ALMA Atacama Compact Array Tiger Team
Teleconference, 5 October 2001 1415 UT
Draft Minutes
Participants: P. Cox, R. Crutcher, S. Guilloteau, F. Gueth, M. Gurwell, M. Holdaway, J. Mangum, Koh-Ichiro Morita, J. Pety, A. Wootten, E. van Dishoeck, Michiel Hogerheidje, M. Ishiguro, S. Sakamoto. T. Hasegawa, K. Tatematsu, M. Gurwell, R. Crutcher and J. Welch
1. Progress Reports. The ASAC is in the process of
writing up the science case for the ACA based upon the material which the
Tiger Team has furnished. One new set of images has been simulated by the
IRAM team, based upon a polarization set of I, Q, U images from Crutcher.
Results
can be downloaded at here.
Stephane gave a short summary of these results:
This simulations shows the impact of the compact array quite well.
Cox, struggling with the science case, agreed. It was discussed whether
this simulation could be done with the MEM reconstruction, since the image
contains both positive and negative numbers. Holdaway mentioned that
maximum emptiness could be used. It was included within the
SDE package.
Cox discussed the science case, difficult to summarize concisely and
compellingly, but the most convincing cases are the HCO+ disk and the
polarization case, potentially. Bryan's analysis of the debris
disk suggests it is not so compelling.
Holdaway discussed his simulations, which include the illumination offset.
This limits quality below about 500 GHz. Most of this problem, perhaps
80 %, may be corrected by taking out the illumination offset with a correction
to (u,v,w). He will redo the simulations, though only one computer is
currently available. The cluster model is now being done. MEM does a poor
job for not completely understood reasons with the HCO+ disk; with pointing
errors the results are similar for 115 and 850 GHz.
Crutcher joined and the polarization case was discussed an additional
amount.
Hasegawa commented that the Q map indeed looks different. Indeed in the
protostellar disk model, the line ratio became unrepresentative in the outer
parts of the disk. The cases where the compact array adds robustness are those
in which high dynamic range can be achieved. For other science targets,
it may not add so much.
Wootten commented that one reason he is interested in ALMA is to reach
high dynamic range, to understand the details of the final few percent of
structure in an image. For this reason, ALMA has been constructed with
great sensitivity and care for excellent imaging.
Holdaway commented that although peak flux in some outlying parts of images
such as the protostellar disk image, may be small, it is spread over a
substantial area, thus contributing a substantial part of the flux. So
while it may be the final per cent of a large dynamic range, it is important
for understanding global parameters.