Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud

Francesco di Mille; Hak-Sub Kim; Hwihyun Kim; Hyun-Il Sung; Jae-Woo Lee; Tae-Hyeong Kim

REVIEW 3 major objections 4 minor 89 references

Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud

T0 review · 3 major / 4 minor · reviewed 2026-08-10 · deepseek-v4-flash

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Pith's one-line read The old LMC globular cluster NGC 2257 carries the same multiple-population signatures as Milky Way globular clusters, implying that host-galaxy environment did not shape how these stellar generations formed.

desk verdict The direct NGC 2257 measurement is worth having, but the environmental-independence claim leans on a circular use of the relation being tested. read the letter →

arxiv 2501.04979 v1 pith:JR53KCAQ submitted 2025-01-09 astro-ph.GA astro-ph.SR

Jae-Woo Lee , Tae-Hyeong Kim , Hak-Sub Kim , Hyun-Il Sung , Hwihyun Kim , Francesco Di Mille This is my paper · ORCID

classification astro-ph.GAastro-ph.SR

keywords multiplepopulationsglobularclustersLargeMagellanicCloudNGC2257CN-CHphotometrystellarchemicalabundancesredgiantbranch

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper asks whether the environment of a host galaxy changes how globular clusters build their multiple populations, the coexisting stellar generations with different light-element abundances seen in nearly all old clusters. It answers by dissecting the old, metal-poor Large Magellanic Cloud cluster NGC 2257 with custom Ca-CN-CH photometry and comparing it to a Milky Way reference sample. The paper reports a first-to-second generation ratio of 61:39, similar radial distributions for the two generations, a slightly larger metallicity spread in the first generation, and no detectable helium enhancement in the second. Placed on the Galactic trends connecting RGB pseudo-color width, first-generation fraction, and cluster mass, NGC 2257 and two other old LMC clusters fall on the same relations. The conclusion is that the host galaxy environment played no major role in forming these populations, with cluster-internal properties carrying the behavior.

What carries the argument

The load-bearing tool is the Ca-CN-CH photometric system on Gemini-South/GMOS, with indices hkJWL for metallicity, cnJWL for CN at 3883 Å, and chJWL for CH at 4250 Å. Population tagging uses luminosity-normalized indices ||cnJWL and ||chJWL defined by the 5th and 95th percentile fiducials; their difference (||chJWL − ||cnJWL) acts as a surrogate for [C/Fe] − [N/Fe], and its double-peaked histogram is decomposed by an expectation-maximization Gaussian mixture into first- and second-generation stars. The same indices feed synthetic-spectrum grids to derive [Fe/H], [C/Fe], [N/Fe], and surface carbon depletion rates, which anchor the comparison with Galactic clusters in the mass and first-generation-fraction domains.

What would settle it

Take a large sample of NGC 2257 red-giant stars with high-resolution spectroscopy and measure Na-O and C-N abundances directly. If the spectroscopic first-to-second-generation ratio and the relative metallicity dispersions disagree with the photometric 61:39 split and σ values, the photometric population tagging is biased and the trend-line placement of NGC 2257 would need revision. Alternatively, a simulated single-population cluster with NGC 2257's photometric errors that reproduces the double-peaked (||chJWL − ||cnJWL) histogram would falsify the claim that the double peaks are real populations.

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Extended reading notes

Core claim

The paper's central claim is that old LMC globular clusters obey the same multiple-population scaling relations as normal Galactic globular clusters, so the differing galactic environment of the LMC did not materially affect the formation or evolution of their multiple populations. For NGC 2257 the evidence is a predominantly first-generation ratio of n(FG):n(SG) = 61:39 ± 4, a C-N anticorrelation, a first-generation metallicity dispersion (σ = 0.052 dex) slightly larger than the second-generation dispersion (σ = 0.044 dex), and identical carbon depletion rates and red-giant-bump magnitudes between generations, indicating no second-generation helium enhancement. The paper then shows that in the ΔW_CF336W,F438W,F814W versus N_FG/N_tot and log M/M_⊙ planes, NGC 2257, NGC 1786, and NGC 1898 fall on the relations defined by Galactic normal clusters. This placement is the direct observational argument that host-galaxy environment did not play a major role in the formation and evolution of globular-cluster multiple populations.

Load-bearing premise

The classification assumes that after normalizing by percentile fiducials, the (||chJWL − ||cnJWL) distribution is a clean two-component Gaussian mixture, so field-star contamination, differential reddening, or a skewed single population cannot have produced the 61:39 split.

