We discuss the recent status of astrophysical analyses with digitized astronomical plate archives with emphasis on high‐energy and transient astrophysics. These data represent huge scientific, ...historical, and cultural value, but only the recent digitization has enabled their effective use in astrophysics.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We will briefly present the proposal for the UV experiment based on low‐dispersion spectroscopy (LDS) of stars for cubesat mission, as well as the potential of LDS with digitized photographic plates ...taken mostly by Schmidt telescopes. Extended databases of these records are available at numerous observatories, mainly in the United States, with the total estimated number exceeding 100,000. They represent a valuable source of astrophysical information, especially for automated searches for objects with peculiar spectra as well as for (prominent) spectral changes.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Following common usage, we broaden the term “salt” to include all rock bodies composed primarily of halite (NaCl). Salt is mechanically weak and flows like a fluid, even at geologically rapid strain ...rates. Salt is also relatively incompressible so is less dense than most carbonates and all moderately to fully compacted siliciclastic rocks. Salt's fluid rheology and incompressibility make it inherently unstable under a wide range of geologic conditions.
The primary driving force for salt tectonics is differential loading, which may be induced by gravitational forces, by forced displacement of one boundary of a salt body relative to another, or by a thermal gradient. Buoyancy, long considered a key driver for salt tectonics, is of secondary importance in many settings. Two factors resist salt flow: strength of the overburden and boundary drag along the edges of the salt body. Salt will move only if driving forces exceed the resistance to flow.
In order for a salt diapir to be emplaced into its overburden, any rock previously occupying that space must be removed or displaced. Emplacement may occur by extension, erosion, or uplift of the overburden or by overthrusting of the salt. Once salt reaches the surface, it can continue to rise by passive diapirism, in which the diapir grows as sediments accumulate around it. A rapidly rising passive diapir may spread over the sediment surface to form an allochthonous salt sheet. A variety of salt-sheet lineages are possible, depending on the geometry of the feeder and the tectonic setting.
Because salt is weak, its tectonism is closely tied to regional deformation. In extension or transtension, diapirs rise up graben axes, taking advantage of the space created by thinning and separation of fault blocks. Later, once the salt source layer is exhausted, diapirs may fall as they continue to widen. In addition, salt typically acts as a detachment in both gravity-driven and basement-involved extension. In compression or transpression, preexisting diapirs are rejuvenated as salt is displaced upward by lateral shortening. This rise is enhanced by buckling and disruption of the diapir roof. In the absence of precursor structures, salt's primary role in compression is to act as a detachment. Some salt sheets may be emplaced in the hanging walls of thrust faults.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Structural systems involving mobile shale represent one of the most difficult challenges for geoscientists dedicated to exploring the subsurface structure of continental margins. Mobile-shale ...structures range from surficial mud volcanoes to deeply buried shale diapirs and shale-cored folds. Where mobile shales occur, seismic imaging is typically poor, drilling is hazardous, and established principles to guide interpretation are few. The central problem leading to these issues is the poor understanding of the mechanical behaviour of mobile shales. Here we propose that mobile shales are at critical state, thus we define mobile shales as "bodies of clay-rich sediment or sedimentary rock undergoing penetrative, (visco-) plastic deformation at the critical state". We discuss how this proposition can explain key observations associated with mobile shales. The critical-state model can explain the occurrence of both fluidized (no grain contact) shales (e.g., in mud volcanoes) and more viscous shales flowing with grain-to-grain contact (e.g., in shale diapirs), mobilization of cemented and compacted shales, and the role of overpressure in shale mobility. Our model offers new avenues for understanding complex and fascinating mobile-shale structures.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent
inversion. An early stage of extension generated ...structural topography consisting of a series of en-échelon graben. Our salt analog filled these
graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems, whereas deformation in
suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle
deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults,
forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was
enhanced along and up the major relay or transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation
geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent
downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest, and salt had risen diapirically on the horst
blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New pop-up structures also
formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to
natural examples such as those in the Moroccan High Atlas.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We report on historical optical outbursts in the OJ287 system in 1900 and 1913, detected on archival astronomical plates of the Harvard College Observatory. The 1900 outburst is reported for the ...first time. The first recorded outburst of the periodically active quasar OJ287 described before was observed in 1913. Up to now the information on this event was based on three points from plate archives. We used the Harvard plate collection, and added another seven observations to the light curve. The light curve is now well covered and allows one to determine the beginning of the outburst quite accurately. The outburst was longer and more energetic than the standard 1983 outburst. Should the system be strictly periodic, the period determined from these two outbursts would be 11.665 yr. However, this does not match the 1900 outburst or other prominent outbursts in the record. On the other hand, the precessing binary black hole model of Lehto and Valtonen (1996) can explain these and other known outbursts in OJ287. Finally, we discuss the upper limits for the expected 1906 outburst and the 1910 outburst, which was observed.
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FMFMET, NUK, UL, UM, UPUK
Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and ...future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the shape of the load margin and the shape of the salt structure at depth, resulting in complex deformation patterns. These physical modeling results provide more evidence for a possible interplay between ice sheets and subsurface salt structures, highlighting the significance of three-dimensional effects in dynamic geological settings. Our results lead to a better understanding of spatial patterns of the surface cracks that were mapped at the surface above salt structures and offer further room for interpretation of the influence of salt movements on the present-day landscape.
We briefly present the status of digitization and astrophysical use of the Hewitt Camera Archive, UK. These wide‐field images, so far little used for astrophysical work, cover both northern as well ...as southern sky down to limiting mag 13. We also discuss the potential of photographic images taken by satellite tracking cameras for recent astrophysics in general.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
The work is focused on the analysis of modern observations of meteoroids included in the data bank formed by both professional researchers and amateur astronomers. Based on the modern ...physical theory of meteoroids (PTM), a new method for analyzing measurements developed, which provides the accuracy comparable with the results of radar observations. Due to the fact that the accuracy of the new method for analyzing meteoroids observations has increased significantly, it became possible to process observations of the Perseid and Leonid showers over a period of 120 years. The use of PTM made it possible for the first time to explain the distribution of meteor echo signals observed at an altitude of 2 MHz, at which the upper part of this distribution refers to an altitude of 140 km. In the process of work, a database of orbital characteristics of meteoroids was created. A method has been developed for modeling the probability of hitting a certain area of a meteor particle with a mass greater than a certain specified value and determining the density of a meteor shower from radio observations as well as a new “tomography” method for calculating the density distribution of sporadic meteors in the sky using radar observations of meteors at the same station with a goniometer. The method allows calculating the density of a meteor shower on the celestial sphere with an angular resolution of 2°. The use of these methods served as a proof that the distribution density of meteoroid showers on the celestial sphere has two planes of symmetry: the first coincides with the plane of the ecliptic, passing through the poles of the Earth, the other one is perpendicular to the plane of the ecliptic.
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