• 천문학회보
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• 제12권
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• pp.9.1-9.1
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• 1987

• 천문학회보
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• 제25권2호
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• pp.31-31
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• 2000

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1994년도 한국우주과학회보 제3권2호
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• pp.19-19
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• 1994

• 천문학회보
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• 제27권2호
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• pp.46-46
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• 2002

• 천문학회보
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• 제27권2호
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• pp.22-22
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• 2002

• 천문학회보
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• 제33권2호
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• pp.68.1-68.1
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• 2008

• 천문학회보
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• 제16권
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• pp.14.2-14.2
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• 1991

• 천문학회보
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• 제39권1호
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• pp.82.1-82.1
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• 2014

The presence of multiple populations is now well-established in most globular clusters (GCs) in the Milky Way. In light of this progress, here we suggest a new model explaining the origin of the Sandage period-shift and the difference in mean period of type ab RR Lyrae variables () between the two Oosterhoff groups. In our models, while matching the observed color-magnitude diagrams, the difference in is naturally reproduced as the instability strip is occupied by different subpopulations with increasing metallicity. The instability strip in the metal-poor group II clusters is populated by second generation stars (G2) with enhanced helium and CNO abundances, while the RR Lyraes in the metal-rich group I clusters are mostly produced by first generation stars (G1) without these enhancements. This population shift within the instability strip can create the observed period-shift between the two groups, since both helium and CNO abundances play a role in increasing the period of RR Lyrae variables. The presence of more metal-rich Oosterhoff group III clusters having RR Lyraes with longest can also be reproduced, if more helium-rich third generation stars (G3) are present in these GCs.

• Journal of Astronomy and Space Sciences
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• 제13권1호
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• pp.1-8
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• 1996

CCD time series photometry was performed for two Oosterhoff type II field RR Lyrae stars, SV Eri and XX And, to construct light curves in B and V bands. The maximum light times from our observations were combined with those in the literature to construct phase shift diagrams, from which we determined the period change rates ${\beta}$. We obtained large positive period change rates for these stars, which are expected from current evolutionary models if these stars are evolving rapidly from blue to red toward the end of core helium burning phase.

• 천문학논총
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• 제26권4호
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• pp.141-146
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• 2011

In the region of the open cluster M48 (NGC 2548), time-series BV CCD images were taken for 22 nights from February 28 in 2008 to March 17 in 2011. From this observation, we found 10 new variable stars. They include five eclipsing binaries, an RR Lyrae, two ${\delta}$ Scuti, and two semi-periodic and/or slow irregular type variable stars. We fail to find the member stars of the open cluster among the 10 variable stars.