Category: Astronomy

Image credit: NASA

Scientists got the best ever ultraviolet view of the Sun using a telescope and camera launched on board a sounding rocket. The pictures will help researchers understand how the Sun’s outer atmosphere heats up to over one million degrees Celsius. The telescope was able to resolve areas in the ultraviolet spectrum as small as 240 kilometres across; three times better than any space-based observatory. The rocket trajectory only let the telescope take 21 images during its 15 minute flight.

Scientists got their closest-ever ultraviolet look at the Sun from space, thanks to a telescope and camera launched aboard a sounding rocket. The images revealed an unexpectedly high level of activity in a lower layer of the Sun’s atmosphere (chromosphere). The pictures will help researchers answer one of their most burning questions about how the Sun works: how its outer atmosphere (corona) heats up to over one million degrees Celsius (1.8 million Fahrenheit), 100 times hotter than the chromosphere.

A team of Naval Research Laboratory (NRL) scientists used the Very high Angular resolution ULtraviolet Telescope (VAULT) to take pictures of ultraviolet (UV) light (1216 ?) emitted from the upper chromosphere. Resolving areas as small as 240 kilometers (150 miles or 0.3 arcseconds) on each side, the June 14, 2002, flight captured images about three times better than the previous-best pictures from space. A few ground-based telescopes can observe the Sun in 150-kilometer (93-mile) increments, but only at visible wavelengths of light. UV and X-ray wavelength observations most directly matter to solar weather.

Since most solar weather originates as explosions of the electrified gas (plasma) in the corona, understanding the heating and magnetic activity of the coronal plasmas will lead to better predictions of solar weather events. Severe solar weather, like solar flares and coronal mass ejections, can disrupt satellites and power grids, affecting life on Earth.

The VAULT observations reveal a highly structured, dynamic upper chromosphere, with structures visible for the first time thanks to the detailed resolution. A large number of structures in the pictures change rapidly from one image to the next, 17 seconds later. Scientists previously thought these changes occurred over five minutes or more. The transience of the physical processes in this layer has significant theoretical implications, such as the fact that proposed heating mechanisms must now also be effective over relatively short time scales.

Scientists found chromospheric features in the VAULT images that match features, based on shape and spatial correlation, which they see in Transition Region And Coronal Explorer (TRACE) satellite images of the corona taken simultaneously. This comparison shows that these two layers have much higher correlation than previously thought and implies that similar physical processes likely heat each. However, theory predicts the activity in the chromosphere should be lower than what scientists observed in the VAULT emissions. “[There are] more things happening below [in the upper chromosphere] than you see in the corona,” says VAULT project scientist Angelos Vourlidas of the NRL.

VAULT also revealed unexpected structures in quiet areas of the Sun. The plasma and magnetic field bubble up like boiling water on the Sun’s visible surface (photosphere), and, like bubbles gathering and forming a ring at the edge of a pot, the field builds up in rings (network cells) in the quiet areas. VAULT captured images of smaller features and significant activity within the network cells, surprising scientists.

The telescope took 21 images in the Lyman-alpha wavelength of the electromagnetic spectrum during a six-minute-nine-second picture-taking window on its 15-minute flight. Offering the brightest solar emissions, the Lyman-alpha wavelength assured the best likelihood for pictures from the rocket and allowed for shorter exposure times and more pictures. An increase in Lyman-alpha radiation may indicate an increase in solar radiation reaching Earth.

The VAULT payload consists of a 30-centimeter (11.8-inch) Cassegrain telescope with a dedicated Lyman-alpha spectroheliograph focusing images onto a charge-coupled device (CCD) camera. The CCD, also employed in consumer digital cameras, has a photosensitivity 320 times greater than photographic film previously used. The Normal Incidence X-ray Telescope (NIXT) from the Harvard-Smithsonian Center for Astrophysics took the previous best-resolution pictures of the Sun from space in September 1989, also aboard a sounding rocket.

The scientists verified the payload performance with an engineering flight from White Sands Missile Range, N.M., May 7, 1999. The June 14, 2002, flight from White Sands was the first scientific flight of the payload. The NRL team led a campaign combining observations from satellites and ground-based instruments. Scientists plan a third launch in Summer 2004. The mission was conducted through NASA’s Sounding Rocket Program.

Original Source: NASA News Release

Image credit: Hubble/NOAO

A team of astronomers have created a model to explain how the Owl Nebula (NGC 3587) got its unique shape. They believe that the outer halo was formed when the star first lost mass and blew off its outer layer; the circular middle shell was caused by solar wind from the star blowing additional material; and then an even faster solar wind created the inner layer. Other planetary nebulae show a similar triple-shell appearance, so it’s likely they formed the same way.

Astronomers have assembled the first effective model for both the shape and evolutionary history of the Owl Nebula, the well-known planetary nebula in the constellation Ursa Major.

Named for its ghostly similarity to the face of the carnivorous bird of prey, the Owl Nebula (NGC 3587) has a complex structure consisting of three concentric shells. The aptly named nebula boasts a faint outer halo, a circular middle shell, and a roughly elliptical inner shell. The inner shell houses a bipolar cavity that forms the owl?s ?eyes,? and two areas of enhanced brightness are seen as the owl?s ?forehead? and ?beak.?

In an article published in the June 2003 Astronomical Journal, researchers from the University of Illinois at Urbana-Champaign, the Instituto de Astrofisica de Canarias in Spain, and Williams College in Williamstown, MA, present the first cohesive model for the appearance and evolution of the Owl Nebula.

Using observations made with the William Herschel Telescope in La Palma, Spain, and the 0.6-meter Burrell Schmidt telescope at Kitt Peak National Observatory, the researchers concluded that the halo of the Owl was formed when the parent star first underwent significant mass loss after the cessation of fusion in its core. The resulting instabilities then produced a stellar wind, driven by a combination of stellar pulsations and radiation pressure.

Evolution of the Owl?s parent star caused the stellar wind to intensify to a ?superwind,? driving even more gas and dust outward to form the middle shell. A subsequent faster stellar wind compressed the superwind to form the inner shell and bipolar cavity, but that wind has since ceased. The cavity is currently being back-filled with nebular material in the absence of the fast stellar wind, much as air flows back out of a balloon if you stop blowing into it.

?Different evolutionary models can produce the same structure for the nebula, but until now none has been able to also account for its motion,? says Martin A. Guerrero of the University of Illinois, the lead author of the recent study. ?There are many investigations of physical structures of planetary nebulae, but most studies only look at one piece of data and tend to ignore the bigger picture.?

Other planetary nebulae show triple-shell structure similar to the Owl Nebula and it is likely that they followed this same evolutionary path, according to co-author Karen Kwitter of Williams College. ?These nebulae form an illuminating sample to study, and the Owl Nebula is the nearest one, only about 2,000 light-years from Earth.?

Despite the name, planetary nebulae are not related to planets. Sir William Herschel gave these fascinating objects their misleading name in 1782 because, through his telescope, they resembled the appearance of Uranus and Neptune. In reality, planetary nebulae are shells of gas and dust ejected from aging stars. When the mass loss is finished, the hot core of the star is exposed, causing the ejected gas to glow.

A newly processed image of the Owl Nebula from this study is available above.

The Burrell Schmidt telescope is part of the Warner and Swasey Observatory of Case Western Reserve University, Cleveland, OH. The telescope is located at Kitt Peak National Observatory near Tucson, AZ, which is part of the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NRAO News Release

Image credit: NASA

A team of astronomers from MIT reported today that Pluto’s atmosphere is expanding, even as the planet is getting further away from the Sun on its elliptical orbit. The team made their findings by watching the dimming of a star as Pluto passed in front. Astronomers were expecting to find the opposite situation; that its atmosphere would shrink as it gets further from the Sun, but it’s similar to the Earth, where early afternoon is hotter than noon, when the Sun is at its brightest. If all goes well, NASA will launch its New Horizons mission by 2006 to reach Pluto in 2015.

