63 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&
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
On the nature of the FBS blue stellar objects and the completeness of the Bright Quasar Survey. II
In Paper I (Mickaelian et al. 1999), we compared the surface density of QSOs
in the Bright Quasar Survey (BQS) and in the First Byurakan Survey (FBS) and
concluded that the completeness of the BQS is of the order of 70% rather than
30-50% as suggested by several authors. A number of new observations recently
became available, allowing a re-evaluation of this completeness. We now obtain
a surface density of QSOs brighter than B = 16.16 in a subarea of the FBS
covering ~2250 deg^2, equal to 0.012 deg^-2 (26 QSOs), implying a completeness
of 53+/-10%.Comment: LaTeX 2e, 11 pages, 3 tables and 3 figures (included in text). To
appear in Astrophysics. Uses a modified aaspp4.sty (my_aaspp4.sty), included
in packag
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
Historical light curve and search for previous outbursts of Nova KT Eridani (2009)
Context. Nova Eridani (2009) caught the eye of the nova community due to its
fast decline from maximum, which was initially missed, and its subsequent
development in the radio and X-ray wavelengths. This system also exhibits
properties similar to those of the much smaller class of recurrent novae;
themselves potential progenitors of Type Ia Supernovae. Aims. We aim to
determine the nature and physical parameters of the KT Eri progenitor system.
Methods. We searched the Harvard College Observatory archive plates for the
progenitor of KT Eri to determine the nature of the system, particularly the
evolutionary stage of the secondary.We used the data obtained to search for any
periodic signal and the derived luminosity to estimate a recurrence timescale.
Furthermore, by comparing the colours of the quiescent system on a
colour-magnitude diagram we may infer the nature of the secondary star.
Results. We identified the progenitor system of KT Eri and measured a quiescent
magnitude of = 14.7 \pm 0.4. No previous outburst was found. However, we
suggest that if the nova is recurrent it should be on a timescale of centuries.
We find a periodicity at quiescence of 737 days which may arise from reflection
effects and/or eclipses in the central binary. The periodicity and the
quiescence magnitude of the system suggest that the secondary star is evolved
and likely in, or ascending, the Red Giant Branch. A second period is evident
at 376 days which has a sinusoidal like light curve. Furthermore, the outburst
amplitude of ~ 9 magnitudes is inconsistent with those expected for fast
classical novae (~ 17 magnitudes) which may lend further support for an evolved
secondary. (Abridged)Comment: 6 pages, 5 figures, accepted for publication in A&
Swift follow-up of unidentified X-ray sources in the XMM-Newton Slew Survey
We present deep Swift follow-up observations of a sample of 94 unidentified
X-ray sources from the XMM-Newton Slew Survey. The X-ray Telescope on-board
Swift detected 29% of the sample sources; the flux limits for undetected
sources suggests the bulk of the Slew Survey sources are drawn from one or more
transient populations. We report revised X-ray positions for the XRT-detected
sources, with typical uncertainties of 2.9", reducing the number of catalogued
optical matches to just a single source in most cases. We characterise the
sources detected by Swift through their X-ray spectra and variability and via
UVOT photometry and catalogued nIR, optical and radio observations. Six sources
can be associated with known objects and 8 may be associated with unidentified
ROSAT sources within the 3-sigma error radii of our revised X-ray positions. We
find 10 of the 30 XRT-detected sources are clearly stellar in nature, including
one periodic variable star and 2 high proper motion stars. For 11 sources we
propose an AGN classification, among which 4 are detected with BAT and 3 have
redshifts spanning z = 0.2 - 0.9 obtained from the literature or from optical
spectroscopy presented here. The 67 Slew Survey sources we do not detect with
Swift are studied via their characteristics in the Slew Survey and by
comparison with the XRT and BAT detected population. We suggest that these are
mostly if not all extragalactic, though unlikely to be highly absorbed sources
in the X-rays such as Compton thick AGN. A large number of these are highly
variable soft X-ray sources. A small fraction of mainly hard-band detections
may be spurious. This follow-up programme brings us a step further to
completing the identifications of a substantial sample of XMM-Newton Slew
Survey sources, important for understanding the nature of the transient sky and
allowing flux-limited samples to be constructed.Comment: 19 pages, 7 figures. Accepted for publication in MNRA
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