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  • richardmitnick 12:57 pm on October 14, 2017 Permalink | Reply
    Tags: , Hard X-rays, , JAXA Hinode, Nanoflares, , NASA Sounding Rocket Instrument Spots Signatures of Long-Sought Small Solar Flares, NASA UC Berkeley FOXSI sounding rocket, One of the consequences of nanoflares would be pockets of superheated plasma, ,   

    From Goddard: “NASA Sounding Rocket Instrument Spots Signatures of Long-Sought Small Solar Flares” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Oct. 13, 2017
    Sarah Frazier
    sara.frazier@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Like most solar sounding rockets, the second flight of the FOXSI instrument – short for Focusing Optics X-ray Solar Imager – lasted 15 minutes, with just six minutes of data collection. But in that short time, the cutting-edge instrument found the best evidence to date of a phenomenon scientists have been seeking for years: signatures of tiny solar flares that could help explain the mysterious extreme heating of the Sun’s outer atmosphere.

    FOXSI detected a type of light called hard X-rays – whose wavelengths are much shorter than the light humans can see – which is a signature of extremely hot solar material, around 18 million degrees Fahrenheit. These kinds of temperatures are generally produced in solar flares, powerful bursts of energy. But in this case, there was no observable solar flare, meaning the hot material was most likely produced by a series of solar flares so small that they were undetectable from Earth: nanoflares. The results were published Oct. 9, 2017, in Nature Astronomy.

    “The key to this result is the sensitivity in hard X-ray measurements,” said Shin-nosuke Ishikawa, a solar physicist at the Japan Aerospace Exploration Agency, or JAXA, and lead author on the study. “Past hard X-ray instruments could not detect quiet active regions, and combination of new technologies enables us to investigate quiet active regions by hard X-rays for the first time.”

    1
    The NASA-funded FOXSI instrument captured new evidence of small solar flares, called nanoflares, during its December 2014 flight on a suborbital sounding rocket. Nanoflares could help explain why the Sun’s atmosphere, the corona, is so much hotter than the surface. Here, FOXSI’s observations of hard X-rays are shown in blue, superimposed over a soft X-ray image of the Sun from JAXA and NASA’s Hinode solar-observing satellite.
    Credits: JAXA/NASA/

    JAXA/NASA HINODE spacecraft


    NASA UC Berkeley JAXA FOXSI sounding rocket

    These observations are a step toward understanding the coronal heating problem, which is how scientists refer to the extraordinarily – and unexpectedly – high temperatures in the Sun’s outer atmosphere, the corona. The corona is hundreds to thousands of times hotter than the Sun’s visible surface, the photosphere. Because the Sun produces heat at its core, this runs counter to what one would initially expect: normally the layer closest to a source of heat, the Sun’s surface, in this case, would have a higher temperature than the more distant atmosphere.

    “If you’ve got a stove and you take your hand farther away, you don’t expect to feel hotter than when you were close,” said Lindsay Glesener, project manager for FOXSI-2 at the University of Minnesota and an author on the study.

    The cause of these counterintuitively high temperatures is an outstanding question in solar physics. One possible solution to the coronal heating problem is the constant eruption of tiny solar flares in the solar atmosphere, so small that they can’t be directly detected. In aggregate, these nanoflares could produce enough heat to raise the temperature of the corona to the millions of degrees that we observe.

    One of the consequences of nanoflares would be pockets of superheated plasma. Plasma at these temperatures emits light in hard X-rays, which are notoriously difficult to detect. For instance, NASA’s RHESSI satellite – short for Reuven Ramaty High Energy Solar Spectroscopic Imager – launched in 2002, uses an indirect technique to measure hard X-rays, limiting how precisely we can pinpoint the location of superheated plasma. But with the cutting-edge optics available now, FOXSI was able to use a technique called direct focusing that can keep track of where the hard X-rays originate on the Sun.

    “It’s really a completely transformative way of making this type of measurement,” said Glesener. “Even just on a sounding rocket experiment looking at the Sun for about six minutes, we had much better sensitivity than a spacecraft with indirect imaging.”

    FOXSI’s measurements – along with additional X-ray data from the JAXA and NASA Hinode solar observatory – allow the team to say with certainty that the hard X-rays came from a specific region on the Sun that did not have any detectable larger solar flares, leaving nanoflares as the only likely instigator.