Editorial extensions

If this is right

Old LMC globular clusters can be interpreted with the same archeological assumptions used for Milky Way globulars, because their light-element abundance spreads obey the same mass and ratio relations.
Cluster mass, more than host-galaxy environment, sets the degree of carbon and nitrogen variation in old globular clusters.
A second generation does not have to be helium-rich: NGC 2257 shows C-N variations without a detectable helium enhancement, so helium spread is not a universal property of multiple populations.
Measures like Δσ[C,N/Fe] and ΔW_CF336W,F438W,F814W can act as pseudo-invariant proxies for a cluster's initial mass, letting observers infer early conditions from present-day abundance spreads.
Metal-complex Galactic globulars and M4 depart from the normal-cluster relations, so their multiple-population formation histories must be distinct; the environmental-independence conclusion applies to the normal-cluster family, not to them.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If host-galaxy environment is truly irrelevant, the absence of old metal-poor clusters in the Small Magellanic Cloud is more plausibly a cluster-formation-rate effect than a suppression of multiple-population formation; the paper's logic implies this without saying so.
The tight ΔW–N_FG/N_tot relation predicts that old clusters of similar mass and metallicity in other dwarf galaxies should show the same first-generation fractions, a check for future extragalactic photometry.
The apparent lack of helium enhancement in the second generation means helium-sensitive diagnostics such as red-giant-bump luminosity and horizontal-branch morphology could miss second-generation stars in extragalactic clusters; NGC 2257's compact blue horizontal branch is a visible example.
Applying the same Ca-CN-CH tagging to intermediate-age Magellanic clusters could test whether the mass-only scaling survives in clusters young enough to still show spatial segregation between generations.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

The actual new result here is the first Ca-CN-CH photometric study of NGC 2257, giving an FG/SG ratio of 61:39, a slightly wider FG metallicity dispersion, and a no-He-enhancement constraint. Those are useful measurements for the old LMC cluster system, and the authors are careful about zero-points, reddening, and internal consistency. The paper deserves a serious referee for that part.

The broad conclusion—that host-galaxy environment did not matter for GC multiple populations—is considerably more fragile than the abstract suggests. The stress-test note is right. In Section 3.11, for NGC 1786 and NGC 1898, the authors say explicitly that N_FG/N_tot is not known and they simply apply the N_FG/N_tot versus delta-W relation from Figure 18 to get values, then use those values to argue the old LMC GCs follow the Galactic trend. That is circular for those two clusters; they carry no independent information about the trend. For NGC 2257, delta-W is not directly measured either; it is inferred from the authors' delta-sigma–delta-W calibration under the assumption that the cluster is normal. So the independent evidence for environmental independence is really one cluster, not three. The paper overstates the strength of the evidence.

The EM classification in Section 3.3 is a secondary concern. A two-component Gaussian mixture on a normalized color-difference index can easily be biased by field-star contamination or by real structure beyond two populations, and the subsequent abundance dispersions inherit that decomposition. I would ask the authors to release the photometric catalog and show the sensitivity of the FG/SG ratio to the chosen normalization and number of components. The helium-non-enhancement claim is plausible but rests on small-number RGBB data and the CDR argument, which the authors themselves acknowledge is limited. I would treat that as preliminary rather than a firm null detection.

What the paper does well: the metallicity measurement, the zero-point agreement with M55 and prior photometry, and the explicit statement of assumptions. The authors don't hide the circular step; they flag it in the text. That transparency is good, but it doesn't make the step valid.

In short: keep the NGC 2257 measurements, tighten the language about what follows from them, and re-derive the comparison without using the target relation to assign the population fractions of NGC 1786 and NGC 1898. I would recommend peer review with major revision, not desk rejection.

Referee Report

3 major / 4 minor

Summary. The paper presents new Ca-CN-CH photometry of the old, metal-poor LMC globular cluster NGC 2257, obtained with Gemini-South/GMOS. Using synthetic-color calibrations and an EM two-component Gaussian mixture applied to the normalized (chJWL - cnJWL) index, the authors classify RGB stars into first- and second-generation populations, finding n(FG):n(SG) = 61:39. They derive photometric [Fe/H] = -1.78 dex, compare the FG and SG metallicity dispersions and carbon/nitrogen abundances, find no significant helium enhancement in the SG from RGBB and carbon-depletion-rate diagnostics, and conclude that NGC 2257 shows the same multiple-population trends as normal Galactic globular clusters. Combining their result with literature values, they argue that old LMC GCs follow the same Delta-W - N_FG/N_tot - mass relations as Galactic GCs and therefore that host-galaxy environment does not play a major role in multiple-population formation.

