases within and between the individual measurement techniques. A closed-loop optical time and frequency distribution system and a common inter-technique reference target provide the possibility to remove variable system delays. The main motivation for the newly established central reference target, locked to the station clock, is the combination of all space geodetic instruments at a single reference point at the observatory. On top of that it provides the unique capability to perform a closure measurement based on the observation of time.     

Simulations of VLBI observations of a geodetic satellite providing co-location in space

We performed Monte Carlo simulations of very-long-baseline interferometry (VLBI) observations of Earth-orbiting satellites incorporating co-located space-geodetic instruments in order to study how well the VLBI frame and the spacecraft frame can be tied using such measurements. We simulated observations of spacecraft by VLBI observations, time-of-flight (TOF) measurements using a time-encoded signal in the spacecraft transmission, similar in concept to precise point positioning, and differential VLBI (D-VLBI) observations using angularly nearby quasar calibrators to compare their relative performance. We used the proposed European Geodetic Reference Antenna in Space (E-GRASP) mission as an initial test case for our software. We found that the standard VLBI technique is limited, in part, by the present lack of knowledge of the absolute offset of VLBI time to Coordinated Universal Time at the level of microseconds. TOF measurements are better able to overcome this problem and provide frame ties with uncertainties in translation and scale nearly a factor of three smaller than those yielded from VLBI measurements. If the absolute time offset issue can be resolved by external means, the VLBI results can be significantly improved and can come close to providing 1 mm accuracy in the frame tie parameters. D-VLBI observations with optimum performance assumptions provide roughly a factor of two higher uncertainties for the E-GRASP orbit. We additionally simulated how station and spacecraft position offsets affect the frame tie performance.     

New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean

Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of ²⁰⁸Pb/²⁰⁷Pb vs. ε_Nd, ²⁰⁸Pb/²⁰⁷Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and ε_Nd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5?μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean.     

ShakeMap-based prediction of earthquake-induced mass movements in Switzerland calibrated on historical observations

Natural Hazards - In Switzerland, nearly all historical Mw?~?6 earthquakes have induced damaging landslides, rockslides and snow avalanches that, in some cases, also resulted in damage...