Pluto?s atmosphere is expanding even as it continues on its long orbit away from the sun, a team of astronomers from MIT, Boston University, Williams College, Pomona College, Lowell Observatory and Cornell University report in the July 10 issue of Nature.

The team, led by James Elliot, professor of planetary astronomy at MIT and director of MIT?s Wallace Observatory, made this finding by watching the dimming of a star when Pluto passed in front of it on Aug. 20, 2002. The team carried out observations using eight telescopes at Mauna Kea Observatory, Haleakala, Lick Observatory, Lowell Observatory and Palomar Observatory.

Elliot said the new results seem counterintuitive, because observers assumed Pluto?s atmosphere would begin to collapse as it cooled. In fact, the temperature of Pluto?s mostly nitrogen atmosphere has increased around 1 degree Celsius since it was closest to the sun in 1989.

Elliot attributes the increase to the same lag effect that we experience on Earth?even though the sun is most intense at its highest point at noon, the hottest part of the day is around 3 p.m. Because Pluto’s year is equal to 248 Earth years, 14 years after Pluto’s closest approach to the Sun is like 1:15 p.m. on Earth. At the rate of Pluto?s orbit, it may take another 10 years to cool down and would just be beginning to cool when the NASA New Horizons mission to Pluto, scheduled to be launched in 2006, reaches it in 2015.

Pluto?s predominantly nitrogen atmosphere is in vapor pressure equilibrium with its surface ice, and can therefore undergo large changes in pressure in response to small changes in surface ice temperature. As its icy surface gets colder, it condenses into fresh white frost that reflects more of the sun?s heat and gets colder still. As space dirt and objects collect on its surface, it darkens and absorbs more heat, accelerating the warming effect. Pluto has been darkening since 1954.

?The August 2002 data have allowed us to probe much more deeply into Pluto’s atmosphere and have given us a more accurate picture of the changes that have occurred,” Elliot said.

Pluto?s orbit is much more elliptical than that of the other planets, and its rotational axis is tipped by a large angle relative to its orbit. Both factors could contribute to drastic seasonal changes.

Since 1989, for example, the sun?s position in Pluto?s sky has changed by more than the corresponding change on the Earth that causes the difference between winter and spring. Pluto’s atmospheric temperature varies between around -235 and -170 degrees Celsius, depending on the altitude above the surface.

Pluto has nitrogen ice on its surface that can evaporate into the atmosphere when it gets warmer, causing an increase in surface pressure. If the observed increase in the atmosphere also applies to the surface pressure?which is likely the case?this means that the average surface temperature of the nitrogen ice on Pluto has increased slightly more than 1 degree Celsius over the past 14 years.

STUDYING ATMOSPHERES WITH SHADOWS
Researchers study faraway objects through occultations?eclipse-like events in which a body (Pluto in this case) passes in front of a star, blocking the star?s light from view. By recording the dimming of the starlight over time, astronomers can calculate the density, pressure and temperature of Pluto?s atmosphere.

Observing two or more occultations at different times provides researchers with information about changes in the planet?s atmosphere. The structure and temperature of Pluto?s atmosphere was first determined during an occultation in 1988. Pluto?s brief pass in front of a different star on July 19 led researchers to believe that a drastic atmospheric change was under way, but it was unclear whether the atmosphere was warming or cooling.

The data resulting from this occultation, when Pluto passed in front of a star known as P131.1, led to the current results. ?This is the first time that an occultation has allowed us to probe so deeply into Pluto’s atmosphere with a large telescope, which gives a high spatial resolution of a few kilometers,? Elliot said. He hopes to use this method to study Pluto and the Kuiper Belt objects more frequently in the future.

MISSION TO PLUTO
NASA recently authorized the New Horizons Pluto-Kuiper Belt mission to start building spacecraft and ground systems. The mission will be the first to Pluto and the Kuiper Belt. Richard P. Binzel, professor of earth, atmospheric and planetary sciences (EAPS) at MIT, is co-investigator.

The New Horizons spacecraft is scheduled to launch in January 2006, swing past Jupiter for a gravity boost and scientific studies in 2007, and reach Pluto and Charon moon of Pluto as early as summer 2015. Pluto is the only planet not yet observed at close range. This mission will seek to answer questions about the surfaces, atmospheres, interiors and space environments of the solar system?s outermost planet and its moon.

In the meantime, researchers hope to use SOFIA, a 2.5-meter telescope mounted in an aircraft being built by NASA in collaboration with the German space agency, starting in 2005. SOFIA would be able to be sent to the right location around the globe to best observe occultations, providing high-quality data on a much more frequent basis than is possible using ground-based telescopes alone.

In addition to Elliot, MIT co-authors are recent physics graduate Kelly B. Clancy; graduate students Susan D. Kern and Michael J. Person; recent MIT graduate Colette V. Salyk; and aeronautics and astronautics senior Jing Jing Qu.

The Williams College collaborators included Jay M. Pasachoff, professor of astronomy; Bryce A. Babcock, staff physicist; Steven V. Souza, observatory supervisor; and undergraduate David R. Ticehurst. They used the University of Hawaii’s telescope at the 13,800-foot altitude of the Hawaiian volcano Mauna Kea and a Williams College electronic detector normally part of eclipse expeditions.

Pomona College collaborators are Alper Ates and Ben Penprase. The Boston University collaborator is Amanda Bosh. Lowell Observatory collaborators are Marc Buie, Ted Dunham, Stephen Eikenberry, Cathy Olkin, Brian W. Taylor, and Lawrence Wasserman. Boeing collaborators are Doyle Hall and Lewis Roberts.

The United Kingdom Infrared Telescope collaborator is Sandy K. Leggett. U.S. Naval Observatory collaborators are Stephen E. Levine and Ronald C. Stone. The Cornell collaborator is Dae-Sik Moon. David Osip and Joanna E. Thomas-Osip were at MIT and are now at the Carnegie Observatories. John T. Rayner is at NASA’s Infrared Telescope Facility. David Tholen is at the University of Hawaii.

This work is funded by Research Corp., the Southwest Research Institute, the National Science Foundation and NASA.

Original Source: MIT News Release

Image credit: NASA

It’s possible that the spin rate of pulsars is limited by gravitational radiation according to new data gathered by NASA’s Rossi X-ray Timing Explorer – a phenomenon predicted by Albert Einstein. Pulsars are the core remains of exploded stars, no larger than 15 kilometres across, and some rotate as fast as once/millisecond. Scientists believe that as a pulsar speeds up, it flattens out, and the distortions in its shape cause it to emanate waves of gravity which stop it from rotating so fast it flies apart.

Gravitational radiation, ripples in the fabric of space predicted by Albert Einstein, may serve as a cosmic traffic enforcer, protecting reckless pulsars from spinning too fast and blowing apart, according to a report published in the July 3 issue of Nature.

Pulsars, the fastest spinning stars in the Universe, are the core remains of exploded stars, containing the mass of our Sun compressed into a sphere about 10 miles across. Some pulsars gain speed by pulling in gas from a neighboring star, reaching spin rates of nearly one revolution per millisecond, or almost 20 percent light speed. These “millisecond” pulsars would fly apart if they gained much more speed.

Using NASA’s Rossi X-ray Timing Explorer, scientists have found a limit to how fast a pulsar spins and speculate that the cause is gravitational radiation: The faster a pulsar spins, the more gravitational radiation it might release, as its exquisite spherical shape becomes slightly deformed. This may restrain the pulsar’s rotation and save it from obliteration.

