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Start Over Subject quasars Validation Level 2
1001. Variability of optically selected quasars
ID:
ivo://CDS.VizieR/J/MNRAS/268/305
Title:
Variability of optically selected quasars
Short Name:
J/MNRAS/268/305
Date:
21 Oct 2021
Publisher:
CDS
Description:
The variability properties of a sample of ~300 optically selected quasars near the South Galactic Pole (SGP) have been studied over a baseline of 16 years using a series of twelve UK Schmidt Telescope B_J_ plates at seven epochs. In this sample there is a correlation between variability and both quasar luminosity and redshift, at greater than the 99 per cent significance level. Quasars of high luminosity show significantly less variability than those with low luminosity, the rms variation ranging from about 0.25mag at M_B_=-23 to 0.1mag at M_B_=-28. The observed trends can be explained by an intrinsic dependence of quasar variability on luminosity combined with the effects of time dilation, and have implications for quasar samples selected by variability or multicolour techniques. The change in the slope of the n(m) relation at the break can be less pronounced in variability-selected samples. Our results can be used to test models for the origin and reprocessing of the continuum emission in quasars.
1002. Variability of SDSS broad absorption line QSOs
ID:
ivo://CDS.VizieR/J/ApJ/814/150
Title:
Variability of SDSS broad absorption line QSOs
Short Name:
J/ApJ/814/150
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a qualitative analysis of the variability of quasar broad absorption lines using the large multi-epoch spectroscopic data set of the Sloan Digital Sky Survey Data Release 10. We confirm that variations of absorption lines are highly coordinated among different components of the same ion or the same absorption component of different ions for CIV, SiIV, and NV. Furthermore, we show that the equivalent widths (EWs) of the lines decrease or increase statistically when the continuum brightens or dims. This is further supported by the synchronized variations of emission and absorption-line EWs when the well-established intrinsic Baldwin effect for emission lines is taken into account. We find that the emergence of an absorption component is usually accompanied by the dimming of the continuum while the disappearance of an absorption-line component is accompanied by the brightening of the continuum. This suggests that the emergence or disappearance of a CIV absorption component is only the extreme case, when the ionic column density is very sensitive to continuum variations or the continuum variability the amplitude is larger. These results support the idea that absorption-line variability is driven mainly by changes in the gas ionization in response to continuum variations, that the line-absorbing gas is highly ionized, and in some extreme cases, too highly ionized to be detected in UV absorption lines. Due to uncertainties in the spectroscopic flux calibration, we cannot quantify the fraction of quasars with asynchronized continuum and absorption-line variations.
1003. Variability of seven blazars in six bands
ID:
ivo://CDS.VizieR/J/A+A/562/A79
Title:
Variability of seven blazars in six bands
Short Name:
J/A+A/562/A79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the light curves of six BL Lac objects, PKS 0537-441, PKS 0735+17, OJ 287, PKS 2005-489, PKS 2155- 304, W Comae, and of the Flat Spectrum Radio Quasar PKS 1510-089, as a part of a photometric monitoring program in the near-infrared/optical bands started in 2004. All sources are Fermi Blazars. Our purpose is to investigate flux and spectral variability at short and long time scales. Systematic monitoring, independent of the activity of the source, guarantees high statistics, and allows to draw an unbiased view of different activity states on weekly/daily time scales for the whole timeframe, and on nightly timescales for some epochs. Data were obtained with the REM telescope located at the ESO premises of La Silla (Chile). Light curves were gathered in the optical/near-infrared VRIJHK bands from 2005 April to 2012 June. Variability >~3mag is observed in PKS 0537-441, PKS 1510-089 and PKS 2155-304, the largest ranges spanned in the near-infrared. The color intensity plots show rather different morphologies. The spectral energy distributions in general are well fitted by a power law, with some deviations which are more apparent in low states. Some variability episodes during a night interval are well documented for PKS 0537-441 and PKS 2155-304. For the latter source the variability time scale implies a large relativistic beaming factor.
1004. Variability of the fine-structure constant
ID:
ivo://CDS.VizieR/J/MNRAS/345/609
Title:
Variability of the fine-structure constant
Short Name:
J/MNRAS/345/609
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have previously presented evidence for a varying fine-structure constant, {alpha}, in two independent samples of Keck/HIRES quasi-stellar object (QSO) absorption spectra. Here we present a detailed many-multiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also re-analyse the previous samples, providing a total of 128 absorption systems over the redshift range 0.2<zabs<3.7.
