Search for Variable Extragalactic Objects
Dario Trevese1987, Observational Evidence of Activity in Galaxies
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Abstract
Preliminary results of a study of automatically detected variable objects are presented. The sample is divided into stellar and diffuse objects and the corresponding integrated counts as a function of magnitude are evaluated and compared with results in the literature.
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Machine-Learning Identification of Extragalactic Objects in the Optical-Infrared All-Sky Surveys
2018 IEEE 13th International Scientific and Technical Conference on Computer Sciences and Information Technologies (CSIT)
We present new fully-automatic classification model to select extragalactic objects within astronomy photometric catalogs. Construction of the our classification model is based on the three important procedures: 1) data representation to create feature space; 2) building hypersurface in feature space to limit range of features (outliers detection); 3) building hyperplane separating extragalactic objects from the galactic ones. We trained our model with 1.7 million objects (1.4 million galaxies and quasars, 0.3 million stars). The application of the model is presented as a photometric catalog of 38 million extragalactic objects, identified in the WISE and Pan-STARRS catalogs cross-matched with each other.
The University of New South Wales Extrasolar Planet Search: a catalogue of variable stars from fields observed between 2004 and 2007
Monthly Notices of the Royal Astronomical Society, Vol. 385(4), pp. 1749-1763, 2008
We present a new catalogue of variable stars compiled from the data taken for the University of New South Wales Extrasolar Planet Search. From 2004 October to 2007 May, 25 target fields were each observed for one to four months, resulting in ~87000 high-precision light curves with 1600-4400 data points. We have extracted a total of 850 variable light curves, 659 of which do not have a counterpart in the General Catalogue of Variable Stars, the New Suspected Variables catalogue or the All Sky Automated Survey southern variable star catalogue. The catalogue is detailed here, and includes 142 Algol-type eclipsing binaries, 23 β Lyrae-type eclipsing binaries, 218 contact eclipsing binaries, 53 RR Lyrae stars, 26 Cepheid stars, 13 rotationally variable active stars, 153 uncategorized pulsating stars with periods <10 d, including δ Scuti stars, and 222 long period variables with variability on time-scales of >10 d. As a general application of variable stars discovered by extrasolar planet transit search projects, we discuss several astrophysical problems which could benefit from carefully selected samples of bright variables. These include (i) the quest for contact binaries with the smallest mass ratio, which could be used to test theories of binary mergers; (ii) detached eclipsing binaries with pre-main-sequence components, which are important test objects for calibrating stellar evolutionary models and (iii) RR Lyrae-type pulsating stars exhibiting the Blazhko effect, which is one of the last great mysteries of pulsating star research.
Variable stars as tracers of stellar populations in Local Group galaxies: Leo I and NGC 6822
2004
Results are presented of a study of the variable star populations in the dwarf spheroidal galaxy Leo I and in the dwarf irregular galaxy NGC 6822, based on time series photometry obtained with the Wide Field Imager of the 2.2 m ESO/MPI telescope (Leo I) and the Very Large Telescope (NGC 6822). We found about 250 (lower limit) variables in
O ct 2 00 5 Variable Stars in the Large Magellanic Cloud : Discovery of Extragalactic W UMa Binaries 1
2005
We observed a field in the disk of the LMC on two consecutive nights in search of rapid variable stars. We have found two pulsating stars of type RRab and δ Sct, and four binary stars, among the latter one sdB or CV below the LMC blue Main Sequence and three very close binary systems on the MS. At least one of the MS binaries, and possibly all three, are the first solar-type (W UMa-type) contact binaries to be detected in any extragalactic system and observed to obey the same MV = MV (log P,B − V ) calibration as the Galactic systems. Given the selection effects due to small amplitudes at faint magnitudes, the frequency of such binaries in the disk of the LMC with its large spread in population ages is not inconsistent with that in the disk of our Galaxy, and contrasts with the lack of binaries found in earlier observations of the much younger LMC cluster LW55. Subject headings: galaxies: individual: (Large Magellanic Cloud) – – galaxies: star clusters – Magellanic Clouds – stars: b...
