NGC 7790의 UBVI CCD 측광 = UBVI CCD Photometry of NGC 7790

다국어 초록 (Multilingual Abstract)

CCD photometry of the intermediate age open cluster NGC 7790 has been obtained using AZT-22 1.5m telescope (f/7.74) at the Maidanak Astronomical Observatory in Uzbekistan. NGC 7790 contains three Cep variable stars including CEa Cas, CEb Cas, and CF Cas. PSF photometry was carried out using IRAF/DAOPHOT for all observations. The total number of stars observed both in and filter was 1008 and the limiting magnitude was V≈22. To determine atmospheric extinction coefficients and photometric zero points, many blue and red standard stars as well as the standard stars in the celestial equator under various airmass were observed. Photometric data were transformed into the standard Johnson-Cousins’ UBVI standard system.
From the analysis of UBVI color-magnitude diagram and color-color diagram, the color excess in and filter, the selective extinction ratio in and filter and distance modulus of the cluster were determined. The age of the cluster was estimated to be based on the position of these three Cepheid variables in the color-magnitude diagram, the isochrone of the Geneva group (Ekström et al., 2012-Z=0.019), and the isochrone of the Padova group (Bressan et al., 2012-Z=0.014) were used to compare each other. Of them, the Geneva models that considered stellar rotation well described the position of Cepheid variables in the blue loop. Although they were well consistent with standard period-luminosity relation of Cepheid variables, three Cepheid variables in NGC 7790 were, on average, brighter by about 0.5 mag than the absolute magnitude estimated from the mean period-luminosity relation at a given period.등급도, 세페이드 변광성, 주기-광도 관계

국문 초록 (Abstract)

우즈베키스탄 Maidanak 천문대 AZT-22 1.5m 망원경(f/7.74)과 SITe CCD를 사용하여 3개의 Cep 변광성 CEa Cas, CEb Cas 및 CF Cas가 있는 중년 산개성단 NGC 7790의 측광 관측을 수행하였다. 관측자료는 IRAF/DAOPHOT를 이용하여 PSF 측광을 수행하였으며, 와 필터에서 모두 측광된 별의 수는 총 1008개이며, 측광의 한계등급은 V≈22등급이다. 대기소광계수 및 측광영점을 결정하기 위하여 천구적도에 있는 여러 표준별과 청색 및 적색 표준별을 다양한 대기투과량에서 관측하였다. 표준별 측광을 통해 대기소광계수 및 측광영점을 결정하고, 성단의 측광자료는 Johnson-Cousins UBVI 표준계로 변환하였다.
NGC 7790의 색-등급도와 색-색도에서 이 성단의 와 필터에서의 색초과량, B와 V 필터에서의 선택적 소광량 및 거리지수를 얻었다. H-R도에서 세페이드 변광성의 위치를 고려하여 나이를 결정하였다. 이 과정에서 Padova연구집단(Bressan et al., 2012)의 등연령곡선()과 Geneva 연구집단(Ekström et al., 2012)의 등연령곡선()을 모두 사용하였고, 그중에서 자전을 고려한 Geneva 연구집단의 진화모형이 관측자료와 잘 일치하여 NGC 7790의 나이로 를 얻었다. 또 NGC 7790내 세페이드 변광성의 절대등급은 세페이드 변광성의 평균 주기-광도 관계에 비해 분산 범위 내에 있기는 하지만 주어진 주기에서 평균적으로 약 0.5등급 정도 밝음을 확인하였다.

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