Category Archives: Space Science

Astronomy, Exoplanets, Space Science

ESO: ALMA observes largest molecule yet in a planet-forming disc

A new report from the European Southern Observatory (ESO):

Astronomers discover largest molecule yet in a planet-forming disc

This composite image features an artistic impression of the planet-forming disc around the IRS 48 star, also known as Oph-IRS 48. The disc contains a cashew-nut-shaped region in its southern part, which traps millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets. Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) spotted several complex organic molecules in this region, including dimethyl ether, the largest molecule found in a planet-forming disc to date. The emission signaling the presence of this molecule (real observations shown in blue) is clearly stronger in the disc’s dust trap. A model of the molecule is also shown in this composite.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers at Leiden Observatory in the Netherlands have for the first time detected dimethyl ether in a planet-forming disc. With nine atoms, this is the largest molecule identified in such a disc to date. It is also a precursor of larger organic molecules that can lead to the emergence of life.

“From these results, we can learn more about the origin of life on our planet and therefore get a better idea of the potential for life in other planetary systems. It is very exciting to see how these findings fit into the bigger picture,“

says Nashanty Brunken, a Master’s student at Leiden Observatory, part of Leiden University, and lead author of the study published today in Astronomy & Astrophysics.

Dimethyl ether is an organic molecule commonly seen in star-forming clouds, but had never before been found in a planet-forming disc. The researchers also made a tentative detection of methyl formate, a complex molecule similar to dimethyl ether that is also a building block for even larger organic molecules.

“It is really exciting to finally detect these larger molecules in discs. For a while we thought it might not be possible to observe them,”

says co-author Alice Booth, also a researcher at Leiden Observatory.

The molecules were found in the planet-forming disc around the young star IRS 48 (also known as Oph-IRS 48) with the help of ALMA, an observatory co-owned by the European Southern Observatory (ESO). IRS 48, located 444 light-years away in the constellation Ophiuchus, has been the subject of numerous studies because its disc contains an asymmetric, cashew-nut-shaped “dust trap”. This region, which likely formed as a result of a newly born planet or small companion star located between the star and the dust trap, retains large numbers of millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets.

These images from the Atacama Large Millimeter/submillimeter Array (ALMA) show where various gas molecules were found in the disc around the IRS 48 star, also known as Oph-IRS 48. The disc contains a cashew-nut-shaped region in its southern part, which traps millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets. Recent observations spotted several complex organic molecules in this region, including formaldehyde (H2CO; orange), methanol (CH3OH; green) and dimethyl ether (CH3OCH3; blue), the last being the largest molecule found in a planet-forming disc to date. The emission signaling the presence of these molecules is clearly stronger in the disc’s dust trap, while carbon monoxide gas (CO; purple) is present in the entire gas disc. The location of the central star is marked with a star in all four images. The dust trap is about the same size as the area taken up by the methanol emission, shown on the bottom left.

Many complex organic molecules, such as dimethyl ether, are thought to arise in star-forming clouds, even before the stars themselves are born. In these cold environments, atoms and simple molecules like carbon monoxide stick to dust grains, forming an ice layer and undergoing chemical reactions, which result in more complex molecules. Researchers recently discovered that the dust trap in the IRS 48 disc is also an ice reservoir, harbouring dust grains covered with this ice rich in complex molecules. It was in this region of the disc that ALMA has now spotted signs of the dimethyl ether molecule: as heating from IRS 48 sublimates the ice into gas, the trapped molecules inherited from the cold clouds are freed and become detectable.

“What makes this even more exciting is that we now know these larger complex molecules are available to feed forming planets in the disc,” explains Booth. “This was not known before as in most systems these molecules are hidden in the ice.”

The discovery of dimethyl ether suggests that many other complex molecules that are commonly detected in star-forming regions may also be lurking on icy structures in planet-forming discs. These molecules are the precursors of prebiotic molecules such as amino acids and sugars, which are some of the basic building blocks of life.

By studying their formation and evolution, researchers can therefore gain a better understanding of how prebiotic molecules end up on planets, including our own.

“We are incredibly pleased that we can now start to follow the entire journey of these complex molecules from the clouds that form stars, to planet-forming discs, and to comets. Hopefully with more observations we can get a step closer to understanding the origin of prebiotic molecules in our own Solar System,”

says Nienke van der Marel, a Leiden Observatory researcher who also participated in the study.

Annotated image from the Atacama Large Millimeter/submillimeter Array (ALMA) showing the dust trap in the disc that surrounds the system Oph-IRS 48. The dust trap provides a safe haven for the tiny dust particles in the disc, allowing them to clump together and grow to sizes that allow them to survive on their own. The green area is the dust trap, where the bigger particles accumulate. The size of the orbit of Neptune is shown in the upper left corner to show the scale.

