The presence of circumstellar matter was discovered over 150 years ago through visual observations of emission lines in spectra of B-type stars. This effect is called the Be phenomenon, found only in fast-rotating stars and not yet fully understood. One explanation of the fast rotation is a consequence of mass transfer from a secondary component, which have been hard to reveal because they are...
The shape of the light curve and the time scales of brightness variations are the main defining factors for classification of variable stars. However, different variability mechanisms can produce light curves of similar shape and period, hindering the determination of their origin. I will discuss the origin of TIC 229741985 variability. Based on TESS photometry, the star can be classified...
Our study reports the discovery of ELM WDs as companions to BSS in the Galactic globular cluster NGC 362. We used data from AstroSat’s UVIT, UVOT, Gaia EDR3, and the 2.2 m ESO/MPI telescope to create SEDs for 26 FUV bright member BSSs. Binary-SED fits revealed ELM WDs as binary companions in 12 of the 26 BSSs studied, suggesting that 12 BSSs are post-mass-transfer systems formed through the...
We present the results of photometric CCD observations of the magnetic cataclysmic variable V405 Aurigae obtained using different instruments. We analysed variability of the spin period of the white dwarf in this system using our observations and previously published maxima timings. We confirmed one of the 2 hypotheses of the spin period variability of this system published earlier. This...
"Betelgeuse, a red supergiant star of semi-regular variability, underwent a historical minimum of brightness in February 2020, the Great Dimming. Even though the brightness has returned to the values prior to the Great Dimming by now, it continues to exhibit highly unusual behavior.
Understanding the long-term atmospheric motions of Betelgeuse and its variability could be a clue to the nature...
About 10 % of upper main sequence stars, classified as chemically peculiar (CP) stars have anomalous abundance of chemical elements on their surface layers. A subgroup of hot CP stars with strong abundance of helium have not only a stellar wind, but also a strong magnetic field. The spin-down of these stars is probably caused by angular momentum loss through their magnetic stellar wind.
The galactic chemical evolution (GCE) describes how the composition of a galaxy changes over time. This variation of the interstellar medium is due to the nuclear reactions in stars and supernovae that enrich the interstellar gas with heavy elements, as well as the inflowing gas from the extragalactic space. This field may be the most exciting when we study the history of the Milky Way, being...
This study, the first light curve analysis of BD-02 873, an spectroscopic binary star system, is presented. We obtained spectroscopic data using the Whoppshel spectrograph attached to the 0.8-meter telescope at Ankara University Kreiken Observatory to derive radial velocity. The light curve from the TESS data was combined with the radial velocity measurements and were analyzed using the PHOEBE...
Since 2007, the TUBITAK National Observatory (TUG) has been conducting precise Doppler surveys of G-K giant stars, which have identified several stars with radial velocities between 1 and 10 $kms^{-1}$. Among these stars is HD 10259, which exhibits a radial velocity variation with an amplitude of about 5 $kms^{-1}$ over a period of 550 days. Using the 1.5m RTT150 telescope at TUG and an iodine...
In this study, we present preliminary stellar parameters of HD 60935 using the spectroscopic and photometric data. We obtained medium resolution spectroscopic data using the Shelyak spectrograph attached to the $0.4$-meter telescope at Ankara University Kreiken Observatory. We utilized two methods to derive stellar parameters: the Bayesian Spectral Energy Distribution Model fitting for...
I will report on the optical-radio study of outbursting cataclysmic variable star CRTS J033349.8-282244 in the LADUMA field. The source has extensively been observed with multiple facilities. I will present the results from observations of CRTS J033349.8-282244 done with MeerLICHT, MeerKAT and SAAO telescopes throughout outbursts, super-outbursts and during quiescence. The LADUMA field is...
Research and scientific scope of the Division of Astronomy and Astrophysics, which belongs to the Department of Astronomy, Physics of the Earth and Meteorology, is focused on the interplanetary mass, physics and dynamics of small bodies of the Solar system, their relations and evolution and on modeling of the orbital evolution of the dust particles. Research also focuses on space debris and...
Comets of the Jupiter family are quite popular for study by both space missions and ground-based observations due to their orbits. This makes it possible to study these comets during their several approaches to the Sun and observe their evolutionary changes. The results of imaging photometric and long-slit spectroscopic observations of comet 108P/Ciffreo obtained in 2014 are presented. The...
"Low-albedo asteroids are predominantly located on the outer part of the main belt and
consist of the most primitive matter formed in the early stages of the formation of the Solar
System. A detailed study of their surface structure and mineralogical composition can
provide insight into the processes that formed the planets and other celestial bodies in our Solar System. One of the...
