ACSIS and HARP

May 23, 2007 — Leave a comment

The James Clerk Maxwell Telescope (JCMT) in Hawaii has two new instruments called HARP and ACSIS.They work in conjunction and together they recently took measurements of the Orion Nebula and assocaited Giant Molecular Cloud (GMC). These new instruments, called “revolutionary” by the Science and Technology Facilities Council (STFC), record the internal motions of gas taking part in star formation.

HARP is the Heterodyne Array Reciever Programme and consists of a 4×4 grid of supercoducting detectors capable of detecting the submillimetre wavelgnths at which star formation seems to be best observed. ACSIS is the AutoCorrelation Spectrometer and Imaging System and is a scomples of electronics and processors which analyse the HARP data, as well as data from other instruments. When attached the 15m JCMT dish this enables researchers to study the motion of gas.

Orion HARP ACSIS Image Slicing

The instruments produce a 3D ‘cube’ of data. Essntially andi mage which has a third, wavelength, dimesion. Different molecules give off radiation at different wavelengths and also the motions of gas can slighty affect the precise wavelength valuesd as well. These two factors allow not only the chemical make up of the cloud to be determined but also the movements of those chemicals within the cloud to be traced.

HARP and ACSIS allow astronomers to see the motion of this gas with a clarity and precision not previously available at these wavelengths. Together they give the JCMT the powerful ability to record information in three dimensions. Unlike the previous generation of receiver systems, HARP/ACSIS can produce camera-like images of the sky across thousands of adjacent wavelengths simultaneously; forming a three-dimensional image set called a “spectral cube”. The wavelength dimension permits the telescope to sense molecular tracers as well as to detect the motions of the gas.

“HARP/ACSIS is revolutionising our view of star formation in the galaxy” – Dr. John Richer

The image shown below is of Orion in carbon monoxide. This is just one slice out of the data cube and all the slices together can be combined to form a movie. The gas in the south of the cloud is moving toward the observer, whilst in the north it is moving away. This is because the star forming region at the centre – the familar M42 Orion Nebula – is pushing the gas outward as the stars form inside.

HARP Orion Image in CO

The press release from the STFC also invluded some thoughts from astronomers i8nvolve din the field. Dr. Jane Buckle of the Cavendish Laboratory says: “Commissioning HARP and ACSIS took a lot of hard work and dedication, particularly from the JAC, the Cavendish Laboratory and UK ATC staff, but the new spectral imaging capabilities at the JCMT make this a very exciting time for star formation research.”

Dr. Bill Dent of the UK Astronomy Technology Centre in Edinburgh says:” We often find gas clouds many tens of light-years across containing hundreds of stars all forming simultaneously. With this new system, we can map the structure and measure the speed of the gas that’s forming all these new stars and, furthermore, do a chemical analysis, perhaps looking for regions rich in rare and exotic molecules. Before HARP/ACSIS arrived, it was just not possible to study and understand whole clouds in this way.”

Dr. John Richer has used the JCMT for 19 years to make spectroscopic observations of molecular clouds. “It used to be a painstaking and slow process. Now with HARP’s 16 sensitive detectors, we can take data at a much more rapid rate and begin to answer much more ambitious questions about the formation of new star systems.

You can see the mobie of the data via ths link from the STFC press release.

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