Using our ingeniously designed new filter systems, we investigate the multiple stellar populations (MSPs) of the red giant branch (RGB) and the asymptotic giant branch (AGB) in the globular cluster (GC) M5. Our results are the following. (1) Our cn JWL index accurately traces the nitrogen abundances in M5, while other color indices fail to do so. (2) We find bimodal CN distributions both in the RGB and the AGB sequences, with the number ratios between the CN-weak (CN-w) and the CN-strong (CN-s) of n(CN-w):n(CN-s) = 29:71 (± 2) and 21:79 (± 7), respectively. (3) (5) Although small, the RGB bump of the CN-s is slightly brighter, ∆V bump = 0.07 ± 0.04 mag. If real, the difference in the helium abundance becomes ∆Y = 0.028 ± 0.016, in the sense that the CN-s is more helium enhanced. (6) Very similar radial but different spatial distributions with comparable center positions are found for the two RGB populations. The CN-s RGB and AGB stars are more elongated along the NW-SE direction. (7) The CN-s population shows a substantial net projected rotation, while that of the CN-w population is nil. (8) Our results confirm the deficiency of the CN-w AGB stars previously noted by others. We show that it is most likely due to the stochastic truncation in the outer part of the cluster. Finally, we discuss the formation scenario of M5.Subject headings: globular clusters: individual (M5: NGC 5904) -Hertzsprung-Russell diagram -stars: abundances -stars: evolution INTRODUCTIONDuring the last decade, a drastic paradigm shift on the true nature of the Galactic globular clusters (GCs) has emerged. Almost all GCs exhibit variations in lighter elemental abundances, for example bimodal CN distributions and Na-O anticorrelations (e.g., Smith 1987;Carretta et al. 2009). Understanding this ubiquitous nature of the multiple stellar populations (MSPs) in GCs is one of the outstanding quest in the near field cosmology (e.g., Lee et al. 2009a;Lee 2015;Piotto et al. 2015;Renzini et al. 2015).The key feature of the MSPs in the peculiar GCs, like ω Cen and M22, is the discrete distributions in the heavy elemental abundances and these GCs are considered to be remnants of the dwarf galaxy related 1 Based on observations made with the Cerro Tololo Inter-American Observatory (CTIO) 1m telescope, which is operated by the SMARTS consortium.2 Department of Physics and Astronomy, Sejong University, 209 Neungdong-ro, Gwangjin-Gu, Seoul, 05006, Korea; jaewoolee@sejong.ac.kr, jaewoolee@sejong.edu . Each candidate has pros and cons to explain the observational lines of evidence in GCs. In the context of the self-enrichment scenario for normal GCs, Renzini et al. (2015) proposed that the AGB pollution scenario would be favored. However, most of the proposed candidates cannot solve the so-called "mass-budget problem" with satisfaction (e.g., see Bastian & Lardo 2015). The GCs with MSPs formation scenario proposed by Bastian et al. (2013) can mitigate the mass-budget problem, but their model cannot explain the differences in the spatial distributions ...

We present a multiple stellar population (MSP) study of the globular cluster (GC) NGC 6752. We show that our new photometric CN index accurately traces the CN and the nitrogen abundances in cool giants, finding the discrete double red giant branch (RGB) and asymptotic giant branch (AGB) sequences with number ratios between the CN-weak and the CN-strong populations of n(CN-w):n(CNs) = 25:75 (±3; RGB) and 79:21 (±13; AGB). The discrepancy in these number ratios suggests that a significant fraction of the low-mass CN-s stars failed to evolve into the AGB phase. However, unlike previous studies, our results indicate the presence of an extreme CN-s AGB population in NGC 6752, which may require follow-up spectroscopic study. Similar to what is seen for M5, the evolution of the nitrogen abundance is discrete and discontinuous, while the evolutions of oxygen and sodium are continuous between the two populations in NGC 6752, implying that different astrophysical sources are responsible for the evolutions of these elements. In addition, the helium abundance inferred from the RGB bump magnitude shows hat the CN-s population is slightly more helium-enhanced. Despite the identical cumulative radial distributions between the two populations, the structure-kinematics coupling can be observed in individual populations: the CN-w population has a spatially elongated shape with a faster rotation, while the CN-s population shows weak or no net rotation, with spatially symmetric shape, raising important question about the long-term dynamical evolution of the GCs. Based on observations made with the Cerro Tololo Inter-American Observatory (CTIO) 1 m telescope, which is operated by the SMARTS consortium.

