On the production of chemical elements beyond the iron peak

Astronomy Letters - We discuss the possibility of elements heavier than iron being produced in the cooling central part of a low-mass supernova remnant in terms of a consistent kinetic model that...     

Time series analysis of vegetation-cover response to environmental factors and residential development in a dryland region

Land-use changes as a result of residential development often lead to degradation and alter vegetation cover (VC). Although these are worldwide phenomena, sufficient knowledge about anthropogenic effects caused by various populated areas in dryland ecosystems is lacking. This study explored anthropogenic development in rural areas and its effects on the conservation of protected areas in drylands, focusing on the change in VC, the reasons, extent, and the drivers of change. We propose a novel framework for exploring VC change (VCC) as a function of environmental and human-driven factors including different types of populated areas in drylands. As a case study, we used a 30-year time series of Landsat satellite images over the arid region of Israel to analyze spatiotemporal VCC. The temporal analysis involved the Contextual Mann-Kendall significance test and spatial analysis to model clustering of VCC. A Gradient Boosted Regression machine learning algorithm was applied to study the relative influence of environmental and human-driven factors on VCC. In addition, we used ANOVA to examine differences between the effects of three types of populated areas on the spatiotemporal trends of VC. The results show that the most influential environmental variable on VCC was elevation (relative contribution of 17%), followed by slope (14.8%) and distance from populated areas (14.6%). Moreover, different types of populated areas affected VC differently with varying distances from residential centroids. The nature reserves increased VC positively and significantly, while livestock settlements had a negative effect. Change in vegetation was mostly confined to the stream network and occurred in lower elevations. The study demonstrates how different land-use practices alter the landscape in terms of VC and differ in their extents, patterns, and effects. With the expected growth in population and residential development worldwide, the proposed framework may assist conservation managements and policy makers in minimizing environmental degradation in drylands.     

Die Periode des magnetischen Sterns HD 133 029

The period of 0.741285 days for the light variability of the magnetic star HD 133 029 was obtained from UBV observations. The observations of the effective magnetic field by BABCOCK show variations with a period of 0.7447 days. A small change of the period and a slow change of the magnitude of this magnetic star seems to be present.     

Photometry of the spotted flare star by dra during 1985-1991

Spot photometry in theUBV was obtained for the flare star BY Dra during 1985-1991 at the Bulgarian National Astronomical Observatory. Light curves are presented for 1986, 1987, 1988, and 1991. There are significant variations of the amplitudes of the light curves implying changes of the spot distribution. The phases of the light minima are variable, indicating possible latitudinal migration of the spot and differential rotation. Rough estimate of the corresponding latitudinal shear is in the range 3 × 10^–11 –5 × 10^–10 rad s^–1 deg^–1. The photometric behaviour of BY Dra since 1960 shows no compeling evidence for existence of stellar cycles. This is in contradiction with previous studies. During 1985-1991 a total of 38.47 hours of monitoring in theU-filter were obtained. Analysis of the flare activity of BY Dra shows no significant changes from previous studies.     

CH Cygni in the transition to its cool phase

U, B, V-observations, supplemented by spectrophotometric measurements of the symbiotic variable CH Cyg in the years 1982 to 1984 show that the star has reached its blue maximum phase of its recent outburst in the first half of 1984. From end of July, 1984 on the object underwent a considerable drop in brightness and an increase of its colour indices, and which indicates that it was on the way to its cool phase. Also the spectroscopic observations show that the blue continuum still observed at the beginning of July, 1984 has disappeared in October–November, 1984 and the strong absorption features, typical for a M-type giant were re-appearing. A remarkable intensity increase of the emission features, especially those of the Balmer lines, took place within this time interval. The rapid flickering variations of CH Cyg had also reached the culmination amplitude in July, 1984. There seem to be three periodicities present in these flickering variations with cycle lengths of 7.7 min, 21 min, and 60 min. Though these observational findings would be consistent with the M-type blue subdwarf component binary model with mass flow from the M6-III giant to the companion, the genuine binary nature of CH Cyg could not be established beyond doubt.     

The relativistic spherical accretion by black holes

The relativistic spherical accretion onto black holes is considered. It is shown that electron heat conductivity and ion viscosity increase the ion temperature by roughly two orders of magnitude over the electron temperature at Schwarzschild radius. As a result, the knee arise in gamma-radiation spectrum at 10–30 MeV. The role of magnetic field, electron-positron pairs production and generation of absorption lines in spectrum briefly discussed.     

Jurassic magmatic bodies of mountainous Crimea in the Bodrak River catchment (Southwestern Crimea)

The synthetic (geological and petrochemical) study of Jurassic magmatic bodies in the catchment of the Bodrak River (mountainous Crimea) is conducted. Their structural position and a Middle Jurassic age were determined. The magmatic bodies of mountainous Crimea were compared to those of the Lozovskaya zone. The study considers the geodynamic settings of the Middle Jurassic magmatism in mountainous Crimea.     

The <Emphasis Type="Italic">r</Emphasis>-Process in the region of transuranium elements and the contribution of fission products to the nucleosynthesis of nuclei with <Emphasis Type="Italic">A</Emphasis> ≤ 130

We discuss the influence of nuclear masses and mass distributions of fission products on the formation of heavy elements at the final stages of the r-process recycled through fission on long duration timescales. The fission recycling is of great importance in an environment with a high density of free neutrons (e.g., in neutron star merger scenarios), when the r-process duration is long enough for most of the seed nuclei to be transformed into actinoids. The fission products of transuranium elements are again drawn into the r-process to produce the abundance curve beyond the iron peak. In this case, to explain the abundances of the A ～ 130 peak elements, not only the nuclear masses, fission barriers, and reaction rates, but also the fission product mass distribution must be predicted. Our r-process calculations using new nuclear masses and fission barriers and reaction rates based on them have shown that the simple two-fission-fragment model used previously in r-process calculations cannot describe adequately the position of the second peak in the observed abundance curve. We show that agreement between calculations and observations can be achieved only when we properly consider the mass distribution of fission products by taking into account the emission of instantaneous fission neutrons.     

Fission and the <Emphasis Type="Italic">r</Emphasis>-process: Competition between neutron-induced and beta-delayed fission

We show that for the discussed scenario of a neutron-star merger in highly neutronized ejecta (Y _e ?0.1), neutron-induced fission plays a major role in the r-process cycling and is the main obstacle to the formation of superheavy elements. At the final stage of the r-process, when the free-neutron density is already too low to maintain rapid nucleosynthesis and only beta-decay and beta-delayed fission take place, the leading role in forming the final abundances of chemical elements passes to delayed fission. The latter ultimately changes the abundances of individual isotopes in the region before the second peak and heavier than lead, which, in particular, affects the determination of the age of the Galaxy.