Investigation of He I 10830 Ae 'dark points' at the Sayan Solar Observatory and the Baikal Astrophysical Observatory

• Published in: Solar physics Vol. 199; no. 1; pp. 37 - 45
• Main Authors: Skomorovsky, VI, Firstova, N M, Kashapova, L K, Kushtal, GI, Boulatov, A V
• Format: Journal Article
• Language: English
• Published: 01.03.2001
• Subjects: Russia
• ISSN: 0038-0938

A new two-bandpass birefringent filter has been produced at ISTP, Irkutsk for the investigation of the fine structure of the chromosphere. One filter passband is centered on the He I 10 830 Ae, line, the second one is centered on H alpha . The FWHM of the He I 10 830 Ae, passband is 0.46 Ae, and of the H alpha passband is 0.3 Ae. A large number of filtergrams were obtained with the filter at the Sayan observatory. At the same time, spectral observations with high spatial and spectral resolution were carried out by the large solar vacuum telescope at the Baikal Observatory. We selected 29 'dark point' spectra with sizes from 2" to 13", as well as 'dark points' on the filtergrams. Comparison of spectrograms and filtergrams has shown a good agreement of their size and intensity in relation with the surrounding chromosphere as well as the absence of primary line-of-sight velocities in both observation types. From spectral observations, the depth of 10 830 Ae is over 30% for some 'dark points', and the FWHM is more than 1 Ae. He I 10 830 Ae line profiles in 'dark points' are more deep and wide than in quiet regions. The optical depth of the chromosphere in 'dark points' is estimated. Comparison with the unperturbed chromosphere showed that 'dark points' in He I 10 830 Ae are more optically thin than the nearby chromosphere.