“Nature has set a speed limit for pulsar spins,” said Prof. Deepto Chakrabarty of the Massachusetts Institute of Technology, lead author on the journal article. “Just like cars speeding on a highway, the fastest-spinning pulsars could technically go twice as fast, but something stops them before they break apart. It may be gravitational radiation that prevents pulsars from destroying themselves.”

Chakrabarty’s co-authors are Drs. Edward Morgan, Michael Muno, and Duncan Galloway of MIT; Rudy Wijnands, University of St. Andrews, Scotland; Michiel van der Klis, University of Amsterdam; and Craig Markwardt, NASA Goddard Space Flight Center. Wijnands also leads a second Nature letter complementing this finding.

Gravitational waves, analogous to waves upon an ocean, are ripples in four-dimensional spacetime. These exotic waves, predicted by Einstein’s theory of relativity, are produced by massive objects in motion and have not yet been directly detected.

Created in a star explosion, a pulsar is born spinning, perhaps 30 times per second, and slows down over millions of years. Yet if the dense pulsar, with its strong gravitational potential, is in a binary system, it can pull in material from its companion star. This influx can spin up the pulsar to the millisecond range, rotating hundreds of times per second.

In some pulsars, the accumulating material on the surface occasionally is consumed in a massive thermonuclear explosion, emitting a burst of X-ray light lasting only a few seconds. In this fury lies a brief opportunity to measure the spin of otherwise faint pulsars. Scientists report in Nature that a type of flickering found in these X-ray bursts, called “burst oscillations,” serves as a direct measure of the pulsar’s spin rate. Studying the burst oscillations from 11 pulsars, they found none spinning faster than 619 times per second.

The Rossi Explorer is capable of detecting pulsars spinning as fast as 4,000 times per second. Pulsar break-up is predicted to occur at 1,000 to 3,000 revolutions per second. Yet scientists have found none that fast. >From statistical analysis of 11 pulsars, they concluded that the maximum speed seen in nature must be below 760 revolutions per second.

This observation supports the theory of a feedback mechanism involving gravitational radiation limiting pulsar speeds, proposed by Prof. Lars Bildsten of the University of California, Santa Barbara. As the pulsar picks up speed through accretion, any slight distortion in the star’s dense, half-mile-thick crust of crystalline metal will allow the pulsar to radiate gravitational waves. (Envision a spinning, oblong rugby ball in water, which would cause more ripples than a spinning, spherical basketball.) An equilibrium rotation rate is eventually reached where the angular motion shed by emitting gravitational radiation matches the angular momentum being added to the pulsar by its companion star.

Bildsten said that accreting millisecond pulsars could eventually be studied in greater detail in an entirely new way, through the direct detection of their gravitational radiation. LIGO, the Laser Interferometer Gravitational-Wave Observatory now in operation in Hanford, Washington, and in Livingston, Louisiana, will eventually be tunable to the frequency at which millisecond pulsars are expected to emit gravitational waves.

“The waves are subtle, altering spacetime and the distance between objects as far apart as the Earth and the Moon by much less than the width of an atom,” said Prof. Barry Barish of the California Institute of Technology, the LIGO director. “As such, gravitational radiation has not been directly detected yet. We hope to change that soon.”

Original Source: NASA News Release

Image credit: NASA

Astronomers have directly observed a hot disc of dust and gas surrounding a protostar using the twin W.M. Keck telescopes in Hawaii. This is the first published science observation using a technology called interferometry, which combines the light from several telescopes to act as a larger observatory – the twin 10-metre Keck telescopes act as a virtual 85 metre telescope. The observation was of DG Tau, a T-Tauri object which is so young its centre star hasn’t begun burning hydrogen; it’s surrounded by a disc of dust and gas that could form planets.

Astronomers have observed a young star ringed by a swirling disc that may spin off planets, marking the first published science observation using two linked 10-meter (33- foot) telescopes in Hawaii.

The linked telescopes at the W.M. Keck Observatory on Mauna Kea, known as the Keck Interferometer, comprise the world’s largest optical telescope system. The observation was made of DG Tau, a young star that has not yet begun to burn hydrogen in its core. Such stars are called T-Tauri objects. Observations of DG Tau were made on October 23, 2002, and February 13, 2003, and the findings will appear in an upcoming issue of the Astrophysical Journal Letters.

“We’re trying to measure the size of the hot material in the dust disc around DG Tau, where planets may form,” said Dr. Rachel Akeson, leader of the study team and an astronomer at the Michelson Science Center at the California Institute of Technology in Pasadena. “Studies like this teach us more about how stars form, either alone or in pairs, and how planets eventually form in discs around stars.”

The Keck Interferometer observations revealed a gap of 18 million miles between DG Tau and its orbiting dust disc. Akeson notes that of the extra-solar planets – planets orbiting other stars – discovered so far, roughly one in four lies within 10 million miles of the parent star. Since planets are believed to form within a dust disc, either DG Tau’s disc has a larger-than-usual gap, or the close-in planets form farther from the star and migrate inward.

Since 1995, astronomers have detected more than 100 extra- solar planets, many considered too large and close to their hot, parent stars to sustain life. By measuring the amount of dust around other stars, where planets may form, the Keck Interferometer will pave the way for NASA’s Terrestrial Planet Finder mission. Terrestrial Planet Finder will look for smaller, Earth-like planets that may harbor life. The Keck Interferometer and Terrestrial Planet Finder are part of NASA’s Origins Program, which seeks to answer the questions: Where did we come from? Are we alone?

“T-Tauri objects had been observed with other instruments, but only the brightest ones were detectable until now,” Akeson said. “With the larger telescopes and greater sensitivity of the Keck Interferometer, we can look at fainter T-Tauri objects, like this one.”

The Keck Interferometer gathers light waves with two telescopes and then combines the waves so they interact, or “interfere” with each other. It’s like throwing a rock into a lake and watching the ripples, or waves, and then throwing in a second rock. The second set of waves either bumps against the first set and changes its pattern, or both sets join together to form larger, more powerful waves. With interferometry, the idea is to combine light waves from multiple telescopes to simulate a much larger, more powerful telescope.

In its ability to resolve fine details, the Keck Interferometer is equivalent to an 85-meter (279-foot) telescope. “The system transports the light gathered by the two telescopes to an optical laboratory located in the central building,” said Dr. Mark Colavita of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, interferometer system architect and lead author of the paper. “In the lab, a beam combiner and infrared camera combine and process the collected light to make the science measurement.”

To make these measurements, the interferometer’s optical system adjusts the light paths to a fraction of a wavelength of light, and adaptive optics on the telescopes remove the distortion caused by Earth’s atmosphere.

“This research represents the first scientific application of an interferometer with telescopes that use adaptive optics,” said Dr. Peter Wizinowich, interferometer team lead for the W.M. Keck Observatory and co-author of the paper.

The development of the Keck Interferometer is managed by JPL for NASA’s Office of Space Science, Washington. JPL is a division of the California Institute of Technology in Pasadena. The W.M. Keck Observatory is funded by Caltech, the University of California and NASA, and is managed by the California Association for Research in Astronomy, Kamuela, Hawaii.

Original Source: NASA News Release

Image credit: Hubble

An international team of astronomers have gathered new evidence to support the “domino theory” of star formation; that star formation occurs in sequence in galaxies driven by the movements of gas and stars at the core. A new instrument attached to the 8m Gemini South Telescope, called CIRPASS, allowed the astronomers to measure the composition of a whole range of stars at the centre of galaxy M83. A detailed analysis of the data is now underway.

