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  • richardmitnick 12:54 pm on September 8, 2017 Permalink | Reply
    Tags: , , , , , LAMOST telescope,   

    From Universe Today: “Chinese Astronomers Spot Two New Hypervelocity Stars” 

    universe-today

    Universe Today

    8 Sept , 2017
    Matt Williams

    Most stars in our galaxy behave predictably, orbiting around the center of the Milky Way at speeds of about 100 km/s (62 mi/s). But some stars achieve velocities that are significantly greater, to the point that they are even able to escape the gravitational pull of the galaxy. These are known as hypervelocity stars (HVS), a rare type of star that is believed to be the result of interactions a with supermassive black hole (SMBH).

    The existence of HVS is something that astronomers first theorized in the late 1980s, and only 20 have been identified so far. But thanks to a new study by a team of Chinese astronomers, two new hypervelocity stars have been added to that list. These stars, which have been designated LAMOST-HVS2 and LAMOST-HVS3, travel at speeds of up to 1,000 km/s (620 mi/s) and are thought to have originated in the center of our galaxy.

    The study which describes the team’s findings, titled “Discovery of Two New Hypervelocity Stars From the LAMOST Spectroscopic Surveys“, recently appeared online. Led by Yang Huang of the South-Western Institute for Astronomy Research at Yunnan University in Kunming, China, the team relied on data from Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) to detect these two new hypervelocity stars.

    LAMOST telescope LAMOST telescope located in Xinglong Station, Hebei Province, China

    1
    Footprint of the LAMOST pilot survey and the first three years’ general survey. Credit: LAMOST

    See the full article here .

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

    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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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

      You should take part in a contest for one of the highest quality blogs online.
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      Like

      • 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

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