Significance. If the conclusion holds, this is a valuable extension of multiple-population studies to an old, metal-poor cluster in the LMC and would support the view that the physical processes that create multiple populations are largely independent of host-galaxy environment. The photometric system and the detailed synthetic-color modeling (ATLAS12, MOOG_SCAT, Linemake) provide a self-consistent methodology that yields direct C and N abundance indicators for individual RGB stars, and the paper presents a large set of comparisons with Galactic clusters. The direct measurements for NGC 2257 - the population ratio, the radial distributions, the metallicity dispersion difference between FG and SG, and the absence of a measurable helium enhancement - are useful and interesting in their own right. However, the strongest claim, the environmental independence, rests on the placement of NGC 2257 in the Delta-W - N_FG/N_tot plane using a Delta-W value that is inferred from a Galactic calibration, and on the placement of two other LMC clusters whose N_FG/N_tot values are generated from the very relation being tested.

major comments (3)

[§3.11 (Figures 18–19)] The claim that the old LMC GCs NGC 1786 and NGC 1898 follow the Galactic Delta-W - N_FG/N_tot relation is circular. The text states: 'The N_FG/N_tot values of these two GCs are not known. We simply applied the N_FG/N_tot versus Delta_W_CF336W,F438W,F814W relation in Figure 18, assuming these two GCs are normal GCs.' These two points are therefore placed on the relation by construction and cannot provide independent evidence that old LMC clusters obey the same trend as Galactic clusters. They should be explicitly labeled as predictions from the assumed relation, not as measurements that validate it, or the authors should obtain direct population ratios for these clusters from their own photometry.
[§3.11 (Figures 17 and 18)] The Delta-W value for NGC 2257, 0.050 ± 0.046, is not measured but inferred from the authors' Delta-sigma[C,N/Fe] versus Delta-W relation calibrated with only four Galactic normal GCs. This inference explicitly assumes that NGC 2257 is a normal GC, so its placement in Figure 18 is not an independent test of whether it follows the Galactic relation. Moreover, the quoted uncertainty is almost as large as the value itself; with such precision the point is consistent with a wide range of possible relations. The statement in the abstract and Section 4 that NGC 2257 is in 'excellent agreement' with the Galactic trend is therefore overstated, and the propagation of the four-cluster calibration uncertainty into the inferred Delta-W should be quantified.
[§3.3 (Equations (4)–(5))] The EM-based population tagging assumes that the normalized (chJWL - cnJWL) distribution is a clean two-component Gaussian mixture. As Figures 5a and 5b show, the bimodality is not visible in the individual normalized indices and appears only after taking the difference; the decomposition is therefore sensitive to the choice of two components, the small number of RGB stars, photometric outliers, and any residual field-star contamination. The membership cleaning relies on photometric selection rather than proper motions, and LMC field stars with intermediate metallicities could in principle bias the tails of the distribution. The authors should assess how the derived n(FG):n(SG) and the abundance dispersions change under alternative component numbers or inclusion/removal of marginal stars, since these quantities are the quantitative foundation for the comparison with Galactic trends.

minor comments (4)

[§3.3, Figures 5–6] The symbol for the normalized indices appears inconsistently as '||chJWL' and '||cnJWL' in figure panels and as '‖ chJWL' in the text; the notation should be unified.
[§3.9] The text says that the FG and SG have 'identical CDRs' but then reports d[C/Fe]/dM_V = 0.226 ± 0.017 for the FG and 0.230 ± 0.033 for the SG; these values should be described as equal within uncertainties rather than identical.
[References] The reference 'Fobes 2020' is likely a typo for 'Forbes 2020'; also, 'V alcarce' contains a spurious space in the reference list.
[Abstract and §3.3] The quoted uncertainty on n(FG):n(SG) = 61:39(±4) is not defined; the authors should specify whether it is a 1σ, 95%, or some other confidence interval, and state whether it includes systematic uncertainties from the EM fitting or only statistical sampling.