Future studies of IRS 48 with ESO’s Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade, will allow the team to study the chemistry of the very inner regions of the disc, where planets like Earth may be forming.

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ESO: No black hole found in “closest black hole” system

A new report from the European Southern Observatory (ESO):

“Closest black hole” system found to contain no black hole

New research using data from ESO’s Very Large Telescope and Very Large Telescope Interferometer has revealed that HR 6819, previously believed to be a triple system with a black hole, is in fact a system of two stars with no black hole. The scientists, a KU Leuven-ESO team, believe they have observed this binary system in a brief moment after one of the stars sucked the atmosphere off its companion, a phenomenon often referred to as “stellar vampirism”. This artist’s impression shows what the system might look like; it’s composed of an oblate star with a disc around it (a Be “vampire” star; foreground) and B-type star that has been stripped of its atmosphere (background).

In 2020 a team led by European Southern Observatory (ESO) astronomers reported the closest black hole to Earth, located just 1000 light-years away in the HR 6819 system. But the results of their study were contested by other researchers, including by an international team based at KU Leuven, Belgium. In a paper published today, these two teams have united to report that there is in fact no black hole in HR 6819, which is instead a “vampire” two-star system in a rare and short-lived stage of its evolution.

The original study on HR 6819 received significant attention from both the press and scientists. Thomas Rivinius, a Chile-based ESO astronomer and lead author on that paper, was not surprised by the astronomy community’s reception to their discovery of the black hole.

“Not only is it normal, but it should be that results are scrutinised,” he says, “and a result that makes the headlines even more so.”

Rivinius and his colleagues were convinced that the best explanation for the data they had, obtained with the MPG/ESO 2.2-metre telescope, was that HR 6819 was a triple system, with one star orbiting a black hole every 40 days and a second star in a much wider orbit. But a study led by Julia Bodensteiner, then a PhD student at KU Leuven, Belgium, proposed a different explanation for the same data: HR 6819 could also be a system with only two stars on a 40-day orbit and no black hole at all. This alternative scenario would require one of the stars to be “stripped”, meaning that, at an earlier time, it had lost a large fraction of its mass to the other star.

“We had reached the limit of the existing data, so we had to turn to a different observational strategy to decide between the two scenarios proposed by the two teams,”

says KU Leuven researcher Abigail Frost, who led the new study published today in Astronomy & Astrophysics.

To solve the mystery, the two teams worked together to obtain new, sharper data of HR 6819 using ESO’s Very Large Telescope (VLT) and Very Large Telescope Interferometer (VLTI).

“The VLTI was the only facility that would give us the decisive data we needed to distinguish between the two explanations,“

says Dietrich Baade, author on both the original HR 6819 study and the new Astronomy & Astrophysics paper. Since it made no sense to ask for the same observation twice, the two teams joined forces, which allowed them to pool their resources and knowledge to find the true nature of this system.

“The scenarios we were looking for were rather clear, very different and easily distinguishable with the right instrument,” says Rivinius. “We agreed that there were two sources of light in the system, so the question was whether they orbit each other closely, as in the stripped-star scenario, or are far apart from each other, as in the black hole scenario.”

To distinguish between the two proposals, the astronomers used both the VLTI’s GRAVITY instrument and the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s VLT.

“MUSE confirmed that there was no bright companion in a wider orbit, while GRAVITY’s high spatial resolution was able to resolve two bright sources separated by only one-third of the distance between the Earth and the Sun,” says Frost. “These data proved to be the final piece of the puzzle, and allowed us to conclude that HR 6819 is a binary system with no black hole.”

“Our best interpretation so far is that we caught this binary system in a moment shortly after one of the stars had sucked the atmosphere off its companion star. This is a common phenomenon in close binary systems, sometimes referred to as “stellar vampirism” in the press,” explains Bodensteiner, now a fellow at ESO in Germany and an author on the new study. “While the donor star was stripped of some of its material, the recipient star began to spin more rapidly.”

“Catching such a post-interaction phase is extremely difficult as it is so short,” adds Frost. “This makes our findings for HR 6819 very exciting, as it presents a perfect candidate to study how this vampirism affects the evolution of massive stars, and in turn the formation of their associated phenomena including gravitational waves and violent supernova explosions.”

The newly formed Leuven-ESO joint team now plans to monitor HR 6819 more closely using the VLTI’s GRAVITY instrument. The researchers will conduct a joint study of the system over time, to better understand its evolution, constrain its properties, and use that knowledge to learn more about other binary systems.

