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Paper: Are There Any Ultra-Long Period Cepheids in M31?
Volume: 482, 10th Pacific Rim Conference on Stellar Astrophysics
Page: 55
Authors: Lee, C.-H.; Ngeow, C.-C.; PTF Collaboration
Abstract: Ultra long period Cepheids (ULPCs) are classical Cepheids with period longer than 80 days. These ULPCs followed a different period-luminosity (P-L) relation than their shorter period counterparts, and has the potential to be used as standard candles to determine distances out to 100Mpc. Until today, only about 40 ULPCs have been identified in 10 nearby galaxies, excluding M31. Since M31 is one of the nearest spiral galaxy, which serves as a local benchmark to calibrate the distance scale ladder, the ULPCs found in this galaxy can be used to calibrate the ULPC's P-L relation. We therefore performed a comprehensive search of ULPCs in M31 by using the data from the Palomar Transient Factory (PTF) project. The imaging data from PTF spanned about 3 years, usually with daily sampling when M31 is visible in the sky, makes it an ideal dataset to search for the ULPCs. Eight candidates have be found based on the difference imaging analysis, with three of them are most likely ULPCs. Data based on the follow-up VI-band observations from P60 and LOT will be used to confirm ULPC nature of these candidates.
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