How ALMA Observations are carried out

How ALMA Observations are carried out

Who can apply for ALMA time?

Scientists from all over the world use ALMA!

ALMA will operate for many decades, and it will be used by several generations, including those who are currently elementary and junior high school students.

10% of observation time is allocated to the host country, Chile, and 90% for the partners, according to their financial contribution to ALMA. All partners contribute observing time toward “Open Skies” such that any astronomer, regardless of their affiliation, can apply for ALMA time.

Another important aspect is that ALMA is designed to give calibrated data products to its users. Therefore, even non-experts researchers can use ALMA!

How does ALMA decide which projects to observe?

Once a year, ALMA splits a Call for Proposals where scientists can apply to use ALMA by submitting a observing proposal, which describes the observations they wish to carry out, what they hope to learn from the ALMA data, and how much time on ALMA is needed. These proposals are peer reviewed by other astronomers, who collectively determine which proposals are most scientifically interesting and should have priority to observed. To make the process as fair as possible, the identities of both, the proposing team and the reviewers are not disclosed. Time on ALMA is in high demand, so typically only one proposal out of five will be able to be observed. 

Since the Call for Proposals for Cycle 8, a distributed evaluation system among peers was implemented. Each team of astronomers that requests observation time with ALMA must evaluate about twenty proposals from their peers. Each proposal is thus reviewed by at least 10 different evaluators before it is assigned a ranking and its priority for observation is determined.

Occasionally an urgent, high priority observation may be needed that cannot wait until the next normal Call for Proposals. In these cases, astronomers can submit a proposal to the ALMA Director requesting observing time on ALMA, who will decided whether the proposal should be scheduled.

Researchers from the selected projects do not travel to Chajnantor to carry out the observations, but this task is carried out by ALMA astronomers, working at the Operations Support Facility. The ALMA astronomers will select which proposals to observe based on the priority from the review process, weather conditions, and the antenna array configuration. Science observations are carried out day and night, except when time is needed for hardware and software maintenance, for testing new capabilities, and when the weather conditions are adverse.

The observation data are then calibrated and transmitted, via fiber optics, to the ALMA Regional Centers (ARCs), who, in turn, deliver them to the project’s Principal Investigator.

How are the observations obtained?

The Joint ALMA Observatory (JAO) issues the calls for proposals for scientists from around the world to submit their proposals for observation time through the ARCs. The JAO, with assistance from the ARCs, coordinate the refereeing process. The cycles of observation carried out by ALMA are as follows:

Cycle 0 (Preliminary observations with 16 antennae): September 2011 to January 2013

Cycle 1 (Early Science with 43 antennas): Early 2013.

Cycle 2 (Early Science with 45 antennas): As from June 2014.

Cycle 3 (Early Science with 48 antennas): As from October 2015.

Cycle 4 (Science with 53 antennas): As from October 2016.

Cycle 5 (Science with 53 antennas): As from October 2017.

Cycle 6 (Science with 53 antennas): As from October 2018.

Cycle 7 (Science with 53 antennas): As from October 2019.

Cycle 8 (Science with 53 antennas): As from October 2021.

Cycle 9 (Science with 53 antennas): As from October 2022.

Where is ALMA data stored?

The data produced during an ALMA observing run, as well as their calibrations, are stored in the ALMA Archive, located at the headquarters in Santiago, and copied fully by the ARC’s. Once the observatory reaches its full capability, storage will increase to a range of 80 Gigabytes per day.  

Stored data will eventually become public, but not immediately. Scientists who are allocated observing time with ALMA are granted exclusive access to the gathered data for one year. This period is known as “proprietary period”, which starts when the data are distributed to the Principal Investigator. After this period has elapsed, the data becomes public at the ALMA Archive and any investigator can retrieve them through the ALMA science website. 

The date retrieved through observations are the primary source of new discoveries. It is expected that this archive will have a life of its own and become a treasure of information for all humankind.

Archive in ARC ESO https://almascience.eso.org/alma-data/archive

Archive in ARC NRAO https://almascience.nrao.edu/alma-data/archive

Archive in ARC NAOJ https://almascience.nao.ac.jp/alma-data/archive

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