samedi 10 novembre 2012

Ariane 5’s sixth launch of 2012


















ESA / Arianespace - Flight VA210 Mission poster.


10 November 2012

This evening, an Ariane 5 launcher lifted off from Europe’s Spaceport in French Guiana on its mission to place two telecommunications satellites, Eutelsat-21B and Star One-C3, into their planned transfer orbits.

 Ariane 5 VA210 liftoff

Liftoff of flight VA210, the 66th Ariane 5 mission, came at 21:05 GMT (22:05 CET; 18:05 French Guiana). The target injection orbit had a perigee altitude of 250 km, an apogee altitude at injection of 35 786 km and an inclination of 2°.

The satellites were accurately injected into their transfer orbits about 28 minutes and 33 minutes after liftoff, respectively.

Eutelsat-21B

Eutelsat-21B will be positioned above the equator at 21.5°E. It will deliver telecommunications services, data services for corporate networks and governmental administrations, and IP access in Europe, North and West Africa, the Middle East and Central Asia.

Star One-C3

Star One-C3, to be positioned at 75°W or 84°W, will provide direct TV broadcast, telephone and long-distance domestic communications services for Brazil and South America.

The payload mass for this launch was 9216 kg; the satellites totalled 8250 kg, with payload adapters and dispensers making up the additional 966 kg. 

Flight VA210 was Ariane 5’s 52nd successful launch in a row since December 2002.

video
Replay launch Ariane 5 flight VA210

VA210 flight timeline

Ariane 5’s cryogenic, liquid-propellant main engine was ignited first. Seven seconds later, the solid-propellant boosters also fired, and the vehicle lifted off a fraction of a second later.

The solid boosters were jettisoned 2 min 22 sec after main engine ignition, and the fairing protecting the payload during the climb through Earth’s atmosphere was discarded at 3 min 28 sec.

The launcher’s main engine shut down at 8 min 51 sec; six seconds later, the main cryogenic stage separated from the upper stage and its payload.

Four seconds after main stage separation, the engine of the cryogenic upper stage ignited to continue the journey. The engine shut down at 24 min 58 sec into the flight, at which point the vehicle was travelling at 9352 m/s (33 667 km/hr) at an altitude of 654.6 km. The conditions for geostationary transfer orbit injection had been achieved.

At 28 min 03 sec after main engine ignition, Eutelsat-21B separated from the upper stage, followed by Star One-C3 at 33 min 17 sec. Ariane 5’s flight operations were completed 48 min 47 sec after main engine ignition.

Related links:

Ariane 5: http://www.esa.int/SPECIALS/Launchers_Access_to_Space/SEMEUBRHPOG_0.html

Arianespace: http://www.arianespace.com/

Images, Video, Text, Credits: ESA / Arianespace / Eutelsat.

Greetings, Orbiter.ch

The Van Allen Probes: Honoring the Origins of Magnetospheric Science









NASA - Radiation Belt Storm Probes (RBSP) patch.

Nov. 10, 2012

video

A broad suite of instruments on the Van Allen Probes will help scientists understand more about the myriad types of particles and waves in the radiation belts that encircle Earth, providing a flood of new data for scientists who study the magnetosphere. Credit: NASA/Goddard Space Flight Center.

Earth's magnetism has captured human attention since the first innovator noticed that a freely moving piece of magnetized iron would always align itself with Earth's poles. Throughout most of history, the origins and physics of this magnetism remained mysterious, though by the 20th century certain things had been learned by measuring the magnetic field at Earth's surface. These measurements suggested that Earth's magnetic field was consistent with that of a giant bar magnet embedded deep inside Earth. However, the magnetic field observed at the surface of our planet is constantly fluctuating. During the 1930s scientists pioneered explanations that such fluctuations were due to streams of particles from the sun striking and becoming entrapped within Earth’s magnetic field.

Truly understanding Earth's magnetic environment, however, required traveling to space. In 1958, the first US rocket -- known as Explorer 1 and led by James Van Allen at the University of Iowa -- was launched. By providing observations of a giant swath of magnetized radiation trapped around Earth, now known as the Van Allen Belts, Explorer 1 confirmed that Earth's magnetic environment, the magnetosphere, was not a simple place. We now know that it has a complex shape – compressed on the side facing the sun, but stretched out into a long tail trailing off away from the sun -- affected as much by incoming material from the sun as Earth's own intrinsic magnetism. This magnetic field constantly fluctuates in response to both internal instabilities and events on the sun. It also provides a home for a host of electrified particles spiraling through this complex system.

A Scientific American article in 1963 said: "Conditions in the magnetosphere are so diverse and so variable . . . that millions of observations by scores of satellites and rocket probes have only begun to plot the broad outlines of this extension of the Earth into space." The age of magnetospheric science had begun, and it hasn't stopped yet. In 2012, those observations continue with the latest addition to NASA's heliospheric fleet: twin satellites launched on Aug. 30, 2012, originally named the Radiation Belt Storm Probes.

