Different Characteristics of the Bright Branches of the Globular Clusters M15 and M92

Cho, Donghwan; Lee, Sang-Gak

doi:10.1086/513315

Cited by 6 publications

(19 citation statements)

References 91 publications

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“…Cho & Lee (2007) reported the full data reduction processes for the M92 frames. For accurate relative age measurements of M53 and M92, the same data reduction steps adopted by Cho & Lee (2007) for M92 were used to reduce all the science frames of M53.…”

Section: Data Reductionmentioning

confidence: 99%

“…For accurate relative age measurements of M53 and M92, the same data reduction steps adopted by Cho & Lee (2007) for M92 were used to reduce all the science frames of M53. 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 1990) or by aperture photometry using the IRAF APPHOT package, as in the case of M92.…”

Section: Data Reductionmentioning

confidence: 99%

“…To standardize the instrumental magnitudes of the 2003 May 4 frames of M53, the transformation equations (3a), (3b), and (3c) in Cho & Lee (2007) were used after rejecting spurious detections with magnitude errors ǫ(mag) > 0.15 mag, sharpness of fit |sharpness| > 1.0 (or |r 0 | > 1.0 according to the Stetson & Harris 1988), and goodness of fit χ > 3.0 as in the case of M92, which provided the standard BV I magnitudes for the stars in the M53 and M92 in Johnson-Cousins photometric system defined by Landolt (1992). The transformation equations (3a), (3b), and (3c) in Cho & Lee (2007) were derived using the PG 1633+099 and SA 107 (centered near the star 107-595) regions of Landolt's (1992) …”

Section: Data Reductionmentioning

confidence: 99%

“…Its apparent distance modulus was found to be (m − M ) V = 14.65 mag and its interstellar reddening was estimated to be E(B − V ) = 0.02 mag (Harris 1996(Harris , 2010. M92 has dominantly BHB stars extending down to ≈1.5 mag below the mean HB level with some RR Lyrae variable stars (Buonanno et al 1985;Lee et al 2003;Cho & Lee 2007). According to Lee et al (1994), the (B − R)/(B + V + R) of M92 is 0.88, which indicates that the HB morphology of M92 is slightly bluer than that of M53.…”

Section: Introductionmentioning

confidence: 99%

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Relative Age Difference Between the Metal-Poor Globular Clusters M53 and M92

Cho¹,

Sung²,

Lee³

et al. 2016

Journal of The Korean Astronomical Society

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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 ∆(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.

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Section: Data Reductionmentioning

confidence: 99%

Section: Data Reductionmentioning

confidence: 99%

Section: Data Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Relative Age Difference Between the Metal-Poor Globular Clusters M53 and M92

Cho¹,

Sung²,

Lee³

et al. 2016

Journal of The Korean Astronomical Society

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“…NGC 2808 is more metal rich ([Fe/H] = −1.15, Harris (1996)) than M15 ([Fe/H] = −2.26, Harris (1996)) which may account for the slight difference. On the other hand, the distance modulus for M15 was recently determined to be 15.53 ± 0.21 using the zero-age horizontal branch level as a distance indicator (Cho & Lee 2007) which would bring the luminosities into closer agreement. In the Cacciari et al (2004) spectra taken at highest resolution, the red giants in NGC 2808 have wing emission in Hα indicative of inflow (B/R > 1) in the majority of stars, similar to our results.…”

Section: Comparison With Other Studiesmentioning

confidence: 99%

Mass Outflow and Chromospheric Activity of Red Giant Stars in Globular Clusters. I. M15

Mészáros

Dupree

Szentgyorgyi

2008

The Astronomical Journal

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High-resolution spectra of 110 selected red giant stars in the globular cluster M15 (NGC 7078) were obtained with Hectochelle at the MMT telescope in May, 2006 May, and 2006 October. Echelle orders containing Hα and Ca ii H & K are used to identify emission and line asymmetries characterizing motions in the extended atmospheres. Emission in Hα is detected to a luminosity of log(L/L ) = 2.36, in this very metal-deficient cluster, comparable to other studies, suggesting that the appearance of emission wings is independent of stellar metallicity. The faintest stars showing Hα emission appear to lie on the asymptotic giant branch (AGB) in M15. A line-bisector technique for Hα reveals outflowing velocities in all stars brighter than log(L/L ) = 2.5, and this outflow velocity increases with stellar luminosity, indicating the mass outflow increases smoothly with luminosity. Many stars lying low on the AGB show exceptionally high outflow velocities (up to 10-15 km s −1 ) and more velocity variability (up to 6-8 km s −1 ) than red giant branch (RGB) stars of similar apparent magnitude. High velocities in M15 may be related to the low cluster metallicity. Dusty stars identified from Spitzer Space Telescope infrared photometry as AGB stars are confirmed as cluster members by radial velocity measurements, yet their Hα profiles are similar to those of RGB stars without dust. If substantial mass loss creates the circumstellar shell responsible for infrared emission, such mass loss must be episodic.

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On the Absolute Age of the Globular Cluster M921

Cecco¹,

Becucci²,

Bono³

et al. 2010

PUBL ASTRON SOC PAC

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We present precise and deep optical photometry of the globular M92. Data were collected in three different photometric systems: Sloan Digital Sky Survey (g 0 , r 0 , i 0 , and z 0 ; MegaCam at CFHT), Johnson-Kron-Cousins (B, V , and I; various ground-based telescopes), and Advanced Camera for Surveys (ACS) Vegamag (F475W, F555W, and F814W; Hubble Space Telescope). Special attention was given to the photometric calibration, and the precision of the ground-based data is generally better than 0.01 mag. We computed a new set of α-enhanced evolutionary models accounting for the gravitational settling of heavy elements at fixed chemical composition (½α=Fe ¼ þ0:3, ½Fe=H ¼ À2:32 dex, and Y ¼ 0:248). The isochrones-assuming the same true distance modulus (μ ¼ 14:74 mag), the same reddening [EðB À V Þ ¼ 0:025 AE 0:010 mag], and the same reddening lawaccount for the stellar distribution along the main sequence and the red giant branch in different color-magnitude diagrams (i 0 , g 0 À i 0 ; i 0 , and g 0 À r 0 ; i 0 , g 0 À z 0 ; I, and B À I; and F814W and F475W-F814W). The same outcome applies to the comparison between the predicted zero-age horizontal-branch (ZAHB) and the HB stars. We also found a cluster age of 11 AE 1:5 Gyr, in good agreement with previous estimates. The error budget accounts for uncertainties in the input physics and the photometry. To test the possible occurrence of CNO-enhanced stars, we also computed two sets of αand CNO-enhanced (by a factor of 3) models, both at fixed total metallicity (½M=H ¼ À2:10 dex) and at fixed iron abundance. We found that the isochrones based on the former set give the same cluster age (11 AE 1:5 Gyr) as the canonical α-enhanced isochrones. The isochrones based on the latter set also give a similar cluster age (10 AE 1:5 Gyr). These findings support previous results concerning the weak sensitivity of cluster isochrones to CNO-enhanced chemical mixtures.

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Different Characteristics of the Bright Branches of the Globular Clusters M15 and M92

Cited by 6 publications

References 91 publications

Relative Age Difference Between the Metal-Poor Globular Clusters M53 and M92

Relative Age Difference Between the Metal-Poor Globular Clusters M53 and M92

Mass Outflow and Chromospheric Activity of Red Giant Stars in Globular Clusters. I. M15

On the Absolute Age of the Globular Cluster M921

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