Large-scale structures (LSS) form via relentless action of gravitational forces on density perturbations over cosmic length and time scales. Thus, the non-linear regime of LSS formation is sensitive to the underlying theory of gravity, and hence provides estimates for observables that can help distinguish modified gravity effects from the expected standard GR results. In this work, I focus on...
We studied scalar field φCDM models: ten quintessence models and seven phantom models. We reconstructed these models, using the phenomenological method developed by us. Resulting in, for each potential the following ranges were found: (i) model parameters; (ii) EoS parameters; (iii) initial conditions for differential equations, which describe the dynamics of the universe. Using the MCMC...
We present the results of photometrical observations of hyperbolic comet C/2013 X1 (Pan-STARRS) in broadband Johnson-Cousins filters. Data were obtained during the pre-perihelion passage of the comet in the period December 2015 - January 2016 using the 61-cm telescope at the Scalnat\'{e} Pleco observatory. Analyzing the dust productivity via $Af\rho$ proxy, we revealed a sharp increase in...
Toroidal (or ring) structures are quite common objects in the Universe. For example, these are obscuring dust tori in active galactic nuclei (ANGs), protoplanetary and accretion disks, ring galaxies, etc. In some objects, where the torus can be massive enough, it affects the motion and dynamics of matter. N-body simulations of the torus in the field of the central mass show that the...
Zone of Avoidance (ZoA) is the sky area that is blocked from extragalactic observations by the plane of our own Galaxy. It covers approximately 20% of the sky in the optical and poses significant problems for these cosmological tests that require full-sky coverage, necessitating compensation, usually by artificial filling. There are many possibilities of filling the ZoA with artificial...
The standard hierarchical model of galaxy formation predicts that small objects form first before growing and merging into more massive objects. In this context, the shape of the luminosity and mass distribution of galaxies provides a direct constraint on galaxy formation models. The interplay between gas accretion and feedback is likely reflected in the shape of the luminosity function (LF)...
We present the detailed analysis of 11 local luminous infrared galaxies (LIRGs) from ultraviolet, through far-infrared to radio ($\sim$70\, MHz to $\sim$15\,GHz) bands. We derive the physical properties through spectral energy distribution (SED) modeling using the Code Investigating GALaxy Emission (CIGALE) and UltraNest codes. The radio SEDs include our new observations at 325 and 610\,MHz...
Cosmic voids gravitationally lens the cosmic microwave background(CMB). This weak lensing shows itself as negative convergence(kappa) imprint on the CMB lensing map. We use one of the largest available sky surveys(Dark Energy Survey Y3) and Planck 2018 CMB lensing map along with a simulated CMB lensing convergence map from the MICE N-body simulation to calibrate our detection. We stack void...
Within the standard paradigm of cosmology, the hierarchical growth of dark matter perturbations is an essential assumption to explain galaxy formation. As a consequence, the relevance of dark matter halos for probing large-scale structure has motivated the search for a quantitative understanding of their abundance. Although computational cosmology has so far been the main arena for determining...
Galaxies live in dark matter haloes and hence the galaxy properties are majorly defined by the properties of the haloes. Thus the environmental dependence of dark matter halo properties prompts a correlation between galaxy properties and the environment. In this talk, I will discuss the results from our recent works (arXiv:2102.04177 and arXiv:2201.10480) that explored how luminosities in...
The intergalactic medium is revealed by the numerous absorption lines of neutral Hydrogen H~{\sc i} (the so-called Ly$\alpha$ forest) seen in the spectra of distant quasars ($z > 2$), which traces the thermal and radiative history of the Universe, as well as the evolution of underlying matter distribution over a wide range of scales and redshifts. It is possible due to the relation of the...
The global redshifted 21cm signal emitted by neutral hydrogen at radio frequencies offers novel insights into the birth of the first stars, known as the Cosmic Dawn, which is currently a largely unexplored chapter in our universe's history. The Mapper of the IGM Spin Temperature (MIST) is a multi-institutional collaboration that aims to observe the global 21cm signal from some of the most...
