ALMA Update
1 Recent News
By 8 August 2010, the array at ALMA's high-elevation site
had grown to a total of seven antennas. Having seven antennas means we
have twenty-one independent baselines, which greatly improves our
ability to calibrate and to begin to make images from real ALMA data.
Having more antennas makes a number of commissioning projects much
quicker and easier as well. The array is expected to reach 8 antennas
(half the number planned for Early Science) sometime later this month.
|
Figure 1: Seven antennas at the 5000m elevation Array Operations Site
(AOS) on 10 August 2010. Image courtesy ALMA (ESO/NAOJ/NRAO). |
ALMA plans to begin Early Science when the interferometer becomes the
"best" instrument in the world for millimetre/submillimetre
observations. This is expected to occur when the interferometer
reaches sixteen antennas with at least three receiver bands available
on all antennas, including the Canadian-made (Band 3) 3 millimetre
receiver. The present schedule has the ALMA Early Science Decision
Point in late November, with a Call for Proposals at the start of
December. It is expected that the Call will provide two months for
proposal submission placing a deadline at the end of January 2011.
Now is the time to start thinking about Early Science proposals!
2 Construction Progress
At the Operations Support Facility (OSF), two MELCO 12 m antennas are
close to meeting ALMA's strict technical specifications, at which
point they will begin the acceptance review process. A 7 m MELCO
antenna destined for the ALMA Compact Array has been measured to have
very good surface accuracy, with the best test results indicating a
surface accuracy of better than 6 microns rms. Seven Vertex antennas
are at the OSF in various stages of construction and testing on their way
to being accepted, further tested, and integrated into the ALMA
array. The first ALCATEL antenna is currently undergoing acceptance
testing at the OSF while five additiona antennas are in different stages of
assembly, ranging from final commissioning to just starting to be assembled.
The Joint ALMA Office (JAO) has moved into their new central office in
Santiago, which is located in Vitacura next to the ESO compound. The
ALMA archive will also be hosted in this building, which includes
office space for visitors as well as ALMA staff.
Preparations have increased at the ALMA Regional Centers (ARCs) as
ALMA moves closer to the key decision point on the timing of the Call
for Early Science. A number of tests of user software packages are
being held in late August and September, in preparation for reviews
that will occur in October.
The month of June saw the arrival of some spectacularly good observing
conditions. On the evening of June 30, the precipitable water vapour
(PWV) in the atmosphere above the site fell to a low of 0.13 mm!
Atmospheric transparency at ALMA's highest frequencies is a strong
function of PWV; for reference, the weather conditions on the
summit of Mauna are usually considered to be excellent if the PWV is 1
mm PWV or less.
|
Figure 2: Precipitable water vapour (PWV) versus time on the evening
of June 30, 2010 shows extremely dry and transparent
conditions. Figure from ALMA September 2010 newsletter. |
There has been a lot of work over the last few months to test and
implement ALMA's water vapor radiometers (WVRs). Ground-based millimeter
images are blurred by water in the Earth's atmosphere, in a similar
way that optical images are blurred by the atmospheric fluctuations
commonly referred to as seeing. ALMA has recently made a big step
towards its goal of using WVRs to measure the amount of atmospheric
water vapour in the line of sight to each antenna. These measurements
are used to provide a correction to the astronomical data which not
only improves the image quality but is essential for using ALMA at its
shortest wavelengths and on baselines exceeding several kilometers.
The data shown in Figure 3 would be virtually useless for
wavelengths shorter than about one millimeter without correction, but
with the correction we should be able to obtain sharp images at all
ALMA wavelengths.
|
Figure 3: Phase Correction on a mm source. In the upper plot the red
line is the raw phase of the astronomical signals (converted into a
path difference), and the blue line is the difference as measured by
the radiometer, while the lower plot is the residual after applying
the correction. (Credit Bojan Nikolic; from the September 2010 ALMA newsletter)
|
2.1 Personnel news
In September 2010, Dr. Lewis Ball will join ALMA as the
Deputy Director of the Joint ALMA Observatory.
Lewis began
his career working on the application of the theory of shocks, particle
acceleration, synchrotron emission, and inverse Compton scattering
to supernovae, supernova remnants, pulsar winds and
radio/X-ray transients. He later moved into research management at
Australia's Commonwealth Scientific and Industrial Research
Organization (CSIRO), where he recently integrated the Australia
Telescope National Facility (ATNF) and the Canberra Deep Space
Communication Complex (CDSCC) into a new CSIRO division, Astronomy and
Space Science. We welcome Lewis to the ALMA project, where
his extensive management expertise should serve to strengthen the
leadership in ALMA.
3 ALMA Meetings
3.1 Upcoming ALMA Science Meetings
Registration is now open for "ALMA: Extending the Limits of Astrophysical
Spectroscopy", a conference to be held 15-17 January 2011 in Victoria, and
will remain open until the maximum number of participants has been reached.
An optional workshop on the following day (18 January) will provide
participants an opportunity to get hands-on experience with the ALMA
Observing Tool and related software. This workshop is a joint
initiative of NRAO and HIA and will be the 5th NAASC workshop focusing on
ALMA science.
