HOMECommunications of the Byurakan Astrophysical Observatory (ComBAO)
Volume 71, Issue 2, Dec 2024
ORIGINAL PAPERS
Influence of gas-dynamic flows on the evolution of line spectra in a medium with non-stationary energy sources 
0.7 MB
A. Nikoghossian
Pages: 215-229
Abstract. The theory we developed in previous papers on temporal variations in the spectral line profiles formed in the media with nonstationary energy sources is generalized to take into account the influence of stochastic velocity fields. The radiation transfer problem is treated for the case of completely incoherent scattering. The limiting regimes of micro- and macro-turbulence are considered under the assumption that the gas-dynamic velocity is described by a Markov process. Comparison of the characteristic features of the evolution of spectral line profiles in these two cases with that observed in the absence of turbulence allows us to make an idea of the nature of turbulence and the values of various parameters describing the primary energy sources and optical properties of the medium.
The Master-Space Supergravity: Particle mechanics 0.3 MB
G. Ter-Kazarian
Pages: 230-248
The Master-Space Teleparallel Supergravity: Accelerated frames 0.2 MB
G. Ter-Kazarian
Pages: 249-267
Spotedness of most active flare stars detected by TESS 0.2 MB
A. A. Akopian
Pages: 268-274
Abstract. A new method has been proposed to determine the coverage of starspots by using periodic functions related to flare frequency. The distribution of starspots on flare stars is modeled through a von Mises circular distribution, with parameters derived from the corresponding flare frequency function. Estimates of spot coverage for the stars studied have been obtained.
Complete simplification of the solution of the diffuse reflection problem by the method of “decomposition of resultant field” (DRF)S 0.2 MB
H. Pikichyan
Pages: 275-288
Abstract. The classical diffuse reflection problem (DRP) of radiation from a plane-parallel semi-infinite medium under isotropic scattering in the case of the general law r (x, x′) of radiation redistribution by frequencies in the elementary act of scattering is considered. It is shown that the solution of the DRP ρ (x, μ;x′, μ′), which depends on four independent variables, with the help of author’s recently developed method of ”decomposition of the resultant field-DRF” it is possible to express explicitly through auxiliary functions Gi (z) , Qi (x) that depend on only one independent variable. A significant difference between this DRF method and the widely used traditional approach of ”decomposition of a single act - DSA” of scattering is that it no longer requires any decomposition or a special representation of the characteristics of a single act of scattering (in the case under consideration, the function of redistribution of radiation by frequencies - r (x, x′) . In DRF, the resulting field of multiply scattered radiation itself is searched directly in the decomposed form. It is obvious that after each successive single act of scattering, the resulting radiation field in the medium becomes more and more smoother, so that with the same required accuracy, its decomposition will contain fewer terms than the decomposition of the characteristic of a single act of scattering. This circumstance makes the DRF method especially effective in relation to the DSA approach in cases where the latter requires taking into account a large number of terms of the decomposition of the frequency redistribution function r (x, x′). Explicit analytical expressions of the two-way relationship are also obtained between the desired values of the traditional and the methods proposed by the author.
A deformation of Master-Space and inertia effects within the theory of Master Space-Teleparallel Supergravity 0.2 MB
G. Ter-Kazarian
Pages: 289-306
Radiation and Scattering of Massive Photons 0.2 MB
G. A. Saiyan
Pages: 307-321
Abstract. With the aid of a modified Planck’s law for massive photons, it is shown that the ratio of the mean value of the photon mass equivalent to its rest (invariant) mass tends to be one with a decrease in temperature. A modified Stefan - Boltzmann law is obtained at different temperature regimes, as well as the Wien’s displacement law. At high temperatures the modified Planck’s law approaches the standard Planck’s law. It is also shown that the cross-section of the Thomson scattering slightly increases opacity of the scattering medium. The Compton shift in frequency for a massive photon appears to be frequency-dependent and slightly less than its value for a massless photon, except in the case of forward scattering when no change in frequency takes place. Astrophysical aspects of the massive photon hypothesis are discussed with regard to standard stellar models, early stages of the Universe, and the Breit-Weeler process, as well as active galactic nuclei. Estimates of the spreading time of the wave packet of the massive photon show that for frequencies ν ≥ 4.052 × 109 Hz (λ ≤ 7.4 cm) it exceeds the age of the Universe.