As for the search for black holes, the team remains optimistic.

“Stellar-mass black holes remain very elusive owing to their nature,”

says Rivinius.

“But order-of-magnitude estimates suggest there are tens to hundreds of millions of black holes in the Milky Way alone,”

Baade adds.

It is just a matter of time until astronomers discover them.

This wide-field view shows the region of the sky, in the constellation of Telescopium, where HR 6819 can be found. This view was created from images forming part of the Digitized Sky Survey 2. The two stars in HR 6819 can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope.

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ESO: Five exoplanets found locked in a rhythmic dance

The latest report from the European Southern Observatory (ESO):

Puzzling six-exoplanet system with rhythmic movement
challenges theories of how planets form

This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe.Credits: ESO

Using a combination of telescopes, including the Very Large Telescope of the European Southern Observatory (ESO’s VLT), astronomers have revealed a system consisting of six exoplanets, five of which are locked in a rare rhythm around their central star. The researchers believe the system could provide important clues about how planets, including those in the Solar System, form and evolve.

The first time the team observed TOI-178, a star some 200 light-years away in the constellation of Sculptor, they thought they had spotted two planets going around it in the same orbit. However, a closer look revealed something entirely different.

“Through further observations we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,”

says Adrien Leleu from the Université de Genève and the University of Bern, Switzerland, who led a new study of the system published today in Astronomy & Astrophysics.

The new research has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rhythmic dance as they move in their orbits. In other words, they are in resonance. This means that there are patterns that repeat themselves as the planets go around the star, with some planets aligning every few orbits. A similar resonance is observed in the orbits of three of Jupiter’s moons: Io, Europa and Ganymede. Io, the closest of the three to Jupiter, completes four full orbits around Jupiter for every orbit that Ganymede, the furthest away, makes, and two full orbits for every orbit Europa makes.

The five outer exoplanets of the TOI-178 system follow a much more complex chain of resonance, one of the longest yet discovered in a system of planets. While the three Jupiter moons are in a 4:2:1 resonance, the five outer planets in the TOI-178 system follow a 18:9:6:4:3 chain: while the second planet from the star (the first in the resonance chain) completes 18 orbits, the third planet from the star (second in the chain) completes 9 orbits, and so on. In fact, the scientists initially only found five planets in the system, but by following this resonant rhythm they calculated where in its orbit an additional planet would be when they next had a window to observe the system.

More than just an orbital curiosity, this dance of resonant planets provides clues about the system’s past.

“The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,”

explains co-author Yann Alibert from the University of Bern. If the system had been significantly disturbed earlier in its life, for example by a giant impact, this fragile configuration of orbits would not have survived.

Disorder in the rhythmic system

But even if the arrangement of the orbits is neat and well-ordered, the densities of the planets

“are much more disorderly,” says Nathan Hara from the Université de Genève, Switzerland, who was also involved in the study. “It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to.”

In our Solar System, for example, the planets are neatly arranged, with the rocky, denser planets closer to the central star and the fluffy, low-density gas planets farther out.

“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,”

says Leleu.

Combining techniques

To investigate the system’s unusual architecture, the team used data from the European Space Agency’s CHEOPS satellite, alongside the ground-based ESPRESSO instrument on ESO’s VLT and the NGTS and SPECULOOS, both sited at ESO’s Paranal Observatory in Chile. Since exoplanets are extremely tricky to spot directly with telescopes, astronomers must instead rely on other techniques to detect them. The main methods used are imaging transits — observing the light emitted by the central star, which dims as an exoplanet passes in front of it when observed from the Earth — and radial velocities — observing the star’s light spectrum for small signs of wobbles which happen as the exoplanets move in their orbits. The team used both methods to observe the system: CHEOPS, NGTS and SPECULOOS for transits and ESPRESSO for radial velocities.

By combining the two techniques, astronomers were able to gather key information about the system and its planets, which orbit their central star much closer and much faster than the Earth orbits the Sun. The fastest (the innermost planet) completes an orbit in just a couple of days, while the slowest takes about ten times longer. The six planets have sizes ranging from about one to about three times the size of Earth, while their masses are 1.5 to 30 times the mass of Earth. Some of the planets are rocky, but larger than Earth — these planets are known as Super-Earths. Others are gas planets, like the outer planets in our Solar System, but they are much smaller — these are nicknamed Mini-Neptunes.

Although none of the six exoplanets found lies in the star’s habitable zone, the researchers suggest that, by continuing the resonance chain, they might find additional planets that could exist in or very close to this zone. ESO’s Extremely Large Telescope (ELT), which is set to begin operating this decade, will be able to directly image rocky exoplanets in a star’s habitable zone and even characterise their atmospheres, presenting an opportunity to get to know systems like TOI-178 in even greater detail.

