Subjects -> ASTRONOMY (Total: 94 journals)
 Showing 1 - 46 of 46 Journals sorted alphabetically Advances in Astronomy       (Followers: 51) Annual Review of Astronomy and Astrophysics       (Followers: 39) Annual Review of Earth and Planetary Sciences       (Followers: 63) Artificial Satellites       (Followers: 23) Astrobiology       (Followers: 14) Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society       (Followers: 6) Astronomical Journal       (Followers: 8) Astronomical Review       (Followers: 4) Astronomische Nachrichten       (Followers: 4) Astronomy & Geophysics       (Followers: 48) Astronomy and Astrophysics       (Followers: 60) Astronomy and Astrophysics       (Followers: 32) Astronomy and Computing       (Followers: 2) Astronomy Letters       (Followers: 22) Astronomy Reports       (Followers: 15) Astronomy Studies Development       (Followers: 12) Astroparticle Physics       (Followers: 8) Astrophysical Bulletin       (Followers: 3) Astrophysical Journal       (Followers: 19) Astrophysical Journal Letters       (Followers: 14) Astrophysical Journal Supplement Series       (Followers: 14) Astrophysics       (Followers: 29) Astrophysics and Space Science       (Followers: 46) Astrophysics and Space Sciences Transactions (ASTRA)       (Followers: 56) Astropolitics: The International Journal of Space Politics & Policy       (Followers: 12) Celestial Mechanics and Dynamical Astronomy       (Followers: 11) Chinese Astronomy and Astrophysics       (Followers: 24) Colloid Journal       (Followers: 3) Comptes Rendus Physique       (Followers: 2) Computational Astrophysics and Cosmology       (Followers: 3) COSPAR Colloquia Series       (Followers: 11) Earth, Moon, and Planets       (Followers: 55) Earth, Planets and Space       (Followers: 74) EAS Publications Series       (Followers: 8) EPL Europhysics Letters       (Followers: 8) Experimental Astronomy       (Followers: 39) Expert Opinion on Astronomy and Astrophysics       (Followers: 7) Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society       (Followers: 6) Few-Body Systems       (Followers: 1) Foundations of Physics       (Followers: 41) Frontiers in Astronomy and Space Sciences       (Followers: 12) Galaxies       (Followers: 6) Globe, The       (Followers: 4) Gravitation and Cosmology       (Followers: 4) Icarus       (Followers: 75) International Journal of Advanced Astronomy       (Followers: 28) International Journal of Astrobiology       (Followers: 4) International Journal of Astronomy       (Followers: 19) International Journal of Astronomy and Astrophysics       (Followers: 29) International Journal of Satellite Communications Policy and Management       (Followers: 13) International Letters of Chemistry, Physics and Astronomy       (Followers: 12) ISRN Astronomy and Astrophysics       (Followers: 7) Journal for the History of Astronomy       (Followers: 19) Journal of Astrobiology & Outreach       (Followers: 3) Journal of Astronomical Instrumentation       (Followers: 3) Journal of Astronomical Telescopes, Instruments, and Systems       (Followers: 5) Journal of Astrophysics       (Followers: 26) Journal of Astrophysics and Astronomy       (Followers: 52) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 199) Journal of Cosmology and Astroparticle Physics       (Followers: 38) Journal of Geophysical Research : Planets       (Followers: 179) Journal of Geophysical Research : Space Physics       (Followers: 178) Journal of High Energy Astrophysics       (Followers: 22) Kinematics and Physics of Celestial Bodies       (Followers: 10) KronoScope       (Followers: 1) Macalester Journal of Physics and Astronomy       (Followers: 4) MNASSA : Monthly Notes of the Astronomical Society of South Africa       (Followers: 1) Molecular Astrophysics       (Followers: 1) Monthly Notices of the Royal Astronomical Society       (Followers: 14) Monthly Notices of the Royal Astronomical Society : Letters Nature Astronomy       (Followers: 8) New Astronomy       (Followers: 27) New Astronomy Reviews       (Followers: 17) Nonlinear Dynamics       (Followers: 19) NRIAG Journal of Astronomy and Geophysics       (Followers: 5) Open Astronomy       (Followers: 2) Physics of the Dark Universe       (Followers: 4) Planetary and Space Science       (Followers: 101) Planetary Science       (Followers: 52) Proceedings of the International Astronomical Union       (Followers: 2) Publications of the Astronomical Society of Australia       (Followers: 2) Publications of the Astronomical Society of Japan       (Followers: 3) Publications of the Astronomical Society of the Pacific       (Followers: 4) Research & Reviews : Journal of Space Science & Technology       (Followers: 17) Research in Astronomy and Astrophysics       (Followers: 29) Revista Mexicana de Astronomía y Astrofísica       (Followers: 2) Science China Physics, Mechanics & Astronomy       (Followers: 4) Solar Physics       (Followers: 34) Solar System Research       (Followers: 14) Space Science International       (Followers: 192) Space Science Reviews       (Followers: 97) Space Weather       (Followers: 24) Transport and Aerospace Engineering       (Followers: 13) Universe       (Followers: 5)
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 Astrophysical BulletinJournal Prestige (SJR): 0.447 Citation Impact (citeScore): 1Number of Followers: 3      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1990-3421 - ISSN (Online) 1990-3413 Published by Springer-Verlag  [2626 journals]
• Large Scale Distribution of Galaxies in the Field HS 47.5–22. II.
Observational Data Analysis
• Abstract: We present results of the study of the large scale distribution of galaxies up to z ~ 0.8 in the field HS 47.5–22 based on the photometric data obtained with the 1 m Schmidt telescope of the Byurakan astrophysical observatory (BAO NAS). The complete sample includes 28 398 galaxies brighter than $${{m}_{{{\text{AB}}}}} = {{23}^{{\text{m}}}}~$$ up to $$z \sim 0.8$$ . Clusterings of density in the large scale distribution of galaxies was conducted using two independent methods of determining the density contrast maps in 57 narrow layers of the three-dimensional large scale distribution of galaxies: the algorithm with the adaptive kernel and smoothing of the environment density and the Voronoi tessellation. We determined more than 250 significant large scale overdensities. The results obtained demonstrate the wide range of structures from 0.5 to 10 Mpc (the comoving size) in the full interval of redshifts up to $$z \sim 0.8$$ .
PubDate: 2020-07-01