Ionosphere impact may be critical for radio observations below 100 MHz. The three dominating effects in the ionosphere - attenuation, emission and refraction - not only depend on the observational frequency but also change with time due to day-to-day variations in electron density. To account for these temporal variations, we created a global, dynamic model of the ionosphere. Our model uses a...
The ALBATROS experiment is composed of an array of radio telescopes operating in the 1.2 – 125Mhz range with the aim of laying the groundwork for probing the cosmic dark ages (<30Mhz) through measurement of the 21cm redshifted emission of neutral hydrogen. To better understand the behaviour of the antennas used in this array, we propose to fly a transmission source mounted to a custom-built...
Mapping Dark Matter Using Gravitational Lensing Techniques/SuperBIT
Mila Arasu (Sunanda Thirunavukkarasu)
Galaxy clusters are one of the primary tools for constraining dark matter when combined with the distortion of light from distant galaxies as it travels through a cluster’s gravitational potential. Constraining cosmology by measuring cluster abundance proves to be extremely challenging...
AGNs are very powerful galaxies characterized by extremely bright emissions coming out from their central massive black holes. Knowing the redshifts of AGNs provides us an opportunity to determine their distance to investigate important astrophysical problems such as the evolution of the early stars, their formation along with the structure of early galaxies. The redshift determination is...
We review the study of variable stars using mathematical modeling of
their mean light curves. The simulation is carried out by various methods, using
the observational databases AAVSO, AFOEV, VSOLJ, TESS, ZTF, ASAS-SN,
etc. The purpose of the simulation is to "digitize" the light curves to determine
statistically optimal numerical parameters that characterize brightness...
We present the photometric and spectroscopic analysis of 9 W Uma type contact binaries. The studied targets are selected from the CRTS catalog. The photometric data is collected using the 1.3-m Devasthal Fast Optical Telescope (DFOT) and 1.04-m Sampurnanand Telescope (ST). We use the PHOEBE-legacy code for light curve modeling. The temperature is determined using different color-temperature...
Star formation is among the most intricate processes building the Universe and deep comprehensive studies of its low mass regime are crucial to understand the related processes like circumstellar disk evolution and its properties, brown dwarf formation. Since most of the star formation takes place in clusters, it is crucial to perform deep studies of low mass stellar population in young...
22.2 GHz water masers are generally associated with massive star formation. Recently, a very strong nuclear kilomaser, W1, has been found in a nearby galaxy (NGC 253) that is associated with a forming super star cluster. It has been proposed that kilomasers could arise from the accretion disc around supermassive stars (>1000 Msun). Such hypothetical stars are proposed candidates for polluters...
In this work, we consider the origin of the chemical element lithium (Li) in the Universe, and calculate its abundance in six solar-type stars.
Li is a very light, soft alkali metal. This is a special element, because it is one of the three elements created during the Big Bang. With the evolution of stars, lithium is modified by the process of nucleosynthesis inside and becomes hardly...
Close binary star system Cygnus X-1.
The subject matter of the research is studying and conducting relative and absolute photometry of Cygnus X-1 in optic range.
Relevance: the accretion of matter in the close binaries is an effective mechanism for releasing a huge amount of energy, because of which we observe many astrophysical objects that are at the late stages of their evolution.
...
Eclipsing dwarf novae are considered to be the perfect laboratories to study accretion. As high inclination systems, they allow to reconstruct the brightness distribution across the accretion disk using indirect techniques like Doppler tomography or eclipse mapping. However, such observations are very challenging. High quality data from large telescopes are needed and it is difficult to...
We report the results of long-term time series photometry on RX J2133.7+5107. Using data taken during 2007-2022 (15 yr), we confirmed and improved the results obtained by de Miguel et al. (2017). Due to longer time-base we obtained more accurate value of the spin-up time-scale $1.511(3)*10^5$ yr. The observed rate of spin-up is even faster then reported by de Miguel et al. (2017) and one of...