"The phase-ratio method as well as color-ratio imagery was commonly used to identify structural changes of the upper regolith layer of the lunar surface, especially in the spacecraft landing sites. In the present it's possible to implement these methods to images of other planetary bodies due to extending number of space missions intended to provide remote sensing of planetary surfaces. Such...
(65803) Didymos is a binary asteroid of spectral class S with a primary diameter of 0.78 km and a secondary diameter of 0.15 km. (65803) Didymos was the target of NASA's DART mission (2022), the Italian Space Agency's LICIA mission (2022), and is the target of the European Space Agency's upcoming Hera mission (2026).
In this work, we present the results of our observations (65803) Didymos on...
The long-term evolution of stellar magnetic activity governs the environment of the orbiting planets impacting their habitability. We perform three-dimensional magnetohydrodynamic simulations followed by a detailed parameter space study to understand the effect of variation in stellar wind magnetic field and intrinsic magnetosphere on the planetary magnetic field topology and atmospheric mass...
"In this study, we examine the kinematic and chemical features of the largest number of 2627 exoplanets harbouring stars whose parameters have been uniformly determined. We combine photometric, astrometric, and spectroscopic data from the most recent Gaia DR3 to examine the various populations of exoplanets harbouring stars. Using spectroscopic data, we determined that stars hosting massive...
"Orbital planes of numerous close-in exoplanets are not always perpendicular to the host star spin axis. This means that the current orbital plane of the exoplanet was probably altered after the system was formed. Projected spin-orbit misalignment can be measured in transiting exoplanets using so called Rossiter-McLaughlin effect affecting radial velocity of the host star. For fast-rotating...
The analysis of the light curves of stars hosting planetary systems can potentially provide information about various physical processes taking place in the system: the physical variability of the star itself caused by pulsations, the rotation period of the star revealed by spots, the planet's orbital and rotation periods, etc. The data sets of the orbital telescopes Kepler and TESS...
"Our sun is a magnetic and active star. This has been known since the 17th century from the observations of sunspots at the solar surface. In the 19th century the solar sunspot cycle was discovered as well as the first impacts of disturbances of solar origin on the technology. This is in particular the case of the famous Carrington event on the 1st September 1859 at the Sun which led to the...
The active region of the Sun 2673, which was localised in the southwestern part of the solar disc, with heliographic coordinates (S10 W30) on 6 September 2017, was the source of six solar flares, including two X-class flares: X2.2, which began at 08:57:00 UT and lasted 20 minutes, and X9.3, which began at 11:53:00 UT and lasted 17 minutes, according to NOAA GOES. At 12:06:05 UT, a CME with an...
Turbulence is a complex multiscale phenomenon that controls the transfer of energy, mass, and momentum in space plasmas. Dissipation is an important process of elimination of turbulent energy cascade rate at kinetic scales. In our work, we have considered multiple current sheet crossings to investigate scale features of turbulence dissipation in the Earth’s magnetotail. Analysed measurements...
GRB 221009A - hyper-luminous, long-duration gamma-ray burst (GRB) detected by Neil Gehrels Swift Observatory on October 9, 2022 and classified as the brightest GRB ever detected. In this work, we are presenting the results of our observations and photometric analysis of GRB221009A at the Kyiv comet station, as a part of international GRANDMA network (Global Rapid Advanced Network Devoted to...
I construct a non-thermal emission theory, interpreting the observational properties of the isolated pulsar RX J0420.0-5022 in X-rays that is believed to be a thermally emitting isolated neutron star. This neutron star have previously been observed in soft X-rays to have nearly thermal spectra at temperatures , which are thought to arise from the warm neutron star surfaces. It is well-known...
"The Shapley Supercluster is one of the largest and most massive structures in the nearby Universe at the distance of about 200 Mpc, consisting of thousands of galaxies. Multimessenger research has been a powerful tool in understanding the properties and evolution of this structure. The use of multiple messengers, such as electromagnetic radiation, high energy cosmic rays and neutrino, has...
Large concentrations of mass are now understood to be the products of a Hubble time’s worth of merging and accretion. This history is preserved in the outer regions of galaxies' halos, where the dynamical scales are longer. This makes it possible to preserve fossil records of these events in the form of longlasting substructures imprinted in the physical properties of their stellar...
Recent studies have reported on a possible evolution of the covering factor (CF) with redshift. The goal of the presentation is to answer the question if this evolution is real or whether selection effects play an important role. The presented analysis was based on cross-matched multiwavelength photometrical data from the five major surveys (SDSS, GALEX, UKIDSS, WISE, Spitzer). A sample of...
