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E.G. Schmidt, S. Langan, D. Rogalla, L. Thacker-Lynn (University of Nebraska-Lincoln)
There is good reason to believe that only a small fraction of type II Cepheids in the Galaxy have been discovered. Given their relevance to a number of interesting astrophysical problems, we have undertaken a program to expand the number of these stars known.
As a first step, we selected 205 Cepheid candidates from the list of periodic variable stars discovered in the ROTSE Demonstration Project (Akerlof et al. 2000). Given the galactic latitudes and apparent magnitudes of these stars, any which are Cepheids are very likely to be type II Cepheids. However, the amplitudes are surprisingly small; 80% are less than 0.4 magnitudes in contrast to known type II Cepheids of which only a few percent have such small amplitudes.
In order to obtain color information and accurate light curves, we have conducted RV photometry of the Cepheid candidates using the Behlen Observatory 0.76-m telescope and the CCD photometer. Based on a preliminary analysis of a portion of the data, about 55% of the candidates have colors and light curves appropriate to type II Cepheids.
Since the ROTSE demonstration project included only 5.6% of the fields in the survey, this suggests that the entire ROTSE-I database could yield nearly 2000 new type II Cepheids. However, spectroscopy will be needed to confirm the identification of individual stars as type II Cepheids, particularly those with small amplitudes.
This work makes use of the data from the Northern Sky Variability Survey created jointly by the Los Alamos National Laboratory and University of Michigan. The NSVS was funded by the Department of Energy, the National Aeronautics and Space Administration and the National Science Foundation. This work was supported in part by NSF grant AST 00-97353.
Akerlof, C. et al. 2000, AJ 119, 1901.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.