Atacama Large Millimetre / Submillimetre Array

Antenna

• The main array is composed of fifty, 12 metre diameter antenna each weighing over 100 tonnes.

• The Atacama Compact Array is composed of four, 12 metre antenna, and twelve, 7 metre antenna.

• Each dish is covered with metallic panels rather than polished mirrors.

• All dishes are of a Cassegrain design on an altitude /

azimuth mount.

Top Left – Nov 9/2007, Second North American 12m Vertex RSI antenna, fifth installed at ALMA1

Top Right – Sept 27/2007, Testing of first antenna, mounting of second and third1

Bottom Right – Mounting of metal panels1

• Field of view – FWHM of 21 arc seconds at 300 Ghz. This scales linearly with wavelength.

• Each antenna can be pointed accurately within 0.6 arcseconds.

• The ACA uses its twelve 7 m antenna clustered closely together to provide a wide view, while the four larger 12 m antenna are used to determine absolute magnitude.

Band Frequency (Ghz) Field of View (FWHM)

3 84 – 116 60 “

6 211 – 275 25 “

7 275 – 373 18 “

9 602 – 720 9 “

• At wavelengths of 2 μm a single antenna would have a resolution of about 50 milliarcseconds.

• At mm wavelengths individual antenna would have a resolution of 20 arcseconds.

• Therefore, the array must act as a giant interferometer, with resolving power being determined by distance between individual antenna.

Left - Artists rendering, Atacama Compact Array, ALMA2

Above - Array in extended format 3

• In the most compact configuration (125 m distance between outer antenna) ALMA has a resolution of 0.7 arcseconds at 675 Ghz and 4.8 arcseconds at 110 Ghz.

• In the most extended configuration (~18 km distance between outer antenna), the resolution improves to 6 microarcseconds at 675 Ghz and 37 microarcseconds at 110 Ghz.

• These resolutions refer to FWHM(“) = 76 / max distance between antenna(km) / frequency(Ghz)

• ALMA is used to detect millimetre and submillimetre wavelengths ranging from 3 mm to 400 μm

• This relative large size is the reason why a mirrored reflective telescope is not needed, although each dish must not be more than 20 μm out of a perfect parabola.

Processing• The various receivers are housed

inside vacuum sealed cryo-cooled cells where they are cooled to temperatures of 4 K.

• Each antenna has one of each of the 4 receiver bands and in the future will be equipped with other receivers to fill in a range of 35 Ghz to 950 Ghz

• They also use Water Vapor Radiometers to compensate for water vapor in the atmosphere

Receiver cartridge in coolant cell5

• Inside the receivers, the signal is first converted to a lower frequency (less than 15 Ghz), then converted to a digital signal and even lower frequency (less than 5 Ghz).

• The signal is transmitted to the Correlator (super computer) along fibre optics.

• The Correlator is responsible for control of the entire system as well as the image processing.

Correlator6

Point A to B

• The facility uses two massive 28 wheeled, 130 ton transport vehicles (Otto and Lore) to move the individual antenna around.

• Capable of precise millimetre placements.

Transport vehicles4

History

• Originally a conceptual combination of the Millimetre Array (MMA) of the US, the Large Southern Array (LSA) of Europe, and the Large Millimetre Array (LMA) of Japan.

• The National Radio Astronomy Observatory (NRAO) and the European Southern Observatory (ESO) started the project.

• By Sept 2004 the National Research Council of Canada, National Astronomical Observatory of Japan (NAOJ), and Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) had joined the project as well.

1995 Joint NRAO/ESO/NAOJ site testing in Chile

2001 ALMA project started

2003 - April Testing of first antenna in New Mexico

- November Ground breaking ceremony

2005 – January Japan begins construction of ACA antenna

- July North America begins construction of 32 ALMA antenna

- December Europe begins construction of 32 ALMA antenna

2007 – March First data collected by linked antennas at ATF in New Mexico

- April Arrival of first antenna in Chile

2008 – February Arrival of the two ALMA transporters in Chile

2009 – May First interferometry with two antennas

2010 – December Nine antenna in Chile

Timeline

• Very simply, ALMA will be the world’s most powerful millimetre/submillimetre telescope, used for observing objects such as pulsars, quasars, and radio galaxies.