• Estimation of the Gould Belt Scale Height from T Tauri Type Stars in the
Gaia DR2 Catalog
• Abstract: Abstract—We analyze the spatial and kinematic properties of a large sample of young T Tauri type stars in a 500 pc radius solar neighborhood, closely related to the Gould belt. The following parameters of the exponential density distribution have been determined: the average $${{({{z}_{{\text{G}}}})}_{ \odot }} = - 25 \pm 5$$ pc and scale height $${{h}_{{\text{G}}}} = 56 \pm 6$$ pc. We propose a method of excluding background stars from the samples, which are located at large heights with respect to the symmetry plane of the Gould belt. We discovered that the expansion effect for the entire star system, KG = 6 ± 1 km s−1 kpc−1, is determined mainly by the dynamics of the Scorpius–Centaurus association. We show that the angular velocity of the residual intrinsic rotation of the Gould belt can reach ΩG = 6.9 ± 0.2 km s−1 kpc−1 and that this rotation is opposite to the galactic rotation.
PubDate: 2020-07-01

• Results of Magnetic-Field Measurements with the 6-m Telescope. VI.
Observations in 2012
• Abstract: Abstract—The paper presents complete results of measurements of the magnetic-field longitudinal component Be and radial velocities VR for 163 objects, mainly main-sequence chemically peculiar stars and standards. Observations were carried out in 2012 at the 6-m BTA telescope using the Main Stellar Spectrograph (MSS) equipped with a Zeeman analyzer. Six new chemically peculiar magnetic stars were discovered: HD84 882, HD109 030, HD170 054, HD189 775, HD341 037, and BD + 61°2436. The observations were carried out during 18 nights, 560 circularly-polarizedspectra were detected. New data were obtained for 120 magnetic stars (including 5 standard stars) and 43 non-magnetic stars (including nine standard stars). The radial velocities of all objects were measured; for 46 stars, they were obtained for the first time. Observations of standard magnetic and non-magnetic stars confirm the absence of any significant systematic errors capable of introducing distortions into the measurement results of Be. The paper provides comments on the research results for each of 163 stars.
PubDate: 2020-07-01

