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- ID:
- ivo://CDS.VizieR/J/AJ/139/390
- Title:
- Optically selected BL Lac objects from SDSS-DR7
- Short Name:
- J/AJ/139/390
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 723 optically selected BL Lac candidates from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic database encompassing 8250deg^2^ of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts.
- ID:
- ivo://CDS.VizieR/J/ApJ/651/61
- Title:
- Optically thick absorbers near luminous quasars
- Short Name:
- J/ApJ/651/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With close pairs of quasars at different redshifts, a background quasar sight line can be used to study a foreground quasar's environment in absorption. We search 149 moderate-resolution background quasar spectra from Gemini, Keck, the MMT, and the SDSS to survey Lyman limit systems (LLSs) and damped Ly{alpha} systems (DLAs) in the vicinity of 1.8<z<4.0 luminous foreground quasars. A sample of 27 new quasar-absorber pairs is uncovered with column densities 10^17.2^cm^-2^<NH<10^20.9^cm^-2^ and transverse (proper) distances of 22h^-1^kpc<R<1.7h^-1^Mpc from the foreground quasars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/3509
- Title:
- Optically thin CIII absorbers at z~2.5
- Short Name:
- J/MNRAS/456/3509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Voigt profile analysis of 132 intervening CIV+CIII components associated with optically thin HI absorbers at 2.1<z<3.4 in the 19 high-quality UVES/VLT and HIRES/Keck QSO spectra. For logN_CIV_ in [11.7, 14.1], N_CIII_{propto}N_CIV_^1.42+/-0.11^ and <N_CIII}/N_CIV>=1.0+/-0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at logN_HI_ in [12.2, 16.0] and logN_CIV_ in [11.8, 13.8], the gas temperature T_b_ estimated from absorption line widths is well approximated to a Gaussian peaking at logT_b_~4.4+/-0.3 for logT_b_ in [3.5, 5.5], with a negligible non-thermal contribution. For 32 of 54 tied HI+CIV pairs, also tied with CIII at logN_CIII_ in [11.7, 13.8], we ran both photoionization equilibrium (PIE) and non-PIE (using a fixed temperature T_b_) cloudy models for the Haardt-Madau QSOs+galaxies 2012 UV background. We find evidence of bimodality in observed and derived physical properties. High-metallicity branch absorbers have a carbon abundance [C/H]temp>=-1.0, a line-of-sight length L_temp_<=20kpc and a total (neutral and ionized) hydrogen volume density logn_H,temp_ in [-4.5, -3.3] and logT_b_ in [3.9, 4.5]. Low-metallicity branch absorbers have [C/H]temp<=-1.0, L_temp_ in [20, 480]kpc and logn_H,temp_ in [-5.2, -4.3] and logT_b_~ 4.5. High-metallicity branch absorbers seem to be originated from extended discs, inner haloes or outflowing gas of intervening galaxies, while low-metallicity absorbers are produced by galactic haloes or the surrounding intergalactic medium filament.
- ID:
- ivo://CDS.VizieR/J/AJ/133/303
- Title:
- Optical microvariability in radio-quiet quasars
- Short Name:
- J/AJ/133/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a study of optical microvariability in radio-quiet and radio-intermediate quasars. Observations were obtained on a total of seven objects: five radio-quiet quasars and two radio-intermediate quasars. No microvariability was detected in either the radio-quiet or radio-intermediate objects in our sample, despite intensive monitoring for several consecutive nights. In one object, PG 1257+346, evidence for interday variability was detected. We examined a sample of 117 radio-quiet objects found in the literature that have been studied for microvariability. This sample is discussed in terms of classification, redshift distribution, R (the ratio of the radio [5GHz] flux to the optical [4400{AA}] flux), optical magnitude, luminosity, and observing strategy.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A98
- Title:
- Optical monitoring of extragalactic sources
- Short Name:
- J/A+A/552/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal to this work is to observe a first set of 70 extragalactic sources at optical wavelengths that could achieve the link with the ICRF. Variations in the light curves of these targets are connected with astrophysical processes that could produce displacements of the optical photocenter. Such displacements, if they exist, are critical in the framework of the link of reference systems. Four telescope were used to observe the targets at optical wavelengths. Two of them are located in France, one in Chile, and the last in Australia. First observations were carried out during one year and a half in the R and V bands. A new method of characterizing the compactness of the targets was applied to the images obtained.
- ID:
- ivo://CDS.VizieR/J/A+AS/121/119
- Title:
- Optical monitoring of gamma-ray loud blazars. I
- Short Name:
- J/A+AS/121/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of the optical monitoring between November 1994 and November 1995 of twenty gamma-ray loud blazars included in the Torino blazar monitoring program are presented.
- ID:
- ivo://CDS.VizieR/J/AZh/72/447
- Title:
- Optical Monitoring of Quasar 3C345
- Short Name:
- J/AZh/72/447
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results of long-term monitoring of the quasar 3C345 from 1984 to 1991 are presented. Observations has been conducted on the Byurakanskii station of the St. Petersburg Astronomical Institute since 1968 in the B band, and consist of 365 brightness estimates obtained over the course of 219 nights.
- ID:
- ivo://CDS.VizieR/J/ApJ/662/62
- Title:
- Optical monitoring of SDSS J1004+4112
- Short Name:
- J/ApJ/662/62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 426 epochs of optical monitoring data spanning 1000 days from 2003 December to 2006 June for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is {Delta}t_BA_=38.4+/-2.0days ({Delta}{chi}^2^=4) in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured delay invalidates all published models. The models probably failed because they neglected the perturbations from cluster member galaxies. Models including the galaxies can fit the data well, but conclusions about the cluster mass distribution should await the measurement of the longer, and less substructure sensitive, delays of the C and D images. For these images, a delay of {Delta}t_CB_~=681+/-15days is plausible but requires confirmation, while delays of {delta}t_CB_>560days and {delta}t_AD_>800 days are required. We clearly detect microlensing of the A/B images, with the delay-corrected flux ratios changing from mB-mA=0.44+/-0.01mag in the first season to 0.29+/-0.01mag in the second season and 0.32+/-0.01mag in the third season.
- ID:
- ivo://CDS.VizieR/J/A+A/463/97
- Title:
- Optical observations of GPS radio sources
- Short Name:
- J/A+A/463/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify optical counterparts, address uncertain identifications and measure previously unknown redshifts of the host galaxies of candidate Gigahertz Peaked Spectrum (GPS) radio sources, and study their stellar populations. Long slit spectroscopy and deep optical imaging in the B, V and R bands, were obtained with the Very Large Telescope.
