scholarly journals Optical variability of some quasars important to ICRF-Gaia CRF link

2019 ◽  
pp. 55-64
Author(s):  
Miljana Jovanovic
Keyword(s):  
Light Curves ◽  
Optical Observations ◽  
Radio Sources ◽  
Method Of Least Squares ◽  
Differential Photometry ◽  
Comparison Stars ◽  
Optical Domain ◽  
Celestial Reference Frame ◽  
Brightness Variability ◽  
Stars Photometry

The Gaia optical observations started a few years ago. As a result, the Gaia Celestial Reference Frame (Gaia CRF) should replace the International CRF (ICRF). This could be done via extragalactic radio sources (mostly quasars - QSOs) visible in optical domain. During about 2.5 years (for the period July 2016 { April 2019) of our original observations of some QSOs outside ICRF list we collected observations in the V and R bands for five objects and their 30 comparison stars. Photometry stability of these objects is of importance for astrometry and the mentioned link. Because of it we did investigation of brightness variability of objects and their suitable comparison stars, and the F{test was performed. As a result, only the brightness of one object (1556+335) does not show variability. Other four objects were examined to determine the quasiperiods of their light curves using the method of Least Squares: 1535+231 (3.1 years in V, and 1.7 and 5.2 years in R filter), 1607+604 (2.7 years in V, and 1.3 and 2.3 years in R), 1722+119 (1.3 and 2.7 years in V, and 1.3 and 5.3 years in R), and 1741+597 (6.5 years in V, and 1.3 and 4.0 years in R). After a similar analysis of variability of comparison stars, the conclusion is that all of them are useful for differential photometry. Also, we provide our finding charts for these objects with suitable comparison stars.

A new pipeline for astrometry and photometry of asteroids

2018 ◽  
Vol 14 (A30) ◽  
pp. 43-43
Author(s):  
Y. Klç ◽  
M. Kaplan ◽  
Z. Eker
Keyword(s):  
Open Source ◽  
Light Curves ◽  
Multiple Comparison ◽  
Differential Photometry ◽  
Comparison Stars

AbstractUsing Python 3, astropy and astrometry.net, we have developed a pipeline to obtain photometric light curves of asteroids automatically queried by the SkyBoT database from sequential FITS images. The pipeline provides: pre-reduction of data, astrometry, standard differential photometry and light curves by auto-selecting multiple comparison stars (maximum user-defined) from NOMAD catalog via VizieR. The code is an open source, free and hosted on GitHub with the GNU GPL v3 license.

Optical Observations of Extragalactic Radio Sources

1967 ◽  
Vol 1 (1) ◽  
pp. 23-23
Author(s):  
B. E. Westerlund ◽  
J. V. Wall ◽  
N. R. Stokes
Keyword(s):  
Radio Galaxies ◽  
Optical Observations ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Photometric Observations

Photometric observations on the UBV system have been made of a number of optically identified radio sources. The measurements are basically of two types: (1) offset photometry with the Siding Spring 40-inch reflector of objects identified as probable quasars or N galaxies, and (2) observations with the Siding Spring 24-inch reflector of radio galaxies brighter than V = 14m.0.

scholarly journals Structure Effects for 3417 Celestial Reference Frame Radio Sources

2019 ◽  
Vol 242 (1) ◽  
pp. 5 ◽  
Author(s):  
M. H. Xu ◽  
J. M. Anderson ◽  
R. Heinkelmann ◽  
S. Lunz ◽  
H. Schuh ◽  
...  
Keyword(s):  
Reference Frame ◽  
Radio Sources ◽  
Celestial Reference Frame

Optical Observations of Southern Radio Sources.

1972 ◽  
Vol 172 ◽  
pp. 37 ◽  
Author(s):  
E. M. Burbidge ◽  
G. R. Burbidge
Keyword(s):  
Optical Observations ◽  
Radio Sources

scholarly journals Binary, Pulsating, and Irregular Variables Among Planetary Nuclei

1989 ◽  
Vol 114 ◽  
pp. 473-476 ◽  
Author(s):  
Howard E. Bond ◽  
Robin Ciardullo
Keyword(s):  
Planetary Nebula ◽  
Variable Stars ◽  
Close Binaries ◽  
Two Dimensional ◽  
Ccd Photometry ◽  
Photoelectric Photometry ◽  
The Past ◽  
Ccd Detector ◽  
Differential Photometry ◽  
Comparison Stars

For the past two years, the authors have been carrying out a program of CCD photometry of planetary-nebula nuclei (PNNs), using the 0.9-m telescopes at Kitt Peak National and Cerro Tololo Inter-American Observatories. The aim of this program is to investigate the variability of PNNs on timescales of minutes to days, in order to search for close binaries and pulsators, as well as unexpected new classes of variable stars.The program represents an extension of the photoelectric photometry of PNNs carried out by Bond and Grauer (1987). Use of the two-dimensional CCD detector allows us to model and subtract the nebulosity surrounding a PNN, in addition to providing exactly simultaneous observations of the PNN and several nearby comparison stars. The latter allow us to compensate for variable atmospheric transparency, permitting accurate differential photometry to be obtained even when the observing conditions are not photometric.