• Super-Fast Line-Profile Variability in the Spectra of OBA Stars. II. A0
Star α 2 CVn
• Abstract: Abstract—This study continues the investigation of the super-fast variability of line profiles in the spectra of stars of early spectral classes performed in 2017 and 2018. We investigated the variability of line profiles in the spectra of OBA stars with the SCORPIO multi-mode focal reducer at the 6-m SAO RAS telescope (BTA). Short-period regular variations of the H and He lines were detected in the spectra of the chemically peculiar A0Vp star α2 CVn with periods ranging from approximately 30 to 135 minutes. Using the windowed Fourier transform let us detect the transient quasi-regular variations in the Balmer-line profiles with periods of 3–6 minutes. We discuss a possible origin of fast spectral variations.
PubDate: 2020-07-01

• On the Possibility of Using Mid-Band Filters to Search for Polar
Candidates
• Abstract: Abstract—This paper presents a method for searching for polar candidates using mid-band filters. One of the spectral features of polars is the HeII λ4686 strong emission line. We selected the Edmund Optics color filters with central wavelengths of 470, 540, and 656 nm and a transmission bandwidth of 10 nm. These filters cover the regions of the HeII λ4686 line, continuum, and the Hα line respectively. We constructed a color diagram based on the available spectra of polars and objects with a zero redshift from the SDSS archive. We show that most polars make a group with unique color indices. In practice, the method is implemented in SAO RAS at the Zeiss-1000 telescope with a new multi-mode photometer-polarimeter (MMPP). Approbation of the method with the known polars allowed us to develop two criteria to select candidates with an efficiency of up to 75%.
PubDate: 2020-07-01

• Analysis of Integrated-Light Spectra of Galactic Globular Clusters
• Abstract: We present the results of determination of the age, helium mass fraction (Y), metallicity ([Fe/H]), and abundances of the elements C, O, Na, Mg, Ca, Ti, Cr and Mn for 26 globular clusters of the Galaxy. In this work, we apply a method developed by us that employs medium-resolution integrated-light spectra of globular clusters and models of stellar atmospheres and it is supplemented in this paper by the automatic calculation of microturbulence velocities of stars in the studied objects. Based on the data obtained for 26 objects, as well as the results of our previous studies, it is shown that the abundances of chemical elements that we measured, with the exception of carbon, are consistent with the literature estimates from the analysis of integrated-light spectra of clusters and from high-resolution spectroscopic observations of their brightest stars. Our estimates of [C/Fe] are consistent with the literature values obtained from the integrated-light spectra of clusters. We interpret the systematic difference between the derived [C/Fe] for globular clusters and the literature [C/Fe] values for the brightest stars of the clusters as a change of the chemical composition in the atmospheres of stars during their evolution. The estimated absolute ages and average Y for the clusters are in a reasonable agreement with the literature data from the analysis of color–magnitude diagrams of the objects.
PubDate: 2020-07-01

• Study of Star-Forming Regions in the Peculiar Galaxies NGC 660, NGC 1512,
NGC 4395, and NGC 4618
• Abstract: Abstract—The star-forming regions (SFRs) in the peculiar galaxies NGC 660, NGC 1512, NGC 4395 and NGC 4618 are studied. The relationships between such characteristics of star forming regions as UV, near- and far-IR fluxes, as well as in the Hα and HI lines, surface brightness in these ranges, and the scatter of the radial velocities of ionized and neutral hydrogen are considered. It is shown that in all the galaxies considered, the IR fluxes from SFRs are less than in the “normal” galaxies, but for different reasons: in the galaxies with signs of recent interaction NGC 660 and NGC 1512, this is due to the low surface brightness of SFRs; in the lopsided galaxies NGC 4395 and NGC 4618, the low brightness of SFRs in the infrared range is due to their compact size. These differences indicate that the star formation process depends not only on the morphological type of a galaxy, but also on many other factors.
PubDate: 2020-07-01