In this paper, we present astrophysical parameters of the open cluster King 13 based on the VI CCD and 2MASS JHK s photometric data. This is a poorly studied cluster, for which new results have been found in the present work. To identify probable members, we use proper motion data from Gaia DR2 catalogue. The mean proper motion of the cluster is determined as − 2.8±0.2 and − 0.88±0.14 mas yr −...
We analyzed the photometric data obtained for 4 short-period EW-type binary systems discovered at Astronomical Observatory at Kolonica Saddle using different instruments between 2009 and 2019. The stars USNO-B1.0 1411-0397871 (VSX J213321.5+510857) and USNO-B1.0 1411-0397855 (VSX J213320.0+510819) are W UMa type eclipsing binaries. These stars got GCVS names V2833 Cyg and V2832 Cyg...
We present the results of photometrical observations of hyperbolic comet C/2013 X1 (Pan-STARRS) in broadband Johnson-Cousins filters. Data were obtained during the pre-perihelion passage of the comet in the period December 2015 - January 2016 using the 61-cm telescope at the Scalnat\'{e} Pleco observatory. Analyzing the dust productivity via $Af\rho$ proxy, we revealed a sharp increase in...
The processing and analysis of photometric and spectral data obtained for the long-period comet C / 2015 VL62 (Lemmon-Yeung-PanSTARRS) on the 2nd SAO 6-m telescope in 2015 was processed and analyzed. The comet was observed at a heliocentric distance of 3.8. a.u., where sublimation of water ice is not significant. Several different programs were used for processing (basic reductions) and...
In this work, we are presenting the results of astrometric, photometric, and dust productivity analysis of comet 67P/Churyumov-Gerasimenko. The results are based on 14 nights of observations at the Kyiv Comet Station (MPC Code 585) during the near-perihelion and Earth approach periods of 2021-2022. We also analyzed the photometric and astrometric data of 67P comet appearance in the 1969-2022...
Metal asteroids are lurking somewhere in the asteroid belt, concealing a source of extraterrestrial resources, presenting a danger to life on Earth, and holding keys to the early history of the Solar System.
We know their existence for sure as their fragments are regularly falling on the Earth's surface as iron meteorites.
We understand how metal asteroids originated at the molten...
The last decade has become a significant period for robotic exploration of the Solar system bodies. Among such research programs was The Dawn Mission to asteroid Vesta and dwarf planet Ceres. Results obtained during the mission allow us to carry out a detailed analysis of asteroid (4) Vesta surface properties by using methods that were developed and effectively used in the analysis of the Moon...
Even though more than 4000 extrasolar planets are discovered so far, Earth is the only planet in the Universe known to have life till date. Among them around 60 planets were listed as Potentially Habitable Extrasolar Planets. This list was prepared on the basis of the details from the Habitable Extrasolar planets Catalog (HEC) which is maintained by the Planetary Habitability Laboratory at the...
Currently, an array of 3 telescopes are used to detect objects of the Kuiper belt.
In practice, this is identical to photometric observations of exoplanet transits, but there is a significant difference in the time of star occultation and the shape of the light curve.
This line of research is relatively new and relevant in the field of solar system astronomy. To successfully capture the...
Weather systems are now known to be ubiquitous on brown dwarfs, and probably also on all extrasolar planets with atmospheres. Brightness monitoring of rotating brown dwarfs and exoplanets has revealed storm- and band-like cloud structures, much like on solar system planets. Spectroscopic monitoring has probed the altitudes and chemistry of the constituent cloud layers. Astronomy is thus...
Earth-like exoplanets, defined to be rocky extrasolar planets in the habitable zone of their host stars, are of particular interest in the search for life in the universe. The Photometric Observations of Exoplanet Transits (POET) satellite is a microsatellite in development with a mission to discover Earth-like exoplanets around ultracool dwarfs (UCDs) through the transit method. UCDs are M7...