More information

This research was presented in the paper “Six transiting planets and a chain of Laplace resonances in TOI-178” to appear in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202039767).

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ESO: Telescopes observe final moments of a star eaten by a black hole

A new report from the European Southern Observatory (ESO):

Death by Spaghettification:
ESO Telescopes Record Last Moments of Star Devoured by a Black Hole

This illustration depicts a star (in the foreground) experiencing spaghettification as it’s sucked in by a supermassive black hole (in the background) during a ‘tidal disruption event’. In a new study, done with the help of ESO’s Very Large Telescope and ESO’s New Technology Telescope, a team of astronomers found that when a black hole devours a star, it can launch a powerful blast of material outwards.Credits ESO

Using telescopes from the European Southern Observatory (ESO) and other organisations around the world, astronomers have spotted a rare blast of light from a star being ripped apart by a supermassive black hole. The phenomenon, known as a tidal disruption event, is the closest such flare recorded to date at just over 215 million light-years from Earth, and has been studied in unprecedented detail. The research is published today in Monthly Notices of the Royal Astronomical Society.

“The idea of a black hole ‘sucking in’ a nearby star sounds like science fiction. But this is exactly what happens in a tidal disruption event,”

says Matt Nicholl, a lecturer and Royal Astronomical Society research fellow at the University of Birmingham, UK, and the lead author of the new study. But these tidal disruption events, where a star experiences what’s known as spaghettification as it’s sucked in by a black hole, are rare and not always easy to study. The team of researchers pointed ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT) at a new flash of light that occurred last year close to a supermassive black hole, to investigate in detail what happens when a star is devoured by such a monster.

Astronomers know what should happen in theory.

“When an unlucky star wanders too close to a supermassive black hole in the centre of a galaxy, the extreme gravitational pull of the black hole shreds the star into thin streams of material,”

explains study author Thomas Wevers, an ESO Fellow in Santiago, Chile, who was at the Institute of Astronomy, University of Cambridge, UK, when he conducted the work. As some of the thin strands of stellar material fall into the black hole during this spaghettification process, a bright flare of energy is released, which astronomers can detect.

Although powerful and bright, up to now astronomers have had trouble investigating this burst of light, which is often obscured by a curtain of dust and debris. Only now have astronomers been able to shed light on the origin of this curtain.

“We found that, when a black hole devours a star, it can launch a powerful blast of material outwards that obstructs our view,” 

explains Samantha Oates, also at the University of Birmingham. This happens because the energy released as the black hole eats up stellar material propels the star’s debris outwards.

The discovery was possible because the tidal disruption event the team studied, AT2019qiz, was found just a short time after the star was ripped apart.

“Because we caught it early, we could actually see the curtain of dust and debris being drawn up as the black hole launched a powerful outflow of material with velocities up to 10 000 km/s,” says Kate Alexander, NASA Einstein Fellow at Northwestern University in the US. “This unique ‘peek behind the curtain’ provided the first opportunity to pinpoint the origin of the obscuring material and follow in real time how it engulfs the black hole.”

The team carried out observations of AT2019qiz, located in a spiral galaxy in the constellation of Eridanus, over a 6-month period as the flare grew in luminosity and then faded away.

“Several sky surveys discovered emission from the new tidal disruption event very quickly after the star was ripped apart,” says Wevers. “We immediately pointed a suite of ground-based and space telescopes in that direction to see how the light was produced.”

Multiple observations of the event were taken over the following months with facilities that included X-shooter and EFOSC2, powerful instruments on ESO’s VLT and ESO’s NTT, which are situated in Chile. The prompt and extensive observations in ultraviolet, optical, X-ray and radio light revealed, for the first time, a direct connection between the material flowing out from the star and the bright flare emitted as it is devoured by the black hole.

“The observations showed that the star had roughly the same mass as our own Sun, and that it lost about half of that to the monster black hole, which is over a million times more massive,”

says Nicholl, who is also a visiting researcher at the University of Edinburgh.

The research helps us better understand supermassive black holes and how matter behaves in the extreme gravity environments around them. The team say AT2019qiz could even act as a ‘Rosetta stone’ for interpreting future observations of tidal disruption events. ESO’s Extremely Large Telescope (ELT), planned to start operating this decade, will enable researchers to detect increasingly fainter and faster evolving tidal disruption events, to solve further mysteries of black hole physics.