An international team of astronomers have used a unique instrument on the 8m Gemini South Telescope to determine the ages of stars across the central region of the barred spiral galaxy, M83. Preliminary results provide the first hints of a domino model of star formation where star formation occurs in a time sequence, driven by the movements of gas and stars in the central bar.

The new instrument, called CIRPASS, simultaneously produces 500 spectra, taken from across the whole region of interest, which act as a series of ‘fingerprints’. Encoded in these ‘fingerprints’ is not only all the information the team required to determine when individual groups of stars formed, but also information on their movements and chemical properties. Dr. Johan Knapen, project co-investigator, ‘The unique combination of a state-of-the-art instrument like CIRPASS with one of the most powerful telescopes available is now providing us with truly sensational observations.’

M83 is a grand design spiral galaxy undergoing an intense burst of star formation in its central bar region. Large scale images, of the visible light from the galaxy, taken with ground based telescopes, show a pronounced bar across the middle of the galaxy) seen as the diagonal white structure in figure 1 . Astronomers believe that it is the influence of this bar which leads a concentration of gas in the central regions of the galaxy from which stars are born. ‘The central region of M83 is enshrouded in dust, but by using CIRPASS, which operates in the infra-red not the visible, we are able to see through this dust and investigate the hidden physical processes at work in the galaxy,’ said Dr Ian Parry, leader of the CIRPASS instrumentation team.

Two competing theories strive to explain the burst of star formation in the centre of the galaxy, M83. One theory suggests that stars form randomly across the whole nuclear region. A second model, favoured by the observational team, proposes that star-formation is triggered by the bar structure. In this model, the rotation of gas and stars in the bar causes stars to be formed sequentially, in a domino manner.

Using a technique first demonstrated by Dr. Stuart Ryder and colleagues, the team searched for a hydrogen emission feature, the Paschen-beta line, within the galaxy’s ‘fingerprints’. The measurement of this feature indicates the presence of hot young stars. By comparing the strengths of the Paschen-beta emission with the amount of absorption from carbon-monoxide (arising in the cool atmospheres of old giant stars) the team are able determine the age of the stars in each region of the galaxy. ‘A detailed analysis of the data is underway but initial results hint at a complex sequence of star formation,’ said Dr Robert Sharp, instrument support scientist with CIRPASS.

Preliminary analysis of other emission features (due to Paschen-beta and ionized iron) revealed a potentially intriguing result. ‘Ionized iron enables us to trace past supernova explosions. The observations indicate that energy from exploding stars (supernovae) may be being passed into regions of undisturbed gas causing further massive star formation.’ said Dr. Stuart Ryder, principle investigator.

While some members of the instrument team are presenting their work at the Royal Society Science Exhibition in London, CIRPASS is back on the Gemini South Telescope in Chile, performing the next set of observations.

Original Source: Cambridge News Release

Image credit: NSO

A new adaptive optics system is helping the National Solar Observatory take much more vivid images of the Sun. Earth-based telescopes are limited in resolution by atmospheric distortion, so there was no real point of building them larger than 1.5 metres across – bigger didn’t help. With the new NSO system; however, solar telescopes can now be built 4-metres and larger. This should allow solar astronomers to better understand the processes of solar magnetism and other activities.

Impressive, sharp images of the Sun can be produced with an advanced adaptive optical system that will give new life to existing telescopes and open the way for a generation of large-aperture solar telescopes. This AO system removes blurring introduced by Earth’s turbulent atmosphere and thus provides a clear vision of the smallest structure on the Sun.

The new AO76 system — Adaptive Optics, 76 subapertures — is the largest system designed for solar observations. As demonstrated recently by a team at the National Solar Observatory at Sunspot, NM, AO76 produces sharper images under worse seeing conditions for atmospheric distortion than the AO24 system employed since 1998.

“First light” with the new AO76 system was in December 2002, followed by tests starting in April 2003 with a new high-speed camera that significantly enhanced the system.

“If the first results in late 2002 with the prototype were impressive,” said Dr. Thomas Rimmele, the AO project scientist at the NSO, “I would call the performance that we are getting now truly amazing. I’m quite thrilled with the image quality delivered by this new system. I believe its fair to say that the images we are getting are the best ever produced by the Dunn Solar Telescope.” The Dunn is one of the nation’s premier solar observing facilities.
Dual-purpose program

The new high-order AO system serves two purposes. It will allow existing solar telescopes, like the 76-cm (30-inch) Dunn, to produce higher resolution images and greatly improve their scientific output under a wider range of seeing conditions. It also demonstrates the ability to scale the system up to enable a new generation of large-aperture instruments, including the proposed 4-meter Advanced Technology Solar Telescope (see below) that will see at higher resolutions than current telescopes can achieve.

High resolution observations of the Sun have become increasingly important for solving many of the outstanding problems in solar physics. Studying the physics of flux elements, or solar fine structure in general, requires spectroscopy and polarimetry of the fine structures. The exposures are typically about 1 second long and the resolution currently achieved in spectroscopic/polarimetric data typically is 1 arc-second, which is insufficient for study of fine solar structures. Further, theoretical models predict structures below the resolution limits of 0.2 arc-sec of existing solar telescopes. Observations are needed below the 0.2 arc-sec resolution limit to study the important physical processes that occur on such small scales. Only AO can provide a consistent spatial resolution of 0.1 arc-sec or better from ground based observatories.

AO technology combines computers and flexible optical components to reduce the effects of atmospheric blurring (“seeing”) on astronomical images. Sunspot’s solar AO76 system is based on the Shack-Hartmann correlating technique. In essence, this divides an incoming image into an array of subapertures viewed by a wavefront sensor camera. One subaperture is selected as a reference image. Digital signal processors (DSPs) calculate how to adjust each subaperture to match the reference image. The DSPs then command 97 actuators to reshape a thin, 7.7 cm (3-inch) deformable mirror to cancel much of the blurring. The DSP also can drive a tilt/tip mirror, mounted in front of the AO system, that removes gross image motion caused by the atmosphere.

Closing the loop for sharper images
“A major challenge for astronomers is correcting the light entering their telescopes for the effect of the Earth’s atmosphere,” explained Kit Richards, NSO’s AO lead project engineer. “Air of different temperatures mixing above the telescope makes the atmosphere like a rubber lens that reshapes itself about a hundred times each second.” This is more severe for solar astronomers observing during the day with the Sun heating Earth’s surface, but still causes the stars to twinkle at night.

Further, solar physicists want to study extended bright regions with low contrast. That makes it more challenging for an AO system to correlate the same parts of several slightly different subapertures, and to maintain the correlation from one image frame to the next as the atmosphere changes shape.

(Nighttime astronomy has used a different technique for several years. Lasers generate artificial guide stars in the atmosphere, letting astronomers measure and correct for atmospheric distortion. This is not practical with instruments that observe the Sun.)

In 1998 NSO pioneered use of a low-order AO24 system for solar observations. It has 24 apertures and compensates 1,200 times/second (1,200 Hertz [Hz]). Since August 2000, the team focused on scaling the system up to the high-order AO76 with 76 apertures and correcting twice as fast, 2,500 Hz. The breakthroughs started in late 2002.

First, the servo loop was successfully closed on the new high-order AO system during its first engineering run at the Dunn in December. In a “closed loop” servo system the output is fed back to the input and the errors are driven to 0. An “open loop” system detects the errors and makes corrections but the corrected output is not feed back to the input. The servo system doesn’t know if it is removing all the errors or not. This type of system is faster but very hard to calibrate and keep calibrated. At this point the system used a DALSA camera, which operates at 955 Hz, as the interim wavefront sensor. The optical setup was not finalized and preliminary; “bare-bone” software operated the system.

