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• Main Authors: Shiuan-Wen Luo, 羅烜玟
• Other Authors: Chow-Choong Ngeow
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/f748pz

碩士 === 國立中央大學 === 天文研究所 === 105 === In previous research, the classical and Type II Cepheids can be distinguished from their optical light curves. Our research is about exploring the possibility to separate these two groups of variable stars in near-infrared bands. I use the SSP-4 photometer to observe a number of bright Galactic Cepheids in J, H band. This photometer will output the counts of standard stars and variable stars. Because the output counts is linearly proportion to the flux, we can calibrate the apparent magnitude by the method of linear regression. In order to fit the light curve of our targets, we need to get about 20 data points per light curves. We choose the two sites for our observations on Cepheids: one is at Lulin Observatory with LOT (Lulin One-meter Telescope), the other one is NCUO (National Central University Observatory) with the 24-inch telescope. Because the weather condition is very different on these two sites, we can compare the data of observations between them. On the other hand, the data from NCUO can be use to complement the data taken with LOT. Fernie & Ethers (1999) used the data of optical B, V band to distinguish the Cepheids of type I & II by Fourier decomposition. We use the same method in J, H band to the type I and II Cepheids in the Milky way (MW) and Large Magellanic cloud (LMC) galaxy. The type I data for MW Cepheids are taken from Monson and Pierce (2011), while the type II are taken from Matsunaga et al (2006). The LMC data for both types are taken from Bharwaj et al (2016). We use the software of Plotypus to fit the J, H band light curves. After choosing the ideal light curves, we can get the parameter like Fourier phase difference: φ_21 and the ratio of the amplitude: R_21. We have found the distribution of LMC ’s data are similar to Fernie and Ethers (1999). When we change to use Fourier parameters of φ_31、φ_41、R_31、R_41. we found that these parameters are not suitable to separate two types of Cepheids. We also tried the phase difference between J and J-H (Δφtot), but this parameter still cannot separate the two types of Cepheids as in the optical bands. The only good result is Warren-Harvey test. This method can separate type I and type II Cepheids successfully.