RUI: Search for Mode Switching in Semiregular Variable Stars

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Under a previous RUI (Research in Undergraduate Institutions) grant, Cadmus has established the equipment and reduction procedures needed to monitor photometrically about three dozen semiregular variable stars. He shall monitor those stars during the next three years, as originally planned. Cadmus recently observed one variable star to change its period during a quiescent state. Interesting results will also be pursued spectroscopically. Many stars grow and shrink regularly. The observation of their pulsations has provided much information about stellar interiors and evolution. Now interest grows in understanding stars that appear to pulsate irregularly, perhaps occasionally changing pulsation modes. They are likely to provide qualitatively new insights into stellar structure. Cadmus has established a program to measure the brightness of selected irregularly variable stars over long enough time periods so that the causes of the irregularity may be identified. This grant supports the monitoring program and the spectroscopic follow-up of interesting results. Students are closely involved in this research, and support is provided under both the Research in Undergraduate Institutions and the Research Experiences for Undergraduates programs.