On Nov. 9, NASA announced that to honor the scientist who helped launched the field, the probes will be renamed the Van Allen Probes. The renaming comes simultaneously with a standard milestone for any NASA mission: the end of commissioning. Commissioning occurs after launch when all the instruments have been turned on and tested. The end of commissioning also marks the beginning of the prime science mission.

"We are excited to be honoring James Van Allen in this way," says David Sibeck, NASA's mission scientist for the Van Allen Probes at NASA's Goddard Space Flight Center in Greenbelt, Md. "This is an important mission that carries on early magnetospheric work. In the past we have only had one spacecraft at a time looking at the radiation belts. The state-of-the-art instruments we have now are going to be able to comprehensively observe all the types of particles and waves in this part of the magnetosphere."


On Nov. 9, 2012, NASA renamed the Radiation Belt Storm Probes to the Van Allen Probes. The probes, shown here in an artist's rendition, will help scientists study two giant belts of radiation around Earth. Credit: NASA/Goddard Space Flight Center.

Indeed, the preliminary data returned from the Van Allen Probes' first two months already has scientists very excited. The instruments all meet or exceed mission specifications and some papers and publications are already planned based on just the first few weeks of observations.

The probes have a planned two-year mission, each with a similar orbit that will carry the spacecraft through all parts of the radiation belts. The basic goal of the mission is to understand what causes the belts to swell and shrink in response to incoming radiation from the sun. Such changes in the belts can endanger satellites in space that orbit near the belts.

To distinguish between a host of theories developed over the years on the radiation belts, Van Allen Probe scientists have designed a suite of instruments to answer three main questions. Where do the extra energy and particles come from? Where do they disappear to, and what sends them on their way? How do these changes affect the rest of the magnetosphere? In addition to its broad range of instruments, the mission will make use of its two spacecraft to better map out the full spatial dimensions of a particular event and how it changes over time.

Scientists want to understand not only the origins of electrified particles – possibly from the solar wind constantly streaming off the sun; possibly from an area of Earth's own outer atmosphere, the ionosphere – but also what mechanisms gives the particles their extreme speed and energy.

"We know examples where a storm of incoming particles from the sun can cause the two belts to swell so much that they merge and appear to form a single belt," says Shri Kanekal, the Van Allen Probes' deputy mission scientist at Goddard. "Then there are other examples where a large storm from the sun didn't affect the belts at all, and even cases where the belts shrank. We need to figure out what causes the differences."

Of course, just like Explorer 1, any new spacecraft will provide unexpected observations that can dramatically change the models and theories about a given region of space. The magnetospheric science that James Van Allen helped initiate will surely provide additional surprises as the Van Allen Probes sweep their way through the radiation belts.

For more information about Radiation Belt Storm Probes (RBSP), renamed Van Allen Probes, visit: http://www.nasa.gov/offices/ipce/ipao/home/rbsp_highlight.html

Image (mentioned), Video (mentioned), Text, Credit: NASA Goddard Space Flight Center / Karen C. Fox.

Best regards, Orbiter.ch

vendredi 9 novembre 2012

ESA’s IXV reentry vehicle prepares for soft landing









ESA - IXV Intermediate eXperimental Vehicle.

9 November 2012

Europe’s IXV Intermediate eXperimental Vehicle is completing a series of descent and landing tests, including a full-scale splashdown planned for early next year, allowing the mission to move ahead towards launch in 2014.

The ambition for a spacecraft to return autonomously from low orbit is a cornerstone for a wide range of space applications, including space transportation, exploration and robotic servicing of space infrastructure.

IXV parachute drop test

IXV will achieve this goal. More manoeuvrable and able to make precise landings, it is the ‘intermediate’ element of Europe’s path to future developments with limited risks.

Launched into a suborbital trajectory on ESA’s small Vega rocket from Europe’s Spaceport in French Guiana, the vehicle will return to Earth as though from a low-orbit mission.

video

For the first time, it will test and qualify European critical reentry technologies in hypersonic flight, a requirement for all future applications that include a return from orbit.

The experimental nature of the mission means that the vehicle’s trajectory is designed to avoid inhabited regions – it will fly the experimental hypersonic phase over the Pacific Ocean, descend by parachute and land in the ocean to await recovery and analysis.

The descent and landing are key because they will allow the recovery of the vehicle and its precious recorded data for inspection, and serve as a backup in the event of a telemetry failure with ground stations.

Multiple failures during these phases in past national and international test flights have prompted ESA to ensure the recovery of the vehicle and data by using a robust design and rigorous verification.

Specific tests at system and subsystems level have been added to the standard qualification approach, including splashdown attitude verification tests in Rome, Italy, at the INSEAN research institute, a parachute subsystem qualification test at the US Yuma Proving Ground, and a descent and landing system test in Sardinia, Italy, at Poligono Interforze Salto di Quirra (PISQ).