An Astronomical Interpretation of a Small Example from Armenian Folklore 0.3 MB
H. A. Malkhasyan
Pages: 322-329
Abstract. This article examines an individual fragment of Armenian folklore about the Aratsani (Euphrates) River from an astronomical perspective, focusing on the central characters - the dragon-fish and the bear. Through this analysis, a wealth of “astronomical knowledge” rooted in ancient mythological perceptions is revealed. Specifically, the mentioned figures in the sky correspond respectively to the modern constellations of the Southern Fish (Piscis Austrinus) and the Great Bear (Ursa Major). The described scenes are correlated with the heliacal rising and setting of the main star of Southern Fish constellations. Furthermore, all defining characteristics of the figures are given precise astronomical and mythological interpretations. The legend also highlights expressions related to the unfolding time, which are thoroughly explained based on celestial phenomena and ancient Armenian calendrical concepts. It is demonstrated that the described celestial events are associated with a 65–70-day period, referred to in the Protohaykian calendar structure as the “extra-annual period.” Additionally, the legend reveals close calendrical and ritualistic connections with the astronomical context of Fish-shaped Dragon Stones (Vishapakars). The comprehensive astronomical analysis enables the dating of the legend described to 18800 BC. This serves as a small but striking example of how folklore can act as a unique source of rich astronomical information.
INTRODUCTION 0.1 MB
Editorial Board
Pages: 330
IAU South-West and Central Asian Regional Office of Astronomy for Development 0.2 MB
A. M. Mickaelian, S. V. Farmanyan, and G. A. Mikayelyan
Pages: 331-339
Abstract. The International Astronomical Union (IAU) announced its Strategic Plan on Astronomy for Development in 2009, during the International Year of Astronomy (IYA) (for 2011-2020, extended to 2021-2030). One of its main components was the creation of the Office of Astronomy for Development (OAD) and corresponding Regional Offices (ROADs) for implementation and coordination of its aims. The OAD was created in Cape Town, South Africa and later on ROADs were created in 11 regions. Since 2015, Armenia has hosted one of them, IAU South West Asian (SWA) IAU ROAD, later renamed South West and Central Asian (SWCA) ROAD. At present, already six countries have officially joined (Armenia, Georgia, Iran, Kazakhstan, Tajikistan, and Turkey), but the Office serves for a rather broad region, from Eastern Europe to Central Asia. Armenia’s geographical location and its historical role in astronomy (both for well-known archaeoastronomical heritage and the presence of the famous Byurakan Astrophysical Observatory (BAO) founded by Viktor Ambartsumian in 1946) serve as a link between Europe and Eastern Partnership countries, Middle East and Asia in general. We run activities in 3 directions, Task Forces (TF): TF1 Universities and Research, TF2 Children and Schools and TF3 Public Outreach. In addition, we participate in the OAD Flagship Projects; Flagship 1: Astrotourism, Flagship 2: Astro for Mental Health, Flagship 3: Hack4Dev. We present our projects and all other accomplishments and discuss the role of our ROAD in maintaining contacts and development of astronomy in the region, as well as contacts between Europe and the Eastern Partnership countries. The most up-to-date information about the IAU SWCA ROAD is available on its webpage at http://iau-swa-road.aras.am/eng/index.php.
Astronomy in Georgia 0.1 MB
B. B. Chargeishvili
Pages: 340-344
Abstract. We provide a brief history of Georgian astronomy and discuss its current state. The discussion also covers the scientific facilities of Georgia’s leading astrophysical institute, the Evgeni Kharadze Georgian National Astrophysical Observatory, as well as current scientific projects and specialists involved in them. It also includes educational activities on astronomy in Georgia.
Deciphering Galactic Halos: A Detailed Review of Star Formation in NGC 5128 (Cen A) 0.4 MB
M. Abdollahi, S. T. Aghdam, A. Javadi, S. A. Hashemi, J. Th. van Loon, H. Khosroshahi, R. Hamedani Golshan, E. Saremi, and M. Saberi
Pages: 345-350
Abstract. NGC 5128 (Centaurus A), the closest giant elliptical galaxy outside the Local Group to the Milky Way, is one of the brightest extragalactic radio sources. It is distinguished by a prominent dust lane and powerful jets, driven by a supermassive black hole at its core. Using previously identified long-period variable (LPV) stars from the literature, this study aims to reconstruct the star formation history (SFH) of two distinct regions in the halo of NGC 5128. These regions reveal remarkably similar SFHs, despite being located about 28 kpc apart on opposite sides of the galaxy’s center. In Field 1, star formation rates (SFRs) show notable increases at approximately 800 Myr and 3.8 Gyr ago. Field 2 exhibits similar peaks at these times, along with an additional rise around 6.3 Gyr ago. The increase in SFR around 800 Myr ago is consistent with earlier research suggesting a merger event. Since no LPV catalog exists for the central region of NGC 5128, we focused our investigation on its outer regions, which has provided new insights into the complex evolutionary history of this cornerstone galaxy. The SFH traced by LPVs supports a scenario in which multiple events of nuclear activity have triggered episodic, jet-induced star formation.
