Dr. Bojan Nikolic Profile

Dr. Bojan Nikolic

at Univ of Cambridge

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Publications (5)

Proceedings Article | 13 December 2020 Poster + Paper

Holographic surface measurement system for the Fred Young Submillimeter Telescope

Xiaodong Ren, Pablo Astudillo, Urs Graf, Richard Hills, Sebastian Jorquera, Bojan Nikolic, Stephen Parshley, Nicolás Reyes, Lars Weikert

Proceedings Volume 11445, 114456D (2020) https://doi.org/10.1117/12.2560459

KEYWORDS: Telescopes, Holography, Receivers, Wavefronts, Data modeling, Off axis mirrors, Spectroscopy, Reflectors

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Proceedings Article | 8 August 2016 Paper

ALMA long baseline phase calibration using phase referencing

Yoshiharu Asaki, Satoki Matsushita, Edward Fomalont, Stuartt Corder, Lars-Åke Nyman, William R. Dent, Neil Philips, Akihiko Hirota, Satoko Takahashi, Baltasar Vila-Vilaro, Bojan Nikolic, Todd Hunter, Anthony Remijan, Catherine Vlahakis

Proceedings Volume 9906, 99065U (2016) https://doi.org/10.1117/12.2232301

KEYWORDS: Telescopes, Troposphere, Calibration, Antennas, Spatial resolution, Phase interferometry, Interferometers, Switching, Atmospheric modeling, Astronomy

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The Atacama Large Millimeter/submillimeter Array (ALMA) is the world's largest millimeter/submillimeter telescope and provides unprecedented sensitivities and spatial resolutions. To achieve the highest imaging capabilities, interferometric phase calibration for the long baselines is one of the most important subjects: The longer the baselines, the worse the phase stability becomes because of turbulent motions of the Earth's atmosphere, especially, the water vapor in the troposphere. To overcome this subject, ALMA adopts a phase correction scheme using a Water Vapor Radiometer (WVR) to estimate the amount of water vapor content along the antenna line of sight. An additional technique is phase referencing, in which a science target and a nearby calibrator are observed by turn by quickly changing the antenna pointing. We conducted feasibility studies of the hybrid technique with the WVR phase correction and the antenna Fast Switching (FS) phase referencing (WVR+FS phase correction) for the ALMA 16 km longest baselines in cases that (1) the same observing frequency both for a target and calibrator is used, and (2) higher and lower frequencies for a target and calibrator, respectively, with a typical switching cycle time of 20 s. It was found that the phase correction performance of the hybrid technique is promising where a nearby calibrator is located within roughly 3◦ from a science target, and that the phase correction with 20 s switching cycle time significantly improves the performance with the above separation angle criterion comparing to the 120 s switching cycle time. The currently trial phase calibration method shows the same performance independent of the observing frequencies. This result is especially important for the higher frequency observations because it becomes difficult to find a bright calibrator close to an arbitrary sky position. In the series of our experiments, it is also found that phase errors affecting the image quality come from not only the water vapor content in the lower troposphere but also a large structure of the atmosphere with a typical cell scale of a few tens of kilometers.

Proceedings Article | 27 July 2016 Paper

Atmospheric phase characteristics of the ALMA long baseline

Satoki Matsushita, Yoshiharu Asaki, Edward Fomalont, Denis Barkats, Stuartt Corder, Richard Hills, Ryohei Kawabe, Luke Maud, Koh-Ichiro Morita, Bojan Nikolic, Remo P. J. Tilanus, Catherine Vlahakis

Proceedings Volume 9906, 99064X (2016) https://doi.org/10.1117/12.2231846

KEYWORDS: Atmospheric corrections, Atmospheric sciences, Atmospheric corrections, Atmospheric sensing, Calibration, Antennas, Turbulence, Atmospheric modeling, Astronomy, Signal detection, Statistical analysis

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Proceedings Article | 10 October 2012 Paper

ALMA temporal phase stability and the effectiveness of water vapor radiometer

Satoki Matsushita, Koh-Ichiro Morita, Denis Barkats, Richard Hills, Edward Fomalont, Bojan Nikolic

Proceedings Volume 8444, 84443E (2012) https://doi.org/10.1117/12.925872

KEYWORDS: Atmospheric corrections, Radiometry, Astronomy, Antennas, Atmospheric optics, Data corrections, Radio astronomy, Data integration, Imaging systems, Interferometry

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Proceedings Article | 17 September 2012 Paper

ACA phase calibration scheme with the ALMA water vapor radiometers

Yoshiharu Asaki, Satoki Matsushita, Koh-Ichiro Morita, Bojan Nikolic

Proceedings Volume 8444, 84443K (2012) https://doi.org/10.1117/12.925986

KEYWORDS: Antennas, Interferometry, Phase interferometry, Calibration, Interferometers, Radiometry, Phase measurement, Astronomy, Observatories, Data corrections

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