Water splashdown

Attitude verification tests during splashdown were concluded in September 2011 with a prototype. They verified several vehicle splashdown scenarios at different angles, ranging from –35° to +71°, and wind conditions, in longitudinal and lateral directions.

This has revealed the ideal water impact angle to minimise loads and preserve the vehicle’s structure to be +35°.

video

Parachute

The parachute qualification test was completed in June 2012, verifying the behaviour of the complex subsystem, including its multiple stages.

A second prototype integrating the subsystem was dropped from a plane at an altitude of 5.7 km and landed safely in the Arizona desert.

video

Descent and landing

Flight testing of the descent and landing system is planned for the first quarter of 2013. It aims to verify the behaviour of the complete descent and landing system chain, ensuring the recovery of the vehicle.

A third full-scale prototype is undergoing integration at Italy’s CIRA research centre, including flight hardware and software. It will be dropped from a helicopter at an altitude of 3 km, splashing down in the Mediterranean Sea in the PISQ test range off the coast of Sardinia.

Third full-scale prototype undergoing integration

In parallel, industry is moving ahead with building and qualifying all flight elements, including the vehicle and the ground support equipment, and ground elements such as the mission control centre and tracking stations.

“In addition to the retrieval of flight data in real time via telemetry, securing the descent and landing phases of the IXV mission for the recovery of the vehicle intact is the requirement of utmost importance for the project,” says Giorgio Tumino, IXV Project Manager.

“Following past national and international experimentation failures, a lot of pressure is on industry to strengthen the failure tolerance in the design and verification approach of such critical flight phases."

“The IXV mission into space is now becoming a concrete reality. It will provide Europe with credible and unique knowhow on atmospheric reentry system aspects and unknowns and flight-proven technologies essential to support the realisation of the Agency’s future ambitions in the field.”

Related link:

Intermediate eXperimental Vehicle (IXV): http://www.esa.int/SPECIALS/Launchers_Technology/SEMDPQ2PGQD_0.html

Images, Videos, Text, Credits: ESA / Pioneer Aerospace / CIRA.

Cheers, Orbiter.ch

Happy Little Crater on Mercury












NASA - MESSENGER Mission to Mercury patch.

Nov. 9, 2012


It looks like even the craters on Mercury have heard of Bob Ross! The central peaks of this complex crater have formed in such a way that it resembles a smiling face. This image taken by the MESSENGER spacecraft is oriented so north is toward the bottom.

Artist's concept of the NASA's MESSENGER spaceraft at Mercury. (Credit: NASA)

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MESSENGER acquired 88,746 images and extensive other data sets. MESSENGER is now in a yearlong extended mission, during which plans call for the acquisition of more than 80,000 additional images to support MESSENGER's science goals.

For more information about MESSENGER Mission to Mercury, visit: http://www.nasa.gov/mission_pages/messenger/main/index.html

Images, Text,  Credit: NASA.

Greetings, Orbiter.ch

Astronomers develop new method to determine neutron star mass














ESA - Integral Mission patch / ESA - XMM-Newton Mission patch.

09 Nov 2012

Astronomers have used INTEGRAL and XMM-Newton to look into the neutron star in IGR J17252-3616, a highly obscured X-ray binary system. The data show how the neutron star, which is being fuelled by the stellar wind from its companion, is substantially deflecting the flow of the accreted material. Comparison with numerical simulations provides an estimate of the neutron star's mass, suggesting a new method to determine the mass of these extremely dense, exotic objects.

Neutron stars are created at the end of a massive star's life from the gravitational collapse of the stellar core. They are among the most dense objects in the Universe and provide astronomers with marvellous laboratories to explore the physics of matter at extremely high densities.


Artist's impression of a neutron star in a highly obscured high-mass X-ray binary system. Credit: ESA/AOES Medialab.

An important factor to constrain the properties of matter in such exotic environments, which are still largely unclear, is the mass of neutron stars. Astronomers have determined the mass of about 60 neutron stars so far, and most of them seem to have masses around 1.4 times the mass of the Sun. Only a handful neutron stars are known with masses around two solar masses, well below the upper limit prescribed by the theory, which is 3.2 solar masses. Astrophysicists are keen to find massive neutron stars.

 A study based on observations from two ESA missions – INTEGRAL and XMM-Newton – as well as on numerical simulations, has now provided a new method to determine the mass of neutron stars that may have the potential to unveil a few massive ones in the future.

"To estimate neutron star masses, we look at the ones that are part of binary stellar systems because, in a binary system, the relative motions of the two components are determined by their masses," explains Antonios Manousakis, who led this study.

 "To estimate neutron star masses, we look at the ones that are part of binary stellar systems because, in a binary system, the relative motions of the two components are determined by their masses," explains Antonios Manousakis, who led this study.