scholarly journals OPTICAL SPECTRA OF CANDIDATE SOUTHERN HEMISPHERE INTERNATIONAL CELESTIAL REFERENCE FRAME (ICRF) RADIO SOURCES

2011 ◽  
Vol 142 (5) ◽  
pp. 165 ◽  
Author(s):  
O. Titov ◽  
D. L. Jauncey ◽  
H. M. Johnston ◽  
R. W. Hunstead ◽  
L. Christensen
Keyword(s):  
Reference Frame ◽  
Southern Hemisphere ◽  
Optical Spectra ◽  
Radio Sources ◽  
Celestial Reference Frame

scholarly journals Gaia Data Release 2

2018 ◽  
Vol 616 ◽  
pp. A14 ◽  
Author(s):  
◽  
F. Mignard ◽  
S. A. Klioner ◽  
L. Lindegren ◽  
J. Hernández ◽  
...  
Keyword(s):  
Reference Frame ◽  
Large Scale ◽  
Point Sources ◽  
Vector Spherical Harmonics ◽  
Homogeneous Set ◽  
Rotating Reference Frame ◽  
Optical Domain ◽  
Celestial Reference System ◽  
Celestial Reference Frame ◽  
Cross Match

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ≃ 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = mag. Large-scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.

scholarly journals First CCD observations of Magellanic Cloud variable stars from the Mt John University Observatory, New Zealand

1991 ◽  
Vol 148 ◽  
pp. 381-381
Author(s):  
William Tobin ◽  
A. C. Gilmore ◽  
Alan Wadsworth ◽  
S.R.D. West
Keyword(s):  
New Zealand ◽  
Evaluation Process ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Ccd Observations ◽  
Differential Photometry

Late in 1988 the Mt John University Observatory acquired a cryogenic CCD system from Photometrics Ltd (Tucson). The chip is a Thomson CSF TH7882 CDA comprising 384 × 576 pixels. As part of the evaluation process, we have begun two differential photometry programs of the Magellanic Clouds using the Mt John 0.6m Boller & Chivens telescope. On this telescope each CCD pixel corresponds to 0.6 arcsec. Mt John's southerly latitude (44°S) permits year-round observations of the Clouds.The first program concerns B, V and I photometry of five blue eclipsing binaries selected, on the basis of Gaposchkin's (1970, 1977) photographic light curves, to have roughly equal components with minimal interaction. HV 12634 has also been observed for comparison with the CCD light curves published by Jensen et al. (1988). Fig. 1 shows the B observations so far obtained for HV 1761, but the reduction is preliminary, being based on aperture-integrated magnitudes. The field is populous, and a final reduction will require use of a crowded-field reduction package such as ROMAFOT.

scholarly journals Instability of the celestial reference frame and effect on UT1

2009 ◽  
Vol 5 (H15) ◽  
pp. 209-209
Author(s):  
Vladimir E. Zharov
Keyword(s):  
Reference Frame ◽  
Apparent Motion ◽  
Radio Sources ◽  
Secular Variations ◽  
Celestial Reference Frame

AbstractIt was shown that the ICRF radio sources including the defining sources have significant apparent motion that leads to rotation of the ICRF. This rotation is transformed to secular variations of EOP that is decreased or removed if motion of sources is took into account.

scholarly journals High-temporal resolution optical observations of the gamma-ray blazar PG 1553+113

2010 ◽  
Vol 6 (S275) ◽  
pp. 190-191
Author(s):  
I. Andruchow ◽  
J. A. Combi ◽  
S. A. Cellone ◽  
A. J. Muñoz-Arjonilla ◽  
G. E. Romero ◽  
...  
Keyword(s):  
Time Scales ◽  
Temporal Resolution ◽  
Gamma Ray ◽  
Position Angle ◽  
Optical Observations ◽  
High Temporal Resolution ◽  
Night Time ◽  
Differential Photometry ◽  
Optical Wavelengths ◽  
Optical Flux

AbstractWe present here the results of an observational photo-polarimetry campaign at optical wavelengths of the blazar PG 1553+113, which was recently detected at very high energies (>100 GeV) by the H.E.S.S and MAGIC γ-ray experiments.Our high-temporal resolution data show significant variations in the linear polarization percentage and position angle at inter-night time-scales, while at shorter (intra-night) time-scales both parameters varied less significantly, if at all. Simultaneous differential photometry (at the B and R bands) shows no significant variability in the total optical flux.

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