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Crossing Borders and the Equator: An Astronomy Ambassador in Chile. Part 3 – The Journey to ALMA

By Derek Wallentinsen posted 03-10-2023 15:46

  


Moving around inside Chile is all about changes in latitude. So it was back down from La Serena to Santiago, then connections to Calama to reach Norte Grande and the Atacama.

(In Part 1 – ACE Ambassador Adventure – Optical Observatories – Cerro Pachon, I covered the ACEAP 2020 cohort’s travels in Santiago, La Serena, Vicuña and Cerro Pachon (Gemini South, SOAR and Vera Rubin Observatory).

In Part
2 – ACE Ambassador Adventure – Optical Observatories – Cerro Tololo, I covered the ACEAP 2020 cohort’s travels to Cerro Tololo.)

ACEAP's changes in latitude during the expediation of December 2022

 

A huge incendio gigante or wildfire south of Santiago

 

On the flight north from Santiago, peach-colored sunlight and smoke smells inside the aircraft announced the presence of an incendio gigante or wildfire. During the middle of summer in the dry climate, just like in the American West, there are blazes torching thousands of acres. The jet turned to avoid the dramatic plume, providing a great view out the window.

Calama is a mining town. Immediately to its north is one of the largest copper mines in the world, with a tailings pile looking like a huge mesa. We rented 3 big diesel Toyota Hilux trucks with 
4-wheel-drive manual 6-speed transmissions. These mining pickups would convey us to the Atacama. LATAM had lost the bags of most of our group, delaying our departure until after dark. We passed through San Pedro in the late evening, raising dust clouds off its dirt streets. Finally, at midnight, we arrived at the Operation Support Facility (OSF) of ALMA.

ALMA icon at the Operation Support facility at 10,000 feet in the Andes


The Atacama Large Millimeter/submillimeter Array
is billed as the largest astronomical project in existence, a single telescope composed of 66 high precision antennas located on the Chajnantor Plateau at 17,000 feet (5000 meters) altitude in northern Chile. It’s an international partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan, together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile.

A beautiful residencia provided for us at ALMA


The OSF at 10,000 feet is a large compound with hundreds of people working on the project. We arrived and were quickly checked into the high quality residencia, a 5-star astronomers hotel. Another fantastically good cafeteria was there to feed us desayuno, almuerzo y cena.

Sean Dougherty, Canadian astrophysicist and ALMA director, explains water's effect on microwaves
In ALMA's control room at OSF
A receiver for one of the 9 wavebands that ALMA regularly observes

We spent a whole day behind the scenes, learning from the Canadian observatory director, Japanese antenna engineer and Chilean support personnel, among many others. Truly an international technological triumph!

ACE Ambassador Dave Falkner learns about ALMA's electronics
Mark Guillette and Michael O'Shea, ACE Ambassadors, with a 12-meter ALMA antenna
ALMA Public Relations Officerr Danilo Vidal explains antenna construction
Otto, one of two 130-ton antenna transporters used at ALMA

There are two different apertures of antennas at ALMA, 12 meters and 7 meters. As part of the international collaboration, the 7m dishes are manufactured in Japan, while the 12m dishes are made in the US and in Europe.

The antennas are moved from assembly and maintenance areas at the OSF to the Array Operations Site (AOS) at 17,000 feet by two monster machines, the 130-ton transporters Otto and Lloyd. These diesel-powered vehicles are also tasked moving antennas weighing up to 115 tons around the site to change the array size.

ALMA works as an interferometer, where each antenna’s signal is paired with each other antenna’s signal. A signal from a source in the sky will arrive at different times for each antenna in the pair, providing positional information for the source. Up to 2145 baselines are possible with all 66 antennas in operation, refining the positions into an image. The earth’s motion during the observation adds in more baseline orientations, further refining an image with the technique of earth aperture rotation synthesis. Baselines between antennas at ALMA range from 9 meters to 16.2 kilometers. Larger baselines will give the greatest detail, while trading off the area of sky imaged. As a result, ALMA's function is often described as a "zoom telescope".

Credit Peck et al. Introduction to Radio Interferometry


Precise positions of the antennas and timing of signal arrival times are needed to make this work. A specialized supercomputer is used to combine – correlate – all the signals from all the baselines.

It was time to go to the high site and see it all for ourselves. We all had to take a blood pressure physical to be cleared to go from 10,000 to 17,000 feet. Everyone going higher than the OSF into the mountains was required to have oxygen. I was chosen to drive one of the trucks up there and my Hilux got the green AOS Access Authorization sticker.

AOS statistics
The EMTs at ALMA's clinic had to test our blood pressure to clear us for 17,000 feet with oxygen
Cleared to drive at 17,000 feet!

There was traffic on the road. Otto was loaded with a 12-meter dish and we passed the 250 tons of moving machinery going up and later allowed it to pass us coming down.

Heavy traffic three miles high
ALMA correlator, AOS, December 2022
Area not oxygenated, ALMA correlator
Break room view, AOS, 5000 meters, 17,000 feet


Soon we were there in the small operations building at the high site. Parts of it are oxygenated, other
areas with the correlator supercomputer are not. A big window allowed a beautiful panorama of the soul on the mountain.

ALMA means soul in Spanish

Driving away from the ops building, the ACE ambassadors enjoyed the magnificent desolation of the panorama of ALMA looking rather tiny atop the Chajnantor Plateau. It was a beautiful summer day, with temperatures around 40 and a 15 mile breeze blowing. I dressed in several layers of fleece and down, with a watch cap and a sun hat stacked on my head, cannula in my nose and a backpack bottle of oxygen. Above half the atmosphere, I needed measures against both sunburn and hypoxia.

ALMA is small compared to the mighty Andes
Magnificent desolation - the Chajnantor Plateau at 5000 meters

 

Personal protective equipment shields me in a harsh environment

The numerous antennas were clustered in one of the smaller configurations while we were visiting. Calibrations were going on after downtime due to a malware attack. In the widest baselines of 16 kilometers, the resolution of the array in millimeter wavelengths is 18 milli-arc-seconds, about the apparent size of the width of a human hair at half a kilometer. This is about the same as the Gemini South using GEMS adaptive optics in the wavelengths 2000 times smaller of yellow light.

ALMA’s high resolution allows it to probe exoplanetary systems and galaxies. The array has imaged many protoplanetary disks in unprecedented detail, revealing the concentric rings of forming solar systems like grooves on an old-fashioned phono record. ALMA contributed to the Event Horizon Telescope image of the supergiant galaxy Messier 87, revealing the supermassive black hole at its center.

ALMA is seeing unprecedented details in young exosolar systems and galactic cores


Next up: Crossing Borders and the Equator: An Astronomy Ambassador in Chile. Part
4 – The Chilean Experience.

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