"In this case, we looked at a special type of binary system: an X-ray binary, where the neutron star is accreting mass from its companion star. In these systems, the accreted material is heated up to millions of degrees and emits large amounts of X-rays," he adds.

Manousakis undertook this research as a PhD student under the supervision of Roland Walter at the ISDC Data Centre for Astrophysics at the University of Geneva, Switzerland. He is currently a researcher at the Nicolaus Copernicus Astronomical Center in Warsaw, Poland.

The binary system investigated in this study, known as IGR J17252-3616, belongs to a special class of sources named highly obscured high-mass X-ray binaries. In a high-mass X-ray binary (HMXB) system, the companion star fuelling the accreting neutron star is a bright, massive star. Highly obscured HMXBs are a subset of these systems that exhibit very faint emission at soft X-ray energies: as a result had eluded all searches in this portion of the electromagnetic spectrum. They were discovered via hard X-ray observations with INTEGRAL in 2003.

"We believe that soft X-rays from highly obscured high-mass X-ray binaries are absorbed by the wind released by the neutron star's companion, a supergiant star," notes Chris Winkler, INTEGRAL project scientist at ESA. "On the other hand, hard X-rays are not affected by the stellar wind, making these sources easier to spot in hard X-rays," he adds.

Manousakis and his collaborators made use of extensive observations of the hard X-ray emission from IGR J17252-3616 obtained with INTEGRAL, which monitored this source frequently over the past decade. In addition, XMM-Newton was also used to obtain dedicated observations of the soft X-ray emission from this source.

"Although highly obscured HMXBs are intrinsically fainter at soft X-rays, they can still be detected with XMM-Newton. In particular, the observations of the soft X-ray emission from this binary system were crucial to reveal variations in this absorbed component," comments Norbert Schartel, XMM-Newton project scientist at ESA.


Image above: Variations in the absorption of the soft X-ray emission from an eclipsing, highly obscured high-mass X-ray binary as a function of its orbital phase. Credit: ESA/AOES Medialab.

 The astronomers were able to gather more information about the dynamics of this system because IGR J17252-3616 is an eclipsing binary: the inclination of the orbital plane with respect to our line of sight is such that the two components are seen to periodically transit in front of one another.

"The occurrence of eclipses allows us to tackle the dynamics of this binary system by studying how much the soft X-ray emission is absorbed by the stellar wind as the neutron star and its companion move around one another," notes Roland Walter of the Data Centre for Astrophysics (ISDC) at the University of Geneva, Switzerland.

"The variations we observed in the XMM-Newton data exhibit a regular pattern that shows us how the stellar wind is being deflected by the neutron star's gravity," Walter adds.

video

Video above: The stellar wind is deflected by the neutron star's gravity in a numerical simulation of highly obscured HMXB. Courtesy of Antonios Manousakis, ISDC, Geneva, Switzerland.

The team of astronomers tried to reproduce this behaviour using numerical simulations. In particular, they looked at how the density and shape of the accreted material evolve in highly obscured HMXBs with different values for the velocity of the stellar wind and the mass of the neutron star.

"The simulations we ran show that binary systems with slower stellar winds are more likely to develop streams and trailing tails in the proximity of the neutron star. These features could cause absorption variations such as those seen in IGR J17252-3616," explains co-author John Blondin from North Carolina State University at Raleigh, USA. "This seems to suggest that slow stellar winds and highly obscured HMXB are somehow correlated."

The simulations also showed that the mass of the neutron star plays an important role in shaping the observed variations in the absorption. More massive neutron stars induce a more pronounced deflection on the flow of accreted matter. This results into a thicker and denser tail that trails the neutron star, causing stronger absorption.

"The dependence of the absorption variations on the neutron star's mass in the simulations suggests that we can use this approach to estimate the mass of neutron stars in this type of system. In the case of IGR J17252-3616, the comparison between simulations and observations suggests that the neutron star hosted in this binary system is a rather massive one, with a mass of about 1.9 solar masses," says Manousakis.


Graphic above: Absorption variations and neutron-star masses in highly obscured high-mass X-ray binaries. Credit: From Manousakis et al, 2012.

This value, determined by using the flow of accreted matter as a test particle to trace the neutron star's gravitational field, is in agreement with previous estimates of this object mass based on independent measurements.

The method proposed in this study provides an independent and robust alternative to currently used techniques to assess the mass of these exotic objects, proving a fruitful synergy between two missions in ESA's Science Programme.

Notes for editors:

The study presented here is based on observations of the highly obscured high-mass X-ray binary IGR J17252-3616, an eclipsing binary system where a neutron star is accreting matter from a supergiant blue star.

