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  • richardmitnick 9:50 am on January 12, 2017 Permalink | Reply
    Tags: , Auroral Displays at Brown Dwarfs, Auroras, ,   

    From astrobites: “Auroral Displays at Brown Dwarfs” 

    Astrobites bloc

    Astrobites

    Title: Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence
    Authors: G.Hallinan, S. P. Littlefair, G. Cotter, et al.
    First Author’s Institution: California Institute of Technology
    Caltech Logo
    Status: Published in Nature (2015), open access

    Auroras are the spectacular light shows visible in the polar regions at Earth and other planets. In 2015 they were detected for the first time outside of the solar system. Brown dwarfs are objects often described as “failed stars”, meaning they are insufficiently massive to ignite hydrogen fusion in their cores. Today’s paper reports on the remarkable discovery that a particular brown dwarf plays host to auroral displays far more powerful than those found anywhere in the solar system.

    Brown dwarfs

    Artist's concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech
    Artist’s concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech

    Brown dwarfs occupy the region between giant planets and the lowest mass stars. It is generally accepted that they form in a manner similar to stars, i.e. the gravitational collapse of interstellar gas, but never reaching a mass sufficient to sustain hydrogen fusion in the core. As such, brown dwarfs are extremely cool, faint objects, making their detection much more difficult than ordinary stars. However, they provide an excellent opportunity to for us to better understand the physics that differentiates the stellar and planetary domains. Since their discovery many surveys have been performed which have revealed, amongst other things, the existence of complex weather systems and strong global magnetic fields.

    Auroras

    Understanding the interaction of the magnetic field at a brown dwarf with its nearby space environment is a key scientific goal. At Earth, space scientists observe the aurora as a means of revealing the structure and dynamics of the magnetic field, and the plasma which interacts with it. Before turning to auroras at brown dwarfs we shall briefly review at what we know about auroras from our studies at Earth and other solar system planets.

    The vibrant displays that we see are a result of charged particles (i.e. electrons and ions) from the plasma population around the Earth raining down along magnetic field lines, and colliding with molecules in the atmosphere. These collisions excite the atmospheric constituents to a higher energy state, causing the emission of a photon as they return to their original state.

    Auroral emissions aren’t just confined to Earth; they are found at other magnetised planets in the solar system, with Jupiter being a particularly spectacular example.

    3
    JUNE 30, 2016: Astronomers are using NASA’s Hubble Space Telescope to study auroras — stunning light shows in a planet’s atmosphere — on the poles of the largest planet in the solar system, Jupiter. The auroras were photographed during a series of Hubble Space Telescope Imaging Spectrograph far-ultraviolet-light observations taking place as NASA’s Juno spacecraft approaches and enters into orbit around Jupiter. The aim of the program is to determine how Jupiter’s auroras respond to changing conditions in the solar wind, a stream of charged particles emitted from the sun. Auroras are formed when charged particles in the space surrounding the planet are accelerated to high energies along the planet’s magnetic field. When the particles hit the atmosphere near the magnetic poles, they cause it to glow like gases in a fluorescent light fixture. Jupiter’s magnetosphere is 20,000 times stronger than Earth’s. These observations will reveal how the solar system’s largest and most powerful magnetosphere behaves. The full-color disk of Jupiter in this image was separately photographed at a different time by Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of the outer planets.
    Date 30 June 2016
    Source http://hubblesite.org/newscenter/archive/releases/2016/24
    Author NASA, ESA, and J. Nichols (University of Leicester)

    Neither are they confined only to the visible part of the spectrum; auroral emissions occur from radio frequencies through to UV and X-ray.

    Now we return to brown dwarfs. Since 2006 it has been known that a handful of brown dwarfs emit very regular and persistent radio bursts. These burst are pulsed at the rotation period of the dwarf, leading some researchers to suggest that they may be caused by auroras that are generated in a similar manner to Jupiter’s main auroral oval. The pulsing in this case may be due to the magnetic axis being tilted from the spin axis, so that as the dwarf rotates the auroral emission cones into our line of sight. This motivated the authors of today’s paper to target a particular brown dwarf, LSR J1835 + 3259, with simultaneous radio and optical observation, pursuing a possible relation between the two.

    4
    LSR J1835 + 3259. Image: http://images.zeit.de/ http://www.theweeklyobserver.com/ailed-star-shows-dazzling-display-of-northern-lights/5575/

    Radio observations were made using the Very Large Array (VLA) radio telescope, while simultaneously, optical measurements were made with the 5.1 m Hale telescope at the Palomar Observatory with follow-up observations from the 10 m Keck telescope.