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ESO: Planetary disc warped and distorted in three star system

A new report from ESO (European Southern Observatory):

New Observations Show Planet-forming Disc Torn Apart
by its Three Central Stars

ALMA, in which ESO is a partner, and the SPHERE instrument on ESO’s Very Large Telescope have imaged GW Orionis, a triple star system with a peculiar inner region. The new observations revealed that this object has a warped planet-forming disc with a misaligned ring. In particular, the SPHERE image (right panel) allowed astronomers to see, for the first time, the shadow that this ring casts on the rest of the disc. This helped them figure out the 3D shape of the ring and the overall disc. The left panel shows an artistic impression of the inner region of the disc, including the ring, which is based on the 3D shape reconstructed by the team.

A team of astronomers have identified the first direct evidence that groups of stars can tear apart their planet-forming disc, leaving it warped and with tilted rings. This new research suggests exotic planets, not unlike Tatooine in Star Wars, may form in inclined rings in bent discs around multiple stars. The results were made possible thanks to observations with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA).

Our Solar System is remarkably flat, with the planets all orbiting in the same plane. But this is not always the case, especially for planet-forming discs around multiple stars, like the object of the new study: GW Orionis. This system, located just over 1300 light-years away in the constellation of Orion, has three stars and a deformed, broken-apart disc surrounding them.

“Our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disc,”

says Stefan Kraus, a professor of astrophysics at the University of Exeter in the UK who led the research published today in the journal Science. The misaligned ring is located in the inner part of the disc, close to the three stars.

The new research also reveals that this inner ring contains 30 Earth-masses of dust, which could be enough to form planets.

“Any planets formed within the misaligned ring will orbit the star on highly oblique orbits and we predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging campaigns, for instance with the ELT,”

says team member Alexander Kreplin of the University of Exeter, referring to ESO’s Extremely Large Telescope, which is planned to start operating later this decade. Since more than half the stars in the sky are born with one or more companions, this raises an exciting prospect: there could be an unknown population of exoplanets that orbit their stars on very inclined and distant orbits.

ALMA, in which ESO is a partner, and the SPHERE instrument on ESO’s Very Large Telescope have imaged GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. The ALMA image (left) shows the disc’s ringed structure, with the innermost ring separated from the rest of the disc. The SPHERE observations (right) allowed astronomers to see for the first time the shadow of this innermost ring on the rest of the disc, which made it possible for them to reconstruct its warped shape.

To reach these conclusions, the team observed GW Orionis for over 11 years. Starting in 2008, they used the AMBER and later the GRAVITY instruments on ESO’s VLT Interferometer in Chile, which combines the light from different VLT telescopes, to study the gravitational dance of the three stars in the system and map their orbits.

“We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc,”

says Alison Young of the Universities of Exeter and Leicester and a member of the team.

They also observed the system with the SPHERE instrument on ESO’s VLT and with ALMA, in which ESO is a partner, and were able to image the inner ring and confirm its misalignment. ESO’s SPHERE also allowed them to see, for the first time, the shadow that this ring casts on the rest of the disc. This helped them figure out the 3D shape of the ring and the overall disc.

The international team, which includes researchers from the UK, Belgium, Chile, France and the US, then combined their exhaustive observations with computer simulations to understand what had happened to the system. For the first time, they were able to clearly link the observed misalignments to the theoretical “disc-tearing effect”, which suggests that the conflicting gravitational pull of stars in different planes can warp and break their discs.

Their simulations showed that the misalignment in the orbits of the three stars could cause the disc around them to break into distinct rings, which is exactly what they see in their observations. The observed shape of the inner ring also matches predictions from numerical simulations on how the disc would tear.

ALMA, in which ESO is a partner, and the SPHERE instrument on ESO’s Very Large Telescope have imaged GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. This composite image shows both the ALMA and SPHERE observations of the disc.  The ALMA image shows the disc’s ringed structure, with the innermost ring (part of which is visible as an oblong dot at the very centre of the image) separated from the rest of the disc. The SPHERE observations allowed astronomers to see for the first time the shadow of this innermost ring on the rest of the disc, which made it possible for them to reconstruct its warped shape.

Interestingly, another team who studied the same system using ALMA believe another ingredient is needed to understand the system.

“We think that the presence of a planet between these rings is needed to explain why the disc tore apart,”

says Jiaqing Bi of the University of Victoria in Canada who led a study of GW Orionis published in The Astrophysical Journal Letters in May this year. His team identified three dust rings in the ALMA observations, with the outermost ring being the largest ever observed in planet-forming discs.

Future observations with ESO’s ELT and other telescopes may help astronomers fully unravel the nature of GW Orionis and reveal young planets forming around its three stars.

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