| 1. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station Activities During 2021–2022, in International VLBI Service for Geodesy and Astrometry 2021+2022 Biennial Report, edited by K. L. Armstrong, D. Behrend, and K. D. Baver, NASA/TP-20230014975
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- During 2021 and 2022 we participated in a total of 81 IVS 24-hour legacy S/X sessions with the Onsala 20-m telescope. We observed in a total of 73 VGOS 24-hour sessions with one or both of the Onsala twin telescopes (OTT) in 2021 and 2022. In total we observed 114 VGOS one-hour Intensive sessions during 2021 and 2022, the majority together with the partner station Ishioka in Japan, but also five with Kokee Park. More than 50 % of these sessions involved both Onsala twin telescopes.We also performed 22 local interferometry measurements at Onsala during 2021 and 2022 for measuring the local ties between our telescopes that are used for geodetic VLBI. In 2021 we also performed 91 short (20-minute) flux-monitoring sessions with the OTT as a standalone instrument.
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| 2. |
- Hovey, Gary, 1955, et al.
(författare)
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Characterization of the Beam and the Aperture of the Onsala Twin Telescopes
- 2023
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Ingår i: 2023 International Conference on Electromagnetics in Advanced Applications, ICEAA 2023. ; , s. 351-
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Konferensbidrag (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) was originally developed to perform high angular resolution radio imaging, but it has also proven useful in geodesy. VLBI has played a key role in defining the International Celestial Reference Frame (ICRF), providing measurements of the Earth Orientation Parameters (EOP), and contributing to the International Terrestrial Reference Frame (ITRF) [1]. The legacy S/X VLBI systems have achieved positional accuracies of up to 5 mm.
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| 3. |
- Thomas, Cynthia C., et al.
(författare)
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Performance of the IVS R1 and R4 sessions
- 2024
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Ingår i: Advances in Space Research. - 1879-1948 .- 0273-1177. ; 73:1, s. 317-336
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Tidskriftsartikel (refereegranskat)abstract
- The International VLBI Service for Geodesy and Astrometry (IVS) has observed the weekly IVS-R1 (R1) and IVS-R4 (R4) series of sessions since 2002. These regular series are generally stable in the sense that the networks were designed to be similar from week to week. The uniformity of these series has allowed researchers to conduct many scientific investigations. The IVS also observes with other networks that allow continued sampling of data from all VLBI stations, but the R1 and R4 observing sessions are a dominant part of overall VLBI observing accounting for 1841 sessions out of a total of 3129 24-hour sessions from 2002.0 to 2020.0 (where the last R1 and R4 in 2019 was on December 30 and December 26, respectively). In this paper, we investigate the evolution of these series in terms of their observing networks. We also discuss the construction of the R1 and R4 networks and the scheduling of these sessions. The performance of these networks in terms of the formal precision of polar motion have improved by factors of 2–3 over the period from 2002.0 to 2018.0. UT1 precision improved by a factor of about 1.2–1.5. The main reason for this improvement is the increased size of the networks. We also discuss the effect on this improvement arising from changes in the data rate and the number of observed sources. There is some degradation in performance after 2018 that is most likely due to a decline in the number of available network stations.
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| 4. |
- Varenius, Eskil, 1986, et al.
(författare)
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Broad band flux-density monitoring of radio sources with the Onsala twin telescopes
- 2022
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 54, s. 137-155
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Tidskriftsartikel (refereegranskat)abstract
- The Onsala twin telescopes (OTT) are two 13 m telescopes located at the Onsala Space Observatory in Sweden. With dual linear polarized broad-band (3-14 GHz) receivers, they are part of the next generation Very Long Baseline Interferometry (VLBI) Global Observing System (VGOS) for geodesy and astrometry. In addition to purely geodetic data products, VGOS will regularly produce full-polarisation images of hundreds of radio sources. These rich monitoring data will be valuable for both astronomy and geodesy. In this pilot study we aimed at monitoring ten bright radio sources to search for flares or similar activity, and at testing the instrument calibration on long (months) and short (hours) time scales. Using the OTT as a standalone instrument, we observed and analysed 91 short (<30 min) sessions spanning seven months. We monitored seven potentially variable radio sources (0059+581, 0552+398, 1144+402, 1156+295, 1617+229, 3C418, OJ287) and three reference calibrators (3C147, 3C286, 3C295). We used the Common Astronomy Software Applications (CASA) package to fringe-fit, bandpass-correct and scale the data to obtain flux densities in the four standard VGOS bands: 3.0-3.5 GHz (band 1), 5.2-5.7 GHz (band 2), 6.3-6.8 GHz (band 3), and 10.2-10.7 GHz (band 4). We obtained simultaneous multi-frequency light curves for ten radio sources. A bright multi-frequency flare is observed in the radio source 0059+581. OJ287 and 1156+295 show significant long-term variability in their light curves. After correcting for instrumental biases, we determine the empirical flux density uncertainty as similar to 5 %.
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| 5. |
- Weston, S., et al.
(författare)
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On More than Two Decades of Celestial Reference Frame VLBI Observations in the Deep South: IVS-CRDS (1995 - 2021)
- 2023
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Ingår i: Publications Astronomical Society of Australia. - 1448-6083 .- 1323-3580. ; 40
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Tidskriftsartikel (refereegranskat)abstract
- The International VLBI Service for Geodesy & Astrometry (IVS) regularly provides high-quality data to produce Earth Orientation Parameters (EOP), and for the maintenance and realization of the International Terrestrial and Celestial Reference Frames, ITRF and ICRF. The first iteration of the celestial reference frame (CRF) at radio wavelengths, the ICRF1, was adopted by the International Astronomical Union (IAU) in 1997 to replace the FK5 optical frame. Soon after, the IVS began official operations and in 2009 there was a significant increase in data sufficient to warrant a second iteration of the CRF, ICRF2. The most recent ICRF3, was adopted by the IAU in 2018. However, due to the geographic distribution of observing stations being concentrated in the Northern hemisphere, CRFs are generally weaker in the South due to there being fewer Southern Hemisphere observations. To increase the Southern Hemisphere observations, and the density, precision of the sources, a series of deep South observing sessions was initiated in 1995. This initiative in 2004 became the IVS Celestial Reference Frame Deep South (IVS-CRDS) observing program. This paper covers the evolution of the CRDS observing program for the period 1995 to 2021, details the data products and results, and concludes with a summary of upcoming improvements to this ongoing project.
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