Posted on by Fraser Cain

Puzzling Jets Seen Blasting Out from a Nebula

Image credit: ESA

Astronomers from the European Space Agency have uncovered a bizarre mystery. They?ve found strange jets emerging from a planetary nebula called Henize 3-1475. Even more unusual is the shape of the jets, which curve back on opposite sides like water coming from a rotating garden sprinkler. Their theory is that a large star at the centre of the nebula is emanating the jets as it slowly turns, once every 1,500 years. Furthermore, the flow isn?t smooth, it?s all bubbled and knotted, leading the astronomers to believe new gas blasts out every 100 years or so.

There are many mysterious objects seen in the night sky which are not really well understood. For example, astronomers are puzzled by the ‘jets’ emerging from planetary nebulae. However, the S-shaped jet from Henize 3-1475 is the most perplexing of all.

‘Jets’ are long outflows of fast-moving gas found near many objects in the Universe, such as around young stars, or coming from black holes, neutron stars, and planetary nebulae, for example. The NASA/ESA Hubble Space Telescope has imaged the young planetary nebula Henize 3-1475 and its bizarre jet. Astronomers have nicknamed it the ‘Garden-sprinkler’ Nebula.

The origin of jets in the Universe is unclear, but they appear to originate in small regions of space where even Hubble’s sharp vision cannot penetrate. To produce a jet, you require some sort of nozzle mechanism. So far, these theoretical ‘nozzles’ remain hidden by dust that obscures our view of the centres of planetary nebulae.

Despite decades of intense effort, there is no single example of a jet whose origin is clearly understood. The curious S-shape and extreme high speed of its gaseous outflow gives Henize 3-1475 a special place in the study of planetary nebulae.

Henize 3-1475 is located in the constellation of Sagittarius around 18 000 light-years away from us. The central star is more than 12 000 times as luminous as our Sun and weighs three to five times as much. With a velocity of around 4 million kilometres per hour, the jets are the fastest ever discovered. Scientists are also intrigued by the converging, funnel-shaped structures that connect the innermost ‘knots’ and the core region.

A group of international astronomers led by Angels Riera from Universitat Polit?cnica de Catalunya, Barcelona, Spain, have combined observations from Hubble’s Wide Field and Planetary Camera 2, the Space Telescope Imaging Spectrograph and ground-based telescopes. Their work suggests that the nebula’s S-shape and hypervelocity outflow is created by a central source that ejects streams of gas in opposite directions and precesses once every 1500 years. It is like an enormous, slowly rotating garden sprinkler.

The flow is not smooth, but rather episodic with an interval of about 100 years, creating clumps of gas moving away at velocities up to 4 million kilometres per hour. The reason for these intermittent ejections of gas is not known. It may be due to either cyclic magnetic processes in the central star (similar to the Sun’s 22-year magnetic cycle), or to interactions with a companion star.

Original Source: ESA News Release

Posted on by Fraser Cain

New Site Design

I’ve been frustrated with the previous design of Universe Today for the better part of a year now, so I finally got some time together and redesigned the site from top to bottom. While I was at it, I also took better advantage of the publishing system I’m using (Article Manager from interactivetools.com) to tie in links to other resources on the site.

I also changed my webhost. My previously fabulous webhost (Communitech) was bought by another service provider whose technical support wasn’t nearly as good (that’s me putting it delicately). So, I switched to a new provider called Blue Virtual. It’s way faster, cheaper, and has a bunch of new software that I’m going to be taking advantage of.

Instead of majordomo, my new server uses a service called Mailman, which seems to be 100x better. It’s got a handy web interface so you can all manage your subscribe/unsubscribe stuff yourself.

So, thanks for your patience, please give me any feedback you can ([email protected]): either on the design or any problems you find with the new site (I’m still fixing older articles so they work in the new format, some of their links will be broken).

Take care,

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Foam Does Seem to Be the Culprit in the Columbia Disaster

Investigators said today that they believe chunks of foam have torn off shuttle fuel tanks in the past, and that this is still the mostly likely cause of the destruction of Columbia. By analyzing launch videos, the investigators found instances in six previous flights where foam peeled off the tanks and struck the shuttle. The group?s final report is expected to be delivered later this summer, and is expected to include recommendations for NASA?s management practices, safety programs and culture.