    “This is a proof of existence for these kinds of events,” said Steve Christe, the project scientist for FOXSI at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and an author on the study. “There’s basically no other way for these X-rays to be produced, except by plasma at around 10 million degrees Celsius [18 million degrees Fahrenheit]. This points to these small energy releases happening all the time, and if they exist, they should be contributing to coronal heating.”

    There are still questions to be answered, like: How much heat do nanoflares actually release into the corona?

    “This particular observation doesn’t tell us exactly how much it contributes to coronal heating,” said Christe. “To fully solve the coronal heating problem, they would need to be happening everywhere, even outside of the region observed here.”

    Hoping to build up a more complete picture of nanoflares and their contribution to coronal heating, Glesener is leading a team to launch a third iteration of the FOXSI instrument on a sounding rocket in summer 2018. This version of FOXSI will use new hardware to eliminate much of the background noise that the instrument sees, allowing for even more precise measurements.

    A team led by Christe was also selected to undertake a concept study developing the FOXSI instrument for a possible spaceflight as part of the NASA Small Explorers program.

    FOXSI is a collaboration between the United States and JAXA. The second iteration of the FOXSI sounding rocket launched from the White Sands Missile Range in New Mexico on Dec. 11, 2014. FOXSI is supported through NASA’s Sounding Rocket Program at the Goddard Space Flight Center’s Wallops Flight Facility in Virginia. NASA’s Heliophysics Division manages the sounding rocket program.

    Related:

    JAXA press release on these findings (Japanese)
    NASA-funded FOXSI to Observe X-rays from Sun
    https://www.nasa.gov/mission_pages/sounding-rockets/index.html

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 11:21 am on March 18, 2016 Permalink | Reply
    Tags: , JAXA Hinode, ,   

    From NAOJ Universe of Spectroscopy: “Spectra of the Solar Corona” 

    NAOJ

    NAOJ

    Universe of Spectroscopy
    Universe of Spectroscopy

    To observe the corona surrounding the Sun, we have to wait for an opportunity to view a total solar eclipse when the Moon fully blocks the solar disk. In visible light, the bright solar surface hampers observation of the faint corona.

    Observations at shorter wavelength light such as ultraviolet and X-ray are appropriate to investigate the corona in detail. The high-temperature corona emits more radiation at shorter wavelength. However, ultraviolet and X-ray radiation cannot penetrate the Earth’s atmosphere. That is the reason why we need a space observatory.

    The observational satellite Hinode’s onboard instrument, called Extreme-ultraviolet Imaging Spectrometer (EIS), was designed for obtaining spectra of the solar corona. The extreme-ultraviolet is a wavelength range of the shorter wavelength region of ultraviolet radiation. We can find many spectral lines radiating from high temperature (higher than one million Kelvin) plasma.

    JAXA HINODE spacecraft
    JAXA HINODE spacecraft

    The extreme-ultraviolet is a wavelength range of the shorter wavelength region of ultraviolet radiation. We can find many spectral lines radiating from high temperature (higher than one million Kelvin) plasma.

    The most frequent lines are emission lines originating in ionized iron. Iron, with the symbol Fe, is atomic number 26 and will have 26 electrons. In such a hot corona, a part of the electrons is removed from iron atoms, and more electrons are removed at higher temperature. Analysis of the emission lines of the ionized iron yields information on the temperature of the corona.

    1
    A part of the extreme-ultraviolet spectrum obtained by the EIS installed on Hinode. Many emission lines caused by ionized iron are visible. For example, “Fe X” means an iron ion removed nine electrons from a neutral iron atom. Combining ratios between other iron charge states yields the temperature of the corona. In addition, analyzing the wavelength shift of emission lines, we will derive the corona’s motion velocity.

    Is the corona’s temperature one million Kelvin?

    It is generally believed that the corona’s temperature is one million Kelvin. However, plasma of various temperatures is distributed throughout the corona. “Warm” plasma has a temperature of about one million Kelvin, while “hot” plasma is higher than two million Kelvin. Moreover, super hot plasma with a temperature of higher than ten million Kelvin is observed when a giant solar flare erupts. Studying the solar spectra at extreme-ultraviolet is essential to developing an understanding of the temperature distribution and the dynamics of the solar corona that has such a diversity of temperatures.

    2
    The solar corona’s image in the extreme-ultraviolet emission line of an ionized iron. The typical temperature of each iron charge state is indicated.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
    Subaru

    ALMA Array
    ALMA

    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
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