We present Ca–CN–CH–NH photometry for the well-known globular cluster (GC) M3 (NGC 5272). We show new evidence for two M3 populations with distinctly different carbon and nitrogen abundances, seen in a sharp division between CN-weak and CN-strong red-giant branches (RGBs) in M3. The CN-strong population shows a C–N anticorrelation that is a natural consequence of the CN cycle, while the CN-weak population shows at most a very weak C–N anticorrelation. Additionally, the CN-weak population exhibits an elongated spatial distribution that is likely linked to its fast rotation. Our derived metallicities reveal bimodal distributions in both populations, with 〈[Fe/H]〉 ≈ −1.60 and −1.45, which appear to be responsible for the discrete double RGB bumps in the CN-weak population and the large range. From this discovery, we propose that M3 consists of two GCs, namely C1 (23%, 〈[Fe/H]〉 ≈ −1.60) and C2 (77%, 〈[Fe/H]〉 ≈ −1.45), each of which has its own C–N anticorrelation and structural and kinematical properties, which are strong indications of independent systems in M3. The fractions of the CN-weak population for both C1 and C2 are high compared to Galactic GCs but they are in good agreement with GCs in the Magellanic Clouds. We suggest that M3 is a merger remnant of two GCs, most likely in a dwarf galaxy environment, and accreted to our Galaxy later in time. This is consistent with recent proposals of an ex situ origin for M3.

Apparently similar but multifaceted photometric systems are currently being used to investigate the multiple stellar populations in globular clusters, without the concrete general agreement on the definition of the multiple populations. In recent years, an attractive idea of utilization of the widely used U BI photometry, C UBI , for the populational tagging of the giant stars in globular clusters has been emerged. We perform a critical analysis of the cn JWL and the C UBI indices, finding that the populational tagging from the C UBI index may not be reliable, due to the inherited trait of the broad-band photometry. As a consequence, the populational number ratios and the cumulative radial distributions from the C UBI index can be easily in error. The results for M3, which shows a very strong radial gradient in the populational number ratio, highlights the strengths of our cn JWL index: both the HST imaging and the ground-based spectroscopy failed to grasp the correct picture, that can be easily achieved with our cn JWL index with small aperture ground-based telescopes, due to the small field of view or crowdedness in the central part of the cluster.

We present new large field-of-view (∼1°×1°) Ca-CN photometry of the prototypical metal-rich globular cluster 47 Tucanae (NGC 104). Our results are the following. (1) The populational number ratios of the red giant branch (RGB) and red horizontal branch (RHB) are in excellent agreement: n(CN-w):n(CN-s) = 30:70 (±1–2), where the CN-w and CN-s stand for the CN-weak and CN-strong populations, respectively. Both the CN-s RGB and RHB populations are more centrally concentrated than those of CN-w populations are. (2) Our photometric metallicities of individual RGB stars in each population can be well described by bimodal distributions with two metallicity peaks, [Fe/H] ∼−0.72 and −0.92 dex, where the metal-poor components occupy ∼13% of the total RGB stars. The metal-poor populations are more significantly centrally concentrated than the metal-rich populations, showing a similar result that we found in M3. (3) The RGB bump V magnitudes of individual populations indicate that there is no difference in the helium abundance between the two metal-poor populations, while the helium enhancement of ΔY ∼0.02–0.03 is required between the the two metal-rich populations. (4) The RHB morphology of 47 Tuc appears to support our idea of the bimodal metallicity distribution of the cluster. We suggest that 47 Tuc could be another example of merger remnants of two globular clusters, similar to M3 and M22.