Posted on by Fraser Cain

Countdown for Mars Express Begins

Image credit: ESA

Controllers at the European Space Agency officially began the countdown clock for the launch of the Mars Express spacecraft today. If everything goes according to plan, the spacecraft will launch from the Baikonur cosmodrome in Kazakhstan on June 2, and it will arrive at Mars around December 25th. On board the spacecraft is the Beagle 2 lander, which will search for signs of past and present life on the surface of Mars.

On 2 June 2003, the first European mission to Mars will be launched. It will also be the first fully European mission to any planet. Mars Express has been designed to perform the most thorough exploration ever of the Red Planet.

Mars Express has the ambitious aim of not only searching for water, but also understanding the ‘behaviour’ of the planet as a whole. But maybe the most ambitious aim of all – Mars Express is the only mission in more than 25 years that dares to search for life.

Mars has always fascinated human beings. No other planet has been visited so many times by spacecraft. It has not been easy to unveil its secrets. Martian mysteries seem to have increased in quantity and complexity with every mission. When the first spacecraft were sent – the Mariner series in 1960s – the public was expecting an Earth ?twin?, a green, inhabited planet full of oceans. Mariner shattered this dream by showing a barren surface. This was followed by the Viking probes which searched for life unsuccessfully in 1976. Mars appeared dry, cold and uninhabited: the Earth?s opposite.

Now, two decades later, modern spacecraft have changed that view, but they have also returned more questions. Current data show that Mars was probably much warmer in the past. Scientists now think that Mars had oceans, so it could have been a suitable place for life in the past.

Cracks on Mars suggest the presence of water
“We do not know what happened to the planet in the past. Which process turned Mars into the dry, cold world we see today?” says Agustin Chicarro, ESA’s Mars Express project scientist. “With Mars Express, we will find out. Above all, we aim to obtain a complete global view of the planet – its history, its geology, how it has evolved. Real planetology!”

Mars Express will reach the Red Planet by the end of December 2003, after a trip of just over six months. Six days before injection into its final orbit, Mars Express will eject the lander, Beagle 2, named after the ship on which Charles Darwin found inspiration to formulate his theory of evolution. The Mars Express orbiter will observe the planet and its atmosphere from a near-polar orbit, and will remain in operation for at least a whole Martian year (687 Earth days). Beagle 2 will land in an equatorial region that was probably flooded in the past, and where traces of life may have been preserved.

The Mars Express orbiter carries seven advanced experiments, in addition to the Beagle 2 lander. The orbiter’s instruments have been built by group of scientific institutes from all over Europe, plus Russia, the United States, Japan and China. These instruments are a subsurface sounding radar; a high-resolution camera, several surface and atmospheric spectrometers, a plasma analyzer and a radio science experiment.

The high-resolution camera will image the entire planet in full colour, in 3D, at a resolution of up to 2 metres in selected areas. One of the spectrometers will map the mineral composition of the surface with great accuracy.

The missing water
Data from some of the instruments will be key to finding out what happened with the water which was apparently so abundant in the past. For instance, the radar altimeter will search for subsurface water and ice, down to a depth of a few kilometres. Scientists expect to find a layer of ice or permafrost, and to measure its thickness.

Other observations with the spectrometers will determine the amount of water remaining in the atmosphere. They will also tell whether there is a still a full ‘water cycle’ on Mars, for example how water is deposited in the poles and how it evaporates, depending on the seasons.

“These data will determine how much water there is left. We have clear evidence for the presence of water in the past, we have seen dry river beds and sedimentary layers, and there is also evidence for water on present-day Mars. But we do not know how much water there is. Mars Express will tell us,” says Chicarro.

The search for life
The instruments on board Beagle 2 will investigate the geology and the climate of the landing site. But, above all, it will look for signs of life.

Contrary to the Viking missions, Mars Express will search for evidence for both present and past life. Scientists are now more aware that a few biological experiments are not enough to search for life – they will combine many different types of tests to help discard contradictory results.

To ‘sniff’ out direct evidence of past or present biological activity, Beagle 2’s ‘nose’ is a gas analysis package. This will determine whether carbonate minerals, if they exist on Mars, have been involved in biological processes. Beagle?s nose will also detect gases such as methane, which scientists believe can only be produced by living organisms.

Beagle 2 will also be able to collect samples from below the surface, whether under large boulders or within the interiors of rocks – places that the life-killing ultraviolet radiation from the Sun cannot reach. These samples will be collected with a probe called the ‘mole’, which is able to crawl short distances across the surface, at about 1 centimetre every six seconds, and to dig down to 2 metres deep.

