ALMA observatory gets first antenna

The first ALMA antenna to be handed over to the observatory, pictured here at the ALMA Operations Support Facility. This state-of-the-art 12 m diameter antenna was manufactured by Mitsubishi Electric Corporation. ALMA (ESO/NAOJ/NRAO)

December 22, 2008

Provided by European Southern Observatory

High in the Atacama region in northern Chile, one of the world's most advanced telescopes passed a milestone recently. The first of many state-of-the-art antennae has been handed over to the Atacama Large Millimeter/submillimeter Array (ALMA) project. ALMA is under construction on the plateau of Chajnantor, at an altitude of 3 miles (5 kilometers). The telescope is being built by a global partnership and the European Southern Observatory (ESO) represents the European partner.

ALMA will initially comprise 66 high-precision antennae, with the option to expand in the future. There will be an array of fifty 40-foot (12m) antennae, acting together as a single giant telescope, and a compact array composed of 23-foot (7m) and 40-foot (12m) diameter antennae.

ALMA will help astronomers study the cool universe - the molecular gas and tiny dust grains from which stars, planetary systems, galaxies and even life are formed. ALMA will provide new insights into the formation of stars and planets, and will reveal distant galaxies in the early universe, which we see as they were more than 10 billion years ago.

The Mitsubishi Electric Corporation built the first 40-foot (12m) diameter antenna for the National Astronomical Observatory of Japan, one of the ALMA partners. North American and European antennae will join the first antenna shortly.

"Our Japanese colleagues have produced this state-of-the-art antenna to exacting specifications. We are very excited about the handover because now we can fully equip this antenna for scientific observations," said Thijs de Graauw, ALMA director.

Antennae arriving at the ALMA site undergo a series of tests to ensure that they meet the strict requirements of the telescope. The antennae have surfaces accurate to less than the thickness of a human hair, and can be pointed precisely enough to pick out a golf ball at a distance of 9 miles (15 km).

"ALMA is very important to European astronomers and to ESO, because it allows us to look at the universe in a way that has never been possible before. It really marks the start of a new era in astronomy," said Wolfgang Wild, the European ALMA project manager.

The observatory team now can proceed with integrating the rest of the components, including the sensitive receivers that will collect the faint cosmic signals from space.

The antennae are tested at the Operations Support Facility, at an altitude of 1.8 miles (2.9 km), before being moved to the plateau of Chajnantor at 3 miles (5 kilometers). The Operations Support Facility will also be the observatory's control center.

ALMA is being built on the Chajnantor plateau, high in the Chilean Andes, because the site's extreme dryness and altitude offer excellent conditions for observing the submillimeter-wavelength signals for which the telescope is designed.

In addition, Chajnantor's wide plateau offers ample space for the construction of the antenna array, which is spread out and linked together over distances of more than 10 miles (16 km).

"The ALMA antennae must withstand the harsh conditions at Chajnantor with strong winds, cold temperatures and a thin atmosphere with half as much oxygen as at sea level. This forbidding environment also poses challenges for the workers building ALMA," said de Graauw.

Each antenna weighs about 100 tons and can be moved to different positions to reconfigure the ALMA telescope.

Linked Hawaiian telescopes catch a powerful explosion.

This image shows the two Keck 10-meter (33 feet) telescopes. NASA/JPL

January 30, 2008

Provided by the Jet Propulsion Laboratory

First results from a new NASA-funded scientific instrument at the W. M. Keck Observatory at Mauna Kea, Hawaii, are helping scientists overturn long-standing assumptions about powerful explosions called novae and have produced specific information about one nearby nova.

This sophisticated new system, called the Keck Interferometer, combines the observing power of the two 10-meter (33 feet) Keck telescopes into a single mega-telescope. Using the interferometer's "nulling" mode, data were taken by the Keck Interferometer team on a nearby nova called RS Ophiuchi.

In "nulling" mode, the Keck Interferometer suppresses the blinding light of a star so researchers can study the surrounding environment. The instrument helps them observe very faint objects near bright sources and produces 10 times more resolving power than a single Keck telescope working alone. It is the only instrument of its kind in operation.

The nulling mode was developed to search for dust regions around nearby stars, where planets might be forming, but the bright starlight poses a great challenge. "Because a star is so much brighter than the dust, something has to block the light, which is what the nuller does," says Rachel L. Akeson, Keck Interferometer project scientist at the California Institute of Technology's Michelson Science Center. "This technique turns out to be useful for lots of other kinds of objects, including this one, where dust is near a star that just went nova."

The star in the constellation Ophiuchus went nova at the perfect time for the team, on February 12, 2006. "We were extremely lucky, because we had astronomers in place at two mountain-top interferometers, Keck in Hawaii and Infrared Optical Telescope Array in Arizona. Within minutes of hearing about the discovery of the nova, we alerted both teams to start observing it that night," says Wes Traub, a senior research scientist at NASA's Jet Propulsion Laboratory.

The nova system, known as RS Oph consists of a white dwarf and a red giant. The red giant is gradually shedding its massive gaseous outer layers, and the white dwarf is sweeping up much of this wind, growing in mass over time. As the matter builds up on the white dwarf's surface, it eventually reaches a critical temperature that ignites a thermonuclear explosion that causes the system to brighten 600-fold. RS Oph was previously observed blowing its stack in 1898, 1933, 1958, 1967 and 1985, so astronomers were eagerly anticipating the 2006 eruption.

About 3 days after the nova was detected, the group observed the explosion with the Keck nuller. They set the instrument to cancel the nova's light, allowing them to see the much fainter surrounding material, and then the extremely bright blast zone.

The instrument's versatility was key to a surprising discovery. The nuller saw no dust in the bright zone, presumably because the nova's blast wave vaporized dust particles. But farther from the white dwarf, at distances starting around 20 times the Earth-Sun distance, the nuller recorded the spectral chemical signature of silicate dust. The blast wave had not yet reached this zone, so the dust must have pre-dated the explosion.

"This flies in the face of what we expected. Astronomers had previously thought that nova explosions actually create dust," says Richard Barry of NASA's Goddard Space Flight Center, lead author of the paper on the observations. The team thinks the dust is created as the white dwarf plows through the red giant's wind, creating a pinwheel pattern of higher-density regions that is reminiscent of galaxy spiral arms. Inside these arms, atoms become cool enough and dense enough to allow atoms to stick together to form dust particles. The nova's blast wave has since destroyed RS Oph's pinwheel pattern, but it should re-form over the next few years, and future observations by NASA's Spitzer Space Telescope could see it. Barry is also coauthor of a paper based on Spitzer observations of RS Oph.

Most studies of RS Oph have relied on spectroscopic models, which have not been able to distinguish various nova components with as much detail as the interferometer. The Keck nuller measured one component of the RS Oph system to an accuracy of just 4 milliarcseconds, or about the size of a basketball seen 7,500 miles away.