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NOAO Newsletter - National Solar Observatory - March 2000 - Number 61


Sunspot Spectroscopy

Peter Bernath (University of Waterloo)

The McMath-Pierce Fourier transform spectrometer (FTS) offers strong laboratory astrophysics support for solar physics and for the study of cool astronomical sources. The infrared and visible spectra of cool objects are dominated by the spectra of molecules such as TiO, SiO, H2O and HF. All of these molecules have been detected in sunspots using high-resolution spectra recorded with the McMath-Pierce FTS. L. Wallace (KPNO) has reduced the solar and sunspot spectra into a series of spectral atlases (Wallace et al., ApJ 106, S165, 1996), that are available electronically through the NSO WWW site. P. Bernath (Waterloo) and R. Ram (Arizona) have been assisting with the molecular line identifications by the joint analysis of laboratory and astronomical spectra recorded mainly with the McMath-Pierce FTS.

Solar and sunspot spectra provide a convenient source of very hot molecules (3000-6000 K). Laboratory spectra are generally cooler, but are of higher quality because of the narrower line widths. The two types of data are very complementary and have been combined to improve the spectroscopic constants and the line lists. For example, we have combined sunspot data for the d (Ram et al., ApJ 107, S443, 1996) and g (Ram et al., ApJ 122, S331, 1999) systems of TiO with laboratory measurements recorded with a hollow cathode lamp. These analyses are currently the best available for the near-infrared TiO bands that dominate the spectra of M-type stars and sunspots. Similar joint analyses are continuing for hot water in the infrared, a.k.a."Water on the Sun," (Polyansky et al., Science 277, 346, 1997; ApJ 489, L205, 1997), and have been completed for SiO (Campbell et al., ApJ 101, S237, 1995).


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