High-speed wavefront sensor
Even in this preliminary state — intended to demonstrate that the components worked together as a system– and under mediocre seeing conditions, the high-order AO system produced impressive, diffraction-limited images. Time sequences of corrected and uncorrected images show that the new AO system provides fairly consistent high-resolution imaging even as the seeing varies substantially, as is typical for daytime seeing.

Following this milestone, the team installed a new high-speed wavefront sensor camera custom developed for the AO project by Baja Technology and NSO’s Richards. It operates at 2,500 frames/second, which more than doubles the closed-loop servo bandwidth possible with the DALSA camera. Richards also implemented improved control software. In addition, the system was upgraded to drive the tip/tilt correction mirror either directly from the AO wavefront sensor or from a separate correlation/spot tracker system that operates at 3 kHz.

The new high-order AO76 was first tested in April 2003 and immediately started producing excellent images under a wider range of seeing conditions that normally would preclude high-resolution images. The new high-order AO76 was first tested in April 2003 and immediately started producing excellent images under a wider range of seeing conditions that normally would preclude high-resolution images. Striking differences with the AO on versus off are readily visible in images of active areas, granulation, and other features.

“That’s not to say that seeing does not matter anymore,” Rimmele noted. “To the contrary, seeing effects such as anisoplanatism — wavefront differences between the correlation target and the area we want to study — still are limiting factors. But in halfway decent seeing we can lock up on granulation and record excellent images.”

To make large instruments like the Advanced Technology Solar Telescope possible, the high-order AO system will have to be scaled up more than tenfold to at least 1,000 subapertures. And NSO is looking beyond that to a more complex technique, multiconjugate AO. This approach, already being developed for nighttime astronomy, builds a three-dimensional model of the turbulent region rather than treating it as a simple distorted lens.

For now, though, the project team will focus on the completion of the optical setup at the Dunn, installation of the AO bench at the Big Bear Solar Observatory followed by engineering runs, optimization of reconstruction equations and servo loop controls, and characterization of system performance at both sites. Then, the Dunn AO system is to become operational in fall of 2003. The Diffraction Limited Spectro-Polarimeter (DLSP), the main science instrument that can take advantage of the diffraction-limited image quality delivered by the high-order AO, is scheduled for its first commissioning runs in fall of 2003. NSO is developing the DLSP in collaboration with the High Altitude Observatory in Boulder.

Original Source: NSO News Release

Image credit: ESO

On March 29, 2003 NASA’s High Energy Transient Explorer detected a bright burst of gamma rays, and shortly after telescopes from around the world focused in on the object; now called GRB 030329 and measured to be 2.6 billion light-years away. By measuring the afterglow of the explosion, astronomers realized that it matches the spectrum of a hypernova – explosions of extremely large stars, at least 25 times larger than our own Sun. By matching the spectra, astronomers have compelling evidence that there is some connection between gamma ray bursts and the explosions of very large stars.

A very bright burst of gamma-rays was observed on March 29, 2003 by NASA’s High Energy Transient Explorer (HETE-II), in a sky region within the constellation Leo.

Within 90 min, a new, very bright light source (the “optical afterglow”) was detected in the same direction by means of a 40-inch telescope at the Siding Spring Observatory (Australia) and also in Japan. The gamma-ray burst was designated GRB 030329, according to the date.

And within 24 hours, a first, very detailed spectrum of this new object was obtained by the UVES high-dispersion spectrograph on the 8.2-m VLT KUEYEN telescope at the ESO Paranal Observatory (Chile). It allowed to determine the distance as about 2,650 million light-years (redshift 0.1685).

Continued observations with the FORS1 and FORS2 multi-mode instruments on the VLT during the following month allowed an international team of astronomers [1] to document in unprecedented detail the changes in the spectrum of the optical afterglow of this gamma-ray burst. Their detailed report appears in the June 19 issue of the research journal “Nature”.

The spectra show the gradual and clear emergence of a supernova spectrum of the most energetic class known, a “hypernova”. This is caused by the explosion of a very heavy star – presumably over 25 times heavier than the Sun. The measured expansion velocity (in excess of 30,000 km/sec) and the total energy released were exceptionally high, even within the elect hypernova class.

From a comparison with more nearby hypernovae, the astronomers are able to fix with good accuracy the moment of the stellar explosion. It turns out to be within an interval of plus/minus two days of the gamma-ray burst. This unique conclusion provides compelling evidence that the two events are directly connected.

These observations therefore indicate a common physical process behind the hypernova explosion and the associated emission of strong gamma-ray radiation. The team concludes that it is likely to be due to the nearly instantaneous, non-symmetrical collapse of the inner region of a highly developed star (known as the “collapsar” model).

The March 29 gamma-ray burst will pass into the annals of astrophysics as a rare “type-defining event”, providing conclusive evidence of a direct link between cosmological gamma-ray bursts and explosions of very massive stars.

What are Gamma-Ray Bursts?
One of the currently most active fields of astrophysics is the study of the dramatic events known as “gamma-ray bursts (GRBs)”. They were first detected in the late 1960’s by sensitive instruments on-board orbiting military satellites, launched for the surveillance and detection of nuclear tests. Originating, not on the Earth, but far out in space, these short flashes of energetic gamma-rays last from less than a second to several minutes.

Despite major observational efforts, it is only within the last six years that it has become possible to pinpoint with some accuracy the sites of some of these events. With the invaluable help of comparatively accurate positional observations of the associated X-ray emission by various X-ray satellite observatories since early 1997, astronomers have until now identified about fifty short-lived sources of optical light associated with GRBs (the “optical afterglows”).

Most GRBs have been found to be situated at extremely large (“cosmological”) distances. This implies that the energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00.

During the past years circumstantial evidence has mounted that GRBs signal the collapse of massive stars. This was originally based on the probable association of one unusual gamma-ray burst with a supernova (“SN 1998bw”, also discovered with ESO telescopes, cf. ESO PR 15/98). More clues have surfaced since, including the association of GRBs with regions of massive star-formation in distant galaxies, tantalizing evidence of supernova-like light-curve “bumps” in the optical afterglows of some earlier bursts, and spectral signatures from freshly synthesized elements, observed by X-ray observatories.

VLT observations of GRB 030329
On March 29, 2003 (at exactly 11:37:14.67 hrs UT) NASA’s High Energy Transient Explorer (HETE-II) detected a very bright gamma-ray burst. Following identification of the “optical afterglow” by a 40-inch telescope at the Siding Spring Observatory (Australia), the redshift of the burst [3] was determined as 0.1685 by means of a high-dispersion spectrum obtained with the UVES spectrograph at the 8.2-m VLT KUEYEN telescope at the ESO Paranal Observatory (Chile).

The corresponding distance is about 2,650 million light-years. This is the nearest normal GRB ever detected, therefore providing the long-awaited opportunity to test the many hypotheses and models which have been proposed since the discovery of the first GRBs in the late 1960’s.

With this specific aim, the ESO-lead team of astronomers [1] now turned to two other powerful instruments at the ESO Very Large Telescope (VLT), the multi-mode FORS1 and FORS2 camera/spectrographs. Over a period of one month, until May 1, 2003, spectra of the fading object were obtained at regular rate, securing a unique set of observational data that documents the physical changes in the remote object in unsurpassed detail.

The hypernova connection
Based on a careful study of these spectra, the astronomers are now presenting their interpretation of the GRB 030329 event in a research paper appearing in the international journal “Nature” on Thursday, June 19. Under the prosaic title “A very energetic supernova associated with the gamma-ray burst of 29 March 2003”, no less than 27 authors from 17 research institutes, headed by Danish astronomer Jens Hjorth conclude that there is now irrefutable evidence of a direct connection between the GRB and the “hypernova” explosion of a very massive, highly evolved star.