The European Large Area ISO Survey II. Mid-infrared extragalactic source counts
We present preliminary source counts at 6.7 and 15 mm from the preliminary analysis of the European Large Area ISO Survey, with limiting flux densities of ,2 mJy at 15 mm and ,1 mJy at 6.7 mm. We separate the stellar contribution from the extragalactic using identifications with automated plate measurement sources made with the likelihood ratio technique. We quantify the completeness and reliability of our source extraction using (a) repeated observations over small areas, (b) cross-identifications with stars of known spectral type, (c) detections of the point spread function wings around bright sources and (d) comparison with independent algorithms. Flux calibration at 15 mm was performed using stellar identifications; the calibration does not agree with the pre-flight estimates, probably due to effects of detector hysteresis and photometric aperture correction. The 6.7-mm extragalactic counts are broadly reproduced in the Pearson & Rowan-Robinson model, but the Franceschini et al. model underpredicts the observed source density by ,0.5±1 dex, although the photometry at 6.7 mm is still preliminary. At 15 mm the extragalactic counts are in excellent agreement with the predictions of the Pearson & Rowan-Robinson, Franceschini et al., Guiderdoni et al. models and the evolving models of Xu et al., over seven orders of magnitude in 15-mm flux density. The counts agree with other estimates from the ISOCAM instrument at overlapping flux densities, provided a consistent flux calibration is used. Luminosity evolution at a rate of 1 1 z 3 ; incorporating mid-infrared spectral features, provides a better fit to the 15-mm differential counts than 1 1 z 4 density evolution. Noevolution models are excluded, implying that below around 10 mJy at 15 mm the source counts become dominated by an evolving cosmological population of dust-shrouded starbursts and/or active galaxies.
Preprint typeset using L ATEX style emulateapj v. 11/26/04 EXTRAGALACTIC SOURCE COUNTS IN THE 20–50 KEV ENERGY BAND FROM THE DEEP OBSERVATION OF THE COMA REGION BY INTEGRAL/IBIS
2004
We present the analysis of serendipitous sources in a deep, 500 ksec, hard X-ray observation of the Coma cluster region with the IBIS instrument onboard INTEGRAL. In addition to the Coma cluster, the final 20– 50 keV image contains 12 serendipitous sources with statistical significance> 4σ. We use these data (after correcting for expected number of false detections) to extend the extragalactic source counts in the 20–50 keV energy band down to a limiting flux of 1.0 × 10 −11 erg s −1 cm −2 ( ≃ 1 mCrab). This is a more than a factor of 10 improvement in sensitivity compared to the previous results in this energy band obtained with the HEAO-1 A4 instrument. The derived source counts are consistent with the Euclidean relation, N(> f) ∝ f −3/2. A large fraction of identified serendipitous sources are low-redshift, z < 0.02 AGNs, mostly of Seyfert 1 type. The surface density of hard X-ray sources is (1.4 ± 0.5) × 10 −2 per square degree above a flux threshold of 10 −11 erg s −1 ...
Extragalactic Astronomy and Cosmology
2015
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Deep census of variable stars in a VLT/VIMOS field in Carina
Astronomy and Astrophysics, 2009
We have searched for variable stars in deep V-band images of a field towards the Galactic plane in Carina. The images were taken with VIMOS instrument at ESO VLT during 4 contiguous nights in April 2005. We detected 348 variables among 50897 stars in the magnitude range between V = 15.4 and V = 24.5 mag. Upon detection, we classified the variables by direct eye inspection of their light curves. All variable objects but 9 OGLE transits in the field are new discoveries. We provide a complete catalog of all variables which includes eclipsing/ellipsoidal binaries, miscellaneous pulsators (mostly δ Scuti-type variables), stars with flares and other (irregular and likely long-period) variables. Only two of the stars in our sample are known to host planets. Our result give some implications for future large variability surveys.
