Radial Velocity Variations of K-Giants

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This award is for a two-year pilot study of an innovative instrumental technique to obtain precise radial velocities of stars. The technique is to insert a recently constructed container filled with iodine gas in beam of a coude spectrometer at McDonald Observatory. This gas will absorb starlight at well known wavelengths, thereby providing a set of calibration lines interspersed with the stellar lines in the spectrum. With this innovation, the PI expects to obtain radial velocities to an accuracy of +-5 m/sec (roughly 8 mph). He will then obtain a time series of spectra for several bright red giant stars and search for pulsations in them. The PI has already used a related instrumental technique to verfify the existence of a 1.8-day period in the red giant Arcturus. If this pulsation in Arcturus is typical of other red giants, then a new class of variable stars will have been discovered. The data will be used for a variety of other astrophysical purposes, including the study of convective circulation cells and magnetic "activity" on these stars surfaces. Either pulsations, magnetic activity, or both of these phenomena, could be responsible for heating the outer atmospheres ("chromospheres") of red giants. Chromospheres, in turn, are thought to cause a mass loss, which can significantly affect the subsequent history of the star's evolution.