CCD photometric observations of the globular cluster (GC), M53 (NGC 5024), are performed using the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea on the same nights (2002 April and 2003 May) as the observations of the GC M92 (NGC 6341) reported by Cho and Lee using the same ...
CCD photometric observations of the globular cluster (GC), M53 (NGC 5024), are performed using the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea on the same nights (2002 April and 2003 May) as the observations of the GC M92 (NGC 6341) reported by Cho and Lee using the same instrumental setup. The data for M53 is reduced using the same method as used for M92 by Cho and Lee, including preprocessing, point-spread function fitting photometry, and standardization etc. Therefore, M53 and M92 are on the same photometric system defined by Landolt, and the photometry of M53 and M92 is tied together as closely as possible. After complete photometric reduction, the V versus B − V , V versus V − I, and V versus B − I color-magnitude diagrams (CMDs) of M53 are produced to derive the relative ages of M53 and M92 and derive the various characteristics of its CMDs in future analysis. From the present analysis, the relative ages of M53 and M92 are derived using the Δ(B − V ) method reported by VandenBerg et al. The relative age of M53 is found to be 1.6 ± 0.85 Gyr younger than that of M92 if the absolute age of M92 is taken to be 14 Gyr. This relative age difference between M53 and M92 causes slight differences in the horizontal-branch morphology of these two GCs.
CCD photometric observations of the globular cluster (GC), M53 (NGC 5024), are performed using the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea on the same nights (2002 April and 2003 May) as the observations of the GC M92 (NGC 6341) reported by Cho and Lee using the same instrumental setup. The data for M53 is reduced using the same method as used for M92 by Cho and Lee, including preprocessing, point-spread function fitting photometry, and standardization etc. Therefore, M53 and M92 are on the same photometric system defined by Landolt, and the photometry of M53 and M92 is tied together as closely as possible. After complete photometric reduction, the V versus B − V , V versus V − I, and V versus B − I color-magnitude diagrams (CMDs) of M53 are produced to derive the relative ages of M53 and M92 and derive the various characteristics of its CMDs in future analysis. From the present analysis, the relative ages of M53 and M92 are derived using the Δ(B − V ) method reported by VandenBerg et al. The relative age of M53 is found to be 1.6 ± 0.85 Gyr younger than that of M92 if the absolute age of M92 is taken to be 14 Gyr. This relative age difference between M53 and M92 causes slight differences in the horizontal-branch morphology of these two GCs.
A BV I CCD photometric study was performed on the central 11.7′ × 11.7′ region of the GC M53 from the RGB tip down to ≈2 mag below the MSTO observed on the same nights of the GC M92 by Cho & Lee (2007) using the same telescope, filter set, and CCD camera at BOAO for an accurate relative age measurement of the GCs M53 and M92
대상 데이터
All observations of M53 and M92 were carried out using the 1.8 m telescope (f/8) and SITe 2048 × 2048 CCD camera at the Bohyunsan Optical Astronomy Observatory (BOAO) in Korea in the BV I bands on the same nights using the same instrumental setup, which was also the same as that used by Cho et al. (2005).
The BV I CCD observations of the central 11.7′ × 11.7′ regions of M53 and M92 were made using the BOAO 1.8 m telescope on the night of 2002 April 4
Additional BV I CCD observations were carried out for the central 11.7′ × 11.7′ regions of M53 and M92, and the PG 1633+099 and SA 107 (centered near the star 107-595) regions of Landolt’s (1992) standard regions on the night of 2003 May 4
이론/모형
In addition, the same parameters were used for preprocessing using the IRAF CCDRED package and extracting the instrumental magnitudes of M53 stars by the PSF fitting method using the IRAF version of the DAOPHOT package (Stetson 1987; Stetson et al
The internal photometric errors in the V magnitude and B − V, V − I, and B − I colors were estimated from the photometric errors calculated using the IRAF version of the DAOPHOT package. Then ϵ(V ) was ≈0.
성능/효과
Therefore, special care was taken to ensure that M53 and M92 were on the same photometric system and the photometry of M53 and M92 was tied together as closely as possible using the Landolt’s (1992) stars as standard stars to transform the 2003 data of M53 and M92, which were used to transform the 2002 data of M53 and M92 to the standard system
In M53, the AGB stars were separated quite well from the RGB sequence in all three types of CMDs from ~1.0 mag below the RGB tip down to the bottom of the AGB.
According to these CMDs of M53, there are many BSSs in M53, which were most clearly delineated in the V versus B −I CMD
The zero point errors were estimated to be at a level of 0.010 mag in V, 0.025 mag in B − V, and 0.015 mag in V − I for the photometry of M53 and M92 of the present study except for the small zero point shift, particularly in the case of M53
1998). If this relative age difference between metal-poor GCs M53 and M92 is real, the older age of M92 might have caused the slightly bluer HB morphology of M92 than M53. This can be explained by the results from the theoretical studies from Lee (1992) and Lee et al.
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