    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA
    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA
    Caltech Hale Telescope at Palomar interior
    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory Interior
    Keck Observatory, Mauna Kea, Hawaii, USA

    The results of the observations are shown in Figure 1, where the light curve from the optical measurements (Fig 1a) shows a clear periodicity of 2.84 h. Observations of the radio emission (Fig 1b) show the same periodicity, with a slight offset in phase causing it to lag slightly behind the optical emission. The authors attribute their findings to auroras which are driven by strong electric currents flowing in the magnetosphere of the dwarf.

    2
    Figure 1: (a) Optical measurements of Balmer line emission of LSR J1835 made using the Hale telescope. (b) Corresponding radio observations of the same object made using the VLA radio telescope. [Figure 1 from Hallinan et al. 2015]

    With this discovery many open questions are presented. What is the mechanism driving the auroras? It may be interaction with the interstellar medium, analogous to the process of the Earth’s magnetosphere interacting with the solar wind. Or it could be due to a continuously replenishing source of plasma mass outflow from within a closed magnetosphere, analogous to the mechanism producing Jupiter’s main auroral oval. Additionally, the source of the required plasma population is unknown, with the cool temperatures (∼2000 K) of brown dwarfs being unable to support significant ionisation of their atmospheres, and the lack of nearby stars restricting the possibility ionisation by stellar irradiation.

    Ultimately it is an exciting prospect that this discovery, along with the arrival of even more sensitive radio telescopes (e.g. the Square Kilometre Array), may pave the way towards detecting auroras at exoplanets.

    SKA Square Kilometer Array

    This which would add a novel technique to the exoplanet-detectors toolkit, and enable us to learn about the magnetic fields and plasma populations around those objects.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 7:09 am on January 26, 2016 Permalink | Reply
    Tags: , Auroras, ,   

    From ESA: “Integral X-rays Earth’s aurora” 

    ESASpaceForEuropeBanner
    European Space Agency

    26 January 2016
    Erik Kuulkers
    Integral Project Scientist
    Directorate of Science and Robotic Exploration
    European Space Agency
    Tel: +34 918 131 358
    Email: erik.Kuulkers@sciops.esa.int

    Markus Bauer







    ESA Science and Robotic Exploration Communication Officer








    Tel: +31 71 565 6799








    Mob: +31 61 594 3 954








    Email: markus.bauer@esa.int

    1
    Integral’s X-ray view of Earth’s aurora
    Cool .gif, if it disappears from this post, do not be surprised, WordPress has been screwing these up. Just access it in the full article, see link below.

    Normally busy with observing high-energy black holes, supernovas and neutron stars, ESA’s Integral space observatory recently had the chance to look back at our own planet’s aurora.

    ESA Integral
    Integral

    Auroras from around the world
    Auroras from around the world.

    Auroras are well known as the beautiful light shows at polar latitudes as the solar wind interacts with Earth’s magnetic field.

    As energetic particles from the Sun are drawn along Earth’s magnetic field, they collide with different molecules and atoms in the atmosphere to create dynamic, colourful light shows in the sky, typically in green and red.

    But what may be less well known is that auroras also emit X-rays, generated as the incoming particles decelerate.

    Integral detected high-energy auroral X-rays on 10 November 2015 as it turned to Earth – although it was looking for something else at the time.

    Its task was to measure the diffuse cosmic X-ray background that arises naturally from supermassive black holes that are gobbling up material at the centres of some galaxies.

    To achieve this, Integral records the X-ray brightness with and without the Earth in the way, blocking the background. These types of measurements help astronomers estimate how many distant supermassive black holes there are in the Universe.

    Unfortunately, on this occasion, the X-rays from Earth’s aurora drowned out the cosmic background – but the observations were not a waste.

    They also help us to understand the distribution of electrons raining into Earth’s upper atmosphere, and they reveal interactions between the solar wind and Earth’s protective magnetic bubble, or magnetosphere.

    “Auroras are transient, and cannot be predicted on the timeframe that satellite observations are planned, so it was certainly an unexpected observation,” comments Erik Kuulkers, Integral project scientist.

    “It’s also quite unusual for us to point the spacecraft at Earth: it requires innovative planning by the operations teams to coordinate such a dedicated set of manoeuvres to ensure it can operate safely with Earth inside the instruments’ field of view and then return to its standard observing programme.

    “Although the original background X-ray measurements didn’t go quite to plan this time, it was exciting to capture such intense auroral activity by chance.”

