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  • richardmitnick 1:08 pm on December 22, 2016 Permalink | Reply
    Tags: Asteroseismology, , , ,   

    From Kavli: “Revealing the Orbital Shape Distributions of Exoplanets with China’s LAMOST Telescope” 

    KavliFoundation

    The Kavli Foundation

    12/22/2016

    Using data from China’s LAMOST telescope, a team of astronomers have derived how the orbital shapes distribute for extrasolar planets. The work is recently published in the journal Proceedings of the National Academy of Sciences of the United States of America” (PNAS). The lead authors are Prof. Jiwei Xie from Nanjing University and Prof. Subo Dong, a faculty member of the Kavli Institute of Astronomy & Astrophysics (KIAA) at Peking University.

    LAMOST telescope located in Xinglong Station, Hebei Province, China
    The Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) telescope in Hebei, China. It is the most efficient spectroscopy machine in the world.

    Until two decades ago, the only planetary system known to mankind was our own solar system. Most planets in the solar system revolve around the Sun on nearly circular orbits, and their orbits are almost on the same plane within about 3 degrees on average (i.e., the averaged inclination angle is about 3 degrees). Astronomers use the parameter called eccentricity to describe the shape of a planetary orbit. Eccentricity takes the value between 0 and 1, and the larger the eccentricity, the more an orbit deviates from circular. The averaged eccentricity of solar system planets is merely 0.06. Hundreds of years ago, motivated by circular and coplanar planetary orbits, Kant and Laplace hypothesized that planets should form in disks, and this theory has developed into the “standard model” on how planets form.

    In 1995, astronomers discovered the first exoplanet around a Sun-like star 51 Pegasi with a technique called Radial Velocity, and this discovery started an exciting era of exoplanet exploration. At the beginning of the 21st Century, people had discovered hundreds of exoplanets with the Radial Velocity technique, and most of them are giant planets comparable in mass with the Jupiter. These Jovian planets are relatively rare, found around approximately one tenth of stars studied by the Radial Velocity technique. The shapes of their orbits were a big surprise: a large fraction of them are on highly eccentric orbits, and all the giant planets found by Radial Velocity have a mean eccentricity of about 0.3. This finding challenges the “standard model” of planet formation and raises a long-standing puzzle for astronomers – are the nearly circular and coplanar planetary orbits in the solar system common or exceptional?

    The Kepler satellite launched by NASA in 2009 has discovered thousands of exoplanets by monitoring tiny dimming in the brightness of stars when their planets happen to cross in the front (called “transit”).

    Planet transit. NASA/Ames
    Planet transit. NASA/Ames

    Many of the planets discovered by Kepler have sizes comparable to that of the Earth. Kepler’s revolutionary discoveries show that Earth-size planets are prevalent in our galaxy. However, data from the Kepler satellite alone cannot be used to measure the shape of a transiting exoplanet’s orbit. To do so, one way is to use the size of the planet host star as a “ruler” to measure against the length of the planet transit, while implementing this method needs precise information on the host star parameters such as size and mass. This method has previously been applied to the host stars characterized with the asteroseismology technique but the sample is limited to a relatively small number of stars with high-frequency, exquisite brightness information required by asteroseismology.

    With its innovative design, the LAMOST telescope in China can observe spectra of thousands of celestial objects simultaneously within its large field of view, and it is currently the most efficient spectroscopy machine in the world (Figure 1). In recent years, LAMOST has obtained tens of thousands of stellar spectra in the sky region where the Kepler satellite monitors planet transits, and they include many hundreds of stars hosting transiting exoplanets. By comparing with other methods such as asteroseismology, the research team finds that, high-accuracy characterization of stellar parameters can be reliably obtained from LAMOST spectra, and they can subsequently be used to measure the the orbital shape distributions of Kepler exoplanets.

    They analyze a large sample of about 700 exoplanets whose host stars have LAMOST spectra, and with the LAMOST stellar parameters and Kepler transit data, they measure the eccentricity and inclination angle distributions. They find that about 80% of the analyzed planet orbits are nearly circular (averaged eccentricity less than 0.1) like those in the solar system, and only about 20% of the planets are on relatively eccentric orbits that significantly deviate from circular (average eccentricity large than 0.3). They also find that the average eccentricity and inclination angle for the Kepler systems with multiple planets fit into the pattern of the solar system objects (Figure 2).