The hard X-ray emission from IGR J17252-3616 was monitored extensively with ESA's INTEGRAL space observatory, yielding a regular survey of the source's variability over the past decade. These data were combined with additional observations from NASA's Rossi X-Ray Timing Explorer to constrain the orbital parameters of the binary system. Besides, 10 dedicated observations of the soft X-ray emission from IGR J17252-3616 were obtained with ESA's XMM-Newton X-ray space observatory. The XMM-Newton data were used to study in great detail how much the soft X-rays are absorbed by the stellar wind as a function of the binary system's orbital phase.

The data have then been compared with the predictions from numerical simulations performed using the freely-available hydrodynamical code VH-1, which is maintained at North Carolina State University by Prof. John Blondin.

INTEGRAL is an ESA project with instruments and science data centre funded by ESA Member States (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Spain, Switzerland) and Poland, and with the participation of Russia and the USA.

The European Space Agency's X-ray Multi-Mirror Mission, XMM-Newton, was launched in December 1999. It is the biggest scientific satellite to have been built in Europe and uses over 170 wafer-thin cylindrical mirrors spread over three high throughput X-ray telescopes. Its mirrors are among the most powerful ever developed. XMM-Newton's orbit takes it almost a third of the way to the Moon, allowing for long, uninterrupted views of celestial objects. The scientific community can apply for observing time on XMM-Newton on a competitive basis.

Related Links:

The hydrodynamical code VH-1: http://wonka.physics.ncsu.edu/pub/VH-1/

For more information about Integral & XMM-Newton, visit: http://www.esa.int/SPECIALS/Integral/index.html and http://xmm.esac.esa.int/

Greetings, Orbiter.ch

Super storm tracked by ESA water mission









ESA - SMOS Mission logo.

9 November 2012

When millions of people are bracing themselves for the onslaught of extreme weather, as much information as possible is needed to predict the strength of the impending storm. ESA’s SMOS mission again showed its versatility by capturing unique measurements of Hurricane Sandy.

As its name suggests, the Soil Moisture and Ocean Salinity (SMOS) satellite was designed to measure how much moisture is held in soil and how much salt is held in the surface waters of the oceans.

Hurricane Sandy from SMOS

This information is helping to improve our understanding of the water cycle – an essential component of the Earth system.

However, this state-of-the-art Earth Explorer mission has demonstrated that its instrumentation and measuring techniques can be used to offer much more.

Since SMOS has the ability to see through clouds and it is little affected by rain, it can also provide reliable estimates of the surface wind speeds under intense storms. 

Parts of the Caribbean and northeastern US are still suffering the aftermath of Hurricane Sandy, which is the largest Atlantic hurricane on record.

Hurricane Sandy

Unusually, Sandy was a hybrid storm, tapping energy from the evaporation of seawater like a hurricane and from different air temperatures like a winter storm. These conditions generated a super storm that spanned an incredible 1800 km.

As it orbited above, the satellite intercepted parts of Hurricane Sandy at least eight times as the storm swept over Jamaica and Cuba around 25 October, until its landfall in New Jersey, US, four days later.

The data from these encounters have been used to estimate the speed of the wind over the ocean’s surface.

SMOS carries a novel microwave sensor to capture images of ‘brightness temperature’. These images correspond to radiation emitted from the surface of Earth, which are then used to derive information on soil moisture and ocean salinity.

SMOS

Strong winds over oceans whip up waves and whitecaps, which in turn affect the microwave radiation being emitted from the surface. This means that although strong storms make it difficult to measure salinity, the changes in emitted radiation can, however, be linked directly to the strength of the wind over the sea.

This method of measuring surface wind speeds was developed by scientists at the French Research Institute for Exploration of the Sea and Collect Localisation Satellites, CLS, within ESA’s Earth Observation Support to Science Element programme.

The method was originally used during Hurricane Igor in 2010, but has again proven accurate. During Hurricane Sandy, SMOS data compare well with realtime measurements from meteorological buoys as the super storm passed between the coast of the US and the Bermuda Islands.

SMOS and aircraft measurements

Moreover, NOAA’s Hurricane Research Division flew a P-3 aircraft seven times into Hurricane Sandy to gather measurements of surface wind speeds, rain and other meteorological parameters. One of these airborne campaigns coincided with an overpass of the satellite.

Keeping in mind the significantly differing sampling characteristics between the SMOS radiometer and the aircraft sensor, there was excellent agreement in the measurements. Both instruments consistently detected a wind band 150 km south of the hurricane eye, with a speed of just over 100 km/h.

Being able to measure ocean surface wind in stormy conditions with the synoptic and frequent coverage of SMOS is paramount for tracking and forecasting hurricane strength.

Although ESA’s Earth Explorers are developed to address specific scientific issues, they continue to demonstrate their versatility.