This is based on the gradual “emergence” with time of a supernova-type spectrum, revealing the extremely violent explosion of a star. With velocities well in excess of 30,000 km/sec (i.e., over 10% of the velocity of light), the ejected material is moving at record speed, testifying to the enormous power of the explosion.

Hypernovae are rare events and they are probably caused by explosion of stars of the so-called “Wolf-Rayet” type [4]. These WR-stars were originally formed with a mass above 25 solar masses and consisted mostly of hydrogen. Now in their WR-phase, having stripped themselves of their outer layers, they consist almost purely of helium, oxygen and heavier elements produced by intense nuclear burning during the preceding phase of their short life.
“We have been waiting for this one for a long, long time”, says Jens Hjorth, “this GRB really gave us the missing information. From these very detailed spectra, we can now confirm that this burst and probably other long gamma-ray bursts are created through the core collapse of massive stars. Most of the other leading theories are now unlikely.”
A “type-defining event”

His colleague, ESO-astronomer Palle M?ller, is equally content: “What really got us at first was the fact that we clearly detected the supernova signatures already in the first FORS-spectrum taken only four days after the GRB was first observed – we did not expect that at all. As we were getting more and more data, we realised that the spectral evolution was almost completely identical to that of the hypernova seen in 1998. The similarity of the two then allowed us to establish a very precise timing of the present supernova event”.

The astronomers determined that the hypernova explosion (designated SN 2003dh [2]) documented in the VLT spectra and the GRB-event observed by HETE-II must have occurred at very nearly the same time. Subject to further refinement, there is at most a difference of 2 days, and there is therefore no doubt whatsoever, that the two are causally connected.

“Supernova 1998bw whetted our appetite, but it took 5 more years before we could confidently say, we found the smoking gun that nailed the association between GRBs and SNe” adds Chryssa Kouveliotou of NASA. “GRB 030329 may well turn out to be some kind of ‘missing link’ for GRBs.”

In conclusion, GRB 030329 was a rare “type-defining” event that will be recorded as a watershed in high-energy astrophysics.

What really happened on March 29 (or 2,650 million years ago)?
Here is the complete story about GRB 030329, as the astronomers now read it.

Thousands of years prior to this explosion, a very massive star, running out of hydrogen fuel, let loose much of its outer envelope, transforming itself into a bluish Wolf-Rayet star [3]. The remains of the star contained about 10 solar masses worth of helium, oxygen and heavier elements.

In the years before the explosion, the Wolf-Rayet star rapidly depleted its remaining fuel. At some moment, this suddenly triggered the hypernova/gamma-ray burst event. The core collapsed, without the outer part of the star knowing. A black hole formed inside, surrounded by a disk of accreting matter. Within a few seconds, a jet of matter was launched away from that black hole.

The jet passed through the outer shell of the star and, in conjunction with vigorous winds of newly formed radioactive nickel-56 blowing off the disk inside, shattered the star. This shattering, the hypernova, shines brightly because of the presence of nickel. Meanwhile, the jet plowed into material in the vicinity of the star, and created the gamma-ray burst which was recorded some 2,650 million years later by the astronomers on Earth. The detailed mechanism for the production of gamma rays is still a matter of debate but it is either linked to interactions between the jet and matter previously ejected from the star, or to internal collisions inside the jet itself.

This scenario represents the “collapsar” model, introduced by American astronomer Stan Woosley (University of California, Santa Cruz) in 1993 and a member of the current team, and best explains the observations of GRB 030329.

“This does not mean that the gamma-ray burst mystery is now solved”, says Woosley. “We are confident now that long bursts involve a core collapse and a hypernova, likely creating a black hole. We have convinced most skeptics. We cannot reach any conclusion yet, however, on what causes the short gamma-ray bursts, those under two seconds long.”

Original Source: ESO News Release

Interested in space and astronomy but you’ve never actually looked through a telescope? Until you’ve actually gone out and done some actual observing with your own two eyes, you won’t know what you’re missing. In this article, Fraser gives you a kick in the pants to get out there under the skies and start enjoying the heavens above. You don’t need any special equipment or advanced university degrees, just some enthusiasm, a little time and the ability to look up.

I know there are a lot of subscribers interested in space and astronomy, but I’m wondering how many of you have actually taken a look through a telescope and seen some of the objects I talk about with your own eyes.

One of my fondest memories was when I was 13 years old, and set up my 4″ telescope at my Dad’s birthday party. I was in a darkish corner of our property and would sneak away a few partygoers to show them Saturn. Fortunately the rings were at their greatest angle, and people looking through the eyepiece couldn’t believe their eyes. Looking at pictures taken by Hubble is one thing, but when you’re actually looking through the eyepiece at Saturn, it’s an incredible experience.

Stargazing has since played a big part of my life: I organized a star party, hit on my future wife by pointing out constellations, and started a space-related website, but I’m still amazed at the number of people who’ve never actually gone out there and gotten to know their sky.

With all the new observatories and space news, I think that people are starting to think that astronomy is one of those sciences reserved for people with the expensive instruments, but that couldn’t be further from the truth. It’s one of the few sciences that amateurs still make valuable contributions, and it costs absolutely nothing to get started – you just need your eyes, and a little knowledge.

Find your community
The first thing you need to do is make a commitment to get involved in astronomy. It’s not as easy as just turning on your television; you’ve got to get organized; make some phone calls; set aside some time to explore.

I’ll bet you didn’t know, but there’s an astronomical society lurking in almost every population centre on the planet. We’ve got dozens just here in Canada, and there are literally thousands in the US. The members of the society will usually meet on a regular basis and will have observing nights where they all get together and point their telescopes at different objects. This is a great way to quickly see what the night sky has to offer.

Do a search on Google with the search terms: yourtown astronomical society. For example, I would do a search for: Vancouver astronomical society. If nothing turns up for your specific location, broaden the search a bit. Eventually you should come up with something. Find the contact information for the society and drop them an email or give them a phone call. Trust me, they’ll be happy to give you more information and have you join them for an evening.

Next, see if there’s an observatory in your region. Although most of the largest telescopes are fully booked up for years in advance, some of the smaller ones have open nights where people can come down, ask to see stuff and they’ll move the scope around. Often these open nights are run by the local astronomical society. Once again, contact the society and find out if they can recommend an observatory to check out. Or, you can do a search on Google (search for: yourtown observatory) and contact them directly.

Learn your constellations
Whether you actually contact a society or just decide to go solo is up to you, but your first step is to learn some of your constellations. Maybe you already know the Big Dipper or Orion’s belt, but there are 88 constellations in Northern and Southern hemispheres. It’s pretty cool to be able to ask a person what their sign is, and then point it out in sky.

Learning your constellations is also the first step to finding some of the more interesting stuff to look at in the night sky. They’re like your guides. For example, our nearest galaxy, Andromeda (aka M31) is easily visible in binoculars or a telescope. It’s just a little up from the middle of the constellation Andromeda, which is just above Aries. I can spot M31 in a second whenever a look up in the sky (at the right time of year). Once you start to learn your constellations, they all start to fit together like a puzzle. And the great thing is the knowledge never goes away, even if it’s been a few years since you’ve done any observing.

There are many great resources for learning your constellations. One option is to do a search, once again on Google, for the term: astronomy sky charts. Some of these are fairly detailed, however, and make it hard to just learn the basic constellations.