A double-precision format can be used easily for single-precision computa- tions, while for double-precision computations, extended or higher precision may not be enough in some formats such as binary64 in IEEE 754-2008 standard. In this study, by using floating-point arithmetics, the required algorithms to solve the N-body problem more accurately than ordinary computations have been...
We report the results of the investigation of five planetary systems TrES-3b, Kepler-17b, WASP-3b, Qatar-1b, and Qatar-2b. For the exoplanets TrES-3b, Kepler-17b, WASP-3b, and Qatar-1b, the obtained results of the center-transit time, depth and length of transit agree with the ephemeris data, while for two observations of the Qatar-2 system for the planet Qatar-2b there is a clear decreasing...
We present a comparative analysis of observations of the selected exoplanet transits obtained at the Kyiv Comet station with the database of the TESS (Transiting Exoplanet Survey Satellite) and Kepler space telescopes. The light curves obtained by the TESS and Kepler orbital telescopes were processed using a program based on the Python package Lightkurve 2.3v which is freely available in the...
We have studied the maps of radio active mineral distribution in Earth, Moon and Mars obtained from in situ and remote sensing observations. The distribution of U and Th in these rocky planets show some interesting features in association with internal heat distribution and volcanism. The results of our studies will be helpful for mining , space exploration and understanding the...
The Earth Planetary (or Bond) albedo is one of the crucial indicators of the Earth system energy budget. State-of-the-art approach to estimate the Earth Bond albedo is by processing satellite measurements of the Earth outgoing short-wave radiation. An exceptionally large albedo values (up to $0.35$ daily maximum) in December 2020 were obtained using the data by Earth Polychromatic Imaging...
Atmospheric aerosols significantly affect human health and climate change. These particles have a strong impact on the energy balance in the Earth`s atmosphere. At the same time, intense aerosol contamination causes different diseases and decreases life quality. Therefore, many countries and cities already have systems and networks for monitoring air quality. The quantitative characteristics...
The theme of the research project: "Antarctic tropopause over the station Marambio in the conditions of the ozone hole during 2004-2019". The object of study is the polar tropopause of the Southern Hemisphere. The subject of the study is the change in the height of thermal and ozone tropopauses in the ozone hole. The aim of this work is to improve the understanding of the distributions and...
Comprehensive low-frequency multispacecraft wave study of flapping current sheet oscillations in the Earth's magnetotail with different morphologies of oscillation behavior was carried out. Measurements from the Magnetospheric Multiscale (MMS) mission during 2020/08/26 were analyzed. Comparison of the results calculated by methods of phase difference, wave surveyor and Multipoint Signal...
The problem with penetration of the ULF electric field, exited by the current source in the atmosphere, into the upper ionosphere is investigated both within the dynamic and the quasi-electrostatic approach. It had been shown that (1) both approaches yield practically similar results for the penetration of the electric field in the case of closed geomagnetic field lines; (2) in the case of...
X-ray monitoring of the Sun inspired Eugen Parker's description of the elementary unit of energy release in the corona as nanoflare. He predicted the observation of even smaller events with more sensitive instruments of the 21st century. Until recently, it was impossible to confirm their existence in the corona. Moreover, the physical threshold for solar flares has been set at 10²⁴ ergs (one...
An accurate understanding of the propagation of coronal mass ejections (CMEs) is crucial in the prediction of space weather. CMEs generate geomagnetic storms causing catastrophic damages to power grids on Earth and are a serious radiation threat to satellites on low-Earth orbit and their crew during spacewalks. Basic parameters such as their velocity and acceleration varying with time and...
Sunspot observations over the past few centuries reveal that the Sun occasionally slips into quiescent phases, known as solar grand minima. In our dynamo model, we employ stochastic fluctuation in the source term of the polar fields to simulate such grand minima episodes. Our simulations detect a gradual decay of the polar field at the onset of a solar grand minimum followed by a halt in the...