Related links:

SMOS: http://www.esa.int/SPECIALS/smos/index.html

SMOS has a better look at salinity: http://www.esa.int/esaEO/SEMG4CERI7H_index_0.html

SMOS water mission turns hurricane hunter: http://www.esa.int/esaEO/SEMJFHWX7YG_index_0.html

In depth, SMOS: http://www.esa.int/esaLP/LPsmos.html

SMOS+storms: http://smosstorm.ifremer.fr/

Access SMOS data: http://earth.esa.int/SMOS/

Ifremer–Cersat Salinity Center: http://www.salinityremotesensing.ifremer.fr/home

CLS: http://www.cls.fr/welcome_en.html

CESBIO–SMOS blog: http://www.cesbio.ups-tlse.fr/SMOS_blog/

Images, Text, Credits: ESA / AOES Medialab / Ifremer / Eumetsat / NOAA / HRD.

Best regards, Orbiter.ch

jeudi 8 novembre 2012

Cosmic Sprinklers Explained












ESO - European Southern Observatory logo.

8 November 2012

Odd pair of aging stars sculpt spectacular shape of planetary nebula

 The planetary nebula Fleming 1 seen with ESO’s Very Large Telescope

Astronomers using ESO’s Very Large Telescope have discovered a pair of stars orbiting each other at the centre of one of the most remarkable examples of a planetary nebula. The new result confirms a long-debated theory about what controls the spectacular and symmetric appearance of the material flung out into space. The results are published in the 9 November 2012 issue of the journal Science.

Planetary nebulae [1] are glowing shells of gas around white dwarfs — Sun-like stars in the final stages of their lives. Fleming 1 is a beautiful example that has strikingly symmetric jets [2] that weave into knotty, curved patterns. It is located in the southern constellation of Centaurus (The Centaur) and was discovered just over a century ago by Williamina Fleming [3], a former maid who was hired by Harvard College Observatory after showing an aptitude for astronomy.

The planetary nebula Fleming 1 in the constellation of Centaurus (The Centaur)

Astronomers have long debated how these symmetric jets could be created, but no consensus has been reached. Now, a research team led by Henri Boffin (ESO, Chile) has combined new Very Large Telescope (VLT) observations of Fleming 1 with existing computer modelling to explain in detail for the first time how these bizarre shapes came about.

The team used ESO’s VLT to study the light coming from the central star. They found that Fleming 1 is likely to have not one but two white dwarfs at its centre, circling each other every 1.2 days. Although binary stars have been found at the hearts of planetary nebulae before, systems with two white dwarfs orbiting each other are very rare [4].

Wide-field view of the sky around the planetary nebula Fleming 1

“The origin of the beautiful and intricate shapes of Fleming 1 and similar objects has been controversial for many decades,” says Henri Boffin. “Astronomers have suggested a binary star before, but it was always thought that in this case the pair would be well separated, with an orbital period of tens of years or longer. Thanks to our models and observations, which let us examine this unusual system in great detail and peer right into the heart of the nebula, we found the pair to be several thousand times closer.”

When a star with a mass up to eight times that of the Sun approaches the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star to radiate strongly, causing this outward-moving cocoon of gas to glow brightly as a planetary nebula.

Artist’s view of how a planetary nebula’s wobbling jets are sculpted

While stars are spherical, many of these planetary nebulae are strikingly complex, with knots, filaments, and intense jets of material forming intricate patterns. Some of the most spectacular nebulae — including Fleming 1 — present point-symmetric structures [5]. For this planetary nebula it means that the material appears to shoot from both poles of the central region in S-shaped flows. This new study shows that these patterns for Fleming 1 are the result of the close interaction between a pair of stars — the surprising swansong of a stellar couple.

video
Zooming in on the planetary nebula Fleming 1

“This is the most comprehensive case yet of a binary central star for which simulations have correctly predicted how it shaped the surrounding nebula — and in a truly spectacular fashion,” explains co-author Brent Miszalski, from SAAO and SALT (South Africa).

video
A close-up view of the planetary nebula Fleming 1 seen with ESO’s Very Large Telescope

The pair of stars in the middle of this nebula is vital to explain its observed structure. As the stars aged, they expanded, and for part of this time, one acted as a stellar vampire, sucking material from its companion. This material then flowed in towards the vampire, encircling it with a disc known as an accretion disc [6]. As the two stars orbited one another, they both interacted with this disc and caused it to behave like a wobbling spinning top — a type of motion called precession. This movement affects the behaviour of any material that has been pushed outwards from the poles of the system, such as outflowing jets. This study now confirms that precessing accretion discs within binary systems cause the stunningly symmetric patterns around planetary nebulae like Fleming 1.

video
Artist’s view of how a planetary nebula’s wobbling jets are sculpted

The deep images from the VLT have also led to the discovery of a knotted ring of material within the inner nebula. Such a ring of material is also known to exist in other families of binary systems, and appears to be a telltale signature of the presence of a stellar couple.