Circularity Check

1 steps flagged · score 6.0 of 10

Partial circularity: two of the three old LMC GCs used to support the environmental-independence claim have their N_FG/N_tot generated from the very ΔW–N_FG/N_tot relation being tested.

fitted input called prediction [Section 3.11, final paragraph (after Figure 18; see Figure 19)]
"The N_FG/N_tot values of these two GCs are not known. We simply applied the N_FG/N_tot versus ΔWCF336W,F438W,F814W relation in Figure 18, assuming these two GCs are normal GCs, and we obtained NFG/Ntot = 0.204 ± 0.073 and 0.273 ± 0.053 for NGC 1786 and NGC 1898, respectively. Similar what Vanaraj, Niederhofer, Goudfrooij (2021) argued, three old LMC GCs are in good agreement with Galactic normal GCs in these domains."

The paper has no measured N_FG/N_tot for NGC 1786 or NGC 1898; it computes these values by inverting the Figure 18 ΔW–N_FG/N_tot relation, then presents the same calculated points as evidence that old LMC GCs follow that relation. A point generated from a fitted line cannot falsify that line: its agreement is guaranteed by construction. The sentence 'three old LMC GCs are in good agreement' is therefore true by construction for two of the three clusters, and those two carry no independent weight for the paper's environmental-independence conclusion. Only NGC 2257, with its directly measured 61:39 ratio, provides an independent placement.

full rationale

The paper's main new measurement, NGC 2257, is not circular in its core: the FG/SG ratio 61:39 comes from an EM decomposition of the normalized (||chJWL − ||cnJWL) distribution, and the abundance dispersions Δσ[C,N/Fe] come from the same photometry, independent of the Galactic ΔW–N relation. A second, model-dependent step—using the Galactic Δσ–ΔW calibration to infer ΔW = 0.050 ± 0.046 for NGC 2257—does not by itself reduce to the tested relation, because the predicted ΔW does not use N_FG/N_tot as input. The clear circularity is the treatment of NGC 1786 and NGC 1898: the text explicitly states that their N_FG/N_tot values 'are not known' and that the authors 'simply applied the N_FG/N_tot versus ΔW relation in Figure 18, assuming these two GCs are normal GCs.' Those derived values are then plotted in Figure 19 and cited as evidence that the three old LMC GCs agree with the Galactic trend. This is a fitted input presented as an independent validation: the points are manufactured from the very relation they are supposed to confirm. Consequently the plural claim 'old LMC GCs follow the same trends' is partially circular, though the paper's independent NGC 2257 data keep the central result from being entirely forced.

Assumptions & free parameters 5 free parameters · 6 assumptions · 0 invented entities

The central claims rest on the authors' previously calibrated photometric abundance system, on model-dependent synthetic colors, and on small calibrations of abundance dispersions. No new physical entities are introduced. The main free parameters are the regression coefficients used to residualize abundance dispersions and to convert them to the HST pseudo-color width, plus the adopted oxygen abundances for FG and SG.

free parameters (5)

Linear regression coefficients for sigma[C,N/Fe] and sigma[C+N/Fe] versus [Fe/H] = Not quoted numerically; shown as green lines in Figure 14
Fitted to four Galactic normal GCs and used to residualize NGC 2257's abundance dispersions into Delta sigma[C,N/Fe] and Delta sigma[C+N/Fe].
Linear regression coefficients for Delta sigma[C,N/Fe] and Delta sigma[C+N/Fe] versus Delta W_CF336W,F438W,F814W = Not quoted numerically; used to infer Delta W = 0.050 +/- 0.046 for NGC 2257
Fitted to four Galactic normal GCs in Figure 17; the inferred Delta W for NGC 2257 is obtained by applying this relation, so its uncertainty is tied to this small calibration.
Linear regression coefficients for Delta W versus N_FG/N_tot = Correlation coefficient rho = -0.750 quoted for the 41-GC sample
Used in Section 3.11 to assign N_FG/N_tot = 0.204 +/- 0.073 (NGC 1786) and 0.273 +/- 0.053 (NGC 1898), the two clusters that then are claimed to agree with the same relation.
Adopted [O/Fe] for FG and SG = [O/Fe] = 0.5 dex (FG) and 0.1 dex (SG)
Assigned by hand because individual oxygen abundances are unavailable; the authors state it does not significantly affect results, but it is an input to the abundance grid.
Two-component Gaussian mixture parameters in the EM classifier = Resulting n(FG):n(SG) = 61:39 (+/- 4)
The EM fit to the (||chJWL - ||cnJWL) histogram returns the population ratio and per-star probabilities; the number of components and the Gaussian shape are model choices rather than independent measurements.