• Superfast Line Profile Variations in the Spectra of OBA Stars. III. A0
Star α 2 Cvn, New Results
• Abstract: Abstract—This work is a continuation of the studies of the ultrafast variability of line profiles in the spectra of early-type stars. Line profile variations in the spectrum a chemically peculiar A0Vp star α2 CVn are investigated using the January 6, 2020 observations carried out with the 6-meter BTA telescope at SAO RAS equipped with the MSS spectrograph. Regular short-term periodic variations of the Hβ, FeII, and CrII lines were detected with periods ranging from 4 to 140 minutes. The magnetic field of the star was determined for all observations. The average measured longitudinal magnetic field component over the entire duration of observations is about 600 G, which is close to the value expected from the well-known magnetic field phase curve.
PubDate: 2020-07-01

• Progenitor and Remnant of the Luminous Red Nova V838 Monocerotis
• Abstract: Abstract—The article presents the results of multicolor photometry, medium and low resolution spectroscopy of the red nova V838 Mon remnant for 16 years after the 2002 outburst. We also used the archival photometry with the photographic plates of the Sonneberg and Moscow collections from 1928 to 1994. Analysis of these observational data confirmed that the progenitor of the V838 Mon explosion was a wide pair of B3V type stars of reduced luminosity. A brighter component exploded; it was 36 per cent brighter than its companion, and located on the zero-age main sequence of the Spectrum–Luminosity Diagram. Immediately after the outburst, in the fall of 2002, the remnant was a brown L-type supergiant (sgL), but in the fall of 2003 its spectrum changed to M type with a blue radiation excess appeared in the spectral energy distribution, which we interpreted as the reflection effect of the B type companion on the dust formed on the M star. In 2008, the companion was engulfed by the expanding explosion remnant, a type M supergiant (sgM). When the companion was immersing in the expanding M-star, a void was discovered under the M-star upper layer, in which the companion moved for about 200 days. Over the past 10 years, the luminosity of the M star has increased in the V filter by a factor of 10, and the spectral type has changed from M7.5 to M5.5. Based on radial velocities in the BaII 6497 Å and CaI 6572 Å lines, a deceleration of the expanding envelope of the M supergiant was detected, and in 2018, the envelope velocity approached to the heliocentric velocity of the star +71 km s−1. Quasi-periodic changes with a period of 320 days appeared then in the light curves, especially clearly expressed in I filter. We assume that the remnant has an elongated structure, and its rotation period is about 640 days. This is probably a gigantic contact system that will become a detached binary system in future development. The observations do not confirm the assumption that the explosion of one of the V838 Mon components was due to the merger of a compact binary system components located in a hierarchical triple one. Two hypotheses were proposed on the nature of the explosion of one of the V838 Mon components, directly based on the early age of this system: (1) the ignition of thermonuclear burning of hydrogen in the core after the gravitational compression of a protostar; (2) the fragmentation of the core inside a rapidly rotating star in the stage of gravitational compression of a protostar, and later, the subsequent defragmentation (merger of the core components) due to the loss of torque.
PubDate: 2020-07-01

• Theseus–BTA Cosmological Crucial Tests Using Multimessenger
Gamma-Ray Bursts Observations
• Abstract: Abstract—Modern Multimessenger Astronomy is a powerful instrument for performing crucial tests of the Standard Cosmological Model in the wide redshift interval up to z ∼ 10. This testing is principally important for discussion related to discrepancies between local and global measurements of cosmological parameters. We present a review of multimessenger gamma-ray burst observations currently performed and planed for THESEUS–BTA cooperative program. Such observations provide a unique opportunity to test the fundamental foundations of cosmological models: gravitation theory, cosmological principle of homogeneity and isotropy of large-scale distribution of matter, and space expansion paradigm. Important role of various selection effects leading to systematic distortions of true cosmological relations is discussed.
PubDate: 2020-07-01

