Studying the sun as a star to understand stellar flares and exoplanets


Date:
October 12, 2020
Source:
National Institutes of Natural Sciences
Summary:
New research shows that sunspots and other active regions can change
the overall solar emissions. The sunspots cause some emissions
to dim and others to brighten; the timing of the changes also
varies between different types of emissions. This knowledge will
help astronomers characterize the conditions of stars, which has
important implications for finding exoplanets around those stars.



FULL STORY ==========================================================================
New research shows that sunspots and other active regions can change
the overall solar emissions. The sunspots cause some emissions to dim
and others to brighten; the timing of the changes also varies between
different types of emissions. This knowledge will help astronomers
characterize the conditions of stars, which has important implications
for finding exoplanets around those stars.


==========================================================================
An international research team led by Shin Toriumi at the Japan Aerospace Exploration Agency added up the different types of emissions observed
by a fleet of satellites including "Hinode" and the "Solar Dynamics Observatory" to see what the Sun would look like if observed from far
away as a single dot of light like other stars.

The team investigated how features like sunspots change the overall
picture.

They found that when a sunspot is near the middle of the side of the
Sun facing us, it causes the total amount of visible light to dim. In
contrast, when the sunspots are near the edge of the Sun the total visible light brightens because at that viewing angle bright structures known as faculae surrounding the sunspots are more visible than the dark centers.

In addition, X-rays which are produced in the corona above the solar
surface grow brighter when a sunspot is visible. The coronal loops
extending above the sunspots are magnetically heated, so this brightening appears before the sunspot itself rotates into view and persists even
after the sunspot has rotated out of view.

Because the changes in the overall solar emissions and their timings
carry information about the location and structure of features on the
surface of the Sun, astronomers hope to be able to deduce the surface
features of other stars such as starspots and magnetic fields. This will
help astronomers to better recognize dimming caused by the shadow of an exoplanet. With better knowledge about the effects of starspots, we can estimate the parameters, such as the radii and orbits, of exoplanets
more accurately.

As in-depth investigations into the Sun proceed, a better understanding
of the detailed mechanisms of atmospheric heating and flare eruptions
will be gained.

Toriumi comments, "To this end, the next-generation solar-observing
satellite Solar-C(EUVST), being developed by Japan in close collaboration
with US and European partners, aims to observe the Sun in emissions that
probe the chromosphere, transition region, and corona as a single system."

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========================================================================== Journal Reference:
1. Shin Toriumi, Vladimir S. Airapetian, Hugh S. Hudson, Carolus J.

Schrijver, Mark C. M. Cheung, Marc L. DeRosa. Sun-as-a-star
Spectral Irradiance Observations of Transiting Active
Regions. The Astrophysical Journal, 2020; 902 (1): 36 DOI:
10.3847/1538-4357/abadf9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201012115943.htm

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