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Christopher renamed Discussion of process.tex to Setup.tex
about 10 years ago
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\section{Setup}
\subsection{Obsersation}
Images provided were in data cubes of edge length 256. This represented an area of 0.26pc by 0.26pc, with a “depth” of spectrum of 20 km/s centered at the 0-1 transition of 13CO and 12CO.
Using CASA, these images were observed at a distance of ~450pc. This was chosen as it is the distance of HH46/47, a star that is forming and has been observed using ALMA.
CASA parameters were set as follows.
Indirection, the RA and Dec of the object to be observed, was set to be the same as that as HH46/47: J2000 8h25m44 -51d00m00
Incell, the angular width of a pixel at the desired distance was calculated using the small angle formula with a pixel size of ~0.001pc and a distance of 450pc. This gave an angle of approximately 0.5arcsec.
Incenter specified the frequency on which the spectrum was centered. For 12CO, the 0-1 transition is at 110.201354GHz and for 13CO it is at 115.271201GHz.
Inbright was chosen to be the brightest individual pixel in the data cube. This was calculated for each cube. As the cubes were provided in CGS units, this was converted to Janskys.
Noise was set to be tsys-atm which used CASA's pwc (perceptible water vapour) variable to calculate noise. 0.5 was chosen for this (CASA default). Temperature on the ground and in the sky was set to be 269K (also the CASA default).
Pointing time (CASA's 'integration') was chosen to be between 10s and 100s. The effects of this choice will be discussed.
Integration time was another variable tested, with various values between 300s and 10800s chosen for different setups.
Various telescope configurations (antenna list variable in CASA) were used, ranging from the cycle0 compact configuration, two cycle 1 configurations and a configuration with the full array. The differences between these will also be discussed.
\subsection{Analysis}
The paramters used for CASA's analysis were also considered.
niter was chosen to be large, generally between 1000 and 10000. The threshold for cleaning was chosen to be 0.1mJ/y. These choices will be justified.
The other settings were simply CASA defaults.