• Determination of the Coordinates of Radio Sources on the Sun from
RATAN-600 Observations in Multiazimuth Mode
• Abstract: We provide an analytical description of the method for the determination of the coordinates of solar radio sources from multi-azimuth observations on RATAN-600. We analyze models of the displacement of the object across the scan depending as a function of azimuth taking into account solar rotation and suggest a method for estimating the rate of displacement due to rotation. We demonstrate the results of the application of the method using the determination of the coordinates of a radio source in the active region NOAA 11 520 as example. After eliminating gross scan referencing errors we obtained the coordinates, which agree well with observational data. We discuss the scan coordinate reference errors.
PubDate: 2020-07-01

• Peculiarities of Abundances of Selected Elements in Metal-Rich Field RR
Lyrae Stars
• Abstract: We use the data of our extended catalog of spectroscopic determinations of elemental abundances in the atmospheres of Galactic-field RR Lyrae type variables to show that metal-rich RR Lyraes ([Fe/H] > −1.0) have anomalous abundances of some elements. In particular, the relative abundances of scandium, titanium, and yttrium in metal-rich RR Lyrae type variables are lower than the corresponding abundances in field stars of similar metallicity beyond the errors. We discuss the errors of the determination of the abundances of the above elements and point out the fact that no europium, zirconium, and lanthanum abundance determinations are available for metal-rich RR Lyrae type variables. We also analyze various possible causes of the observed peculiarities of the chemical composition of metal-rich RR Lyrae type variables.
PubDate: 2020-07-01

• Cas5 Association at the GaiaDR2 Era
• Abstract: Abstract—Using the data from the second release of the Gaia exoatmospheric astrometric observatory archive the structure of the Cas5 OB association and the parameters of stars of extremely high luminosity that it contains have been refined. Two groups of OB stars have been isolated in the direction of the association at distances 3.3 and 4.3 kpc.
PubDate: 2020-04-01

• Nonstationarity of the Atmosphere of κ Cas. III. Atmosphere
Kinematics
• Abstract: Abstract—The variability of radial velocities, equivalent widths and central line depths in the spectrum of the κ Cas supergiant was studied using CCD coude-echelle spectra with high spectral resolution and signal-to-noise ratio. The radial velocity variability of all the studied lines is due to non-radial pulsations. The variability parameters (period P, amplitude A and average value γ) of radial velocity, equivalent width and central depth of the lines were determined. These parameters differ for different lines. Based on the calculation of the formation depth of the lines log τλ, the stratification of these parameters in the atmosphere of the star was studied. For the radial velocity, the period, amplitude, and rate of expansion (γ-velocity) increase from the lower to the upper layers of the atmosphere. The amplitudes of variability of the equivalent widths and central depths of the lines also increase with the height in the atmosphere.
PubDate: 2020-04-01

• Search for Candidate Objects with the Sunyaev–Zeldovich Effect on Planck
Maps in the Neighborhood of RCR Catalog Radio Sources
• Abstract: Millimeter- and submillimeter-wave maps are used to select potential candidate objects with the Sunyaev–Zeldovich effect in the vicinity of RCR (RATAN Cold Refined) radio sources. The properties of “hot” and “cold” spots in the right-ascension interval 2h ≤ RA ≤ 17h and the declination strip $${\text{De}}{{{\text{c}}}_{{2000}}} = 45^\circ .9' \pm 15'$$ are studied. In the entire strip a total of 135 candidate objects with the Sunyaev–Zeldovich effect are found. A total of 86 objects are located within 7′ from RCR catalog sources. The effect shows up most conspicuously in the vicinity of 25 RCR sources. Clusters of galaxies or radio sources are found near the overwhelming majority of spots with the Sunyaev–Zeldovich effect. The distributions of radio spectral indices of the objects and the signal on microwave maps in the direction of radio sources are statistically analyzed. It is shown that when observed at microwave frequencies a number of objects are associated with sources with inverted spectra.
PubDate: 2020-04-01

