Identification of Cepheid Variables in ASAS Data (Poster abstract)

Volume 42 number 1 (2014)

Vanessa Swenton

Department of Physics and Earth Sciences, Central Connecticut State University, 1615 Stanley Street, New Britain, CT 06053; address email correspondence to Larsen@ccsu.edu

Kristine Larsen

Department of Physics and Earth Sciences, Central Connecticut State University, 1615 Stanley Street, New Britain, CT 06053; Larsen@ccsu.edu

Abstract

(Abstract only) Through studying the characteristics of Cepheid variables, we can further understand the nature and evolution of stars, as well as the scale of the Universe (through the famous period-luminosity relationship). Classical Cepheid stars, or Type I Cepheids, are radially-pulsating supergiants. Type II Cepheids are older and have lower mass than Type I Cepheids. They are rarer and existing classifications of these stars have been shown to be erroneous at unusual high rates. Computerized automatic classification programs sift through the data of large photometric surveys to produce a list of (what the program recognizes as) Cepheid star candidates. Unfortunately, this automatic classification of light curves has demonstrated to be ambiguous. Therefore, it takes a human to further sift through the list in order to come up with a more accurate (and, as a result, a more useful) list of probable Cepheids. This study was based on a list of 3,548 Cepheid candidates in the ASAS data provided by Patrick Wils (through Doug Welch). Patrick Wils had previously examined eighty-four stars on the spreadsheet and positively identified only five of these stars as Cepheids. The methodology of the current study was to use known properties of Cepheids including available infrared photometry (2MASS), proper motion (PPMXL), and X-Ray emission (ROTSE) data (for which we received helpful guidance from Sebastian Otero) to cull the list down to the most likely Cepheids. The ASAS light curves of these candidates were investigated to determine whether the shapes were truly consistent with those of Cepheids. This poster will summarize the methodology used and give examples of how individual Cepheid candidates were evaluated. Candidates of interest are currently being crosschecked for any updated information on VSX, and the light curves more closely analyzed using VStar. Results concerning the misidentification of candidate Cepheids will be reported to VSX and summarized in JAAVSO.