Short time-scale variability in the spectrum of the hot B3V star ηUMa

We report the results of observations of short time-scale variability in the Hydrogen Balmer lines and HeI lines in the hot B star ηUMa. Spectral observations were carried out with the low-resolution slitless spectrograph (R∼200) installed on the 60 cm Carl Zeiss telescope in the Andrushivka Observatory, Ukraine. Spectra were obtained with a time resolution in the sub-second range. It has been found that the hot B star ηUMa shows rapid variations in the Hydrogen lines Hβ, Hγ, Hδ, Hε and the Helium lines HeI 5016Å HeI 5047Å, as well as variations in the atmospheric oxygen lines. This can be interpreted that their variations are non-radial pulsations and strong stellar wind.

Modelling the solar, geomagnetic and periodic variations of the ionosphere over Ethiopia

A careful and continuous ionospheric modelling can significantly influence the performance of activities such as Positioning, Navigation and Timing services related with the Global Navigation Satellite System applications as well as the Earth Observations System, satellite communication and Space weather forecasting applications. In this paper, the linear time-series modelling that consists of the solar, geomagnetic and periodic components has been carried out on the daily ionospheric vTEC at two different Ethiopian GPS locations, at Arbaminch, ARMI (geographic 6.06ºN, 37.56ºE) and Bahir Dar, BDMT (geographic 11.60ºN, 37.38ºE), for the year 2012, 2014 and 2016 in the 24th solar cycle. The variations of vTEC due to the solar activities, geomagnetic activities and periodic oscillations have been explicitly investigated. The results confirmed that the correlation coefficient of the linear model based estimated vTEC and the observed GPS-vTEC is around 80% in the year 2014. Besides, solar activity is identified as the key component for the 27 days period variations of vTEC whereas geomagnetic activity is identified as the key component that influences the short-period variations of the daily average vTEC. In addition to the correlation analysis, the accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI 2016) model based vTEC and GPS-vTEC measurements as well as with the quadratic model based vTEC. Consequently, the linear model formulated with the solar, geomagnetic and periodic components significantly captured the variations (78-80%) of the observed vTEC compared with both the IRI 2016 and the quadratic models during the years 2012, 2014 and 2016. The comparison of the observed and predicted vTEC variations has also been examined using the continuous wavelet transform. The decomposed waves from the wavelet analysis have revealed that the predicted and observed vTEC have had simultaneous periods of variations specifically with the period of 27 days whereas the IRI 2016 could capture the short-period variations of vTEC. Moreover, the analysis from the transformed data in the year 2014 over both Arbaminch and Bahir Dar has indicated that the linear model based vTEC and the observed GPS-vTEC have had common pattern of variations with the period of 27 days that had lasted for 150 days (from day of the year 100 to 250).

Ammonia in circumstellar environment of V Cyg

The HIFI instrument on board of the Herschel Space Observatory (HSO) has been very successful in detecting molecular lines from the circumstellar envelopes around evolved stars, like massive red supergiants, Asymptotic Giant Branch (AGB) and post-AGB stars, as well as the planetary nebulae. Among others, ammonia have been found in the circumstellar envelopes of C-rich AGB stars in amounts that significantly exceeded the theoretical predictions for C-rich stars. Few scenarios have been proposed to resolve this problem: formation of ammonia behind the shock front and photochemical processes in the inner part of the envelope partly transparent to UV background radiation due to the clumpy structure of the gas and formation of ammonia on dust grains. Careful analysis of observations may help to put the constraints on one or another mechanism of ammonia formation. Here, we present results of the non-LTE radiative transfer modeling of ammonia transitions including the crucial process of radiative pumping via the v2=1 vibrational band (at ∼10 μm) for V Cyg. Only the ground-based ammonia transition NH3 J = 10-00 at 572.5 GHz has been observed by HIFI. Therefore, to determine the abundance of ammonia we estimate the photodissociation radius of NH3 using chemical model of the envelope consistent with the dust grain properties concluded from the spectral energy distribution.

Geomagnetic storms and their impacts on Ethiopian power grid

In present work we analysed eight geomagnetic storm events in 2015/2016 and studied the possible influence of these events on Ethiopian power grids. The results showed that the majority of the forced power outages occurred in the period of the main phase of events and the recovery period of the geomagnetic storms. The geomagnetic storms are characterised by different indices and parameters such as the disturbance storm time (Dst) values, coronal mass ejection (CME) speed, solar wind speed (V sw) and interplanetary magnetic field (IMF-Bz) on the selected dates. In most cases the observed geomagnetic storms were produced by the CME-driven storms as they show a storm sudden commencement (SSCs) before the main storms, and also have the short recovery periods. The sudden jumps of the solar wind velocities and IMF-Bz are also consistent with occurrence of the CMEs. Moreover, this effect can be traced in changes of Earth magnetic field during geomagnetic storm and quiet days. The observed CME-driven storms can produce highly variable magnetic fields on the transformers and provide forced outages, however the studied outages have not been recognised as those one driven by a geomagnetic storm.