Mars Express will add substantial information to the international effort to explore Mars. “Mars Express is crucial for providing the framework within which all further Mars observations will be understood,” says Chicarro.

The Mars Express spacecraft is now in Baikonur, Kazakhstan, being prepared for its launch in early June 2003.

Original Source: ESA News Release

Posted on by Fraser Cain

Newly Discovered Star Could Be the Third Closest

Image credit: NASA

NASA astronomers have discovered what they believe could be the third closest star to our own Sun. The star, now called SO25300.5+165258, is a faint red star estimated to be about 7.8 light years away in the constellation of Aries. This is just beyond Alpha Centauri (which is actually a group of three stars) and Bernard?s Star. This new star hasn?t been discovered until now because it only has 7% of the mass of our own Sun, and is 300,000 times fainter.

The local celestial neighborhood just got more crowded with a discovery of a star that may be the third closest to the Sun. The star, “SO25300.5+165258,” is a faint red dwarf star estimated to be about 7.8 light-years from Earth in the direction of the constellation Aries.

“Our new stellar neighbor is a pleasant surprise, since we weren’t looking for it,” said Dr. Bonnard Teegarden, an astrophysicist at NASA’s Goddard Space Flight Center, Greenbelt, Md. Teegarden is lead author of a paper announcing the discovery to be published by the Astrophysical Journal. This work has been done in close collaboration with Dr. Steven Pravdo of NASA’s Jet Propulsion Laboratory (JPL).

If its distance estimate is confirmed, the newfound star will be the Sun’s third-closest stellar neighbor, slightly farther than the Alpha Centauri system, actually a group of three stars a bit more than four light-years away, and Barnard’s star, about six light-years away. One light-year is almost six trillion miles, or nearly 9.5 trillion kilometers.

The new star has only about seven percent of the mass of the Sun, and it is 300,000 times fainter. The star’s feeble glow is the reason why it has not been seen until now, despite being relatively close.

“We discovered this star in September 2002 while searching for white dwarf stars in an unrelated program,” said Teegarden. The team was looking for white dwarf stars that move rapidly across the sky. Celestial objects with apparent rapid motion are called High Proper Motion (HPM) objects. A HPM object can be discovered in successive images of an area of sky because it noticeably shifts its position while its surroundings remain fixed. Since either a distant star moving quickly or a nearby star moving slower can exhibit the same HPM, astronomers must use other measurements to determine its distance from Earth.

During its star search, the team used the SkyMorph database for the Near Earth Asteroid Tracking (NEAT) program. NEAT is a NASA program, run by the Jet Propulsion Laboratory (JPL), Pasadena, Calif., to search for asteroids that might be on a collision course for Earth. SkyMorph was separately supported by NASA’s Applied Information Systems Research Program. Like HPM stars, asteroids reveal themselves when they shift their position against background stars in successive images. Automated telescopes scan the sky, accumulating thousands of images for the NEAT program, which have been incorporated into SkyMorph, a web-accessible database, for use in other types of astronomical research.

Once the star revealed itself in the NEAT images, the team found other images of the same patch of sky to establish a rough distance estimate by a technique called trigonometric parallax. This technique is used to calculate distances to relatively close stars. As the Earth progresses in its orbit around the Sun, the position of a nearby star will appear to shift compared to background stars much farther away — the larger the shift, the closer the star.

The team refined their initial distance estimate with another technique called photometric parallax. They used the 3.5-meter Astrophysical Research Consortium telescope at the Apache Point observatory, Sunspot, N.M., to observe the star and separate its light into its component colors for analysis. This allowed the team to determine what kind of star it is. The analysis indicates it’s similar to a red dwarf star (spectral type M6.5) that’s shining by fusing hydrogen atoms in its core, like our Sun (called a main sequence star).

Once the type of star is known, its true brightness, called intrinsic luminosity, can be determined. Since all light-emitting objects appear dimmer as distance from them increases, the team compared how bright the new star appeared in their images to its intrinsic luminosity to improve their distance estimate.

Although the star resembles a M6.5 red dwarf, it actually appears three times dimmer than expected for this kind of star at the initial distance estimate of 7.8 light-years. The star could therefore really be farther than the rough trigonometric distance indicates; or, if the initial estimate holds, it could have unusual properties that make it shine less brightly than typical M6.5 red dwarfs. A more precise measurement of the new star’s position to establish an improved trigonometric parallax distance is underway at the U.S. Naval Observatory. This will confirm or refute its status as one of our closest neighbors by late this year. Either way, we might get even more company soon: “Since the NEAT survey only covered a band of the sky (+/- 25 degrees in declination), it is entirely possible that other faint nearby objects remain to be discovered,” said Teegarden.