We present the Ca-CN-CH photometry of the metal-complex globular cluster (GC) M22 (NGC 6656). Our photometry clearly shows the discrete double CN-CH anticorrelations in M22 red giant branch (RGB) stars, due to the difference in the mean metallicity. The populational number ratio between the two main groups is n(G1):n(G2) = 63:37(±3), with the G1 being more metal-poor. Furthermore, the G1 can be divided into two subpopulations with the number ratio of n(CN-w):n(CN-s) = 51:49 (±4), while the G2 can be divided into three subpopulations with n(CN-w):n(CN-i):n(CN-s) = 24:32:44 (±5). The proper motion of individual stars in the cluster shows an evidence of internal rotation, showing the G2 with a faster rotation, confirming our previous results from radial velocities. The cumulative radial distributions (CRDs) of individual subpopulations are intriguing in the following aspects: (1) In both main groups, the CRDs of the CN-s subpopulations are more centrally concentrated than other subpopulations. (2) The CRDs of the the G1 CN-s and the G2 CN-s are very similar.(3) Likewise, the G1 CN-w and the G2 CN-w and CN-i have almost identical CRDs. We also estimate the relative helium abundance of individual subpopulations by comparing their RGB bump magnitudes, finding that no helium abundance variation can be seen in the G1, while significant helium enhancements by ∆Y ≈ 0.03 -0.07 are required in the G2. Our results support the idea that M22 formed via a merger of two GCs.

We introduce new color indices cn ′ JWL (= Ca CTIO − Ca JWL ) and ch JWL [=(JW L43 − b) − (b − y)], accurate photometric measures of the CN band at λ3883 and the CH G band, respectively, in the study of the multiple populations (MPs) in globular clusters (GCs). Our photometric CN-CH relation for a large number of red-giant branch (RGB) in M5 shows that the evolutions of the CN and CH between the CN-w and CN-s populations are not continuous. Armed with our new color indices, we investigate the MPs of NGC 6723, finding the RGB populational number ratio of n(CN-w):n(CN-s) ≈ 35.5:64.5 (±2.8) with no radial gradient. Similar to other normal GCs with MPs, the helium abundance of the CN-s population inferred from the RGB bump magnitude is slightly enhanced by ∆Y = 0.012 ± 0.012. Our cn JWL and cn ′ JWL color-magnitude diagrams clearly show the discrete double AGB populations in NGC 6723, whose bright AGB populational number ratio is in marginally agreement with that of the RGB stars within the statistical errors. Finally, our synthetic cn JWL index is in good agreement with observations, except for the CN-w asymptotic giant branch (AGB). To mitigate the discrepancy in the CN-w AGB may require a mild nitrogen enhancement and/or a large decrement in the 12 C/ 13 C ratio with respect to the bright RGB.

With our new Ca-CN-CH-NH photometry, we revisit the globular cluster (GC) M5. We find that M5 is a mono-metallic GC with a small metallicity dispersion. Our carbon abundances show that the σ[C/Fe] of the M5 CN-s population, with depleted carbon and enhanced nitrogen abundances, is significantly large for a single stellar population. Our new analysis reveals that the M5 CN-s population is well described by the two stellar populations: the CN-sI, being the major CN-s component, with the intermediate carbon and nitrogen abundance and the CN-sE with the most carbon-poor and nitrogen-rich abundance. We find that the CN-sE is significantly more centrally concentrated than the others, while CN-w and CN-sI have similar cumulative radial distributions. The red giant branch bump V magnitude, the helium abundance barometer in mono-metallic populations, of individual populations appears to be correlated with their mean carbon abundance, indicating that carbon abundances are anticorrelated with helium abundances. We propose that the CN-sE formed out of gas that experienced proton-capture processes at high temperatures in the innermost region of the proto-GC of M5 that resided in a dense ambient density environment. Shortly after, the CN-sI formed out of gas diluted from the pristine gas in the more spatially extended region, consistent with the current development of numerical simulations by others.