“Our results bring further confirmation of the role played by interaction between pairs of stars to shape, and perhaps even form, planetary nebulae,” concludes Boffin.

Notes:

[1] Planetary nebulae have nothing to do with planets. The name arose in the eighteenth century as some of these objects resembled the discs of the distant planets when seen through small telescopes.

[2] Jets are outflows of very fast-moving gas that are ejected from the core regions of planetary nebulae. They are often collimated — the material comes out in parallel streams — meaning that they spread out only very slightly as they propagate through space.

[3] Fleming 1 is named after Scottish astronomer Williamina Fleming, who discovered it in 1910. Initially working as a maid to the director of the Harvard College Observatory in the 1880s, Fleming was later hired to process astronomical data at the observatory as one of the Harvard Computers, a group of skilled female workers carrying out mathematical calculations and clerical work. During her time she discovered — and was credited for — numerous astronomical objects, including 59 gaseous nebulae, over 310 variable stars, and 10 novae. This object also has many other names, including PN G290.5+07.9, ESO 170-6 and Hen 2-66.

[4] The team studied the stars using the FORS instrument on the Very Large Telescope at ESO’s Paranal Observatory in Chile. As well as taking images of the object they also split the light up into its component colours to obtain information about the motions as well as the temperature and chemical composition of the central object.

The primary and secondary stars were found to have approximately 0.5 to 0.86 and 0.7 to 1.0 times the mass of the Sun, respectively. The team was able to rule out the possibility of there being a “normal” star like our Sun in the binary by analysing the light from the two stars, and studying the system’s brightness. As the system rotates its brightness only changes by tiny amounts. A normal star would have been heated by its hot white dwarf, and because it would be always presenting the same face to its companion (as the Moon does with the Earth), it would present a “hot and luminous” and “cold and dark” side, easily seen as a regular variation in brightness. The central object is thus very likely a pair of white dwarfs — a rare and exotic find.

[5] In this case each part of the nebula has an exact counterpart at the same distance from the star, but in the opposite direction — the kind of symmetry shown by the court cards in a conventional pack of playing cards.

[6] Such a disc is formed when the stream of material escaping from a star overflows a certain boundary, known as the Roche lobe. Within this lobe, all matter is bound to its host star by gravity and cannot escape. When this lobe fills up and the boundary is exceeded, mass tumbles away from the star and transfers to a nearby body, for example the second star in a binary system, forming an accretion disc.

More information:

This research was presented in a paper “An Interacting Binary System Powers Precessing Outflows of an Evolved Star”, H. M. J. Boffin et al., to appear in the journal Science on 9 November 2012.

The team is composed of H. M. J. Boffin (European Southern Observatory, Chile), B. Miszalski (South African Astronomical Observatory; Southern African Large Telescope Foundation, South Africa), T. Rauch (Institute for Astronomy and Astrophysics, University of Tübingen, Germany), D. Jones (European Southern Observatory, Chile), R. L. M. Corradi (Instituto de Astrofísica de Canarias; Departamento de Astrofísica, Universidad de La Laguna, Spain), R. Napiwotzki (University of Hertfordshire, United Kingdom), A. C. Day-Jones (Universidad de Chile, Chile), and J. Köppen (Observatoire de Strasbourg, France).

To obtain a copy of the Science paper please contact the Science Press Package office at either scipak@aaas.org (email), or +1 202 326 6440 (phone).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Link:

    Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/

Images, Text, Credits: ESO/H. Boffin/L. Calçada/IAU and Sky & Telescope/Digitized Sky Survey 2. Acknowledgement: Davide De Martin/Videos: ESO/Digitized Sky Survey 2/Nick Risinger (skysurvey.org)/Music: delmo "acoustic".

Greetings, Orbiter.ch

A Nearby Stellar Cradle











NASA - Chandra X-ray Observatory patch.

Nov. 8, 2012


The Milky Way and other galaxies in the universe harbor many young star clusters and associations that each contain hundreds to thousands of hot, massive, young stars known as O and B stars. The star cluster Cygnus OB2 contains more than 60 O-type stars and about a thousand B-type stars. Deep observations with NASA’s Chandra X-ray Observatory have been used to detect the X-ray emission from the hot outer atmospheres, or coronas, of young stars in the cluster and to probe how these fascinating star factories form and evolve. About 1,700 X-ray sources were detected, including about 1,450 thought to be stars in the cluster. In this image, X-rays from Chandra (blue) have been combined with infrared data from NASA’s Spitzer Space Telescope (red) and optical data from the Isaac Newton Telescope (orange).

Young stars ranging in age from one million to seven million years were found. The infrared data indicates that a very low fraction of the stars have circumstellar disks of dust and gas. Even fewer disks were found close to the massive OB stars, betraying the corrosive power of their intense radiation that leads to early destruction of their disks. There is also evidence that the older population of stars has lost its most massive members because of supernova explosions. Finally, a total mass of about 30,000 times the mass of the sun is derived for Cygnus OB2, similar to that of the most massive star forming regions in our Galaxy. This means that Cygnus OB2, located only about 5,000 light years from Earth, is the closest massive star cluster.