The book that taught me, and I can’t recommend it highly enough is Nightwatch, by Terrence Dickinson. The book breaks the night sky into seasons and then has single pages for each chunk of sky with clearly defined stars and constellations – similar to one of those road maps that sit open on the car seat next to you. The book also has fabulous information on starting equipment, etc. (Order Nightwatch from Amazon.com – $20.97)

Another handy tool is Astronomy magazine. The middle of each issue is a star chart for the current month. The advantage of using a magazine like Astronomy is that it also has the current positions of the planets. (Click here to get a subscription to Astronomy for 32% off the newsstand price)

Finally, you can use a software product like Starry Nights, which lets you define your location and time to produce a custom star chart that includes the locations of the planets. (Click here for more information on Starry Nights)

Once you’ve got your sky chart together, I suggest you also get a flashlight with a red-light filter. You can usually pick them up at camping stores or army surplus. This way you can look at your charts without ruining your night vision.

Now, hit the road! If you live in an area with reasonably dark skies, you can just turn out the lights in your house and head into your back yard. If you live in a city, you’ll have to get a little ways out. Even a dark park or dimly lit suburb will be a vast improvement over the downtown core. City lights cause two problems: the streetlights will send a glare up into your night sky, dimming your visibility; and the lights will ruin your night vision directly.

Give yourself a couple of hours, and by the end of it you’ll be familiar with most of the constellations in the sky. You’ll probably also see a few meteors and even some satellites. Quality family entertainment if you ask me.

Improving your stargazing experience
Astronomy is one of those hobbies that you can enjoy for free, but you can really improve your experience with some basic equipment.

Binoculars
Chances are you’ve already got one of the most useful pieces of stargazing equipment already in your home: binoculars. Anywhere you look in the night sky is significantly improved by a simple pair of astronomical binoculars, from the Moon to star clusters. In fact, some stuff looks better in binoculars than a more powerful telescope.

Binoculars generally have two measurements: magnification and field of view. For example, a common kind is 7×35. This means it has a 7x magnification and 35mm field of view. For astronomy, power isn’t necessarily a good thing. Some go as high as 20x or even 30x, but this usually creates a very small field of view. And since you’re holding the binoculars with your hands, it can get very shaky.

It’s much better to go with a lower power set of binoculars with a large field of view: 8×50 is a perfect combination of power and field of view.

Obviously it’s important to have good quality optics, but that’s one of those things that you should experience with first to get a sense of the equipment you already have. If it’s too high-power, or you can’t focus the image to get really crisp stars, you might want to consider upgrading your gear.

It’s also really useful to have a tripod adapter hole on the bottom of your binoculars. This will let you screw them onto the top of a tripod and then let other people come and take a look through the eyepieces to share your view.

Here are some links to Binoculars.com for some good astronomical binoculars:

Celestron 7×50 Enduro. Straightforward pair of binoculars with good magnification and field of view. $57.40 USD

Bausch & Lomb 10×50 Legacy. Higher magnification with 50mm field of view. $111.00 USD.

Canon 15×50 IS. Pretty much the best binoculars you can get. Higher resolution but image stabilization keeps the image from shaking. $899.00 USD

Telescope
If you’re thinking of buying a telescope, then you’ve really got the bug. However, don’t just run down and purchase a telescope from a department or toy store. These usually have low quality optics, a jiggly mount and generally stink for astronomy – those “in the know” call them “Christmas trash scopes”.

For the same price or a little more you can purchase a real telescope with quality optics and mount and have a much better experience with the night sky.

There are many different kinds of telescopes, and explaining the differences of how to select a good telescope can fill a book so I won’t go into the details here. Remember your contacts at your local astronomical society? Let them know your budget and objectives and they can probably recommend a good telescope. They might even know someone who’s selling one used. Of course, these folks are going to be astronomy fans, so they might have bigger ideals than what you’re looking for.

There are two main kinds of telescopes: refractors and reflectors.

Refractors work through a series of lenses which focus light into the telescope’s eyepiece (think of your traditional ship captain’s spyglass) and typically have a main lens between 70mm and 100mm. These can be solid telescopes, but the optics can make them more expensive than reflectors.

One example refractors would be the Meade EXT-70AT ($298.00 USD). A small portable refractor with with a computer-controlled mount. Put the telescope on a flat surface, align it with the sky and then it can automatically pick out targets in the sky. These automated telescopes can take some of the fun out of stargazing, but it definitely speeds things up.

Reflectors use a big mirror to reflect and focus incoming light to the telescope’s eyepiece. They’re usually shorter and fatter than a refractor, starting at 4 inches and going up from there. I started, and still use a 4″ telescope, which is perfectly fine to see the major planets and all kinds of astronomical objects.

An example reflector is a Celestron 4.5″ Firstscope ($149.00). No computer on this telescope, so you’ll get a chance to learn the location of sky objects on your own.

Bigger telescopes gather more light, so they can display fainter objects, but they come with a higher price. My recommendation is to start small, get some experience before considering a higher-end telescope.

Probably the best starting telescope is something like a 6″ Dobsonian reflector. Unlike most telescopes you’ve seen, the Dobsonians have their mount down at the base and then point up. They’re solid, inexpensive, and easy to use. Some of the largest, most powerful amateur-built telescopes are Dobsonians.

Here’s a link to a Swift Instruments 6″ Dobsonian telescope ($382.95 USD).

An a link to a much larger Meade Starfinder 16″ Dobsonian ($1,386.00 USD).

Now Get Out There!
Enough reading, start sky watching. Early Summer is a great time to get involved in astronomy (and a terrible time to watch TV) – warm summer nights and stargazing go hand in hand. Do a little research, grab some supplies, gather the friends and family, and get out under the stars. And please, email me your summer experiences. Trust me, you’ll get some memories you’ll never forget.

Image credit: ESO

A new series of photographs taken by the European Southern Observatory show a rare look into the very early stages of heavy star formation. This time in a star’s life is usually obscured from sight because of thick clouds of gas and dust, but in star cluster NGC 3603, the stellar wind from hot stars are blasting away the obscuring material. Inside this cluster, astronomers are finding massive protostars which are only 100,000 years old. This is a valuable discovery because it helps astronomers understand how the early stages of heavy star formation begins – is it through gravity pulling together gas and dust, or something more violent, like smaller stars colliding together.

Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter N?rnberger has obtained a first glimpse of the very first stages in the formation of heavy stars.

These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet “caught” nascent heavy stars in the act and little is therefore known so far about the related processes.

Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing.

Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0?C), probably partly arranged in disks around these very young objects.

Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses.

How do massive stars form?
This question is easy to pose, but so far very difficult to answer. In fact, the processes that lead to the formation of heavy stars [1] is currently one the most contested areas in stellar astrophysics.

While many details related to the formation and early evolution of low-mass stars like the Sun are now well understood, the basic scenario that leads to the formation of high-mass stars still remains a mystery. It is not even known whether the same characterizing observational criteria used to identify and distinguish the individual stages of young low-mass stars (mainly colours measured at near- and mid-infrared wavelengths) can also be used in the case of massive stars.

Two possible scenarios for the formation of massive stars are currently being studied. In the first, such stars form by accretion of large amounts of circumstellar material; the infall onto the nascent star varies with time. Another possibility is formation by collision (coalescence) of protostars of intermediate masses, increasing the stellar mass in “jumps”.

Both scenarios impose strong limitations on the final mass of the young star. On one side, the accretion process must somehow overcome the outward radiation pressure that builds up, following the ignition of the first nuclear processes (e.g., deuterium/hydrogen burning) in the star’s interior, once the temperature has risen above the critical value near 10 million degrees.

On the other hand, growth by collisions can only be effective in a dense star cluster environment in which a reasonably high probability for close encounters and collisions of stars is guaranteed.