The University of New South Wales Extrasolar Planet Search: methods and first results from a field centred on NGC 6633
Monthly Notices of the Royal Astronomical Society, 2005
We report on the current status of the University of New South Wales Extrasolar Planet Search project, giving details of the methods we use to obtain millimagnitude precision photometry using the 0.5-m Automated Patrol Telescope. We use a novel observing technique to optimally broaden the point spread function and thus largely eliminate photometric noise due to intrapixel sensitivity variations on the CCD. We have observed eight crowded Galactic fields using this technique during 2003 and 2004. Our analysis of the first of these fields (centred on the open cluster NGC 6633) has yielded 49 variable stars and four shallow transit candidates. Follow-up observations of these candidates have identified them as eclipsing binary systems. We use a detailed simulation of our observations to estimate our sensitivity to short-period planets, and to select a new observing strategy to maximize the number of planets detected.
Astrophysical and cosmological information from large‐scale submillimetre surveys of extragalactic sources
Monthly Notices of …, 2007
We present a quantitative analysis of the astrophysical and cosmological information that can be extracted from the many important wide-area, shallow surveys that will be carried out in the next few years. Our calculations combine the predictions of the physical model by for the formation and evolution of spheroidal galaxies with up-to-date phenomenological models for the evolution of starburst and normal late-type galaxies and of radio sources. We compute the expected number counts and the redshift distributions of these source populations separately and then focus on proto-spheroidal galaxies. For the latter objects we predict the counts and redshift distributions of strongly lensed sources at 250, 350, 500, and 850 µm, the angular correlation function of sources detected in the surveys considered, the angular power spectra due to clustering of sources below the detection limit in Herschel and Planck surveys. An optimal survey for selecting strongly lensed proto-spheroidal galaxies is described, and it is shown how they can be easily distinguished from the other source populations. We also discuss the detectability of the imprints of the 1-halo and 2-halo regimes on angular correlation functions and clustering power spectra, as well as the constraints on cosmological parameters that can be obtained from the determinations of these quantities. The novel data relevant to derive the first sub-millimeter estimates of the local luminosity functions of starburst and late-type galaxies, and the constraints on the properties of rare source populations, such as blazars, are also briefly described.
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Variable Stars in the Large Magellanic Cloud: Discovery of Extragalactic W UMa Binaries
Astronomical Journal - ASTRON J, 2006
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Ivezic, Zeljko; Menou, Kristen; Knapp, Gillian R.; Strauss, Michael A.; Lupton, Robert H.; Vanden Berk, Daniel E.; Richards, Gordon T.; Tremonti, Christy; Weinstein, Michael A.; Anderson, Scott; Bahcall, Neta A.; Becker, Robert H.; Bernardi, Mariangela; Blanton, Michael; ...
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Memorie Della Societa Astronomica Italiana, 2003
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Extragalactic Source Counts in the 20–50 keV Energy Band from the Deep Observation of the Coma Region by INTEGRAL IBIS
The Astrophysical Journal, 2005
We present the analysis of serendipitous sources in a deep, 500 ksec, hard X-ray observation of the Coma cluster region with the IBIS instrument onboard INTEGRAL. In addition to the Coma cluster, the final 20-50 keV image contains 12 serendipitous sources with statistical significance > 4 σ . We use these data (after correcting for expected number of false detections) to extend the extragalactic source counts in the 20-50 keV energy band down to a limiting flux of 1.0 × 10 −11 erg s −1 cm −2 (≃ 1 mCrab). This is a more than a factor of 10 improvement in sensitivity compared to the previous results in this energy band obtained with the HEAO-1 A4 instrument. The derived source counts are consistent with the Euclidean relation, N(> f ) ∝ f −3/2 . A large fraction of identified serendipitous sources are low-redshift, z < 0.02 AGNs, mostly of Seyfert 1 type. The surface density of hard X-ray sources is (1.4 ± 0.5) × 10 −2 per square degree above a flux threshold of 10 −11 erg s −1 cm −2 . These sources directly account for ∼ 3% of the cosmic X-ray background in the 20-50 keV energy band. Given the low redshift depth of our sample, we expect that similar sources at higher redshifts account for a significant fraction of the hard X-ray background. Our field covers only 3% of the sky; a systematic analysis of other extragalactic INTEGRAL observations can produce much larger source samples and is, therefore, critically important.
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