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23471. Variability monitoring of QSO B1156+295 at 4.8GHz
ID:
ivo://CDS.VizieR/J/A+A/555/A134
Title:
Variability monitoring of QSO B1156+295 at 4.8GHz
Short Name:
J/A+A/555/A134
Date:
21 Oct 2021
Publisher:
CDS
Description:
The quasar 1156+295 (4C +29.45) is one of the targets in the Urumqi monitoring program which aimed to search for evidence of annual modulation in the timescales of Intra-Day Variable (IDV) sources. The IDV observations of 1156+295 were carried out nearly monthly from October 2007 to October 2009, with the Urumqi 25m radio telescope at 4.8GHz. The source has shown prominent IDV of total flux density in most observing sessions with variability timescales of 1 day at 4.8GHz. The estimated IDV timescales seem to follow an annual cycle, which can be fitted with an anisotropic interstellar scintillation (ISS) model, suggesting that a significant part of the flux density variations is due to ISS. The source underwent a dramatic flare in 2008. We studied the possible consequences of the flare on the IDV of 1156+295, by comparing the changes in its variability characteristics with the evolution of the 43 GHz VLBA core size of the source. The quasar 1156+295 shows evidence for an annual modulation of its IDV timescales at 4.8GHz, the ISS-induced IDV timescales and variability strength might be affected by the overall activity state of the source core. More frequent IDV and VLBI measurements are required to confirm the relation between the IDV appearance and the core-size evolution of the source.
23472. Variability of A- and F-stars from Kepler
ID:
ivo://CDS.VizieR/J/A+A/534/A125
Title:
Variability of A- and F-stars from Kepler
Short Name:
J/A+A/534/A125
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars, and observationally investigate the relation between {gamma} Doradus ({gamma} Dor), {delta} Scuti ({delta} Sct), and hybrid stars.
23473. Variability of bright X-ray point sources
ID:
ivo://CDS.VizieR/J/other/RAA/14.1251
Title:
Variability of bright X-ray point sources
Short Name:
J/other/RAA/14.1
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array (ACIS-S) and observations from the Hubble Space Telescope (HST) Advanced Camera for Surveys. Out of the 46 bright (X-ray counts >60) sources that are in the common field of view of the Chandra and HST observations, 34 of them have potential optical counterparts, while the rest of them are optically dark. After taking into account systematic errors, estimated using optical sources in the field as a reference, we find that four of the X-ray sources (three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance. The X-ray luminosities of these sources are ~10^38^erg/s and are also variable on similar time scales. The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster. For one source, the change in optical magnitude is >0.3, which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity. However, the optically variable sources in NGC 1399 have been reported to have blue colors (g-z>1). All four sources have been detected in the infrared (IR) by Spitzer as point sources, and their ratios of 5.8 to 3.6um flux are >0.63, indicating that their IR spectra are like those of Active Galactic Nuclei (AGNs). While spectroscopic confirmation is required, it is likely that all four sources are background AGNs. We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.
23474. Variability of broad emission lines in QSOs
ID:
ivo://CDS.VizieR/J/MNRAS/434/1411
Title:
Variability of broad emission lines in QSOs
Short Name:
J/MNRAS/434/1411
Date:
21 Oct 2021
Publisher:
CDS
Description:
We examine the variability of the high-ionization Ly{alpha} {lambda}1216 broad emission line (BEL) in a sample of 61 high-luminosity, high-redshift quasars observed at two epochs by the Sloan Digital Sky Survey. These bright objects lie in the redshift interval z=[2.5, 4.3] and have luminosities 3.4x10^45^<~{lambda}*L_{lambda}_<~3.4x10^46^erg/s at 1450{AA}. Utilizing improved spectrophotometric flux calibrations relative to nearby compact stars observed simultaneously, we are able to measure the flux changes in Ly{alpha} and the nearby continuum at two epochs. We find 20 objects that exhibit Ly{alpha} BEL flux variability at a significance level greater than 5{sigma} on time-scales ranging from days to years in the quasar rest frame.
23475. Variability of classical T Tauri
ID:
ivo://CDS.VizieR/J/A+A/461/183
Title:
Variability of classical T Tauri
Short Name:
J/A+A/461/183
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a study the long term variability of Classical T Tauri stars (CTTS) over up to 20 years, characterize it from a set of statistical parameters and discuss its origin. We characterize the long term photometric variations of 49 CTTs with sufficient data for allowing a robust statistical analysis and propose an empirical classification scheme. Several patterns of long term photometric variability are identified. The most common pattern, exhibited by a group of 15 stars which includes T Tau itself, consists of low level variability (with V-amplitude less than 0.4mag) with no significant changes occurring from season to season over many years. A related subgroup of 22 stars exhibit a similar stable long term variability pattern, though with larger amplitudes (up to 1.6mag). Besides these representative groups, we identify three smaller groups of 3-5 stars each of which have distinctive photometric properties. The long term variability of most CTTS is fairly stable and merely reflects shorter term variability due to cold and hot surface spots. Only a small fraction of CTTS undergo significant brightness changes on the long term (months, years), which probably arise from slowly varying circumstellar extinction.
