Overview and Status of the International Celestial Reference Frame as Realized by VLBI

Witt, Aletha de; Charlot, P.; Gordon, D.; Jacobs, Christopher S.

doi:10.3390/universe8070374

Cited by 8 publications

(8 citation statements)

References 67 publications

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“…We also developed [27] a second-stage LNA using OMMIC's 70 nm gate-length mHEMT MMIC fabrication process. 1 This second LNA was also designed for 8 GHz−50 GHz of bandwidth utilizing 4 finger mHEMT devices. Similarly to Fig.…”

Section: B Wba850: 4-finger 70 Nm Gaas Mhemt Mmic Chipmentioning

confidence: 99%

“…We have now extended this idea to enable 'sailing' the solar system for exploring the planets. Related to that work, we use radio sources to track the motion of the planets and thus improve our knowledge of the planetary ephemeris [1], [2]. Even farther from home, the Celestial Reference Frame (CRF) [3] enables differential astrometry of the position, parallax, and proper motions of objects in our galaxy such as water masers which trace out the spiral arms of our galaxy [4].…”

Section: Introductionmentioning

confidence: 99%

“…Right) Progressively reduced S-, X-and K-band images source structure with frequency. For K-band we use a different object as the 0148+274 source image is not available [1], noting that the general principal of reduced source structure with frequency applies. and ammonia (NH 3 , multiple lines).…”

Section: Introductionmentioning

confidence: 99%

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A Multioctave 8 GHz$-$40 GHz Receiver for Radio Astronomy

et al. 2023

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Accurate measurement of angular positions on the sky requires a well-defined system of reference, something that in practice is realized by the International Celestial Reference Frame (ICRF) with observations of distant (typical redshift ∼1) Active Galactic Nuclei (AGN). At such great distances a subset of these objects exhibit as little as 10−50 μas/year observed parallax or proper motion, thus giving the frame excellent spatial and temporal stability. Until fairly recently the majority of AGN centered imaging was accomplished in the S (2.3 GHz) and X (8.4 GHz) radio frequency bands, however S-band observations for reasons such as sensitivity "plateauing", increased source structure (jets), and radio frequency interference (RFI) have become less productive. Following spacecraft telemetry moves to higher frequencies and a desire to strengthen JPL's leadership in defining the next-generation of celestial reference frames has motivated the development of a "Quad-band" prototype receiver that operates in X, Ku, K, and Ka band in both right hand (RCP) and left hand (LCP) circular polarization. The goal of this receiver is to achieve less than a 20 % increase in noise over the Jansky Very Large Array (JVLA, NRAO) performance specification, which in such a wide bandwidth represents a revolutionary capability. To evaluate the various technical developments of the 8 GHz−40 GHz receiver the feedhorn optical beam was designed to interface to the US based Very Long Baseline Array (VLBA). The receiver's intermediate frequency (IF) spans 4 GHz−8 GHz, giving rise to up to eight 4 GHz IF channels for a fully populated instrument. This paper outlines the technical development of a 2 1 / 2 octave wide (8 GHz−40 GHz) X-Ka band prototype receiver, fulfilling a need for super broadband technology within the VLBI network. An important additional benefit of the wideband receiver approach is its simplicity and low cost of operation.

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Section: B Wba850: 4-finger 70 Nm Gaas Mhemt Mmic Chipmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Multioctave 8 GHz$-$40 GHz Receiver for Radio Astronomy

et al. 2023

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“…and no coverage below −45°, as well as several large regions north of −45°with no sources. Starting from this foundation, in 2014, a new K-band collaboration was formed in order to produce full sky coverage, improve spatial density, and improve astrometric accuracy (e.g., de Witt et al 2019). As of early 2022, the K-band CRF consists of 1035 relatively uniformly distributed sources derived from more than 1.6 million observations collected in 122 observing sessions (D. Gordon et al 2023, in preparation).…”

Section: Introductionmentioning

confidence: 99%

“…For many sources, images at frequencies above X band are published for the first time, thus enabling the first direct comparisons of source structures at X versus K band for many of the sources common to both bands. In summary, since 2014, significant progress has been made toward an improved CRF at K band and a roadmap for further improvements has been defined (de Witt et al 2019).…”

Section: Introductionmentioning

confidence: 99%

The Celestial Reference Frame at K Band: Imaging. I. The First 28 Epochs

Witt

Jacobs

Gordon

et al. 2023

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We present K-band (24 GHz) images of 731 compact extragalactic radio sources with submilliarcsecond resolution, based on radio interferometric observations made with the Very Long Baseline Array of 10 telescopes during 29 day long sessions spanning from 2015 to 2018 and recorded at 2048 Mbps. Many of these sources are imaged with submilliarcsecond resolution for the first time at frequencies above X band (8 GHz). From each of the K-band images, we derive the following source properties: peak brightness, core and total flux density, the ratio of peak and core to total flux (compactness measure), radial source extent, structure index, source size, and jet direction. The vast majority of sources are imaged at multiple epochs, providing insights into their temporal behavior. The use of K band was motivated by the fact that the sources are generally intrinsically more compact at higher frequencies, as well as by the factor of 3 improvement in interferometer resolution relative to the historically standard S/X band (2.3/8.4 GHz) used for a large amount of reference frame and calibrator work. Lastly, as most of the sources imaged here are in the K-band component of the third International Celestial Reference Frame, these images serve to characterize the objects used in that International Astronomical Union standard.

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On more than two decades of Celestial Reference Frame VLBI observations in the deep south: IVS-CRDS (1995–2021)

Weston

Witt

Krásná

et al. 2023

Publ. Astron. Soc. Aust.

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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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Overview and Status of the International Celestial Reference Frame as Realized by VLBI

Cited by 8 publications

References 67 publications

A Multioctave 8 GHz$-$40 GHz Receiver for Radio Astronomy

A Multioctave 8 GHz$-$40 GHz Receiver for Radio Astronomy

The Celestial Reference Frame at K Band: Imaging. I. The First 28 Epochs

On more than two decades of Celestial Reference Frame VLBI observations in the deep south: IVS-CRDS (1995–2021)

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