Original Source: NASA News Release

Posted on by Fraser Cain

Hubble Sees Springtime on Neptune

Image credit: Hubble

New photos of Neptune taken by the Hubble Space Telescope seem to indicate that the planet is entering its version of Spring. By comparing photos taken in 1996, astronomers believe that bands across the planet are getting wider and brighter, which seems to be a response to increased sunlight. Like the Earth, Neptune is believed to have four seasons, but since the planet takes 165 years to orbit the Sun, they last decades, not months.

Springtime is blooming on Neptune! This might sound like an oxymoron because Neptune is the farthest and coldest of the major planets. But NASA Hubble Space Telescope observations are revealing an increase in Neptune’s brightness in the southern hemisphere, which is considered a harbinger of seasonal change, say astronomers.

Observations of Neptune made over six years by a group of scientists from the University of Wisconsin-Madison and NASA’s Jet Propulsion Laboratory (JPL) show a distinct increase in the amount and brightness of the banded cloud features located mostly in the planet’s southern hemisphere.

“Neptune’s cloud bands have been getting wider and brighter,” says Lawrence A. Sromovsky, a senior scientist at University of Wisconsin- Madison’s Space Science and Engineering Center and a leading authority on Neptune’s atmosphere. “This change seems to be a response to seasonal variations in sunlight, like the seasonal changes we see on Earth.”

The findings are reported in the current issue (May, 2003) of Icarus, a leading planetary science journal.

Neptune, the eighth planet from the Sun, is known for its weird and violent weather. It has massive storm systems and ferocious winds that sometimes gust to 900 miles per hour, but the new Hubble observations are the first to suggest that the planet undergoes a change of seasons.

Using Hubble, the Wisconsin team made three sets of observations of Neptune. In 1996, 1998, and 2002, observations of a full rotation of the planet were obtained. The images showed progressively brighter bands of clouds encircling the planet’s southern hemisphere. The findings are consistent with observations made by G.W. Lockwood at the Lowell Observatory, which show that Neptune has been gradually getting brighter since 1980.

Neptune’s near-infrared brightness is much more sensitive to high altitude clouds than its visible brightness. The recent trend of increasing cloud activity on Neptune has been qualitatively confirmed at near-infrared wavelengths with Keck Telescope observations from July 2000 to June 2001 by H. Hammel and co-workers. Near-infrared observations at NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii are planned for this summer to further characterize changes in the high-altitude cloud structure.

“In the 2002 images, Neptune is clearly brighter than it was in 1996 and 1998,” Sromovsky says, “and is dramatically brighter at near infrared wavelengths. The greatly increased cloud activity in 2002 continues a trend first noticed in 1998.”

Like the Earth, Neptune would have four seasons: “Each hemisphere would have a warm summer and a cold winter, with spring and fall being transitional seasons, which may or may not have specific dynamical features,” the Wisconsin scientist explains.

Unlike the Earth, however, the seasons of Neptune last for decades, not months. A single season on the planet, which takes almost 165 years to orbit the Sun, can last more than 40 years. If what scientists are observing is truly seasonal change, the planet will continue to brighten for another 20 years.

Also like Earth, Neptune spins on an axis that is tilted at an angle toward the Sun. The tilt of the Earth, at a 23.5-degree inclination, is the phenomenon responsible for the change of seasons. As the Earth orbits the Sun over the course of a year, the planet is exposed to patterns of solar radiation that mark the seasons. Similarly, Neptune is inclined at a 29-degree angle and the northern and southern hemispheres alternate in their positions relative to the Sun.

What is remarkable, according to Sromovsky, is that Neptune exhibits any evidence of seasonal change at all, given that the Sun, as viewed from the planet, is 900 times dimmer than it is from Earth. The amount of solar energy a hemisphere receives at a given time is what determines the season.

“When the Sun deposits heat energy into an atmosphere, it forces a response. We would expect heating in the hemisphere getting the most sunlight. This in turn could force rising motions, condensation and increased cloud cover,” Sromovsky notes.