    Therefore, circular orbits are not exceptional for planetary systems, and the orbital shapes of most planets inside and outside the solar system appear to distribute in a similar fashion. This implies that the formation and evolution processes leading to the distributions of the orbital shapes of the solar system may be common in the Galaxy.

    See the full article here .

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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
    • vegetarian dash diet meal pla 1:39 pm on December 22, 2016 Permalink | Reply

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      • richardmitnick 2:27 pm on December 22, 2016 Permalink | Reply

        Thanks, I am just glad my work is appreciated. I do it for the love of bringing this material which the press ignores to the public. I have about 800 readers in North America , Europe, East Asia, Africa, and the Middle East. No contests.

        Like

  • richardmitnick 9:10 am on January 16, 2016 Permalink | Reply
    Tags: Asteroseismology, , , Stellar Revelations,   

    From UCSB: “Stellar Revelations” 

    UC Santa Barbara Name bloc

    January 4, 2016
    Julie Cohen

    Temp 1
    Internal magnetic fields of red giants are up to 10 million times stronger than the Earth’s. No image credit found.

    Temp 2
    Jim Fuller, Matteo Cantiello and Lars Bildsten.Photo Credit: Bill Wolf

    Using a recently developed technique to detect magnetic fields inside stars, a group of astronomers — including Matteo Cantiello and Lars Bildsten from UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP) — has discovered that strong magnetic fields are very common in stars. The group’s findings appear in the journal Nature.

    “We have applied a novel theoretical idea that we developed just a few months ago to thousands of stars and the results are just extraordinary,” said Cantiello, a specialist in stellar astrophysics at KITP.

    Previously, only a very small percentage of stars were known to have strong magnetic fields. Therefore, current scientific models of how stars evolve do not include magnetic fields as a fundamental component.

    “Such fields have simply been regarded as insignificant for our general understanding of stellar evolution,” said lead author Dennis Stello, an astrophysicist at the University of Sydney in Australia. “Our result clearly shows this assumption needs to be revisited because we found that up to 60 percent of stars host strong fields.”

    3
    The life cycle of a Sun-like star.

    4
    Born from clouds of gas and dust, stars like our Sun spend most of their lifetime slowly burning their primary nuclear fuel, hydrogen, into the heavier element helium. After leading this bright and shiny life for several billion years, their fuel is almost exhausted and they start swelling, pushing the outer layers away from what has turned into a small and very hot core. These “middle-aged” stars become enormous, hence cool and red — red giants. All red giants exhibit a slow oscillation in brightness due their rhythmic “breathing” in and out, and one third of them are also affected by additional, slower and mysterious changes in their luminosity. After this rapid and tumultuous phase of their later life, these stars do not end in dramatic explosions, but die peacefully as planetary nebulae, blowing out everything but a tiny remnant, known as white dwarf.

    Until now, astronomers have been unable to detect these magnetic fields because such fields hide deep in the stellar interior, out of sight from conventional observation methods that measure only the surface properties of stars. The research team turned to asteroseismology, a technique that probes beyond the stellar surface, to determine the presence of very strong magnetic fields near the stellar core.

    “The stellar core is the region where the star produces most of its energy through thermonuclear reactions,” Cantiello explained. “So the field is likely to have important effects on how stars evolve since it can alter the physical processes that take place in the core.”

    Most stars — like the sun — are subject to continuous oscillations. “Their interior is essentially ringing like a bell,” noted co-author Jim Fuller, a postdoctoral scholar from the California Institute of Technology in Pasadena. “And like a bell or a musical instrument, the sound produced reveals physical properties, such as size, temperature and what they are made of.”

    The researchers used very precise data from NASA’s Kepler space telescope to measure tiny brightness variations caused by the ringing sound inside thousands of stars.

    NASA Kepler Telescope
    NASA/Kepler

    They found that certain oscillation frequencies were missing in 60 percent of the stars due to suppression by strong magnetic fields in the stellar cores.

    “It’s like having a trumpet that doesn’t sound normal because something is hiding inside it, altering the sound it produces,” Stello said.

    This magnetic suppression effect had previously been seen in only a few dozen stars. However, the new analysis of the full data set from Kepler revealed that this effect is prevalent in stars that are only slightly more massive than the sun.

    According to Cantiello, such intermediate mass stars are hotter and more luminous, and their cores are stirred by convection. “We believe that the magnetic field is created by this ‘boiling’ sequence and stored inside the star for the remaining evolutionary phase. Astrophysicists previously have suggested this but it was very speculative; now it seems clear that this is the case,” he said.

