Multiple Stellar Populations of Globular Clusters from Homogeneous Ca-CN Photometry. IV. Toward Precision Populational Tagging*

Abstract

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.

Is helium the key parameter in the extended colour spread of the first generation stars in M3?

“…The HB ratio 2 in the HST sample is HBR ∼ 0.313 ± 0.034, significantly larger than the ratio obtained from ground based observations covering also the external parts of the cluster (HBR ∼ 0.08, Buonanno et al 1994;Ferraro et al 1997;Catelan et al 2001). This difference corroborates the evidence that blue-HB stars are more-centrally concentrated than the red HB (Catelan et al 2001;Lee 2019). This feature is expected if the blue HB is populated by 2G stars, born more concentrated in the cluster core, as envisioned by cooling-flow formation models (e.g.…”

Thirteen facts that you need to know on multiple populations in globular clusters

“…NGC 6752, NGC 6362, M 5) share similar radial distributions (e.g. Nardiello et al 2015;Dalessandro et al 2018;Milone et al 2019;Lee 2017Lee , 2019.…”

“…The set of photometic indices by Jae-Woo Lee and collaborators also provides formidable tools to detect MPs along the RGB (e.g. Lee 2017Lee , 2019Lim et al 2016).…”

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH Photometry. V. as a Surrogate cnJWL Index and NGC 6723∗ †

“…In Figure 1, we show the transmission curves of the Strömgren and the JWL systems along with the Ca filter provided by the CTIO, Ca CTIO , and the Ca filter by Anthony-Twarog et al (1991), Ca AT . The Ca JWL , JW L39 and JW L43 filters were developed by the author of the paper in order to study the MPs in GCs (e.g., see Lee 2015Lee , 2017Lee , 2018Lee , 2019a. As we already noted in our previous work, the Ca JWL filter was designed to have a filter bandwidth and pivot wavelength very similar to that of the F395N filter in the Wide-Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST) and it can measure the Ca II H and K absorption strengths.…”

“…The populational tagging in stellar photometry can be more complex and subtle. In our previous works (Lee 2017(Lee , 2018(Lee , 2019a, we assessed the utility of various photometric systems used in the study of MPs in GCs, finding that some of the widely used photometric systems, such as the Strömgren m1, cy indices, the Sloan Digital Sky Survey (SDSS) photometric system, and the C U BI [=(U − B) − (B − I)] index, for example, may not be well-suited for the accurate populational tagging of individual stars in GCs with MPs.…”