Which of these two possibilties is then the more likely one?

Massive stars are born in seclusion
There are three good reasons that we know so little about the earliest phases of high-mass stars:

First, the formation sites of such stars are in general much more distant (many thousands of light-years) than the sites of low-mass star formation. This means that it is much more difficult to observe details in those areas (lack of angular resolution).

Next, in all stages, also the earliest ones (astronomers here refer to “protostars”), high-mass stars evolve much faster than low-mass stars. It is therefore more difficult to “catch” massive stars in the critical phases of early formation.

And, what is even worse, due to this rapid development, young high-mass protostars are usually very deeply embedded in their natal clouds and therefore not detectable at optical wavelengths during the (short) phase before nuclear reactions start in their interior. There is simply not enough time for the cloud to disperse – when the curtain finally lifts, allowing a view of the new star, it is already past those earliest stages.

Is there a way around these problems? “Yes”, says Dieter N?rnberger of ESO-Santiago, “you just have to look in the right place and remember Bob Dylan…!”. This is what he did.
“The answer, my friend, is blowing by the wind…”

Imagine that it would be possible to blow away most of the obscuring gas and dust around those high-mass protostars! Even the strongest desire of the astronomers cannot do it, but there are fortunately others who are better at it!

Some high-mass stars form in the neighbourhood of clusters of hot stars, i.e., next to their elder brethren. Such already evolved hot stars are a rich source of energetic photons and produce powerful stellar winds of elementary particles (like the “solar wind” but many times stronger) which impact on the surrounding interstellar gas and dust clouds. This process may lead to partial evaporation and dispersion of those clouds, thereby “lifting the curtain” and letting us look directly at young stars in that region, also comparatively massive ones at a relatively early evolutionary stage.

The NGC 3603 region
Such premises are available within the NGC 3603 stellar cluster and star-forming region that is located at a distance of about 22,000 light-years in the Carina spiral arm of the Milky Way galaxy.

NGC 3603 is one of the most luminous, optically visible “HII-regions” (i.e. regions of ionized hydrogen – pronounced “eitch-two”) in our galaxy. At its centre is a massive cluster of young, hot and massive stars (of the “OB-type”) – this is the highest density of evolved (but still relatively young) high-mass stars known in the Milky Way, cf. ESO PR 16/99.

These hot stars have a significant impact on the surrounding gas and dust. They deliver a huge amount of energetic photons that ionize the interstellar gas in this area. Moreover, fast stellar winds with speeds up to several hundreds of km/sec impact on, compress and/or disperse adjacent dense clouds, referred to by astronomers as “molecular clumps” because of their content of complex molecules, many of these “organic” (with carbon atoms).

IRS 9: a “hidden” association of nascent massive stars
One of these molecular clumps, designated “NGC 3603 MM 2” is located about 8.5 light-years south of the NGC 3603 cluster, cf. PR Photo 16a/03. Located on the cluster-facing side of this clump are some highly obscured objects, known collectively as “NGC 3603 IRS 9”. The present, very detailed investigation has allowed to characterise them as an association of extremely young, high-mass stellar objects.

They represent the only currently known examples of high-mass counterparts to low-mass protostars which are detected at infrared wavelengths. It took quite an effort [2] to unravel their properties with a powerful arsenal of state-of-the-art instruments working at different wavelengths, from the infrared to the millimeter spectral region.

Multi-spectral observations of IRS 9
To begin with, near-infrared imaging was performed with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope, cf. PR Photo 16b/03. This allowed to distinguish between stars which are bona-fide cluster members and others which happen to be seen in this direction (“field stars”). It was possible to measure the extent of the NGC 3603 cluster which was found to be about about 18 light-years, or 2.5 times larger than assumed before. These observations also served to show that the spatial distributions of low- and high-mass cluster stars are different, the latter being more concentrated towards the centre of the cluster core.

Millimeter observations were made by means of the Swedish-ESO Submillimeter Telescpe (SEST) at the La Silla Observatory. Large-scale mapping of the distribution of the CS-molecule showed the structure and motions of the dense gas in the giant molecular cloud, from which the young stars in NGC 3603 originate. A total of 13 molecular clumps were detected and their sizes, masses and densities were determined. These observations also showed that the intense radiation and strong stellar winds from the hot stars in the central cluster have “carved a cavity” in the molecular cloud; this comparatively empty and transparent region now measures about 8 light-years across.

Mid-infrared imaging (at wavelengths 11.9 and 18 ?m) was made of selected regions in NGC 3603 with the TIMMI 2 instrument mounted on the ESO 3.6-m telescope. This constitutes the first sub-arcsec resolution mid-IR survey of NGC 3603 and serves in particular to show the warm dust distribution in the region. The survey gives a clear indication of intense, on-going star formation processes. Many different types of objects were detected, including extremely hot Wolf-Rayet stars and protostars; altogether 36 mid-IR point sources and 42 knots of diffuse emission were identified. In the area surveyed, the protostar IRS 9A is found to be the most luminous point source at both wavelengths; two other sources, designated IRS 9B and IRS 9C in the immediate vicinity are also very bright on the TIMMI 2 images, providing further indication that this is the site of an association of protostars in its own right.

The collection of high-quality images of the IRS 9 area shown in PR Photo 16b/03 is well suited to investigate the nature and the evolutionary status of the highly obscured objects located there, IRS 9A-C. They are situated on the side of the massive molecular cloud core NGC 3603 MM 2 that faces the central cluster of young stars (PR Photo 16a/03) and were apparently only recently “liberated” from most of their natal gas and dust environment by strong stellar winds and energetic radiation from the nearby high-mass cluster stars.

The combined data lead to a clear conclusion: IRS 9A-C represent the brightest members of a sparse association of protostars, still embedded in circumstellar envelopes, but in a region of the pristine molecular cloud core, now largely “blown-free” from gas and dust. The intrinsic brightness of these nascent stars is impressive: 100,000, 1000 and 1000 times that of the Sun for IRS 9A, IRS 9B and IRS 9C, respectively.

Their brightness and infrared colours give information about the physical properties of these protostars. They are very young in astronomical terms, probably less than 100,000 years old. They are already quite massive, though, more than 10 times heavier than the Sun, and they are still growing – comparison to the currently most reliable theoretical models suggests that they accrete material from their envelopes at the relatively high rate of up to 1 Earth mass per day, i.e., the mass of the Sun in 1000 years.

The observations indicate that all three protostars are surrounded by comparatively cold dust (temperature around 250 – 270 K, or -20 ?C to 0?C). Their own temperatures are quite high, of the order of 20,000 – 22,000 degrees.

What do the massive protostars tell us?
Dieter N?rnberger is pleased: “We now have convincing arguments to consider IRS 9A-C as a kind of Rosetta Stones for our understanding of the earliest phases of the formation of massive stars. I know of no other high-mass protostellar candidates which have been revealed at such an early evolutionary stage – we must be grateful for the curtain-lifting stellar winds in that area! The new near- and mid-infrared observations are giving us a first look into this extremely interesting phase of stellar evolution.”

The observations show that criteria (e.g., infrared colours) already established for the identification of very young (or proto-) low-mass stars apparently also hold for high-mass stars. Moreover, with reliable values of their brightness (luminosity) and temperature, IRS 9A-C may serve as crucial and discerning test cases for the currently discussed models of high-mass star formation, in particular of accretion models versus coagulation models.

The present data are well consistent with the accretion models and no objects of intermediate luminosity/mass were found in the immediate neighbourhood of IRS 9A-C. Thus, for the IRS 9 association at least, the accretion scenario is favoured against the collision scenario.

Original Source: ESO News Release