• Graduate student Susan Kern (left) and Erica McEvoy, a sophomore in physics, discuss data obtained from the Magellan telescope.

    Photo / Donna Coveney

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MIT catches MagIC from telescopes


The combination of optimized scheduling and a highly efficient, instantly accessible camera designed and constructed by MIT is allowing the twin Magellan telescopes at Chile's Las Campanas Observatory to pursue science programs not possible or practical elsewhere.

Now that one of the two powerful new telescopes is operational, MIT involvement in the project is ramping up -- including that of undergraduate and graduate students -- and results are starting to come in.

The clear, dark skies of the Chilean Andes, which provide a southern-hemisphere view of the center of our galaxy and our nearest neighboring galaxies, allow studies deemed impossible a few years ago.

Such studies include optical follow-up of gamma ray burst sources, monitoring light from gravitationally lensed quasars, occultations (light blockages) of stars by solar system bodies, high-precision photometry of microlensing events in the Magellanic clouds, physical studies of recently discovered near-Earth asteroids, optical follow-up of supernovae in distant galaxies and exploration of the Kuiper Belt of small bodies orbiting the sun beyond Neptune.

The Observatories of the Carnegie Institution of Washington (OCIW), which operates the site, is the lead partner in the project. MIT is a 10 percent partner; other partners include Harvard at 20 percent and the Universities of Michigan and Arizona at 10 percent each.

Each partner in the Magellan project has its own scientific agenda for the new telescopes. The project is providing direct training in astronomical instrumentation for MIT students from the undergraduate through the post-doctoral level, said James L. Elliot, professor of physics and of earth, atmospheric and planetary sciences (EAPS) and director of the Wallace Astrophysical Observatory.

One MIT undergraduate and five graduate students are working on data generated by Magellan. More will be added as additional data come back, Professor Elliot said. When the two telescopes are functional by 2003, MIT is expected to be allotted 65 nights a year.

CAPITALIZING ON MagIC

One of the twin 50-foot-high, 150-ton telescopes saw its first stars in July 2000. MIT's first run occurred March 22-25, with the next scheduled for June 11-14.

The powerful telescopes, which have 22-foot diameter mirrors that are a radical departure from the conventional solid-glass mirrors used in the past, are honeycombed on the inside and made out of Pyrex glass that is melted, molded and spun into shape in a specially designed rotating oven. The massive mirrors are so heavy that gravity bends them out of shape. The MIT team has come up with a method to check on the mirror and realign it when necessary.

"Other telescopes do this intermittently. We do it all the time," Professor Elliot said. "This increases the efficiency of our work."

Users of the telescopes "see fantastic conditions maintained through the night. Everyone who has gone down there says they have never seen anything like this," said Paul L. Schechter, the William A.M. Burden Professor of Astrophysics at MIT and a member of the Magellan research team.

MIT staff from the EAPS and physics departments, as well as from the Center for Space Research, developed and built MagIC (Magellan Instant Camera), one of the main instruments on the telescopes. MagIC allows regular observations on a wide variety of time scales and permits rapid response to time-critical or transient phenomena such as the identification of gamma-ray burst sources. Professor Elliot is principal investigator for MagIC, which was built in collaboration with Harvard's Center for Astrophysics.

Thanks to MagIC, the observatory is able to establish a flexible scheduling system, unlike most observatories that assign telescope time only in full night allocations.

In particular, programs that call for uniform, frequent measurements of relatively short duration are a unique capability that can be capitalized on by MagIC on Magellan.

Programs now in progress or planned by MIT astronomers and their Magellan partners to take advantage of MagIC include:

Optical follow-up of gamma ray burst sources. Since the first gamma ray burst (GRB) was spotted 25 years ago, GRBs have remained one of the most studied and least understood phenomena in modern astronomy. MagIC -- with its instant accessibility and monitoring capability -- is being used to optically identify sources immediately after burst and for longer-term photometric monitoring of the source light curve.

The High Energy Transient Explorer II project, led by senior research scientist George Ricker, is expected to provide detection of around 30 GRBs per year, with their positions known to unprecedented accuracy.

Magellan's large aperture and the expected excellent image quality may permit identification and longer term monitoring of GRBs too faint for cameras on smaller telescopes.

