Macalester College Physics and Astronomy Department:

We are using the Macalester Observatory to study the Population II (or Type II) Cepheids in a number of northern globular clusters. The goal of this project is to determine more accurate periods and magnitudes for these stars using modern instrumentation and techniques. These results will be used to better define the period-luminosity relations for this type of variable star making it a more useful distance indicator.

Population II Cepheids (P2Cs) are post-horizontal branch stars which are passing through the instability strip at various stages in their evolution. There are three different types: BL Herculis, W Virginis, and RV Tauri. The term Population II comes from the fact that these stars derived from older stars as compared to the classical Cepheids which derive from more massive, younger main sequence stars.

As with classical Cepheids, the P2Cs have a relation between their period and their brightness (or luminosity), where a P2C with a longer period than another P2C will also be brighter. However, there has been a difference in opinion regarding the period-luminosity relations for P2Cs. One source for the differences may be due to the fact that most of the data comes from older surveys with poorer photometry. Therefore it was decided to reanalyze as many of the P2Cs in globular clusters as is possible. This project is being conducted in collaboration with Michigan State University(headed by Horace Smith) and Central Michigan University (headed by Wayne Osborn).

As part of Research Experiences for Undergraduates, Reid Lustig and Dylan Semler are observing five globular clusters: M3, M5, M10, M12, and M13. The research is being conducted from late May to early August of 2004. The standard stars used to calibrate the magnitudes are taken from Peter Stetson's photometric standards.

Update! Preliminary light curves for a number of the Type II Cepheids were presented at the Winter 2006 American Astronomical Society Meeting. Click here to view the poster.

M3	M5	M10	M12	M13

Email if you have any questions