Solar chromosphere

Helium is the second most abundant element in the visible Universe and accordingly there is a mass of data from optical and radio emission lines in nebulae, optical emission lines from the solar chromosphere and prominences and absorption lines in spectra of hot stars. Further estimates are derived more indirectly by applying theories of stellar structure, evolution and pulsation. However, because of the relative insensitivity of Tp to cosmological parameters, combined with the need to allow for additional helium from stellar nucleosynthesis in most objects, the requirements for accuracy are very severe better than 5 per cent to place cosmological limits on Nv and better still to place interesting constraints on t] or One can, however, assert with confidence that there is a universal floor to the helium abundance in observed objects corresponding to 0.23 < Fp < 0.25. 

M. Saha, Ionization in the solar chromosphere, Philosophical Magazine 40 (1920) 472-488, on 476. Reprinted in Lang and Gingerich, A Source Book in Astronomy and Astrophysics 1900-1975, 236-242. 

Because helium forms no compounds and is almost absent in the Earth s atmosphere, it was unknown for a long time. The first clue leading to its discovery was an unidentified yellow emission line in the solar chromospheric spectrum observed by French astronomer Pierre Janssen during an eclipse of the Sun in 1868. Lockyer named the unknown element helium for the Greek sun god, helios. Subsequendy it was discovered to be rather abundant in radioactive rocks, where it is trapped after emission from uranium series alpha decays. Ramsay and Soddy showed that the alpha rays were helium atoms whose electrons had been stripped away. In his biography of Lord Rutherford, A. S. Eve wrote ... 

PROBLEM 5.6.1. For radiation from the solar chromosphere at a temperature of 6000 K, estimate the wavelength maximum. Prove the Wien displacement law ... 

Carbon monoxide is a constituent of stellar atmospheres and the solar chromosphere as well as being a product of the combustion of hydrocarbons and other organic compounds. Its spectroscopy has, therefore, been extensively Investigated. 

The sun has the most mass (>99%) of the solar system objects and therefore it is the prime target for studying solar system abundances. Most elements can be measured in the sun s photosphere, but data from the solar chromosphere and corona, solar energetic particles, solar wind, and solar cosmic rays (from solar flares), help to evaluate abundances of elements that have weak absorption lines (because these elements are low in abundance or only have blended absorption lines in the photospheric spectrum). 

Vernazza, J., E.H. Avrett, and R. Loeser, Structure of the solar chromosphere, II. The underlying photosphere and temperature minimum region. Astrophys J 30, 1, 1976. 

Fraunhofer lines Dark lines in the solar spectrum that result irom the absorption by elements in the solar chromosphere of some of the wavelengths of the visible radiation emitted by the hot interior of the sun. 

The emission of forbidden lines in the solar chromosphere and corona has been studied by DE BDER et al (1972), which predicts the wavelength and intensities of these lines when the transition region between the chromosphere and the corona is seen edgewise above the solar limb. Intensities comparable to the continuum with linewidth of the order of AX/A v. 10"5 are... 

R. Grant Athay, The Solar Chromosphere and Corona Quiet Sun. 1976, XI + 504 pp. 

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