BVI PHOTOMETRIC STUDY OF THE OLD OPEN CLUSTER RUPRECHT 6

김상철,경재만,박홍수,한일승,이준협,문대식,이영대,김성재 한국천문학회 2017 Journal of The Korean Astronomical Society Vol.50 No.3

We present a $BVI$ optical photometric study of the old open cluster Ruprecht 6 using the data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. Its color-magnitude diagrams show the clear existence of the main-sequence stars, whose turn-off point is located around $V \approx 18.45$ mag and $B-V \approx 0.85$ mag. Three red clump (RC) stars are identified at $V = 16.00$ mag, $I = 14.41$ mag and $B-V = 1.35$ mag. From the mean $K_s$-band magnitude of RC stars ($K_s=12.39 \pm 0.21$ mag) in Ruprecht 6 from 2MASS photometry and the known absolute magnitudes of the RC stars ($M_{K_S} = -1.595 \pm 0.025$ mag), we obtain the distance modulus to Ruprecht 6 of $(m-M)_0 = 13.84 \pm 0.21$ mag ($d=5.86 \pm 0.60$ kpc). From the $(J-K_s)$ and $(B-V)$ colors of the RC stars, comparison of the $(B-V)$ and $(V-I)$ colors of the bright stars in Ruprecht 6 with those of the intrinsic colors of dwarf and giant stars, and the PARSEC isochrone fittings, we derive the reddening values of $E(B-V) = 0.42$ mag and $E(V-I) = 0.60$ mag. Using the PARSEC isochrone fittings onto the color-magnitude diagrams, we estimate the age and metallicity to be: $\log(t)=9.50 \pm 0.10$ ($t=3.16 \pm 0.82$ Gyr) and [Fe/H] $= -0.42 \pm 0.04$ dex. We present the Galactocentric radial metallicity gradient analysis for old (age $> 1$ Gyr) open clusters of the Dias et al. catalog, which likely follow a single relation of [Fe/H] $=(-0.034\pm0.007) R_{\mathrm{GC}} + (0.190\pm0.080)$ (rms = 0.201) for the whole radial range or a dual relation of [Fe/H] $=(-0.077\pm0.017) R_{\mathrm{GC}} + (0.609\pm0.161)$ (rms = 0.152) and constant ([Fe/H] $\sim -0.3$ dex) value, inside and outside of $R_\mathrm{GC} \sim 12$ kpc, respectively. The metallicity and Galactocentric radius ($13.28\pm 0.54$ kpc) of Ruprecht 6 obtained in this study seem to be consistent with both of the relations.

NGC 7790의 UBVI CCD 측광

최동열,김희수,임범두,성환경 한국지구과학회 2015 한국지구과학회지 Vol.36 No.7

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 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.

Improving CMD Areal Density Analysis: Algorithms and Strategies

R. E. Wilson 한국우주과학회 2014 Journal of Astronomy and Space Sciences Vol.31 No.2

Essential ideas, successes, and difficulties of Areal Density Analysis (ADA) for color-magnitude diagrams (CMD’s) of resolved stellar populations are examined, with explanation of various algorithms and strategies for optimal performance. A CMDgeneration program computes theoretical datasets with simulated observational error and a solution program inverts the problem by the method of Differential Corrections (DC) so as to compute parameter values from observed magnitudes and colors, with standard error estimates and correlation coefficients. ADA promises not only impersonal results, but also significant saving of labor, especially where a given dataset is analyzed with several evolution models. Observational errors and multiple star systems, along with various single star characteristics and phenomena, are modeled directly via the Functional Statistics Algorithm (FSA). Unlike Monte Carlo, FSA is not dependent on a random number generator. Discussions include difficulties and overall requirements, such as need for fast evolutionary computation and realization of goals within machine memory limits. Degradation of results due to influence of pixelization on derivatives, Initial Mass Function (IMF) quantization, IMF steepness, low Areal Densities (A), and large variation in A are reduced or eliminated through a variety of schemes that are explained sufficiently for general application. The Levenberg-Marquardt and MMS algorithms for improvement of solution convergence are contained within the DC program. An example of convergence, which typically is very good, is shown in tabular form. A number of theoretical and practical solution issues are discussed, as are prospects for further development.

Improving CMD Areal Density Analysis: Algorithms and Strategies

Wilson, R.E. The Korean Space Science Society 2014 Journal of Astronomy and Space Sciences Vol.31 No.2

Essential ideas, successes, and difficulties of Areal Density Analysis (ADA) for color-magnitude diagrams (CMD's) of resolved stellar populations are examined, with explanation of various algorithms and strategies for optimal performance. A CMD-generation program computes theoretical datasets with simulated observational error and a solution program inverts the problem by the method of Differential Corrections (DC) so as to compute parameter values from observed magnitudes and colors, with standard error estimates and correlation coefficients. ADA promises not only impersonal results, but also significant saving of labor, especially where a given dataset is analyzed with several evolution models. Observational errors and multiple star systems, along with various single star characteristics and phenomena, are modeled directly via the Functional Statistics Algorithm (FSA). Unlike Monte Carlo, FSA is not dependent on a random number generator. Discussions include difficulties and overall requirements, such as need for fast evolutionary computation and realization of goals within machine memory limits. Degradation of results due to influence of pixelization on derivatives, Initial Mass Function (IMF) quantization, IMF steepness, low Areal Densities ($\mathcal{A}$), and large variation in $\mathcal{A}$ are reduced or eliminated through a variety of schemes that are explained sufficiently for general application. The Levenberg-Marquardt and MMS algorithms for improvement of solution convergence are contained within the DC program. An example of convergence, which typically is very good, is shown in tabular form. A number of theoretical and practical solution issues are discussed, as are prospects for further development.