We are working on predicting the time a CME directed towards earth will require to reach earth. We are using Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO) twin spacecraft when they are in quadrature configuration. This allows us to observe the CMEs from two additional directions and get rid of the projection effect .
In our studies We are...
Alfvén waves are fundamental low frequency electromagnetic plasma wave that permeate the universe. At small kinetic scale these waves known as kinetic Alfvén waves and at this scale these waves transfer the energy between electromagnetic fields and charged particle in solar wind [1]. I study the kinetic Alfvén waves in solar wind at 1AU, when the background plasma density is modified by...
A major discovery of Parker Solar Probe (PSP) was the presence of large numbers of localized increases in the radial solar wind speed and associated sharp deflections of the magnetic field - switchbacks (SB). A possible generation mechanism of SBs is through magnetic reconnection between open and closed magnetic flux near the solar surface, termed interchange reconnection that leads to the...
Supernova remnants (SNRS) are widely considered to be the main candidates for sources of Galactic cosmic rays. The main argument for this remains the energy budget provided by SNRs, which is sufficient to explain the cosmic-ray energy density. It is also established that SNRs can effectively accelerate particles at their shocks, which is confirmed by detection of non-thermal X-ray and...
The non-thermal emission theory is constructed, interpreting the observational properties of the unique pulsar 1RXS J141256.0+792204 (Calvera) in X-rays that is believed to be thermally emitting isolated neutron star. Calvera was observed in the X-rays with XMM Newton /EPIC twice for a total exposure time of 50 ks. It is unique isolated pulsar, because it cannot be detected by radio, optical...
Markarian 421 is a bright high synchrotron energy peaked blazar showing wide featureless non-thermal spectrum. We analyse the large set of its X-ray observations taken with the EPIC-PN instrument onboard XMM-Newton satellite to probe into the intraday variability properties observed in the source. The photon energy band of 0.3 - 10.0 keV, and its sub-bands, soft 0.3-2.0 keV and hard 2.0-10.0...
To explain the experimental results of neutrino oscillations it is necessary to consider
hope that these particles are massive; however, the standard model of particle physics
elements, the most successful theoretical scheme that explains with good precision three of the four interfundamental actions of nature, neutrinos are assumed to be massless particles.
The difficulty in solving this...
The spin-down of a compact star causes perturbations in the internal chemical equilibrium state, and, consequently internal heating dubbed as rotochemical heating.
Moreover, the fact that the cores of compact stars are thought to reach baryon densities as high as a few times the nuclear saturation density, renders them ideal
candidates of being host to deconfined quark matter, the latter...
We propose a novel model of asymmetric bosonic dark matter (DM) with self-repulsion mediated by the vector field coupled to the complex scalar particles. By adopting the two fluid formalism, we study different DM distribution regimes, either, fully condensed inside the core of the star or, otherwise, distributed in a dilute halo around the neutron star (NS). We show that DM condensed in a core...
Stellar and gas kinematics of galaxies are a sensitive probe of the dark matter distribution in the halo. The popular fuzzy dark matter models predict the peculiar shape of density distribution in galaxies: specific dense core with sharp transition to the halo. Moreover, fuzzy dark matter predicts scaling relations between the dark matter particle mass and density parameters. In this work, we...
The Pierre Auger Observatory (PAO) and Telescope Array (TA) collaborations report significant differences in the observed energy spectra of Ultra-High-Energy Cosmic Rays (UHECRs) above 30~EeV. In this work, we present a joint fit of TA and PAO data using the rigidity-dependent maximum energy model, and including full marginalization over all relevant parameters. We show that the presence of a...
"Romero, G.E.The radio emission mechanism in active galactic nuclei (AGN) with high accretion rates is unclear. We propose that clouds from the broad-line region (BLR) propagating with supersonic velocities in the wind of the accretion disk may lead to the production of non-thermal radiation. We determine the conditions under which the BLR clouds are not destroyed by shocks or hydrodynamic...