Bolstering the idea that the Hubble images are revealing a real increase in Neptune’s cloud cover consistent with seasonal change is the apparent absence of change in the planet’s low latitudes near its equator.

“Neptune’s nearly constant brightness at low latitudes gives us confidence that what we are seeing is indeed seasonal change as those changes would be minimal near the equator and most evident at high latitudes where the seasons tend to be more pronounced.”

Despite the new insights into Neptune, the planet remains an enigma, says Sromovsky. While Neptune has an internal heat source that may also contribute to the planet’s apparent seasonal variations and blustery weather, when that is combined with the amount of solar radiation the planet receives, the total is so small that it is hard to understand the dynamic nature of Neptune’s atmosphere.

There seems, Sromovsky says, to be a “trivial amount of energy available to run the machine that is Neptune’s atmosphere. It must be a well-lubricated machine that can create a lot of weather with very little friction.”

In addition to Sromovsky, authors of the Icarus paper include Patrick M. Fry and Sanjay S. Limaye, both of University of Wisconsin-Madison’s Space Science and Engineering Center; and Kevin H. Baines of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

Original Source: Hubble News Release

Posted on by Fraser Cain

Lunar Eclipse Puts on a Show

People with clear skies Thursday night were treated to a total lunar eclipse. The eclipse began at 0203 (10:03pm EDT) and ended approximately three hours later. The weather wasn?t entirely cooperating; however, many astrocameras poised around North America and Europe ended up being rained out. The next lunar eclipse will be on November 9, 2003, and will be visible from roughly the same parts of the Earth ? only this time it?ll be brighter.

Posted on by Fraser Cain

NASA Orders Prototype Martian Airplane

After a series of successful tests with a half-sized prototype, NASA has ordered a full-scale prototype of the Ares (Aerial Regional-scale Environmental Survey of Mars), aircraft, designed to help explore the surface of Mars. If all goes well, the aircraft will be launched to Mars in 2007. When it arrives in 2008, it will enter the atmosphere, deploy its wings and fly 850 kilometres along a route that takes it past the terrain that NASA scientists want to observe.

Posted on by Fraser Cain

Lunar Eclipse Tonight

The Americas and part of Europe will be treated to a total eclipse of the moon on Thursday night ? the first one visible here in three years. A lunar eclipse occurs when the Earth?s shadow falls on the Moon, turning it a deep red colour. Unlike solar eclipses, lunar eclipses are completely safe to watch with the naked eye; and it looks even better with a pair of binoculars or small telescope. The eclipse begins at 0203 GMT Friday (10:03pm EDT Thursday), and reaches the maximum at 0340 GMT (11:40pm EDT). The eclipse will be best viewed from the Eastern Coast of the United States.

Posted on by Fraser Cain

Paranal Observatory Tests New Adapative Optics

Image credit: ESO

A team of engineers from the European Southern Observatory recently tested out a new adaptive optics facility on the Very Large Telescope (VLT) at the Paranal Observatory in Chile. This technology adapts images taken by the telescope to remove the distortion caused by the Earth?s atmosphere ? as if they were seen from space. The next step will be to connect similar systems to all the telescopes at the facility and then hook them up in a large array. This should allow the observatory to resolve objects 100 times fainter than today.

On April 18, 2003, a team of engineers from ESO celebrated the successful accomplishment of “First Light” for the MACAO-VLTI Adaptive Optics facility on the Very Large Telescope (VLT) at the Paranal Observatory (Chile). This is the second Adaptive Optics (AO) system put into operation at this observatory, following the NACO facility (ESO PR 25/01).

The achievable image sharpness of a ground-based telescope is normally limited by the effect of atmospheric turbulence. However, with Adaptive Optics (AO) techniques, this major drawback can be overcome so that the telescope produces images that are as sharp as theoretically possible, i.e., as if they were taken from space.

The acronym “MACAO” stands for “Multi Application Curvature Adaptive Optics” which refers to the particular way optical corrections are made which “eliminate” the blurring effect of atmospheric turbulence.

The MACAO-VLTI facility was developed at ESO. It is a highly complex system of which four, one for each 8.2-m VLT Unit Telescope, will be installed below the telescopes (in the Coud? rooms). These systems correct the distortions of the light beams from the large telescopes (induced by the atmospheric turbulence) before they are directed towards the common focus at the VLT Interferometer (VLTI).

The installation of the four MACAO-VLTI units of which the first one is now in place, will amount to nothing less than a revolution in VLT interferometry. An enormous gain in efficiency will result, because of the associated 100-fold gain in sensitivity of the VLTI.