1005. Variability & polarization of luminous quasars
ID:
ivo://CDS.VizieR/J/A+A/353/77
Title:
Variability & polarization of luminous quasars
Short Name:
J/A+A/353/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use 250 radio loud quasars with UBV photometry available and z<1.65, to study whether there is a gap in the distribution of absolute magnitudes, from M_V_~-25.8 (for H_0_=100km/s/Mpc, q_0_=0.5) to -25.3, as was suggested by Teerikorpi (1981A&A....98..309T; Paper I). In Paper I it was also proposed that there is a class of the most luminous radio quasars, differing in some properties from fainter quasars on the other side of the gap. The main conclusion of Paper I remains intact. The gap in the distribution of absolute magnitudes is confirmed with the new formalism of cosmological Malmquist bias (Teerikorpi, 1998A&A...339..647T), which allows one to use heterogeneous samples with magnitude inhomogeneity.
1006. Variable MgII NALs in SDSS DR14
ID:
ivo://CDS.VizieR/J/ApJS/250/3
Title:
Variable MgII NALs in SDSS DR14
Short Name:
J/ApJS/250/3
Date:
21 Oct 2021
Publisher:
CDS
Description:
Compared to high ionization CIV absorption lines, variable MgII absorption lines are rare. Using spectra from the Sloan Digital Sky Survey, we investigate the variations in MgII narrow absorption lines (NALs) for quasars with multi-epoch observations. We have compiled 8958 MgII NALs in the spectral regions from the red wings of CIV emission lines to the red wings of MgII emission lines. Among these 8958 MgII NALs, 22 variable NALs are detected with |{Delta}W_r_^{lambda}2796^|>=3{sigma}_W_ and with velocity offsets ranging from {upsilon}_r_=522 to 145513km/s. We find that: (1) the detected frequency of MgII NALs with {upsilon}_r_<=10000km/s is significantly larger than the uniformly random value expected for the MgII NALs with {upsilon}_r_>10000km/s, (2) the incidence rates of the variable MgII NALs with {upsilon}_r_<=10000km/s are much larger than those with {upsilon}_r_>10000km/s, (3) the velocity offsets of variable MgII NALs with {upsilon}_r_<=10000km/s are much smaller than the maximum velocities expected from radiation-driven outflows, and (4) the variations of variable MgII NALs with {upsilon}_r_<=10000km/s are obviously correlated with the changes in the quasar radiative output. Therefore, the 16 variable MgII NALs, whose velocities are smaller than the maximum velocities expected from radiation-driven outflows, are likely related to quasar outflows, while the 6 variable MgII NALs, whose velocities are much larger than the maximum velocities expected from radiation-driven outflows, possibly originated in intervening gas. We also find that both the variations and fractional variations in absorption strengths are not related to the velocity offsets of MgII NALs and the time intervals between the two epochs of observations. Also, the fractional variations in absorption strengths are inversely correlated with absorption strengths. In addition, both the associated and intervening MgII NALs can significantly vary on a timescale of days.
1007. Variable quasar sample from SDSS
ID:
ivo://CDS.VizieR/J/ApJ/633/638
Title:
Variable quasar sample from SDSS
Short Name:
J/ApJ/633/638
Date:
21 Oct 2021
Publisher:
CDS
Description:
SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for 2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied.
1008. Variable stars of Draco dSph
ID:
ivo://CDS.VizieR/J/AJ/136/1921
Title:
Variable stars of Draco dSph
Short Name:
J/AJ/136/1921
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a CCD survey of variable stars in the Draco dwarf spheroidal galaxy. This survey, which has the largest areal coverage since the original variable star survey by Baade & Swope (1961AJ.....66..300B), includes photometry for 270 RR Lyrae (RRL) stars, 9 anomalous Cepheids (ACs), 2 eclipsing binaries, and 12 slow, irregular red variables, as well as 30 background QSOs. Twenty-six probable double-mode RRL stars were identified. Observed parameters, including mean V and I magnitudes, V amplitudes, and periods, have been derived.
1009. Variations in QSOs optical flux
ID:
ivo://CDS.VizieR/J/ApJ/698/895
Title:
Variations in QSOs optical flux
Short Name:
J/ApJ/698/895
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze a sample of optical light curves, compiled from the literature, for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z<2.8, 10^42^<~{lambda}L_{lambda}_(5100{AA})<~10^46^, and 10^6^<~M_BH_/M_{sun}_<~10^10^. We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic timescale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic timescale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects.
1010. Variations of the fine-structure constant
ID:
ivo://CDS.VizieR/J/other/MmSAI/80.833
Title:
Variations of the fine-structure constant
Short Name:
J/other/MmSAI/80
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Keck telescope's High Resolution Spectrograph (HIRES) has previously provided evidence for a smaller fine-structure constant, {alpha}, compared to the current laboratory value, in a sample of 143 quasar absorption systems: {Delta}{alpha}/{alpha}=(-0.57+/-0.11)10^-5^. The analysis was based on a variety of metal-ion transitions which, if alpha varies, experience different relative velocity shifts. This result is yet to be robustly contradicted, or confirmed, by measurements on other telescopes and spectrographs; it remains crucial to do so.

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