Pulsars and Millisecond Pulsars I: Advancements, Open Questions and finding Gaps via statistical insights 0.3 MB
M. Rah, A. Mickaelian, F. F. Dotti, R. Spurzem
Pages: 351-359
Abstract. Investigating the development of pulsars and millisecond pulsars (MSPs) highlights for us statistical insights, important research areas, and unresolved aspects to address. Through the following work, we provide a detailed demographical study of these astrophysical objects by combining data from several observational techniques (radio, X-ray, and gamma-ray) in different environments: Galactic Field (GF) and Globular Clusters (GC). Although observational studies provide direct insights into the emission properties, periodic timing (e.g. millisecond pulsars), and spatial distribution of pulsars, theoretical models are essential to interpret these findings and unravel the underlying physical processes driving their unique characteristics. We focus on the “magnetic field-spin” relationship, exploring spin-up — where accretion transfers angular momentum to the pulsar in binary systems — and spin-down, driven by magnetic dipole radiation or particle winds dissipating rotational energy. These mechanisms illuminate the intricate dynamics linking spin evolution to magnetic field decay. Building on these theoretical frameworks and the application of advanced numerical simulation tools such as NBODY6++GPU, CMC, and COMPASS, we provide a critical means to quantitatively test and refine our understanding of spin and magnetic field evolution in such compact objects. However, despite the advances offered by these tools, significant issues remain, particularly in interpreting the intricate dynamics of binary interactions involving pulsars and millisecond pulsars, as well as in accurately incorporating the physics of these compact objects into comprehensive numerical simulations. This analysis underscores the critical need for enhanced modeling frameworks and more refined observational studies to address unresolved questions regarding the formation processes, evolutionary pathways, and magnetic field degradation of pulsars and MSPs. These numerical integrations of compact objects into comprehensive models of objects with a large number of stars will highlight the necessity of advancing simulation techniques. By improving these simulations, we can more accurately model the intricate physics governing pulsar behavior and ultimately resolve these outstanding challenges in astrophysics.
Active galaxies in the field and in Galaxy Clusters 0.2 MB
R. R. Andreasyan, S. A. Hakopian, A. P. Mahtessian, and A. G. Sukiasyan
Pages: 360-366
Abstract. We review the current activities of the Department of Active Galaxies of Byurakan Astrophysical Observatory. The studies include broad areas, ranging from manifestations of activity in our galaxy, other galaxies and clusters of galaxies to the study of magnetic fields, the formation of these fields, and cosmological questions.
Byurakan Astrophysical Observatory Research Department “Astronomical Surveys”: recent results 0.2 MB
A. M. Mickaelian, H. V. Abrahamyan, G. M. Paronyan, G. A. Mikayelyan, R. R. Andreasyan, A. G. Sukiasyan, L. A. Hambardzumyan, V. K. Mkrtchyan, A. A. Gasparyan, and M. Dennefeld
Pages: 367-376
Abstract. We review the field of active galaxies (both AGN and Starbursts) focusing on their multiwavelength search and studies at the Byurakan Astrophysical Observatory (BAO). Many famous historical surveys carried out in Byurakan are known and many more are active and ongoing. We give examples of studies in optical wavelengths, IR, radio and X-ray, as well as multiwavelength studies. The studies are characterized by a multiwavelength approach to statistical analysis of a large amount of data obtained in different wavelengths. Results on HRC/BHRC sample objects (optical identifications of ROSAT X-ray sources), studies of Markarian galaxies in UV and multiwavelength SEDs, abundance and star formation determinations in Mrk galaxies from SDSS spectra, revised optical classification of “LINERs”, study and classification of SDSS spectra for Byurakan-IRAS Galaxies, summary of observations and study of Byurakan-IRAS Galaxies (BIG objects), discovery of new bright ULIRGs from the IRAS PSC/FSC Combined Catalogue and their spectral classification, radio variable sources at 1400 MHz and their optical variability, classification of BZCAT objects having uncertain types (BZU objects), and optical variability
of blazars are presented. At the end, we briefly present our new fine classification of active galaxies based on all our previous studies.