Cosmological models beyond the standard Lambda Cold Dark Matter (ΛCDM) scenario, namely the scalar field 𝝓CDM models are considered in this talk. The dynamics of the universe and the large-scale structure growth rate in these models in comparison with the standard spatially-flat ΛCDM model are investigated. Constraints on model parameters of 𝝓CDM models from various data sets are presented.
We present the detailed analysis of (U)LIRGs from ultraviolet through far-infrared to radio ($\sim$70\, MHz to $\sim$15\,GHz) bands. We derive the astrophysical properties through spectral energy distribution (SED) modeling using the Code Investigating GALaxy Emission (CIGALE) and UltraNest codes. The radio SEDs include our new observations at 325 and 610\,MHz from the GMRT and the...
The GLEAM 4-Jy (G4Jy) Sample, formed from the GLEAM survey, comprises 1,863 of the brightest extragalactic radio-sources in the southern sky, the vast majority of which are active galactic nuclei with powerful radio jets. However, 140 of these sources have uncharacterised/ambiguous host galaxies due to the inadequate resolution (of 25 to 45-arcsec) of existing radio images. In this talk, I...
The morphological evolution of winged radio galaxies are explained using several theoretical models, including galaxy mergers. However, such a direct link between a perturbed radio morphology and a galaxy merger remains observationally sparse. Here we investigate a unique X-shaped radio galaxy J1159+5820, whose host displays the optical signature of a post merger system. Multifrequency radio...
Radio mini-halos are clouds of diffuse, low surface brightness synchrotron emission that surround the Brightest Cluster Galaxy (BCG) in massive cool-core galaxy clusters. In this paper, we use third generation calibration (3GC), also called direction-dependent (DD) calibration, and point source subtraction on MeerKAT extragalactic continuum data. We calibrate and image archival MeerKAT L-band...
In our project we investigate the long term relaxation processes in the initially equilibrium self gravitating stellar systems. As an initial condition for our model star cluster we use the well described and well studied Plummer mass distribution (Plummer, 1911, MNRAS, 71, 460). We try to cover a wide range of observable stellar clusters in our Galaxy, so we generate the models starting from...
On our research we attempt to identify galaxy mergers in modern galaxy surveys. The main results we want to show in this presentation is how we used Machine Learning (ML) to learn a previously unknown photometric property of galaxy mergers.
We built a Neural Network that we trained on photometric measurements from SDSS, using a class-balanced dataset composed by mergers from Darg et al....
"The aim of this presentation is to show how machine learning techniques can be used
for the task of object selection in multiwavelength photometric data. Here, I present a model for automatic active galactic nuclei (AGN) selection in the combined optical and near-IR photometric catalog based on the data from the deep sky survey in the AKARI NEP-Wide field. Specific construction of the...
"Different algorithms for periodogram analysis are reviewed. The mathematically strong definition is that, for a periodical signal $x(t)=x(t+m*P),$ for each moment of Time $t.$ The period is the minimal value, for which this equation is satisfied for all integer values of $m$.
For regularly distributed discrete moments of time $t_k=t_0+k*\delta,$ with a time step (=time resolution) $\delta,$ ...
The upcoming large-scale astronomical surveys, such as the Rubin Observatory Legacy Survey of Space and Time, are expected to detect approximately $10^5$ strong gravitational lenses. However, traditional, non-automated techniques for detecting these lenses are highly time-consuming and impractical for analyzing data on such a large scale. To tackle this issue, we propose a new machine-learning...
Most radio astronomers consider the Sun a nuisance, being considered one of the biggest sources of RFI in MeerKAT observations. The MeerKAT radio telescope is a precursor radio interferometer for the Square Kilometre Array (SKA) mid frequency telescope, that is located in the arid Karoo region of the Northern Cape Province, in South Africa (at 21 degrees East, 30 degrees South) (Jonas and...
Studies of the Sun and solar-terrestrial relations are carried out by a significant number of both ground-based and space-based observational instruments, as a result, data on solar activity indices, geophysical disturbance indices, information on galactic cosmic rays are stored in different formats and different servers, which complicates the work with such data. The report presents the...
Our team are professional astronomers who are currently focused on saving and rebuilding Astronomy in Ukraine, where this science is in a terrible state right now. Our first step was to create experimental astronomical research groups (EARG). Those EARG's mostly consists of students aged 15-25 and their aim is to implement brand new methods of astronomical research, as well as publish articles...