Put in simple words, with MACAO-VLTI it will become possible to observe celestial objects 100 times fainter than now. Soon the astronomers will be thus able to obtain interference fringes with the VLTI (ESO PR 23/01) of a large number of objects hitherto out of reach with this powerful observing technique, e.g. external galaxies. The ensuing high-resolution images and spectra will open entirely new perspectives in extragalactic research and also in the studies of many faint objects in our own galaxy, the Milky Way.

During the present period, the first of the four MACAO-VLTI facilties was installed, integrated and tested by means of a series of observations. For these tests, an infrared camera was specially developed which allowed a detailed evaluation of the performance. It also provided some first, spectacular views of various celestial objects, some of which are shown here.

MACAO – the Multi Application Curvature Adaptive Optics facility
Adaptive Optics (AO) systems work by means of a computer-controlled deformable mirror (DM) that counteracts the image distortion induced by atmospheric turbulence. It is based on real-time optical corrections computed from image data obtained by a “wavefront sensor” (a special camera) at very high speed, many hundreds of times each second.

The ESO Multi Application Curvature Adaptive Optics (MACAO) system uses a 60-element bimorph deformable mirror (DM) and a 60-element curvature wavefront sensor, with a “heartbeat” of 350 Hz (times per second). With this high spatial and temporal correcting power, MACAO is able to nearly restore the theoretically possible (“diffraction-limited”) image quality of an 8.2-m VLT Unit Telescope in the near-infrared region of the spectrum, at a wavelength of about 2 ?m. The resulting image resolution (sharpness) of the order of 60 milli-arcsec is an improvement by more than a factor of 10 as compared to standard seeing-limited observations. Without the benefit of the AO technique, such image sharpness could only be obtained if the telescope were placed above the Earth’s atmosphere.

The technical development of MACAO-VLTI in its present form was begun in 1999 and with project reviews at 6 months’ intervals, the project quickly reached cruising speed. The effective design is the result of a very fruitful collaboration between the AO department at ESO and European industry which contributed with the diligent fabrication of numerous high-tech components, including the bimorph DM with 60 actuators, a fast-reaction tip-tilt mount and many others. The assembly, tests and performance-tuning of this complex real-time system was assumed by ESO-Garching staff.

Installation at Paranal
The first crates of the 60+ cubic-meter shipment with MACAO components arrived at the Paranal Observatory on March 12, 2003. Shortly thereafter, ESO engineers and technicians began the painstaking assembly of this complex instrument, below the VLT 8.2-m KUEYEN telescope (formerly UT2).

They followed a carefully planned scheme, involving installation of the electronics, water cooling systems, mechanical and optical components. At the end, they performed the demanding optical alignment, delivering a fully assembled instrument one week before the planned first test observations. This extra week provided a very welcome and useful opportunity to perform a multitude of tests and calibrations in preparation of the actual observations.
AO to the service of Interferometry

The VLT Interferometer (VLTI) combines starlight captured by two or more 8.2- VLT Unit Telescopes (later also from four moveable1.8-m Auxiliary Telescopes) and allows to vastly increase the image resolution. The light beams from the telescopes are brought together “in phase” (coherently). Starting out at the primary mirrors, they undergo numerous reflections along their different paths over total distances of several hundred meters before they reach the interferometric Laboratory where they are combined to within a fraction of a wavelength, i.e., within nanometers!

The gain by the interferometric technique is enormous – combining the light beams from two telescopes separated by 100 metres allows observation of details which could otherwise only be resolved by a single telescope with a diameter of 100 metres. Sophisticated data reduction is necessary to interpret interferometric measurements and to deduce important physical parameters of the observed objects like the diameters of stars, etc., cf. ESO PR 22/02.

The VLTI measures the degree of coherence of the combined beams as expressed by the contrast of the observed interferometric fringe pattern. The higher the degree of coherence between the individual beams, the stronger is the measured signal. By removing wavefront aberrations introduced by atmospheric turbulence, the MACAO-VLTI systems enormously increase the efficiency of combining the individual telescope beams.

In the interferometric measurement process, the starlight must be injected into optical fibers which are extremely small in order to accomplish their function; only 6 ?m (0.006 mm) in diameter. Without the “refocussing” action of MACAO, only a tiny fraction of the starlight captured by the telescopes can be injected into the fibers and the VLTI would not be working at the peak of efficiency for which it has been designed.