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 2:51 pm on September 12, 2014 Permalink | Reply
    Tags: , , , Auroras, , , ,   

    From SPACE.com: ” Solar Storms Are Bombarding Earth Now, Amped-up Auroras Possible” 

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    SPACE.com

    Two waves of solar material blown out by powerful sun eruptions this week are hitting the Earth now, and could amplify the aurora displays for observers in northern regions.

    aurora
    Images of the aurora australis and aurora borealis from around the world, including those with rarer red and blue lights

    Scientists with NOAA’s Space Weather Prediction Center in Boulder, Colorado, expected the first wave of solar flare particles — unleashed by a so-called coronal mass ejection, or CME, on Monday (Sept. 8) — to reach Earth Thursday night (Sept. 11). A second wave, this one caused by a massive solar flare on Wednesday, is due to arrive between Friday and early Saturday.

    cme
    NASA Captures Image of M1 Coronal Mass Ejection April 18, 2012

    flare
    On August 31, 2012 a long prominence/filament of solar material that had been hovering in the Sun’s atmosphere, the corona, erupted out into space at 4:36 p.m. EDT

    “We do expect these storm levels to cause significant auroral displays across much of the northern U.S. on Friday night,” SWPC Director Thomas Berger told reporters on Thursday. “With clear skies currently forecast for much of these regions, this could be a good opportunity for auroral sightings.”

    The enhanced auroras would likely be most visible across the northern tier U.S. states, along the U.S.-Canada border, as well as in New England, added SWPC program coordinator William Murtagh. Clear, dark skies far from city light pollution are vital to observe any auroras.

    The first of the two solar storm waves reached Earth late Thursday right on time, space weather center officials wrote in an update late Thursday. Also on Thursday, NASA released a new video of the X1.6 solar flare from its sun-watching Solar Dynamics Observatory, showing the event in two different wavelengths.

    Coronal mass ejections are powerful eruptions of super-hot plasma than can be blown out from the sun during major solar flares. This week, the an active sunspot known as AR2158 sun fired off a moderate M4.6 solar flare on Monday, followed by a much more powerful X1.6-class flare on Wednesday, Sept. 10. X-class flares are the most powerful flares the sun experiences.

    Sunspot AR2158 is about the size of between 10 and 20 Earths, but appears to be in the process of breaking up, Berger said. The huge X1.6 solar flare may have been its swan song as it breaks down, he added.

    spot
    This NASA image shows the active sunspot AR2158, which unleashed a massive X1.6 solar flare on Sept. 10, 2014, as it appeared on Sept. 8, when it fired off a moderate M4.6 solar flare. On the right, Jupiter and Earth are superimposed to give a sense of the sunspot’s size. Credit: NASA Solar Dynamics Observatory (Little SDO)

    The two solar flares this week were accompanied by coronal mass ejections, and both were aimed at Earth. When directly aimed at Earth, the most powerful solar flares — events stronger than the X1.6 storm on Wednesday — can pose a danger to satellites and astronauts in space, and interfere with communication, navigation and even power distribution surfaces on the Earth’s surface.

    Berger said that the two CMEs from this week’s solar storms could cause some radio and GPS navigation system hiccups, as well as voltage irregularities in power grids of the northern United States, but nothing too extreme.

    “We don’t expect any unmanageable impacts to national infrastructure from these solar events at this time, but we are watching these events closely,” Berger said.

    flare
    The huge X1.6-class solar flare is seen erupting from the sun in this three-wavelength composite image captured by NASA’s Solar Dynamics Obervatory on Sept. 10, 2014. The solar flare occurred at 1:45 p.m. ET. Credit: NASA Solar Dynamics Observatory (Little SDO)

    Berger did say that it is fairly rare for two significant coronal mass ejections to hit Earth head-on at nearly the same time. A minor radiation storm was detected from the solar flares, as well as temporary radio blackouts, space weather officials said.

    Space weather officials did say that the most intriguing aspect of this week’s solar flares are their potential for boosting this weekend’s northern lights displays.

    When charged particles from solar storms reach Earth, they are funneled to the polar regions by the planet’s magnetic field and can great so-called geomagnetic storms.

    A minor G1-class storm is underway now, with levels expected to rise to a potentially strong G3-class by Saturday evening, Berger said.

    When solar particles collide with the Earth’s upper atmosphere, they let create a glow that can be visible from the ground as auroral light. In the northern regions of Earth, this glow is known as the aurora borealis, or northern lights. In the south, it is called the aurora australis, or southern lights. Significant solar flares can amplify those displays into dazzling dances of ethereal light.

    See the full article, with videos, here.

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