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天文館

臺北天文館學報(出版品)

臺北天文館學報第10期(English)

JTAM VOL. 10 (2012)


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  Field Author Title Received Date Accepted Date
Invited Article -- Chow-Choong Ngeow The Role of Cepheid Variables in Observational Cosmology(pdf檔案) -- --
Refereed Paper  Star Seline Chia-Ling Hu, Wen-Ping Chen, and the Yong Exoplanet Transit Initiative Photometric Observations of the Young Cluster Variable GM Cephei(pdf檔案) 2011.12.09 2012.10.11

 


 

 

邀請論文

Title:The Role of Cepheid Variables in Observational Cosmology

Author:Chow-Choong Ngeow

Keywords:Cepheid, distance scale, Hubble constant

Abstract:
   As a class of pulsating variable stars, Cepheids play an important role in comsology via its period-luminosity (P-L) relation. This is because Cepheid P-L relation, after properly calibrated, is a standard candle that can be used to calibrate distances to a number of secondary distance indicators along the cosmic distance scale ladder. This in turn permits the determination of Hubble constant – an important parameter in modern cosmology, to within 10% accuracy. In this paper, we briefly review four recent major projects that determine the Hubble constant, with emphasize given on the role of Cepheid in these projects.

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Refereed Paper 01

Title:Photometric Observations of the Young Cluster Variable GM Cephei

Author:Seline Chia-Ling Hu, Wen-Ping Chen, and the Yong Exoplanet Transit Initiative

Keywords:variable, young stars, planetesimal formation, GM Cephei, UXor

Abstract:
   We present our photometric observations of GM Cep, a solar type variable in the young (∼ 4 Myr) open cluster Trumpler 37. The star is known as a classical T Tauri star with a circumstellar disk and active accretion. GM Cep was suspected to undergo an outburst, thus a candidate for an EXor-type variable. In our monitoring campaign observations in 2010–2011, GM Cep experienced a ∼ 0.82 mag brightness decrease in the R band continuously for 39 days, and frequent, transient flare-like episodes with the amplitude < 1 mag, each lasting for about 10 days. The brightening was accompanied with a bluer color, presumably arising from increased accretion activity. Interestingly, the star also turned bluer in the fading phase. Combining the AAVSO and literature data, we found a quasi-cyclic period of ∼ 311 days for the fading event. A possible mechanism for the fading could be obscuration by a clump of dust around the star. We proposed that GM Cep therefore should be a UXor-type variable in the transition phase between grain coagulation and planetesimal formation process in the circumstellar disk.

Full Text(pdf檔案)