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Astron. Astrophys. 361, L60-L62 (2000)

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1. Introduction

Atomic lines from Rydberg transitions in HI and heavier elements in the Sun, particularly MgI and SiI , have now been detected from atomic levels as high as n=20-19 (Clark et al. 2000 and references therein). Lines from these transitions change from absorption at lower n to emission at higher n, and exhibit significant limb brightening, particularly at higher-n levels. Although theoretical modelling has successfully explained the detailed characteristics of the MgI features (Carlsson et al. 1992; Chang et al. 1991), only the general behaviour of the HI lines has been reproduced. The limitation arises from the difficulty of modelling the highly structured source region of the HI lines in the low chromosphere (Carlsson & Rutten 1992).

We recently reported the first detection of the n=20-19 transition of HI in the Sun at 29.622 cm-1 using a Fourier transform spectrometer (FTS) at the James Clerk Maxwell Telescope (JCMT) (Clark et al. 2000). The present letter describes the first detection of the n=22-21 transition at 22.095 cm-1 from the JCMT using this same observational technique.

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© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000