Young Magnetic Star Possesses Precise Carbon Dioxide Ring


Catching a ring – or accretion disk – around a star isn’t unusual. However, catching a sharply defined carbon-dioxide ring around a young, magnetic star that’s precisely 1 AU away with a width 0.32 AU or less might raise a few eyebrows. This isn’t just any disk, either… It’s been likened as a “rope-like structure” and there’s even more to the mystery. It’s encircling a Herbig Ae star.

Discovered with the European Southern Observatory’s Very Large Telescope, the edges of this accretion disk are uniquely crisp. Located in the constellation of Centaurus at about 700 light years distant, V1052 (HD 101412) is a parent star with an infrared excess. “HD 101412 is most unusual in having resolved, magnetically split spectral lines which reveal a surface field modulus that varies between 2.5 to 3.5 kG.” says C.R. Cowley (et al). Previous studies “have surveyed molecular emission in a variety of young stellar objects. They found the emission to be much more subdued in Herbig Ae/Be stars than their cooler congeners, the T Tauri stars. This was true for HD 101412 as well, which was among the 25 Herbig Ae/Be stars they discussed. One exception, however, was the molecule CO2, which had a very large flux in HD 101412; indeed, only one T Tauri star had a higher CO2 flux.”

It’s not unusual for carbon dioxide to be found near young stars, but it is a bit more normal for it to be distributed throughout the disk region. “It’s exciting because this is the most constrained ring we’ve ever seen, and it requires an explanation,” explains Cowley, who is professor emeritus at the University of Michigan and leader of the international research effort. “At present time, we just don’t understand what makes it a rope rather than a dish.”

Because V1052 itself is different could be the reason. It is hypothesized the magnetic fields may be holding the rings in the disk structure at a certain distance. The idea has also been forwarded that there may be “shepherding planets”, much like Saturn’s ring structure, which may be the cause. “What makes this star so special is its very strong magnetic field and the fact that it rotates extremely slow compared to other stars of the same type,” said Swetlana Hubrig, of the Leibniz Institute for Astrophysics Potsdam (AIP), Germany.

One thing that is certain is how clean and well-defined the disk lines are centered around the Earth/Sun distance. This accords well with computer modeling where “A wider disk will not fit the observations.” These observations – and the exotic parent star – have been under intense scrutiny since 2008 and the findings have been recently published on-line in Astronomy and Astrophysics. It’s work that helps deepen the understanding of the interaction between central stars, their magnetic fields, and planet-forming disks. It also allows for fact finding when it comes to diverse systems and better knowledge of how solar systems form… even unusual ones.

“Why do turbulent motions not tear the ring apart?” Cowley wondered. “How permanent is the structure? What forces might act to preserve it for times comparable to the stellar formation time itself?”

When it comes to Herbig Ae stars, they are not only rare, but present a rare opportunity for study. In this case, it gives the team something to be quite excited about.

“This star is a gift of nature,” Hubrig said

Original Story Source: Leibniz Institute for Astrophysic News Release. For Further Reading: The narrow, inner CO ring around the magnetic Herbig Ae star, HD 101412.

Suburu Telescope Captures Hidden Planets In Stellar Dust Ring


No. It’s not a new atomic image – it’s a very unusual look at a star which could help further our understanding of stellar disk structure and planetary formation. As part of the SEEDS (Strategic Exploration of Exoplanets and Disks with Subaru Telescope/HiCIAO) project, this image of star HR 4796 was taken with Subaru’s planet-finder camera, HiCIAO (High Contrast Instrument for the Subaru Next Generation Adaptive Optics). At only about 8-10 million years old, the feature of this stellar image is only about 240 light years away from Earth, yet fully displays its ring of dust grains which reach out about twice the distance as Pluto’s orbit from the central star. This image produced by an international group led by Motohide Tamura of NAOJ (National Astronomical Observatory of Japan) is so wonderfully detailed that an offset between its center and the star’s position can be measured. While the offset was predicted by data from the Hubble and another research group, this new photographic evidence not only confirms its presence – but shows it to be larger than expected.

