Chromosphere
A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively.
In the
The chromosphere has a characteristic red color due to
Chromospheres have also been observed on
Physical properties
The density of the Sun's chromosphere decreases exponentially with distance from the center of the Sun by a factor of roughly 10 million, from about 2×10−4 kg/m3 at the chromosphere's inner boundary to under 1.6×10−11 kg/m3 at the outer boundary.
The density of the chromosphere is 10−4 times that of the underlying
The chromosphere's
Phenomena
Many different phenomena can be observed in chromospheres.
Plage
A plage is a particularly bright region within stellar chromospheres, which are often associated with magnetic activity.[9]
Spicules
The most commonly identified feature in the solar chromosphere are spicules. Spicules rise to the top of the chromosphere and then sink back down again over the course of about 10 minutes.[10]
Oscillations
Since the first observations with the instrument SUMER on board SOHO, periodic oscillations in the solar chromosphere have been found with a frequency from 3 mHz to 10 mHz, corresponding to a characteristic periodic time of three minutes.[11] Oscillations of the radial component of the plasma velocity are typical of the high chromosphere. The photospheric granulation pattern usually has no oscillations above 20 mHz; however, higher frequency waves (100 mHz, or a 10 s period) were detected in the solar atmosphere (at temperatures typical of the transition region and corona) by TRACE.[12]
Loops
Plasma loops can be seen at the border of the solar disk in the chromosphere. They are different from solar prominences because they are concentric arches with maximum temperature of the order 0.1 MK (too low to be considered coronal features). These cool-temperature loops show an intense variability: they appear and disappear in some UV lines in a time less than an hour, or they rapidly expand in 10–20 minutes. Foukal[13] studied these cool loops in detail from the observations taken with the EUV spectrometer on Skylab in 1976. When the plasma temperature of these loops becomes coronal (above 1 MK), these features appear more stable and evolve over longer times.
Network
Images taken in typical chromospheric lines show the presence of brighter cells, usually referred to as the network, while the surrounding darker regions are named internetwork. They look similar to granules commonly observed on the photosphere due to the heat convection.
On other stars
Chromospheres are present on almost all luminous stars other than
A spectroscopic measure of chromospheric activity on other stars is the Mount Wilson S-index.[14][15]
See also
- Orders of magnitude (density)
- Moreton wave
References
- S2CID 55909887.
- ^ [1] This article incorporates text from this source, which is in the public domain.
- ^ "The Chromosphere". Archived from the original on 2014-04-04. Retrieved 2014-04-28.
- ^ "Supergiant Atmosphere of Antares Revealed by Radio Telescopes". National Radio Astronomy Observatory. Retrieved 9 September 2022.
- ^
Kontar, E. P.; Hannah, I. G.; Mackinnon, A. L. (2008), "Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop", Astronomy and Astrophysics, 489 (3): L57, S2CID 1651161
- ^ a b "SP-402 A New Sun: The Solar Results From Skylab". Archived from the original on 2004-11-18.
- ISBN 978-1-58381-129-0
- ^
Freedman, R. A.; Kaufmann III, W. J. (2008). Universe. New York, USA: ISBN 978-0-7167-8584-2.
- ^ .
- OCLC 773089685.
- S2CID 119101577.
- doi:10.1086/427181.
- doi:10.1086/154862.
- PMID 27009381.
- ^ A small survey of the magnetic fields of planet-hosting stars (Archived 2016-12-22 at the Wayback Machine) gives "Wright J. T., Marcy G. W., Butler R. P., Vogt S. S., 2004, ApJS, 152, 261" as a ref for s-index.
External links
- Animated explanation of the Chromosphere (and Transition Region) Archived 2015-11-16 at the Wayback Machine (University of South Wales).