Chandra X-ray Observatory

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Read more/access all images: http://chandra.harvard.edu/photo/2012/cygob2/

Chandra's Flickr photoset: http://www.flickr.com/photos/nasamarshall/sets/72157606205297786/

Images, Credits: X-ray: NASA/CXC/SAO/J.Drake et al, Optical: Univ. of Hertfordshire/INT/IPHAS, Infrared: NASA/JPL-Caltech / Text, Credits: NASA / J.D. Harrington / Marshall Space Flight Center / Janet Anderson /  Chandra X-ray Center / Peter Edmonds.

Greetings, Orbiter.ch

mercredi 7 novembre 2012

Lunar Land: AMERE study












ESA - European Space Agency patch.

7 November 2012

ESA General Studies Programme

AMERE is a GSP study for a space experiment that will help quantify the risks to human explorers of exposure to the deep space radiation environment. It does this by imaging repair processes in human cells following damage by cosmic radiation. The study is lead by the Belgian company lambda-x.

AMERE cosmic radiation

Radiation poses one of the greatest potential problems for deep space exploration by humans and reliably quantifying risks for future human missions to the Moon, Mars, asteroids or other deep space locations is extremely challenging.

Uncertainties about the effects of space radiation on human physiology arise primarily because of the difficulties in creating analogous environments on Earth in which to perform appropriate testing. For this reason measurements of the cellular processes that occur in response to radiation damage to human cells in situ provides a vital reference point for evaluating the long term effects of exposure to these environments.

AMERE experiment

The AMERE experiment addresses this by exposing human cells to the galactic cosmic rays in deep space and imaging the repair mechanisms that are expressed in response to the resultant DNA damage. To do this the experiment combines radiation detection, modified human cell lines in a dedicated life support system and both structured light and dark field optical microscopy in an integrated and complex system. Such a system can be applied on deep space mission, orbital platforms and planetary surface missions (e.g. on the Moon).

The AMERE study has been funded through the ESA General Studies Programme and has been led by Lambda-X with University of Gent, Canberra and Delphi Genetics.

More information:

About the GSP: http://www.esa.int/SPECIALS/GSP/SEMGJ6BO3DG_0.html

Participating in GSP studies: http://www.esa.int/SPECIALS/GSP/SEMSOIQWJ1H_0.html

Who we are: http://www.esa.int/SPECIALS/GSP/SEMVAXSX55H_0.html

Images, Text, Credit: ESA / James Carpenter.

Best regards, Orbiter.ch

lundi 5 novembre 2012

Hubble Sees an Unexpected Population of Young-Looking Stars











NASA / ESA - Hubble Space Telescope patch.

Nov. 5, 2012


The NASA/ESA Hubble Space Telescope offers an impressive view of the center of globular cluster NGC 6362. The image of this spherical collection of stars takes a deeper look at the core of the globular cluster, which contains a high concentration of stars with different colors.

Tightly bound by gravity, globular clusters are composed of old stars, which, at around 10 billion years old, are much older than the sun. These clusters are fairly common, with more than 150 currently known in our galaxy, the Milky Way, and more which have been spotted in other galaxies.

Globular clusters are among the oldest structures in the Universe that are accessible to direct observational investigation, making them living fossils from the early years of the cosmos.

Astronomers infer important properties of globular clusters by looking at the light from their constituent stars. For many years, they were regarded as ideal laboratories for testing the standard stellar evolution theory. Among other things, this theory suggests that most of the stars within a globular cluster should be of a similar age.

Recently, however, high precision measurements performed in numerous globular clusters, primarily with the Hubble Space Telescope, have led some to question this widely accepted theory. In particular, certain stars appear younger and bluer than their companions, and they have been dubbed blue stragglers. NGC 6362 contains many of these stars.

Hubble Space Telescope

Since they are usually found in the core regions of clusters, where the concentration of stars is large, the most likely explanation for this unexpected population of objects seems to be that they could be either the result of stellar collisions or transfer of material between stars in binary systems. This influx of new material would heat up the star and make it appear younger than its neighbors.

NGC 6362 is located about 25 000 light-years from Earth in the constellation of Ara (The Altar). British astronomer James Dunlop first observed this globular cluster on 30 June 1826.

This image was created combining ultraviolet, visual and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys and the Wide Field Camera 3. An image of NGC 6362 taken by the MPG/ESO 2.2-meter telescope will be published by the European Southern Observatory on Wednesday.

ESA / NASA Hubble websites: http://www.spacetelescope.org and http://hubblesite.org

Images, Text, Credits: ESA / Hubble & NASA.

Greetings, Orbiter.ch