    “This is a very important result that will enable scientists to test more directly current theories for how magnetic fields form and evolve in stellar interiors,” said co-author Bildsten, the director of KITP. “When a star dies, the presence of strong magnetic fields can have a profound impact, possibly resulting in some of the brightest explosions in the universe.”

    This research could potentially lead to a better general understanding of stellar magnetic dynamos, including the one controlling the sun’s 11-year sunspot cycle, which is known to affect communication systems and cloud cover on Earth.

    “So far, the study of stellar magnetic dynamos principally relied on computer simulations, which now can be tested using these new exciting observations,” said Fuller.

    See the full article here .

    Please help promote STEM in your local schools.

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    UC Santa Barbara Seal

    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

     
  • richardmitnick 5:33 am on October 27, 2015 Permalink | Reply
    Tags: Asteroseismology, , ,   

    From UCSB: “Magnetic Hide and Seek” 

    UC Santa Barbara Name bloc

    KITP Kavli Institute for Theoretical Physics UCSB

    October 22, 2015
    Julie Cohen

    Researchers at the Kavli Institute for Theoretical Physics develop a new technique to detect magnetic fields inside stars

    1
    This artist’s representation of a red giant star with a strong internal magnetic field shows sound waves propagating in the stellar outer layers, while gravity waves propagate in the inner layers where a magnetic field is present.

    Magnetic fields have important consequences in all stages of stellar evolution, from a star’s formation to its demise. Now, for the first time, astrophysicists are able to determine the presence of strong magnetic fields deep inside pulsating giant stars.

    A consortium of international researchers, including several from UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP), used asteroseismology — a discipline similar to seismology — to track waves traveling through stars in order to determine their inner properties. Their findings appear in the journal Science.

    2
    Jim Fuller, Matteo Cantiello and Lars Bildsten Photo Credit: Bill Wolf

    “We can now probe regions of the star that were previously hidden,” said co-lead author Matteo Cantiello, a specialist in stellar astrophysics at KITP. “The technique is analogous to a medical ultrasound, which uses sound waves to image otherwise invisible parts of the human body.”

    Cantiello’s curiosity and that of his co-authors was sparked when astrophysicist Dennis Stello of the University of Sydney presented puzzling data from the Kepler satellite, a space telescope that measures stellar brightness variations with very high precision.

    NASA Kepler Telescope
    NASA/Kepler

    Cantiello, KITP director Lars Bildsten and Jim Fuller, a postdoctoral fellow at the California Institute of Technology, agreed that this was a mystery worth solving. After much debate, many calculations and the additional involvement of Rafael García, a staff scientist at France’s Commissariat à l’Énergie Atomique, a solution emerged. The data were explained by the presence of strong magnetic fields in the inner regions of these stars.

    The puzzling phenomenon was observed in a group of red giants imaged by Kepler. Red giants are stars much older and larger than the sun. Their outer regions are characterized by turbulent motion that excites sound waves, which interact with gravity waves that travel deep into the stellar core. Magnetic fields in the core can hinder the motions produced by the gravity waves.

    “Imagine the magnetic field as stiff rubber bands embedded in the stellar gas, which affect the propagation of gravity waves,” Fuller explained. “If the magnetic field is strong enough, the gravity waves become trapped in the star’s core. We call this the magnetic greenhouse effect.”

    The trapping occurs because the incoming wave is reflected by the magnetic field into waves with a lower degree of symmetry, which are prevented from escaping the core. As a result, stellar surface oscillations have smaller amplitude compared to a similar star without a strong magnetic field.

    “We used these observations to put a limit on — or even measure — the internal magnetic fields for these stars,” Cantiello said. “We found that red giants can possess internal magnetic fields nearly a million times stronger than a typical refrigerator magnet.

    “This is exciting as internal magnetic fields play an important role both for the evolution of stars and for the properties of their remnants,” Cantiello added. “For example, some of the most powerful explosions in the universe — long gamma-ray bursts — are associated with the death of some huge stars. These behemoths — 10 or more times more massive than our sun — most likely ended their lives with strong magnetic fields in their cores.”

    This work was written collaboratively on the web. A public, open Science version of the published paper can be found on Authorea, including a layman’s summary.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

    University of California Seal

     
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