assumptions (6)

domain assumption The hkJWL, cnJWL, and chJWL photometric indices measure [Fe/H], [N/Fe], and [C/Fe] on RGB stars through the calibrated synthetic-color grid.
Basis of the entire abundance analysis; inherited from Lee (2015, 2017, 2019a, 2022, 2023a, 2024) and Lee & Sneden (2021). No independent validation for NGC 2257 is given beyond comparison of CMDs with M55.
domain assumption The normalized indices ||cnJWL and ||chJWL (5th/95th percentile fiducials) remove luminosity and mixing effects, so the (||ch - ||cn) distribution reflects primordial C-N abundance patterns.
Equations (4)-(5); required for the EM population tagging and for treating stars fainter than the RGBB as pristine.
domain assumption The observed RGB stars in NGC 2257 are members and field contamination has been fully removed by the photometric selection around the isochrone and in hkJWL, cnJWL, chJWL.
Section 3.3: Gaia proper motions are incomplete in the field, so membership relies on multi-color cuts.
domain assumption Differential reddening across the GMOS field is negligible.
Invoked in Section 3.1 when attributing the broad cnJWL/chJWL RGB sequences to abundance variations rather than reddening; no quantitative differential-reddening map is presented.
domain assumption The adopted BaSTI isochrones and ATLAS12/MOOG_SCAT synthetic spectra, including the RSNH treatment, reproduce the observed color indices at the needed precision.
Section 3.6: the photometric metallicity and abundance scales depend on the synthetic grid (97 model atmospheres per composition).
domain assumption The RGBB luminosity and the surface carbon depletion rate depend on helium abundance as predicted by the adopted stellar models, with other parameters fixed.
Section 3.5 and 3.9: the conclusion that the SG shows no He enhancement rests on identical RGBB V and identical CDRs, which are small-number and model-dependent diagnostics.

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Cite this review

Pith. "Pith review of Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud." pith.science (2026). https://pith.science/paper/JR53KCAQ

@misc{pith2026250104979,
  author       = {Pith},
  title        = {Pith review of: Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/JR53KCAQ}},
  note         = {Machine review of arXiv:2501.04979}
}

abstract

How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in the near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca--CN--CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly FG-dominated populational number ratio of $n$(FG):$n$(SG) = 61:39($\pm$4), where the FG and SG denote the first and second generations. Both the FG and SG have similar cumulative radial distributions, consistent with the idea that NGC 2257 is dynamically old. We obtain [Fe/H] = $-$1.78$\pm$0.00 dex($\sigma$=0.05 dex) and our metallicity is $\sim$0.2 dex larger than that from the high-resolution spectroscopy by other, due to their significantly lower temperatures by $\sim$ $-$200 K. The NGC 2257 FG shows a somewhat larger metallicity variation than the SG, the first detection of such phenomenon in an old LMC GC, similar to Galactic GCs with MPs, strongly suggesting that it is a general characteristic of GCs with MPs. Interestingly, the NGC 2257 SG does not show a helium enhancement compared to the FG. Our results for the Galactic normal GCs exhibit that the degree of carbon and nitrogen variations are tightly correlated with the GC mass, while NGC 2257 exhibits slightly smaller variations for its mass. We show that old LMC GCs follow the same trends as the Galactic normal GCs in the $\Delta$W$_{\rm CF336W,F438W,F814W}$, $N_{\rm FG}/N_{\rm tot}$, and $\log M/M_{\rm \odot}$ domains. Our result indicates that the environment of the host galaxy did not play a major role in the formation and evolution of GC MPs.

Figures

Figures reproduced from arXiv: 2501.04979 by the authors.

**Figure 1.** CMDs of NGC 2257 for the clean stars. The red error bars indicate the measurement uncertainties at a given V magnitude. 2. OBSERVATIONS AND DATA REDUCTION Observations for NGC 2257 were made on 2021 December 8 and 2022 January 6 using the Gemini-South 8.0 m telescope and the Gemini Multi-Object Spectrograph (GMOS) with our own filter system. The GMOS is a spectro-imager offering a spectral range from 0.36 to 1.03 … view at source ↗

**Figure 2.** Comparison of NGC 2257 (black dots) and M55 (orange dots). The V magnitude and (b−y) color of individual M55 stars are increased by ∆V = 4.524 and ∆(b − y) = 0.066 mag. widths in the cnJWL and chJWL indices are broader than our measurement uncertainties, in particular for stars with V . 21 mag, in our CMDs. These strongly suggest that the variations in carbon and nitrogen abundances in the RGB stars are responsible… view at source ↗