Astrometric and photometric observations of six brightest trans-Neptunian objects at the Kyiv comet station

In this work we focused on observations of six trans-Neptunian objects (TNOs) whose apparent magnitudes are brighter than 20m. We present the results of astrometric and photometric observations of (134340) Pluto, (136108) Haumea, (136472) Makemake, (136199) Eris, (90482) Orcus, and (20000) Varuna obtained at the Kyiv comet station (Code MPC 585) in 2017-2019. For observations we used the 0.7-m (f/4) reflector AZT-8 with FLI PL4710 CCD camera and filters of Johnson-Cousins photometric system. From our images we measured the objects' astrometric positions, calculated apparent magnitudes in the BVRI (mostly R) bands using aperture photometry method, and found absolute magnitudes together with the colour indices in several bands. Analysing our results, we investigate the limitation on the astrometry and photometry of faint objects with the 0.7-m telescope.

Spectra of comet C/2002 T7 (LINEAR)

We present the results of spectral observations of comet C/2002 T7 (LINEAR) carried out at the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory (Russia). The spectra were obtained within the 3500-7500 Å wavelength range on November 13, 14, and 21, 2003, before the perihelion passage, when heliocentric and geocentric distances of the comet were about 2.7 AU and 1.8 AU, respectively. Spectra do not show any emission features from the strongest cometary emissions of the CN, C2, and C3 molecules. The normalised spectral gradient of reflectivity is 2.8% per 1000 Å and 5.4% per 1000 Å for November 14 and 21, respectively. The Afρ parameter, which characterises the dust production rate in the comet, is on average about 800 cm. Comet C/2002 T7 (LINEAR) can be classified as belonging to the group of dusty comets

Photoionisation modelling of the H II regions surrounding star-forming regions within the metallicity range Z=0.003-0.012

We present the new approach to the ionisation structure modelling for the high-metallicity H II regions. The method is based on the multicomponent photoionisation modelling (MPhM) of these objects that takes into account their complicate structure due to superwind from the central star-forming region. The complex structure of H II region has been divided into internal and external components. Internal components correspond to the region of free expanding superwind and the cavity of superwind, respectively, while the external ones — to a thick layer of gas compressed by a superwind shock, and hydrodynamically undisturbed outer part of H II region, where the most of observed strong emission lines are formed. The components of the model were calculated within the assumption of spherical symmetry. The gas photoinisation was caused by the ionising quanta of both direct and diffuse ionising radiation. The fluxes of this radiation were calculated during the simulation using the radiative transfer equations which account for all important processes in the H II region causing this transfer. The diffuse ionising radiation was calculated in the Outward Only approach. In the region of free expansion of the superwind the chemical abundances were determined using the evolutionary population synthesis models of a star-forming region. The distributions of the electron temperature and density in the external components were obtained in such modelling as the solutions of the photoionisation energy balance equation. The stop criterion for evolutionary modelling corresponding to the condition of equilibrium of pressure on the boundary between the third and fourth components was adopted. The evolutionary grid of multicomponent high-metallicity models of the H II regions was calculated. It was shown that the internal structure of a H II region under certain conditions can cause the lack of quanta in the spectrum of ionising radiation.

Comparison of the photoionisation modelling results for planetary nebulae with the observed data

The grid of new photoionisation models for planetary nebulae (PNe) along the evolutionary tracks of their nuclei was calculated, taking into account the dust presence with abundances that correspond to the averaged ones for Milky Way and Large Magellanic Cloud. The calculations were performed by the last version of G. Ferland's code Cloudy v17.01 using the semi-empirical law derived by Golovatyy-Mal'kov to describe the radial density distribution of matter in the nebular envelope of PN. Resulting modelling spectra were compared with the corresponding observed emission line spectra of PNe in optical range, obtained previously by other authors. Also the database of observations by the Infrared Space Observatory and Spitzer have been used to compare the results of synthetic photometry with the observed photometric data. It was shown that the intensities of strong emission lines in optical range as well as the observed color-color diagrams obtained using total fluxes in the 3.6 μm, 4.5μm, 8.0μm and 24.0 μm bands are reproduced very well by our models, while the results of synthetic IR-photometry based on total fluxes in the band 5.8 μm show discrepancies with corresponding observed data.

Some peculiarities of activity for comets with orbits on 2–5 AU

Periodic comets of different dynamical groups with orbits at 2–5 AU still occasionally active. The observed dust activity of such objects can be connected with the processes of water ice sublimation (MBCs) or crystallisation of amorphous water ice (QHCs) as well as with external causes. Despite the absence of connections between cometary flares and cyclic variations of solar activity indexes, some individual solar flares can affect the brightness of comets. Cometary objects in the main asteroid belt have lower statistic of flares than comets at orbits similar to quasi-Hilda objects.

X-ray scaling relations of elliptical galaxies

We present the X-ray scaling relations of a sample of elliptical galaxies using X-ray Chandra observations. We use a single β-model to reconstruct the density gas profile and the hydrostatic equation to measure the total mass. We build X-ray scaling relations between temperature, luminosity and total mass at 5Re. Our sample in- cludes gas-poor objects that help us to extend already published LX − T , M − T and LX − M scaling relations to lower magnitudes. The derived slopes for all three relations are much steeper than those for galaxy clusters and groups, and are extreme compared to self-similar models considering gravity only. This increase of steepness from clusters to galaxies indicates that non-thermal processes (e.g. AGN feedback) have a stronger influence on the small-scale systems. Our results indicate that the hot interstellar medium of gas-poor early-type galaxies is not in the wind/outflow state as suggested by recent hydrodynamical simulations. We also discuss the possible biases of our calculations and compare our results to recent papers.