The mechanical performances and the metrology system of the European ALMA antenna

Rampini, Francesco; Marchiori, Gianpietro; Biasi, Roberto; Stanghellini, Stefano; Ghedin, Leonardo

doi:10.1117/12.859265

Cited by 2 publications

(1 citation statement)

References 1 publication

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“…Temperature gradients in a telescope structure, for instance between the left and right supports of the elevation axis could lead to mechanical distortions and fluctuations in the inclination of the elevation axis, introducing changes in the antenna pointing. Antennas, such as the ALMA antennas, are equipped with temperature sensors and highly sensitive inclinometers (Rampini et al 2010) that are used to monitor the temperature gradients and changes in the inclination of the elevation axis. This information is used to estimate pointing offsets and correct the antenna pointing from those distortions.…”

Section: Temporal Temperature Gradientsmentioning

confidence: 99%

Precipitable Water Vapor, Temperature, and Wind Statistics At Sites Suitable for mm and Submm Wavelength Astronomy in Northern Chile

Otárola

Breuck

Travouillon

et al. 2019

PASP

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Atmospheric water vapor is the main limiting factor of atmospheric transparency in the mm and submm wavelength spectral windows. Thus, dry sites are needed for the installation and successful operation of radio astronomy observatories exploiting those spectral windows. Temperature and wind are variables of special consideration when planning the installation and operation of large-aperture radio telescopes, as these parameters affect the mechanical response of radio telescopes exposed to the environmental conditions. Temperature, and in particular temperature gradients, induce thermal deformation of mechanical structures, while high wind speeds and gusts induce pointing jitter affecting the tracking accuracy of astronomical sources during the observations. This work summarizes the statistics of precipitable water vapor (PWV), temperature, and wind monitored at sites by the coastal mountain range, as well as on the west slope of the Andes mountain range in the region of Antofagasta, Chile. This information could prove useful for the planning of extended baselines for the Atacama Large Millimeter and Accepted for publication under Open Access terms at the Publications of the Astronomical Society of the Pacific (PASP) JournalSubmillimeter Array (ALMA), and/or new radio telescope projects, such as the Atacama Large Aperture Submm/ mm Telescope (AtLAST) initiative. 6 https://sitedata.tmt.org/ 7

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Section: Temporal Temperature Gradientsmentioning

confidence: 99%

Precipitable Water Vapor, Temperature, and Wind Statistics At Sites Suitable for mm and Submm Wavelength Astronomy in Northern Chile

Otárola

Breuck

Travouillon

et al. 2019

PASP

View full text Add to dashboard Cite

show abstract

ALMA High-frequency Long-baseline Campaign in 2017: An Investigation of Phase-referencing Cycle Times and Effective Baseline Lengths Using Band-to-band and In-band Phase Calibration Techniques

Maud¹,

Asaki²,

Dent³

et al. 2022

ApJS

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The Atacama Large Millimeter/submillimeter Array can achieve unprecedented spatial resolutions of 15 to 5 mas with the longest baselines of 16 km and observing at the highest frequencies of 275–950 GHz (1.09–0.30 mm). Two conditions are paramount for successful observations at these frequencies: a phase calibrator in close proximity to the science target and a stable-enough atmosphere to provide a low residual phase rms post-phase-referencing. We investigate the effect of phase-referencing cycle times, for in-band and band-to-band (B2B) observing techniques, using close and distant phase calibrators, at bands 7, 8, and 9 for baselines >2000 m. We find that (1) the phase rms estimated from baselines longer than the effective baseline increases as a function of time . (2) The expected coherence estimated using the expected phase rms corresponds well to the achieved image coherence. (3) Faster phase-referencing cycle times (<1 minute) improve phase calibration accuracy and image coherence when close phase calibrators (<2°) are used. (4) For cycle times <2 minutes the negative impact of distant phase calibrators dominates the phase error budget. We also explore whether a theoretical parameterization of the effective baseline used to estimate the phase rms and a phase stability measurement, combined with an empirical parameterization of coherence degradation as a function of calibrator separation, is suitable in estimating the expected coherence of target images. The latter proves to be more accurate. Finally, we illustrate a pragmatic approach in establishing an optimal observing strategy via dynamic cycle times and on-calibrator scan lengths.

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The mechanical performances and the metrology system of the European ALMA antenna

Cited by 2 publications

References 1 publication

Precipitable Water Vapor, Temperature, and Wind Statistics At Sites Suitable for mm and Submm Wavelength Astronomy in Northern Chile

Precipitable Water Vapor, Temperature, and Wind Statistics At Sites Suitable for mm and Submm Wavelength Astronomy in Northern Chile

ALMA High-frequency Long-baseline Campaign in 2017: An Investigation of Phase-referencing Cycle Times and Effective Baseline Lengths Using Band-to-band and In-band Phase Calibration Techniques

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