- ID:
- ivo://CDS.VizieR/J/A+A/414/487
- Title:
- Optically bright AGN in ROSAT-FSC
- Short Name:
- J/A+A/414/487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To build a large, optically bright, X-ray selected AGN sample we have correlated the ROSAT-FSC (<IX/29>) catalogue of X-ray sources with the USNO (<I/252>) catalogue limited to objects brighter than O=16.5 and then with the APS (<VII/214>) database. Each of the 3212 coincidences was classified using the slitless Hamburg spectra. 493 objects were found to be extended and 2719 starlike. Using both the extended objects and the galaxies known from published catalogues we built up a sample of 185 galaxies with O(APS)<17.0mag, 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 0.02ct/s and at this magnitude, only 40% of all QSOs are detected by ROSAT.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/530/A90
- Title:
- Optically bright post-AGB population of LMC
- Short Name:
- J/A+A/530/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a catalogue of the optically bright post-AGB stars in the LMC. The sample forms an ideal testbed for stellar evolution theory predictions of the final phase of low- and intermediate-mass stars, because the distance and hence luminosity and also the current and initial mass of these objects is well constrained.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/2221
- Title:
- Optically red galaxies in H-ATLAS/GAMA
- Short Name:
- J/MNRAS/456/2221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine Herschel/SPIRE submillimetre (submm) observations with existing multiwavelength data to investigate the characteristics of low-redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01<=z<=0.2, having >5{sigma} detections in the SPIRE 250{mu}m submm waveband. Sources are then divided into two sub-samples of red and blue galaxies, based on their UV-optical colours. Galaxies in the red sample account for ~4.2 per cent of the total number of sources with stellar masses M*>~10^10^M_{sun}_. Following visual classification of the red galaxies, we find that >~30 per cent of them are early-type galaxies and >~40 per cent are spirals. The colour of the red-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, red and blue sources occupy environments with more or less similar densities (i.e. the {Sigma}_5_ parameter). From the analysis of the spectral energy distributions of galaxies in our samples based on MAGPHYS, we find that galaxies in the red sample (of any morphological type) have dust masses similar to those in the blue sample (i.e. normal spiral/star-forming systems). However, in comparison to the red-spirals and in particular blue systems, red-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the red-elliptical sample have much lower mean star formation/specific star formation rates in contrast to their counterparts in the blue sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin.
- 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/other/JAD/24.3
- Title:
- Optically Variable Quasars in AllWISE/PS1
- Short Name:
- J/other/JAD/24.3
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- This catalog presents a sample of 229236 optically variable quasar candidates identified in the AllWISE and Pan-STARRS1 data releases at 2-sigma and 3-sigma variability levels. Mid-IR bands (3.4, 4.6, 12 and 22um) are selected from the AllWISE data release, and 5 optical bands (grizy) are from Pan-STARRS1. 127350 quasars are found to be variable at the 3-sigma level.
- 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/ApJS/185/511
- Title:
- Optical microvariability of S5 0716+714
- Short Name:
- J/ApJS/185/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We monitored the BL Lac object S5 0716+714 in the optical band during 2008 October and December and 2009 February with a best temporal resolution of about 5 minutes in the BVRI bands. Four fast flares were observed with amplitudes ranging from 0.3 to 0.75mag. The source remained active during the whole monitoring campaign, showing microvariability in all days except for one. The overall variability amplitudes are {Delta}B~0.89, {Delta}V~0.80, {Delta}R~0.73, and {Delta}I~0.51mag. Typical timescales of microvariability range from 2 to 8hr. The overall V-R color index ranges from 0.37 to 0.59. Strong bluer-when-brighter chromatism was found on internight timescales. However, a different spectral behavior was found on intranight timescales. A possible time lag of ~11 minutes between B and I bands was found on one night. The shock-in-jet model and geometric effects can be applied to explain the source's intranight behavior.
- 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/ApJ/522/846
- Title:
- Optical monitoring of GeV loud blazars
- Short Name:
- J/ApJ/522/846
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical monitoring between 1994 February and 1997 December of 10 gamma-ray-loud blazars included in our blazar monitoring program. Most of the monitored objects show significant rapid variations. The typical minimum variability timescale in the optical range is about 1 hour. We have analyzed the relationships between optical variability and gamma-ray variability, and discussed theoretical models for the gamma-rayloud blazar emission.