MACAO-VLTI will now allow a gain of a factor 100 in the injected light flux – this will be tested in detail when two VLT Unit Telescopes, both equipped with MACAO-VLTI’s, work together. However, the very good performance actually achieved with the first system makes the engineers very confident that a gain of this order will indeed be reached. This ultimate test will be performed as soon as the second MACAO-VLTI system has been installed later this year.
MACAO-VLTI First Light

After one month of installation work and following tests by means of an artificial light source installed in the Nasmyth focus of KUEYEN, MACAO-VLTI had “First Light” on April 18 when it received “real” light from several astronomical obejcts.

During the preceding performance tests to measure the image improvement (sharpness, light energy concentration) in near-infrared spectral bands at 1.2, 1.6 and 2.2 ?m, MACAO-VLTI was checked by means of a custom-made Infrared Test Camera developed for this purpose by ESO. This intermediate test was required to ensure the proper functioning of MACAO before it is used to feed a corrected beam of light into the VLTI.

After only a few nights of testing and optimizing of the various functions and operational parameters, MACAO-VLTI was ready to be used for astronomical observations. The images below were taken under average seeing conditions and illustrate the improvement of the image quality when using MACAO-VLTI.

MACAO-VLTI – First Images
Here are some of the first images obtained with the test camera at the first MACAO-VLTI system, now installed at the 8.2-m VLT KUEYEN telescope.

PR Photos 12b-c/03 show the first image in the infrared K-band (wavelength 2.2 ?m) of a star (visual magnitude 10) obtained without and with image corrections by means of adaptive optics.

PR Photo 12d/03 displays one of the best images obtained with MACAO-VLTI during the early tests. It shows a Strehl ratio (measure of light concentration) that fulfills the specifications according to which MACAO-VLTI was built. This enormous improvement when using AO techniques is clearly demonstrated in PR Photo 12e/03, with the uncorrected image profile (left) hardly visible when compared to the corrected profile (right).

PR Photo 11f/03 demonstrates the correction capabilities of MACAO-VLTI when using a faint guide star. Tests using different spectral types showed that the limiting visual magnitude varies between 16 for early-type B-stars and about 18 for late-type M-stars.
Astronomical Objects seen at the Diffraction Limit

The following examples of MACAO-VLTI observations of two well-known astronomical objects were obtained in order to provisionally evaluate the research opportunities now opening with MACAO-VLTI. They may well be compared with space-based images.

The Galactic Center
The center of our own galaxy is located in the Sagittarius constellation at a distance of approximately 30,000 light-years. PR Photo 12h/03 shows a short-exposure infrared view of this region, obtained by MACAO-VLTI during the early test phase.

Recent AO observations using the NACO facility at the VLT provide compelling evidence that a supermassive black hole with 2.6 million solar masses is located at the very center, cf. ESO PR 17/02. This result, based on astrometric observations of a star orbiting the black hole and approaching it to within a distance of only 17 light-hours, would not have been possible without images of diffraction limited resolution.

Eta Carinae
Eta Carinae is one of the heaviest stars known, with a mass that probably exceeds 100 solar masses. It is about 4 million times brighter than the Sun, making it one of the most luminous stars known.

Such a massive star has a comparatively short lifetime of about 1 million years only and – measured in the cosmic timescale- Eta Carinae must have formed quite recently. This star is highly unstable and prone to violent outbursts. They are caused by the very high radiation pressure at the star’s upper layers, which blows significant portions of the matter at the “surface” into space during violent eruptions that may last several years. The last of these outbursts occurred between 1835 and 1855 and peaked in 1843. Despite its comparaticely large distance – some 7,500 to 10,000 light-years – Eta Carinae briefly became the second brightest star in the sky at that time (with an apparent magnitude -1), only surpassed by Sirius.

Frosty Leo
Frosty Leo is a magnitude 11 (post-AGB) star surrounded by an envelope of gas, dust, and large amounts of ice (hence the name). The associated nebula is of “butterfly” shape (bipolar morphology) and it is one of the best known examples of the brief transitional phase between two late evolutionary stages, asymptotic giant branch (AGB) and the subsequent planetary nebulae (PNe).

For a three-solar-mass object like this one, this phase is believed to last only a few thousand years, the wink of an eye in the life of the star. Hence, objects like this one are very rare and Frosty Leo is one of the nearest and brightest among them.

Original Source: ESO News Release