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Water on the Sun (1Sep95) (from NOAO HIGHLIGHTS!, NOAO Newsletter No. 43, September 1995) The Sun may be a little on the dry side, but not so dry that we can't detect a touch of water vapor in its atmosphere. A group of solar astronomers at the National Optical Astronomy Observatories and the University of Waterloo have recorded evidence of water in dark sunspots. These new observations are of fundamental importance for understanding the atmospheres of the Sun and stars. Hot water molecules are the most important absorbers of infrared radiation in the atmospheres of cool stars such as variable red giants. Studying the physical effects of hot water in these red giant stars is central to determining the rate at which they evolve and eject material into space. Dark sunspots can be 2000^oK cooler than the surrounding bright surface of the Sun, allowing detailed studies of regions that mimic the surfaces of red giant stars. Since the temperatures of even cool stars are almost impossible to produce in the laboratory, these results are unique and show that current theory is not adequate to model these spectra. Lloyd Wallace, William Livingston, and Ken Hinkle (NOAO) worked with collaborators in obtaining infrared spectra that reveal a large number of water absorption features originating in the solar atmosphere. The observations were obtained with the National Solar Observatory McMath-Pierce Telescope at Kitt Peak, using the Fourier transform spectrometer. Laboratory spectroscopy was carried out by P. Bernath, B. Guo, J. Busler, and K. Zhang (University of Waterloo) in support of the observations. Livingston explained that the results of this research, which are being published in Science, will help "to emphasize that water is an important absorber in the Sun and stars that is underappreciated." He hopes this research will encourage further laboratory work for the purpose of understanding the astrophysical importance of the water spectrum in the Sun and stars. The significance of this information has been overlooked in previous studies, although water features were first identified nearly 25 years ago. [Photo not included] A photograph taken 26 July 1991, of the sunspot observed. The white dot represents the data collection area.
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