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Proceedings Paper

Phase characteristics of the ALMA 3-km baseline data
Author(s): Satoki Matsushita; Yoshiharu Asaki; Ryohei Kawabe; Ed Fomalont; Denis Barkats; Stuartt Corder
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Paper Abstract

We present the phase characteristics study of the Atacama Large Millimeter / submillimeter Array (ALMA) long (up to 3 km) baseline, which is the longest baseline tested so far using ALMA. The data consist of long time-scale (10 20 minutes) measurements on a strong point source (i.e., bright quasar) at various frequency bands (bands 3, 6, and 7, which correspond to the frequencies of about 88 GHz, 232 GHz, and 336 GHz) Water vapor radiometer (WVR) phase correction works well even at long baselines, and the efficiency is better at higher PWV (< 1mm) condition, consistent with the past studies. We calculate the spatial structure function of phase fluctuation, and display that the phase fluctuation (i.e., rms phase) increases as a function of baseline length, and some data sets show turn-over around several hundred meters to km and being almost constant at longer baselines. This is the first millimeter / submillimeter structure function at this long baseline length, and to show the turn-over of the structure function. Furthermore, the observation of the turn-over indicates that even if the ALMA baseline length extends to the planned longest baseline of 15 km, fringes will be detected at a similar rms phase fluctuation as that at a few km baseline lengths. We also calculate the coherence time using the 3 km baseline data, and the results indicate that the coherence time for band 3 is longer than 400 seconds in most of the data (both in the raw and WVR-corrected data) For bands 6 and 7, WVR-corrected data have about twice longer coherence time, but it is better to use fast switching method to avoid the coherence loss.

Paper Details

Date Published: 22 July 2014
PDF: 10 pages
Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91453I (22 July 2014); doi: 10.1117/12.2056424
Show Author Affiliations
Satoki Matsushita, Institute of Astronomy and Astrophysics, Academia Sinica (Taiwan)
Yoshiharu Asaki, Institute of Space and Astronautical Science (Japan)
The Graduate Univ. for Advanced Studies (Japan)
Ryohei Kawabe, National Astronomical Observatory of Japan (Japan)
Ed Fomalont, National Radio Astronomy Observatory (United States)
Joint ALMA Observatory (Chile)
Denis Barkats, Joint ALMA Observatory (Chile)
Stuartt Corder, Joint ALMA Observatory (Chile)


Published in SPIE Proceedings Vol. 9145:
Ground-based and Airborne Telescopes V
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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