127 research outputs found
Astronomical Surveys and Big Data
Recent all-sky and large-area astronomical surveys and their catalogued data
over the whole range of electromagnetic spectrum are reviewed, from Gamma-ray
to radio, such as Fermi-GLAST and INTEGRAL in Gamma-ray, ROSAT, XMM and Chandra
in X-ray, GALEX in UV, SDSS and several POSS I and II based catalogues (APM,
MAPS, USNO, GSC) in optical range, 2MASS in NIR, WISE and AKARI IRC in MIR,
IRAS and AKARI FIS in FIR, NVSS and FIRST in radio and many others, as well as
most important surveys giving optical images (DSS I and II, SDSS, etc.), proper
motions (Tycho, USNO, Gaia), variability (GCVS, NSVS, ASAS, Catalina,
Pan-STARRS) and spectroscopic data (FBS, SBS, Case, HQS, HES, SDSS, CALIFA,
GAMA). An overall understanding of the coverage along the whole wavelength
range and comparisons between various surveys are given: galaxy redshift
surveys, QSO/AGN, radio, Galactic structure, and Dark Energy surveys. Astronomy
has entered the Big Data era. Astrophysical Virtual Observatories and
Computational Astrophysics play an important role in using and analysis of big
data for new discoveries.Comment: 14 pages, 6 figures, 3 tables, 51 references. Presented at EAAS XII
General Meeting, submitted to Baltic Astronom
Optically bright Active Galactic Nuclei in the ROSAT-Faint Source Catalogue
To build a large, optically bright, X-ray selected AGN sample we have
correlated the ROSAT-FSC catalogue of X-ray sources with the USNO catalogue
limited to objects brighter than O=16.5 and then with the APS database. Each of
the 3,212 coincidences was classified using the slitless Hamburg spectra. 493
objects were found to be extended and 2,719 starlike. Using both the extended
objects and the galaxies known from published catalogues we built up a sample
of 185 galaxies with O_APS < 17.0 mag, which are high-probability counterparts
of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and
for another 34 we obtained new spectra. The fraction of Seyfert galaxies in
this sample is 20 %. To select a corresponding sample of 144 high-probability
counterparts among the starlike sources we searched for very blue objects in an
APS-based color-magnitude diagram. Forty-one were already known AGN and for
another 91 objects we obtained new spectra, yielding 42 new AGN, increasing
their number in the sample to 83. This confirms that surveys of bright QSOs are
still significantly incomplete. On the other hand we find that, at a flux limit
of 0.02 count /-1 and at this magnitude, only 40 % of all QSOs are detected by
ROSAT.Comment: 17 pages, 16 figures, accepted by A&
ASTRONOMICAL PLATES SPECTRA EXTRACTION OBJECTIVES AND POSSIBLE SOLUTIONS IMPLEMENTED ON DIGITIZED FIRST BYURAKAN SURVEY (DFBS) IMAGES
Astronomical images extraction process with usage of the Source Extractor (SE) tool is presented in this paper. The specificity of DFBS plates is that objects are presented in low-dispersion spectral form. It does not allow extraction tools to detect the objects exact coordinates and there is need of coordinates' correction. Apart thi
Verification of Photometric Parallaxes with Gaia DR2 Data
Results of comparison of Gaia DR2 parallaxes with data derived from a
combined analysis of 2MASS (Two Micron All-Sky Survey), SDSS (Sloan Digital Sky
Survey), GALEX (Galaxy Evolution Explorer), and UKIDSS (UKIRT Infrared Deep Sky
Survey) surveys in four selected high-latitude sky areas are
presented. It is shown that multicolor photometric data from large modern
surveys can be used for parameterization of stars closer than 4400 pc and
brighter than , including estimation of parallax and
interstellar extinction value. However, the stellar luminosity class should be
properly determined.Comment: 11 pages, 5 figure
RX J1643.7+3402: a new bright cataclysmic variable
We report the discovery of a new bright (V12.6) cataclysmic variable star identified with the ROSAT X-ray source RX J1643.7+3402. Spectroscopic and photometric observations show it to be a novalike variable sharing some of the characteristics of the SW Sex sub-class of novalike CVs. The spectroscopic period may be either 2\fh575 or 2\fh885, within the period "gap." A photometric modulation with a probable period of 2\fh595 and an amplitude of 0.1 mag in V is present on most nights and could be either a "positive" or a "negative" superhump modulation (depending on the exact spectroscopic period), indicating the presence of a precessing accretion disk in this system. Rapid variations of 0.1 to 0.2 mag amplitude in V repeat with a time scale of 15 min
Physics and Earth Science User Communities of Armenian National Grid Initiative
The main purpose of this article is to present the results and activities of physics and earth sciences heavy user communities of Armenian National Grid Initiative (ArmNGI) using computational or storage resources of Armenian National Grid infrastructure (ArmGrid)
Two new hot subdwarf binaries in the GALEX survey
We report the discovery of two new hot, hydrogen-rich subdwarfs (sdB) in
close binary systems. The hot subdwarfs, GALEX J0321+4727 and GALEX J2349+3844,
were selected from a joint optical-ultraviolet catalogue of hot sub-luminous
stars based on GSC2.3.2 and the Galaxy Evolution Explorer all-sky survey. Using
high-dispersion spectra of the Halpha core obtained using the 2m telescope at
Ondrejov Observatory we measured the radial velocities of the sdB primaries and
determined orbital periods of 0.26584+/-0.00004 days and 0.46249+/-0.00007 days
for GALEX J0321+4727 and GALEX J2349+3844, respectively. The time series
obtained from the Northern Sky Variability Survey with an effective wavelength
near the R band show that GALEX J0321+4727 is a variable star (Delta m=0.12
mag) while no significant variations are observed in GALEX J2349+3844. The
period of variations in GALEX J0321+4727 coincides with the orbital period and
the variability is probably caused by a reflection effect on a late-type
secondary star. Lack of photometric variations in GALEX J2349+3844 probably
indicates that the companion is a white dwarf star. Using all available
photometry and spectroscopy, we measured the atmospheric properties of the two
sdB stars and placed limits on the mass and luminosity of the companion stars.Comment: Accepted for publication in MNRA
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