For information and registration go to
http://almatelescope.ca/Spectroscopy2011/
ESO will host a workshop on "The impact of Herschel Surveys on ALMA
Early Science" 16-19 November 2010 in Garching, Germany.
The workshop is designed to explore the powerful combination between
Herschel and ALMA, taking advantage of the Herschel's first results to
best exploit the ALMA Early Science call for proposals expected
towards the end of 2010. ESO hopes also to foster collaborations among
Herschel users and between the Herschel and ALMA communities. The
conference web site is
http://www.eso.org/sci/meetings/almaherschel2010/index.html
Finally, there will be a special session on "Observing with ALMA" at
the 217th AAS meeting in Seattle, Washington on 12 January 2011.
3.2 Early Science workshops in Canada
Want to get a head start on proposing to ALMA during the Early Science
phase (deadline expected Q1 2011)? Members of the Millimetre
Astronomy Group at HIA are willing to travel to your area to conduct
mini-workshops on the use of the ALMA proposal tool and software,
and/or give related science seminars. Please consult with Gerald
Schieven (Gerald.Schieven(at)nrc-cnrc.gc.ca) if you'd be interested in
hosting a mini-workshop in your area this fall or winter.
3.3 ALMA Science Advisory Committee (ASAC)
Doug Johnstone will be attending three ALMA meetings in Chile in
October 2010. The ALMA Commissioning and Science Verification Review will
consider whether ALMA is ready to start Early Science on schedule,
while the ALMA Science Operations Review will determine if sufficient
infrastructure is in place to handle Early Science. Finally, the ALMA
Science Advisory Committee has been charged with reviewing the status
of the Proposal Review Process and consider the overall readiness of
the Project for Early Science.
3.4 ALMA North American Science Advisory Committee (ANASAC)
Doug Johnstone attended the ALMA North American Science Advisory
Committee (ANASAC) yearly face-to-face in Charlottesville in
mid-September. At this meeting the steady advance toward Early
Science with ALMA was clearly demonstrated, including commissioning
results from seven antennas working together. The readiness of the
North American ALMA Science Centre (NAASC) to handle both Early
Science and Full Operations was provided, with the ANASAC asked to
help prioritize the many tasks required by the NAASC over the coming
year. The January tutorial on "Preparing for ALMA Early Science", to
take place in Victoria on January 18th directly after the
Spectroscopy Workshop (see above) was seen as a model for
ALMA outreach to the science community.
4 ALMA Developments in Canada
4.1 Band 3 Receivers and Development
It has been a very hectic but productive summer. The second cartridge
test set was completed in the beginning of this year, increasing the
production rate to two cartridges a month. Nine cartridges have been
delivered since the beginning of April, and five more cartridges are at
various stages of the acceptance process waiting to be shipped to the Front
End Integration Centers. As of the end of August, a total of thirty-five
cartridges have been delivered to the ALMA project. The production is
expected to be completed at the beginning of 2012.
4.2 Software
The sixth Pipeline User Test was completed and the report submitted in
August.
With 9 testers evaluating 15 data sets, including
interferometry mosaics, this was the most ambitious pipeline test to date.
The testing went well, with most of the functions working well and
good feedback from the testers on items such as how to improve the use
of clean boxes and the need for smoothed spline or polynomial fits to
the bandpass calibration. The User documentation needs some additional
improvement, and in particular the large number of plots presented to
the testers (and eventually the PIs) needs to be reduced and organized
better. The pipeline team is already hard at work on these
improvements. The next test is tentatively planned for spring 2011 and
should include the combination of single dish and interferometric data.
4.3 Canadian ALMA email list
An email list has been created for Canadian astronomers
interested in ALMA. This moderated list will periodically send out
updates on ALMA's status, news of software releases, notices of
upcoming ALMA science meetings and workshops, etc., which would be of
interest to Canadian astronomers. Those who wish to be subscribe to
the alma-users list are encouraged to visit the web page
http://lists.astrosci.ca/mailman/listinfo/alma-users
or send an email
to Gerald.Schieven(at)nrc-cnrc.gc.ca.
5 Further Information
With my new position as chair of my
department for one year, these ALMA updates may be somewhat shorter than usual.
A good source for monthly updates on the ALMA project is the new
electronic NRAO newsletter
http://www.nrao.edu/news/newsletters/
And don't forget the ALMA observatory web site
http://www.almaobservatory.org/
which contains
wide range of information about the observatory, including details
about science and technology, infrastructure, geographical location,
etc. A new ALMA newsletter in September 2010 contains
a wealth of detail on the project, including an in-depth discussion of
how ALMA will correct for the effects of the atmosphere to obtain the
sharpest possible images (AO for the submillimetre) and a detailed
description of how ALMA's
receivers work entitled "Sense and Sensitivity", as well as an
update on construction
Chris Wilson wilson@physics.mcmaster.ca
Canadian ALMA Project Scientist
(with input from Doug Johnstone,
Gerald Schieven and Keith Yeung,
as well as material from Al Wootten and the NRAO and ALMA newsletters)
File translated from
TEX
by
TTH,
version 3.40.
On 30 Sep 2010, 07:17.