Machine Learning Classification of Young Stellar Objects and Evolved Stars in the Magellanic Clouds Using the Probabilistic Random Forest Classifier 0.1 MB
S. Ghaziasgar, M. Abdollahi, A. Javadi, J. Th. van Loo, I. McDonald, J. Oliveira, and H. G. Khosroshahi
Pages: 377-382
Abstract. The Magellanic Clouds (MCs) are excellent locations to study stellar dust emission and its contribution to galaxy evolution. Through spectral and photometric classification, MCs can serve as a unique environment for studying stellar evolution and galaxies enriched by dusty stellar point sources. We applied machine learning classifiers to spectroscopically labeled data from the Surveying the Agents of Galaxy Evolution (SAGE) project, which involved 12 multiwavelength filters and 618 stellar objects at the MCs. We classified stars into five categories: young stellar objects (YSOs), carbon-rich asymptotic giant branch (CAGB) stars, oxygen-rich AGB (OAGB) stars, red supergiants (RSG), and post-AGB (PAGB) stars. Following this, we augmented the distribution of imbalanced classes using the Synthetic Minority Over-sampling Technique (SMOTE). Therefore, the Probabilistic Random Forest (PRF) classifier achieved the highest overall accuracy, reaching 89% based on the recall metric, in categorizing dusty stellar sources before and after data augmentation. In this study, SMOTE did not impact the classification accuracy for the CAGB, PAGB, and RSG categories but led to changes in the performance of the OAGB and YSO classes.
Detection of the Long Period Variable Stars of And II Dwarf Satellite galaxy 0.2 MB
H. Abdollahi, A. Javadi, J. Th. van Loon, I. McDonald, M. Abdollahi, E. Saremi, H. G. Khosroshahi, and H. Mahani
Pages: 383-388
Abstract. We conducted an extensive study of the spheroidal dwarf satellite galaxies around the Andromeda galaxy to produce an extensive catalog of LPV stars. The optical monitoring project consists of 55 dwarf galaxies and four globular clusters that are members of the Local Group. We have made observations of these galaxies using the WFC mounted on the 2.5 m INT in nine different periods, both in the i-band filter Sloan and in the filter V -band Harris. We aim to select AGB stars with brightness variations larger than 0.2 mag to investigate the evolutionary processes in these dwarf galaxies. The resulting catalog of LPV stars in Andromeda’s satellite galaxies offers updated information on features like half-light radii, TRGB magnitudes, and distance moduli. This manuscript will review the results obtained for And II galaxy. Using the Sobel filter, we have calculated the distance modulus for this satellite galaxy, which ranges from 23.90 to 24.11 mag.
A Deep Dive into Stellar Populations in M33’s Central Region: Near-Infrared Observations and Analysis 0.2 MB
M. Alizadeh, A. Javadi, J. Th. van Loon, Yo. Abedini, H. Abdollahi, and S. Seifipour
Pages: 389-393
Abstract. Data collection was conducted using three cameras on the UK Infrared Telescope (UKIRT) from 2003 to 2007. Throughout three nights in August 2005, the UKIRT Fast-Track Imager (UFTI) made K-band observations. The J and H bands Wide Field Camera (WFCAM) data were gathered from 2005 to 2007. Furthermore, from 2003 to 2007, UIST data for the central region of M33 were collected in the K-band. Since luminosity is more closely correlated with birth mass in the latter stages of a star’s evolution, we concentrated on these stars. We will combine all the PSF photometry catalogs of the UIST, the UFTI, and the WFCAM to present a novel master catalog of the central square kiloparsec to re-identify the LPV populations. By having more data points for each point source, the probability of detecting more LPVs goes up; also, a period might be derived for some. In addition to that, the SFH will be estimated more accurately by having a larger sample of variable stars.