Monitoring the light curves of gravitationally lensed quasars. Multiple images of a distant quasar -- produced by the gravitational lensing of an intervening galaxy -- have long held the promise of giving direct distances to cosmological objects, but have only recently begun to deliver on that promise. Underlying the method is that the light paths associated with the multiple images have different lengths and therefore different light travel times. Because all relevant angles are known, a difference in path lengths is as good as a path length.

The challenge, then, is to measure the difference in travel times. Most telescopes have only one instrument accessible at any given time, and it is difficult if not impossible to get observations on a regular basis with the same instrument and setup. Also, telescopes tend to be scheduled night by night, in part because instrument changes are time-consuming. Magellan is expected to provide better images than traditional setups.

Professor Schechter is one member of the research team, which included physics graduate student Josh Winn and his research advisor, Professor Jacqueline Hewitt, reporting Magellan's first results: the discovery of a double radio source that is probably a two-image gravitational lens.

An optical spectrum of the bright component -- the object PMN J1632-0033 -- was obtained with the first Magellan telescope. It could be a binary quasar, the small separation and similarity of radio continuum spectra of the components suggest that they are lensed images of a single quasar.

Stellar occultations by solar system bodies. Stellar occultations (blockages, as in an eclipse) can probe ring systems and atmospheres in the outer solar system with spatial resolutions of a few kilometers -- about a thousand times better than the resolution of any other Earth-based method.

Stellar occultation data can be used to establish the structure of atmospheres and rings of solar system bodies at high spatial resolution.

MagIC on Magellan has the capability for recording CCD subframes at high speed, which is essential for occultation observations. Magellan's flexible scheduling will allow occultation observations to be scheduled on short notice (or when MIT schedule blocks do not cover the time of the occultation).

Major goals in these areas are to extend the kinematic ring models for Uranus and Saturn, to study asymmetry in particle size distributions in "clumpy" rings such as Saturn's F ring and Uranus's lambda ring, and to continue investigating the upper atmospheres of Uranus, Jupiter, Titan and Saturn.

Physical studies of near-Earth objects (NEOs). There are several successful survey programs regularly discovering a growing number of near-Earth objects, such as the LINEAR program at MIT's Lincoln Labs. These programs discover new objects but they don't provide any additional physical information about them. The difficulty with NEOs is that they are usually discovered when very close to the Earth and at their brightest, but are moving swiftly away and getting progressively fainter.

The combination of large aperture and responsive scheduling will enable MagIC to help carry out a systematic photometric study of NEOs as they are discovered. It is particularly important to identify composition for potentially Earth-threatening NEOs, since high-density nickel-iron bodies pose the greatest danger.

Kuiper Belt objects and centaurs. The Kuiper Belt beyond Neptune contains around 70,000 objects larger than 100 km in diameter. Kuiper Belt objects are well-preserved fossil remnants from the planetary formation epoch. Studying this region and its objects may shed light on the origin and evolution of outer solar system bodies.

Fewer than 100 Kuiper Belt objects are known, and much more observational work is needed to understand their dynamical and physical properties.MagIC is ideal for documenting additional Kuiper Belt objects because recovery observations must be accomplished soon after the discoveries or the objects will be lost.

Supernovae studies. Type 1a su-pernovae are finally proving their usefulness as standard "candles" at cosmological distances. MagIC, with its instant accessibility over relatively long windows of time and the large aperture of Magellan, is ideal for such measurements.

Massive compact halo objects. Gravitational lensing occurs when objects such as clusters of galaxies distort the light coming from a particular source such as a star. A massive compact halo object (MACHOs) could act as a gravitational lens by focusing the light from a source, making it seem brighter for a while. MACHOs, which could be very dim stars, are candidates for the dark matter that researchers are seeking.

Observations of the gravitational lensing of stars in our own galaxy and in the Magellanic clouds have produced exciting and provocative results. The most straightforward interpretation, but also the most controversial, is that perhaps 50 percent of the galaxy's dark halo consists of objects with about half the mass of our sun.

A version of this article appeared in MIT Tech Talk on May 16, 2001.


Topics: Space, astronomy and planetary science

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