23476. Variability of CP stars
ID:
ivo://CDS.VizieR/J/A+AS/105/125
Title:
Variability of CP stars
Short Name:
J/A+AS/105/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
23477. Variability of Cyg X-1 in 1994-1998
ID:
ivo://CDS.VizieR/J/AZh/78/408
Title:
Variability of Cyg X-1 in 1994-1998
Short Name:
J/AZh/78/408
Date:
21 Oct 2021
Publisher:
CDS
Description:
Photoelectric UBVR photometry of Cyg X-1 obtained during the coordinated international campaign 'Optical Monitoring of Unique Astrophysical objects', carried out in observatories of CIS countries (Georgia, Kazakhstan, Russia, Uzbekistanin and Ukraine) 1994-1998 is presented. The data are presented as a single set, taking into account systematic differences between individual data sets. In total 2258 UBVR observations were obtained during 407 nights.
23478. Variability of Cyg X-1 (V1357) in 1995-1996
ID:
ivo://CDS.VizieR/J/PAZh/26/27
Title:
Variability of Cyg X-1 (V1357) in 1995-1996
Short Name:
J/PAZh/26/27
Date:
21 Oct 2021
Publisher:
CDS
Description:
Photoelectric UBVR photometry of Cyg X-1 with 1-m Tian'-Shan' and 48-cm Maidanak Observatory reflectors from October 1995 through November 1996 are presented.
23479. Variability of 198 extragalactic radio sources
ID:
ivo://CDS.VizieR/J/A+A/553/A107
Title:
Variability of 198 extragalactic radio sources
Short Name:
J/A+A/553/A107
Date:
21 Oct 2021
Publisher:
CDS
Description:
Combining measurements taken using the Wilkinson Microwave Anisotropy Probe (WMAP) from 2001 to 2008 with measurements taken using Planck from 2009 to 2010, we investigate the long-term flux density variability of extragalactic radio sources selected from the Planck Early Release Compact Source Catalogue. The single-year, single-frequency WMAP maps are used to estimate yearly-averaged flux densities of the sources in the four WMAP bands: Ka (33GHz), Q (41GHz), V (61GHz), and W (94GHz). We identify 82, 67, 32, and 15 sources respectively as variable at greater than 99% confidence level in these four bands. The amplitudes of variation are comparable between bands, and are not correlated with either the flux densities or the spectral indices of the sources. The number counts of WMAP Ka-band sources are stable from year to year despite the fluctuation caused by individual source variability. Most of our sources show strong correlation in variability between bands. Almost all the sources that show variability are blazars. We have attempted to fit two simple, four-parameter models to the time-series of 32 sources showing correlated variability at multiple frequencies - a long-term flaring model and a rotating-jet model. We find that 19 sources (60%) can be fit with the simple rotating-jet model, and ten of these also fit the simple long-term flaring model. The remaining 13 sources (40%) show more complex variability behaviour that is not consistent with either model. Extended radio galaxies in our sample show no sign of variability, as expected, with the exception of Pictor A for which we report evidence for a millimetre flare lasting between 2002 and 2010.
23480. Variability of FBS blue stellar objects
ID:
ivo://CDS.VizieR/J/MNRAS/415/1061
Title:
Variability of FBS blue stellar objects
Short Name:
J/MNRAS/415/1061
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new method for combined calculations of magnitudes based on accurate measurements of POSS1 and POSS2 epoch plates is given. The photometric accuracy of various surveys and catalogs has been estimated and established and statistical weights for each of them have been calculated. To achieve the best possible magnitudes, weighted averaging of data from USNO-A2.0, APM, MAPS, USNO-B1.0, and GSC 2.3.2 catalogs have been used. The rms accuracy of magnitudes achieved for POSS1 is 0.184 mag for B and 0.173 mag for R and for POSS2 is 0.138 mag for B and 0.128 mag for R. We have derived the best POSS1 and POSS2 magnitudes for the FBS blue stellar objects. We have refined the transformation formulae between the POSS1 and POSS2 magnitudes and SDSS ones and standard UBV system. Using these accurate magnitudes, we have estimated the variability of the FBS blue stellar objects and revealed probable and possible variables. We have worked out methods to control and exclude accidental errors that appear in any survey. We have compared and combined our results with those given in NSVS database and obtained better candidates for variability. Having excluded variables, we have combined POSS1 and POSS2 data for the rest of objects to achieve even better magnitudes and colors; the rms being smaller than 0.1 mag both in B and R and for the B-R colors. This approach has been applied to the First Byurakan Survey blue stellar objects containing significant number of white dwarfs, cataclysmic variables, as well as extragalactic objects (quasars, Seyferts, BL Lac objects). Altogether 336 variable objects have been revealed with POSS2-POSS1 >= 3{sigma} of the errors. An electronic table of these objects is given. Candidate variables are divided into 4 classes: extreme, strong, probable and possible variables. For a more reliable sample of variable objects we excluded possible ones from the list and were left with 161 objects. Analyzing radio and X-ray properties of these objects, we have revealed their nature and re-discovered or revealed candidate AGN, CVs, WDs and other objects.

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