Star Formation History of the Local Group Dwarf Irregular Galaxy, NGC 6822 0.1 MB
F. Khatamsaz, M. Abdollahi, H. Abdollahi, A. Javadi, and J. Th. van Loon
Pages: 394-397
Abstract. NGC 6822 is an isolated dwarf irregular galaxy in the local group at a distance of ∼ 490 kpc. In this paper, we present the star formation history (SFH) within a field with a radius of ∼ 3 kpc, beyond the optical body of the galaxy (∼ 1.2 kpc). We utilized a novel method based on evolved asymptotic giant branch (AGB) stars. We collected the Near-Infrared data of 329 variable stars, including long-period and -amplitude variables and Carbon-rich AGB stars. We used a stellar evolutionary track and theoretical isochrones to obtain the birth mass, age, and pulsation duration of the detected stars to calculate the star formation rate (SFR) and trace the SFH of the galaxy. We studied the history of galaxy star formation for the mean metallicity value of Z ≈ 0.003. We reconstructed the SFH for two regions: the bar region, a central rectangular area, and the outer region, which covers a circular field beyond the bar region and extends to a radius of 3 kpc. Our results show a significant burst of star formation around 2.6 and 2.9 Gyr ago in the bar and outer regions, respectively. Additionally, we observed a notable enhancement in the SFR in the bar region over the past 200 Myr.
Improving the Efficiency of the AIS System Using Algorithms for Dealing Signal Collisions 0.1 MB
S. B. Makarov, S. V. Zavjalov, S. V. Volvenko, I. Lavrenyuk, A. A. Kuznetsova, Iu. E. Eremenko, A. K. Aharonyan, and V. H. Avetisyan
Pages: 398-401
Abstract. The paper considers methods for receiving and processing automatic identification of ships (AIS) signals by a small satellite (CubeSat). A comparison of various methods for reducing the impact of collisions on the reliability of reception is given, such as the choice of orientation and type of the CubeSat receiving antenna, the use of various demodulation algorithms that take into account the presence of Doppler frequency shifts, as well as decollision processing algorithms. Using simulation modeling that takes into account the parameters of the space scenario (orbit altitude, antenna type, etc.), the efficiency of the considered methods in terms of reducing the packet error in the presence of first-order collisions is shown.
Combining Bispectral Analysis with the Levenberg–Marquardt Algorithm for Enhanced Non-linear Signal Processing in Astronomy 0.2 MB
E. Sivolenko, N. Gasparyan, A. Aharonyan, V. Avetisyan, and M. Vinnichenko
Pages: 402-408
Abstract. The understanding of intricate, non-linear phenomena within astronomical data is pivotal for the progression of our knowledge of the universe. This paper introduces an innovative method that merges bispectral analysis with the Levenberg–Marquardt (LM) algorithm for processing astronomical signals. The LM algorithm is renowned for its effectiveness in non-linear parameter estimation and model fitting. At the same time, bispectral analysis is adept at identifying and measuring non-linear interactions and phase coupling within signals. By integrating these two techniques, our approach facilitates a comprehensive analysis of astronomical signals, encompassing both modeled and unmodeled non-linearities. This integrated methodology is particularly advantageous in fields such as the exploration of pulsars, binary star systems, exoplanet detection, and active galactic nuclei, where non-linear dynamics exert significant influence. The findings illustrate that this collaborative approach amplifies the identification and delineation of non-linear processes, leading to more precise models and profound insights into complex astronomical phenomena.
Techniques for Locating GPS Jammers using GNU Radio 0.1 MB
M. Sahakyan, V. Mkhoyan, E. Sivolenko, B. Hovhannisyan, A. Aharonyan, and S. Makarov
Pages: 409-411
Abstract. Detecting GPS jammers is crucial for ensuring the integrity and reliability of Global Positioning System (GPS) signals, particularly in environments where jamming devices disrupt navigation and communication systems. These jammers emit radio frequency signals that interfere with legitimate GPS signals, leading to significant disruptions. To locate these jammers, advanced techniques such as Angle of Arrival (AOA) and Time Difference of Arrival (TDOA) are utilized. AOA uses phased array antennas to determine the direction of the jamming signal, with algorithms like Multiple Signal Classification (MUSIC) and Minimum Variance Distortionless Response (MVDR) enhancing accuracy. TDOA, on the other hand, triangulates the jammer’s location by measuring the time difference between signal arrival at multiple sensors. The integration of unmanned aerial vehicles (UAVs) equipped with directional antennas and sophisticated algorithms further improves the real-time detection of GPS jammers. These UAVs can cover large areas quickly and provide precise bearing measurements, making them invaluable in both military and civilian applications.