• Long-Period Oscillations of Solar Facular Knots
• Abstract: Abstract—Observations of facular areas of the Sun using the Helioseismic and Magnetic Imager device of the Solar Dynamics Observatory allow detecting long-period oscillations in the magnetic field of facular knots with periods ranging from 30 to 250 minutes. Statistically significant oscillation modes are selected by the method of time series decomposition in empirical modes. During the observation period, which is close to the knot’s lifetime, its parameters (magnetic field, area on the magnetogram, etc.) may change noticeably, although the facular formation retains its structural identity all this time. These changes also affect the effective rigidity of the system (response to external disturbances), which leads to a change in the nature of the oscillations themselves. Based on this, we consider the observed oscillation in the magnetic field of facular knots with periods from 1 to 4 hours as the proper small oscillations of a system whose effective rigidity changes over time. A simple analytical model of the process is presented. It is shown that all three specific modes of low-frequency oscillations detected in facular knots are well described by the proposed model.
PubDate: 2020-04-01

• Contribution of a Non-Thermal Component to the X-Ray Emission of OB Stars
• Abstract: Abstract—In the paper the possibility of the presence of a non-thermal component described by a power law spectrum in the X-ray spectra of OB stars is investigated. The low-resolution spectra of 101 OB stars obtained using the EPIC camera on the XMM satellite are analyzed. It is concluded that the contribution of the non-thermal component of X-ray emission can be significant and even determining for the stars similar to γ Cas. The inclusion of the non-thermal component in the model X-ray spectra reduces the temperature of the thermal components of the X-ray plasma of such stars down to typical for OB stars values. The contribution of the non-thermal component can also be significant for binary stars with colliding stellar winds and for Of'p stars.
PubDate: 2020-04-01

• Evolutionary Features and Other Characteristics of Magnetic Stars with
Helium Anomalies (He-r, He-w)
• Abstract: Abstract—We critically review the results of earlier studies on magnetic stars with anomalous helium lines. We discuss the issues associated with the fossil-field theory and the scenario of the formation of magnetic stars. A special feature of the results of our study is that they are derived from more than 160 direct estimates of average surface magnetic fields Bs or models obtained by the method. The difficulty of this work is in the insufficient amount of data on He-r stars. The problem is caused by a great decrease of the v sini values of stars at the time of internal restructuring.
PubDate: 2020-04-01

• Large-Scale Structure of Gas-and-Dust Disks and Stability of Gas-Dynamic
Equilibrium of the Dust Envelopes of Young Stars
• Abstract: Abstract—The paper analyzes the origin for the separation of gas-and-dust disks around young stars into two large groups: those with circular and spiral structures. Such a separation of disk structures is explained by the existence of stable and unstable gas-dynamic equilibrium of protostellar envelopes. A model of wave disturbances of the gas-dust protostellar envelopes is constructed. The equation of the integrated average radiation intensity in the dust envelope of protostars is obtained. The radii of five protostars at the time of their observation and the time of their entry onto the Main Sequence were determined.
PubDate: 2020-04-01

• Microbial Component Detection in Enceladus Snowing Phenomenon
• Abstract: Enceladus is an attractive place to look for signs of life thanks to liquid water and the availability of energy. Recent research has proven that the ejected material of Enceladus south pole consists of water vapor, water ice, carbon dioxide, methane and molecular hydrogen. Possible similarities of physical and chemical conditions between Enceladus ocean bottom and the carbonate mineral matrix of actively venting chimneys of the Lost City Hydrothermal Field give an opportunity to create a mathematical model of microbial ascent process through the ice shell. In this study we present first results of particle in-cell kinetic simulations of microbial distance through 10 km deep ocean. We have obtained results for microbial component—Methanosarcinales sp. analogue—characterized by 6.6 pg mass and 2.0 μm diameter distribution in Enceladus plumes. We have assumed 0.1 W m−2 heating process, 5 km ice shell and cells concentration near ocean bottom 105 cells/mL. We have confirmed assumption of Porco research team about cells concentration near ocean surface about 104 cells/mL and vertical density diversity in plumes. We have found that the optimal altitude for microbial component detection is less than 1.0 km and that in-situ measurements done previously by Cassini mass spectrometer and proposed for Enceladus Orbiter mission 50 km altitude would be ineffective.
PubDate: 2020-04-01

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