• Current cost estimate is 1.3 billion dollars

• For mainly political reasons, each of the main partners (NRAO, ESO, and NAOJ) were allowed to hire companies of their choice to construct their antenna.

• Currently there are 30 antenna in place and the project should be fully operational by the end of 2012

Location Location Location

• Located in the Atacama Desert in Chile.• The Operation Support Facility is located at an altitude of

2900 m above sea level.• The array of antennas is located on the plateau Altiplano

de Chajnantor at an altitude of 5000 m.• The high altitude, dryness, lack of light pollution and radio

signals make it an ideal spot.• As well, the large flat area is essential to make room for

the multiple configurations of the antenna.• The southern hemisphere is also the location from which

many important objects can be observed, including the centre of our galaxy.

Moon value near San Pedro de Atacama7

Parts Unknown

• ALMA will be the only telescope capable (in theory) of detecting the gravitational collapses involved in the creation of stars.

• Additionally ALMA will be able to study other bodies involved in the creation of stars, including parent molecular clouds.

• Detection of planets in all stages of development will be more viable. ALMA has a higher resolving power than current infrared and visible light telescopes.

• As well the millimetre/submillimetre waves won’t suffer interference from dust clouds as well as the stars these planets orbit.

Ideas?

• ALMA is currently accepting proposals for observing targets using 16 of the 12 m antenna.

• Read the guidelines and download the project submission guide

• https://almascience.nrao.edu/call-for-proposals/proposers-guide

• https://almascience.nrao.edu/call-for-proposals/observing-tool

• Currently there is no way to requisition time.• Observing is done by the contributing partners.

Data

• ALMA is still in the process of verifying the data they have collected is correct, by comparing it with data collected by other telescopes.

• Data for the following objects is available on their website– TW Hya – orange dwarf star in Hydra– NGC 3256 – a barred spiral galaxy in Vela– The Antenna Galaxies – a pair of merging galaxies– M100 – spiral galaxy in Leo– SgrA – radio source believed to be a

supermassive black holes

• http://almascience.eso.org/alma-data/science-verification

Antennae Galaxy image

Citations

• 1) National Radio Astronomy Observatory – Atacama Large Millimetre/Submillimetre Array, http://www.alma.nrao.edu/almanews/almagallery/index.html

• 2) Academia Sinica Institute of Astronomy and Astrophysics – Atacama Large Millimetre/Submillimetre Array, http://biaa.sinica.edu.tw/

• 3) European Southern Obsevatory – Atacama large Millimetre Array http://www.eso.org/public/images/alma-chajnantor-scene1/

• 4) Atacama Large Millimeter / submillimeter Array – Images http://www.almaobservatory.org/en/visuals/images/antennas-and-transporters

• 5) Atacama Large Millimeter / submillimeter Array – Front End http://www.almaobservatory.org/en/technology/front-end

• 6) Atacama Large Millimeter / submillimeter Array – How does ALMA work? - http://www.almaobservatory.org/en/about-alma/how-does-alma-work

• 7) Atacama Large Millimeter / submillimeter Array – Atacama Region http://www.almaobservatory.org/en/about-alma/location/atacama-region

• Atacama Large Millimeter / submillimeter Array - http://www.almaobservatory.org/

• Atacama Large Millimeter / submillimeter Array – National Radio Astronomy Observatory - http://www.nrao.edu/index.php/about/facilities/alma

• Atacama Large Millimeter / submillimeter Array – European Southern Observatory –

-http://www.eso.org/public/teles-instr/alma.html

http://almascience.eso.org/• Atacama Large Millimeter / submillimeter Array - National Astronomical

Observatory of Japan - http://alma.mtk.nao.ac.jp/e/• ALMA Band 3 receivers – National Research Council of Canada -

http://www.nrc-cnrc.gc.ca/eng/projects/hia/receivers.html• Scientific requirements of ALMA and its capabilities for key-projects:

Galactic – John Richer, Cavendish Laboratory, Cambridge (included on website)