Rr Lyraes

1. The Galactic Oosterhoff Dichotomy in Terms of Period-Color Relations at Max/Min Lightby Julia Russ, ShashiKanbur, A Saradjeni, K Kinemuchi, R Cohen, C Ngoew, Jillian Neely, and Timothy De Haas. • Fitting the data • Data fit using Gnuplotand linear and quadratic formulas • The F test was used to examine the linear or quadratic nature of M3 data. There were too few data points in M15 to use this test. • The F test is used to statistically analyze which of two hypothesis is more accurate, the null hypothesis; usually a simpler model, or the alternative hypothesis. • After the M15 outliers in the period vs amplitude and period vs V-I maximum light data sets in M3 were removed, the F-test demonstrated that a quadratic fit is better for the data • Outliers in the Data • In the M15 data most of the outliers were from bad data. • In M3 most of the outliers were decent RR Lyrae curves . Some of the light curve plots had scattered data or looked like another variable star, such as a Cepheid. • There were similar outliers in the M3 and M15 data sets between the period amplitude, and V-I max, min , and mean plots • Conclusions • We were able to demonstrate that the data are more consistent with a quadratic fit than a linear fit in the case of the period amplitude and period V-I at maximum light relationships for M3 . • Future work: Are these quadratic fits consistent with the Magellanic Cloud RR Lyrae data from OGLE III? • Acknowledgements: • The authors thank SUNY Oswego, National Central University and the Graduate Institute for Astronomy and the National Science Foundation's Office of International Science and Engineering's a • RrLyraes • RR Lyrae stars are variable stars .They can be used as distance indicators and are important for studying stellar evolution. • They are very common stars. It is argued they account for 90% of all known variable stars in globular clusters (Smith 2004). • The Galactic OosterhoffDichotomy • The Galactic Oosterhoff dichotomy, discovered in 1939, • suggests that you can divide globular clusters into • two groups, Oo I and II based on the periods of their RR • Lyrae s tars. • RR Lyraes in Oosterhoff I clusters have an average period • of 0.55 days • RR Lyraes in Oosterhoff II clusters have an average period • of 0.65 days Data: M3 and M15 • M3 is the prototype of the OosterhoffI cluster while M15 is the prototype Oosterhoff II cluster. • Data from Benko et al. (2006) and Stetson (2008). Fourier decomposition formula: used to derive Period vs (V-I) light curves at maximum ,minimum, and mean light from Period vs Amplitude light curves. T