SEJONG OPEN CLUSTER SURVEY (SOS). 0. TARGET SELECTION AND DATA ANALYSIS

Sung, Hwankyung,Lim, Beomdu,Bessell, Michael S.,Kim, Jinyoung S.,Hur, Hyeonoh,Chun, Moo-Young,Park, Byeong-Gon The Korean Astronomical Society 2013 Journal of The Korean Astronomical Society Vol.46 No.3

Star clusters are superb astrophysical laboratories containing cospatial and coeval samples of stars with similar chemical composition. We initiate the Sejong Open cluster Survey (SOS) - a project dedicated to providing homogeneous photometry of a large number of open clusters in the SAAO Johnson-Cousins' UBV I system. To achieve our main goal, we pay much attention to the observation of standard stars in order to reproduce the SAAO standard system. Many of our targets are relatively small sparse clusters that escaped previous observations. As clusters are considered building blocks of the Galactic disk, their physical properties such as the initial mass function, the pattern of mass segregation, etc. give valuable information on the formation and evolution of the Galactic disk. The spatial distribution of young open clusters will be used to revise the local spiral arm structure of the Galaxy. In addition, the homogeneous data can also be used to test stellar evolutionary theory, especially concerning rare massive stars. In this paper we present the target selection criteria, the observational strategy for accurate photometry, and the adopted calibrations for data analysis such as color-color relations, zero-age main sequence relations, Sp - MV relations, Sp - $T_{eff}$ relations, Sp - color relations, and $T_{eff}$ - BC relations. Finally we provide some data analysis such as the determination of the reddening law, the membership selection criteria, and distance determination.

UBV I CCD PHOTOMETRY OF THE OPEN CLUSTERS NGC 4609 AND HOGG 15

Kook, Seung-Hwa,Sung, Hwan-Kyung,Bessell, M.S. The Korean Astronomical Society 2010 Journal of The Korean Astronomical Society Vol.43 No.5

UBV I CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V ) = $0.37{\pm}0.03$, $V_0-M_V=10.60{\pm}0.08$, log $\tau$= 7.7 $\pm$ 0.1; Hogg 15 : E(B - V ) = 1.13 $\pm$ 0.11, $V_0-M_V$ = 12.50 $\pm$ 0.15, log $\tau$ $\lesssim$ 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We also determine the mass function of these clusters and obtain a slope $\Gamma$ = -1.2 ($\pm$0.3) for NGC 4609 which is normal and a somewhat shallow slope (${\Gamma}=-0.95{\pm}0.5$) for Hogg 15.

UBVI CCD PHOTOMETRY OF YOUNG OPEN CLUSTERS. II. BOCHUM 7

SUNG HWANKYUNG,BESSELL M. S.,PARK B.-G.,KANG Y. H. The Korean Astronomical Society 1999 Journal of The Korean Astronomical Society Vol.32 No.2

UBVI CCD photometry has been obtained for a region around the Wolf-Rayet star WR 12. We found two young stellar associations in the observed field: the nearer one comprises the field members of Vela OBI association at d = 1.8kpc, while the farther one is the young open cluster Bochum 7 (Bo 7) at d = 4.8kpc. The stars associated with Bo 7 showed no central concentration which suggests that Bo 7 is not a young open cluster but simply a local concentration in the density of young stars belonging to the OB association (Vel OB3). These two associations have similar ages but remarkably different mass function slopes ($\Gamma$ = -2.1 $\pm$ 0.3 for Vel OBI and -1.0 $\pm$ 0.3 for Bo 7). The stars in Vel OBI shows an evident age spread (${\Delta}T\~ 9Myr$). We also found two strong H$\alpha$ emission stars - WR 12 and $\sharp$1066 - from narrow band H$\alpha$ photometry.

NO OPEN CLUSTER IN THE RUPRECHT 93 REGION

Cheon, So-Ra,Sung, Hwan-Kyung,Bessell, M.S. The Korean Astronomical Society 2010 Journal of The Korean Astronomical Society Vol.43 No.4

UBVI CCD photometry is obtained for the Ruprecht 93 (Ru 93)region. We are unable to confirm the existence of an intermediate-age open cluster in Ru 93 from the spatial distribution of blue stars. On the other hand, we find two young star groups in the observed field: the nearer one (Ru 93 group) comprises the field young stars in the Sgr-Car arm at $d{\approx}2.1$ kpc, while the farther one (WR 37 group) is the young stars around WR 37 at $d{\approx}4.8$ kpc. We derive an abnormal extinction law ($R_V$ = 3.5) in the Ruprecht 93 region.

구상성단 M71의 BV CCD 측광: 거리 그리고 나이

임홍서,천문석,변용익,손영종 한국우주과학회 2004 Journal of Astronomy and Space Sciences Vol.21 No.1

HST NIC3 PHOTOMETRY OF METAL-RICH GLOBULAR CLUSTERS PALOMAR 6, LILLER 1, AND 47 TUC (NGC 104)

Lee, Jae-Woo 한국우주과학회 2004 Journal of Astronomy and Space Sciences Vol.21 No.3