Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/projects/askap/Westmeier_WM-0018-01_ASKAP-30_Core_Optimisation.pdf Дата изменения: Thu Aug 6 12:31:58 2015 Дата индексирования: Sun Apr 10 03:56:22 2016 Кодировка: Поисковые слова: обвмадеойс нефептощи рпфплпч

Optimisation of the 2-km core of ASKAP­30
T. Westmeier, 12 May 2015

Overview
is document describes three dierent core congurations for ASKAP­30 that were investigated with respect to their performance for WALLABY. All congurations assume that the outer antennas 32, 33, 34, and 36 are included, while antennas 31 and 35 are le+ out. Hence, the problem reduces to removing four antennas from the 30-antenna core of ASKAP. e three congurations tested include: · e default ASKAP­30 conguration put forward by CASS and submi0ed to AAL. is conguration has the four outermost available antennas within the 2-km core, that are not part of either BETA or ASKAP­12, removed. Such a conguration essentially results in the most compact possible core and hence provides maximum sensitivity at lower resolution ( 30), making it suitable for WALLABY and GASKAP. · An optimised conguration ("Optimised") with the most Gaussian UV coverage in the core. is conguration was created by 0ing a Gaussian to the radial UV histogram of the 2-km core of all possible ASKAP­30 congurations and then selecting the one that results in the best t with the lowest RMS. Again, all ASKAP­12 antennas were required to be included, but BETA antennas were not. is conguration results in a slightly more extended core than the "CASS" conguration by removing some of the inner antennas (including antenna 1), but its UV coverage is more homogeneous, resulting in lower sidelobe levels and be0er sensitivity at higher resolution ( 20­25), making it suitable for DINGO and FLASH. · A compromise conguration ("Compromise") that was created in a similar way as "Optimised", but this time also requiring BETA antennas 1 and 3 to be included to ensure that all of the shortest baselines are present. is conguration is meant to be a compromise between point-source sensitivity and surface brightness sensitivity.

Con&gurations considered
Name CASS Con&g. Missing antennas Description 50145001471 22, 25, 26, 29, 31, 35 Conguration proposed by CASS

Compromise 50196380607 07, 11, 21, 29, 31, 35 Optimisation of core with requirement of antennas 1, 3, 32, 33, 34 and 36, ASKAP­12, and omission of antennas 31 and 35. Optimised 50464816062 01, 07, 11, 21, 31, 35 Optimisation of core with requirement of antennas 32, 33, 34 and 36, ASKAP­12, and omission of antennas 31 and 35.

Assumptions
· All results presented assume = -30° and a symmetric hour-angle coverage of 8 h. · All results are derived at a frequency of = 1420 MHz. · All performance measurements are based on simulations with Miriad's task "uvgen". · Only baselines < 2 km were used when generating images with "invert".


Performance
Con&g. Robustness 2 CASS Compromise Optimised Robustness 0.5 CASS Compromise Optimised CASS Compromise Optimised 26.8 в 21.5 25.0 в 19.9 23.3 в 19.7 32.4 в 27.8 32.8 в 27.4 31.7 в 28.4 0.596 0.605 0.535 0.514 0.551 0.446 -5.4...+4.4 -5.7...+4.7 -5.2...+4.1 -5.4...+5.2 -6.2...+6.2 -6.3...+5.7 2.24 2.22 2.21 2.26 2.32 2.34 2.35 2.70 2.92 1.52 1.56 1.58 33.1 в 26.2 30.7 в 23.5 28.0 в 22.8 0.608 0.644 0.578 -3.4...+6.9 -2.8...+6.9 -3.4...+5.6 2.12 2.11 2.10 1.48 1.77 1.99 Beam size (arcsec) Beam ellipt. Sidelobes (%) RMS (mJy) RMS (K)

Robustness 0.5 + tapering to 30

Main conclusions
· e conguration proposed by CASS generally works best at 30 resolution in terms of improved sensitivity and lower sidelobe levels. · e optimised conguration, Optimised, generally works best at higher resolution in terms of improved sensitivity and lower sidelobe levels. · e compromise conguration, Compromise, is somewhere in between in terms of performance, with marginally be0er sensitivity than "CASS", but slightly higher sidelobe levels.


UV coverage
CASS

Compromise

Optimised


Projected radial UV histograms
CASS

Compromise

Optimised


Beam images
Robustness 0.5 CASS Robustness 2

Compromise

Optimised

Contour levels are ±2%, ±5% and ±10%, with negative contours in white.


Robustness 0.5 + tapering to 30 CASS

Compromise

Optimised