With new data to work from, researchers began to wonder exactly what could have caused the dust torus to run off its axis. The easiest explanation would be gravitational force – where one or more planets located inside the gap within the ring could possibly be affecting the disk. This type of action could account for an “unbalancing” which could act in a predictable manner. Current computer modeling has shown these types of “gravitational tides” can mold a dust torus in unusual ways and they cite similar data gathered from observations of bright star, Formalhaut. Since no planet candidates have yet been directly observed around HR 4796, chances are any planets present are simply too small and dim to be spotted. However, thanks to the new Suburu image, researchers feel confident their presence could be the source of the circumstellar dust ring wobble.

With image accuracy as pinpoint as the Hubble Space Telescope, the Suburu near-infrared depiction allows for extremely accurate measurements by employing its adaptive optics system. This type of advanced astrophotography also allows for angular differential imaging – by-passing the glare of the central star and enhancing the faint signature of the dust ring. Such techniques are able to establish heightened information about the relationship of the circumstellar disk and gelling planets… a process which may begin from the “left-overs” of initial star formation. As surmised, this material could either be picked up by newly formed planets or be pushed out the system via stellar winds. Either way, it is a process which eliminates the majority of the dust within a few tens of millions of years. However, there are a few stars which continue to hold on to a “secondary disk” – a collection of dust which could be attributed to the collision of planetesimals. In the case of HR 4796, this is a likely scenario and studying it may provide a better understanding of how planets could form in this alternate debris disk.

Original Story Source: Suburu Telescope News Release. For Further Reading: Direct Images of Disks Unravel Mystery of Planet Formation.

Cosmic Collisions Could Eject Habitable Planets


When it comes to solar systems, chances are good that we’re a lot more special than we thought. According to a German-British team led by Professor Pavel Kroupa of the University of Bonn, our orderly neighborhood of varied planet sizes quietly orbiting in a nearly circular path isn’t a standard affair. Their new models show that habitable planets might just get ejected in a violent scenario where forming solar systems mean highly inclined orbits where hot Jupiters rule.

Some 4600 million years ago, our local planetary system was surmised to have evolved from a blanket of dust surrounding a rather ordinary star. Its planets orbited the same direction as the solar spin and lined up neatly on a plane fairly close to the solar equator. We were good little children… But maybe other systems aren’t so hospitable. There could be systems where the planets cruise around in the opposite direction of their host star’s spin – and have highly inclined orbits. What could cause one protoplanetary disk to take on quiet properties while another is more radical? Try a cosmic crash.

This new study focuses on the theory of a protoplanetary disk colliding with another cloud of material… not unrealistic thinking since most stars form within a cluster. The results could mean the inclusion of up to thirty times the mass of Jupiter. This added “weight” of extra gas and dust could add a tilt to a forming system. Team member Dr Ingo Thies, also of the University of Bonn, has carried out computer simulations to test the new idea. What he has found is that adding extra material can not only incline a forming disk, but cause a reverse spin as well. It may even speed up the planetary formation, leaving the rogues in retrograde orbits. This inhospitable scenario means that smaller planets get ejected systematically, leaving only hot Jupiters to hug in close to the parent star. Thankfully our path was a bit less disturbing.

Says Dr Thies: “Like most stars, the Sun formed in a cluster, so probably did encounter another cloud of gas and dust soon after it formed. Fortunately for us, this was a gentle collision, so the effect on the disk that eventually became the planets was relatively benign. If things had been different, an unstable planetary system may have formed around the Sun, the Earth might have been ejected from the Solar System and none of us would be here to talk about it.”

Professor Kroupa sees the model as a big step forward. “We may be on the cusp of solving the mystery of why some planetary systems are tilted so much and lack places where life could thrive. The model helps to explain why our Solar System looks the way it does, with the Earth in a stable orbit and larger planets further out. Our work should help other scientists refine their search for life elsewhere in the Universe.”

Original News Source: Royal Astronomical Society News.