**Figure 3.** (a) Comparison of M55 and the model isochrone for [Fe/H] = −1.8 dex and 13.0 Gyr. The distance modulus of (m − M) = 13.80 mag and the interstellar reddening value of E(B−V) = 0.12 mag are used. (b) Comparison of NGC 2257 and the model isochrone for [Fe/H] = −1.8 dex and 11.8 Gyr. The distance modulus of (m − M)0 = 18.38 mag and the interstellar reddening value of E(B−V) = 0.04 mag are used [PITH_FULL_IMAGE:figures/… view at source ↗

Figures from the paper (14 more)

**Figure 4.** Figure 4: CMDs of NGC 2257 with −2.0 mag ≤ V −VHB ≤ 1.5 mag. The blue and red dots denote the FG and SG RGB stars returned from our EM estimator discussed below. lar method that we employed previously for Galactic GCs (e.g., Lee 2015, 2017). First, we selected the RGB candidate…

**Figure 5.** Figure 5: (a) The k chJWL vs. V CMD of NGC 2257 RGB stars. (b) Same as (a) but for the k chJWL. (c) The (k chJWL− k cnJWL) distribution of the NGC 2257 RGB stars. The blue and red plus signs denote the FG and SG RGB stars in NGC 2257 returned from our EM estimator. (d) The his…

**Figure 7.** Figure 7: Plots of the by5 vs. V CMDs and differential LFs. The blue and red lines are LFs of the FG and SG, while the green lines are for the LF of the all stars. We also show the RGBB V magnitudes of each populations with solid gray lines, while the dotted green lines denote …

**Figure 8.** Figure 8: The [Fe/H]hk, [C/Fe]ch, and [N/Fe]cn against V magnitude [PITH_FULL_IMAGE:figures/full_fig_p009_8.png]

**Figure 9.** Figure 9: The hkJWL,0 vs. MV CMDs of NGC 2257 RGB stars, assuming (m − M)0 = 18.376 mag and E(B −V) = 0.038 mag for NGC 2257. We also show fiducial sequences of the eight Galactic GCs with various metallicities from our previous studies. scatter in our photometric metallicity of…

**Figure 10.** Figure 10: A plot of Teff vs. logg for NGC 2257 RGB stars from our evolutionary populational model (black dots). The blue open circles denote the stellar parameters of RGB stars derived by Mucciarelli, Origlia, & Ferraro (2010). The thick green and orange lines are for the BaSTI…

**Figure 11.** Figure 11: The [Fe/H]hk histograms for the FG (the blue solid line) and SG (the red solid line shaded with gray) in NGC 2257. The small vertical lines denote the locations of the 5th and 95th percentiles of [Fe/H]hk distributions for each population. Lee & Carney 2002, δ[Fe/H]/…

**Figure 12.** Figure 12: (a) A plot of the [C/Fe] vs. [N/Fe] for all RGB stars in NGC 2257. (b) A plot of the [C/Fe] vs. [N/Fe] for all RGB stars fainter than RGBBs. Yong et al. (2013) clearly showed that the [Fe/H] variation of the FG is much larger than that of the SG. In recent study, Legn…

**Figure 14.** Figure 14: Plots of the [Fe/H] vs. σ[Fe/H], σ[C/Fe], σ[N/Fe], and σ[C+N/Fe] for NGC 2257 (a filled red circle), four Galactic normal GCs (open circles), and three metal-complex GCs (grey filled circles). The thick green lines denotes the linear regressions of the four Galactic …

**Figure 15.** Figure 15: Same as [PITH_FULL_IMAGE:figures/full_fig_p013_15.png]

**Figure 16.** Figure 16: Plots of the ∆σ[C,N/Fe] vs. NFG/Ntot for four Galactic normal GCs. The green lines show linear regressions, while the grey solid and dashed lines denote 95% confidence and predicted intervals. The red filled circles denote NGC 2257, which is in good agreement with Gal…

**Figure 17.** Figure 17: Plots of ∆σ[C,N/Fe] vs. ∆WCF336W,F438W,F814W of four Galactic normal GCs from [PITH_FULL_IMAGE:figures/full_fig_p014_17.png]

**Figure 18.** Figure 18: (Top) A plot of ∆WCF336W,F438W,F814W vs. NFG/Ntot. The green filled boxes denote the in situ Galactic GCs, the orange filled circles the ex situ Galactic GCs, the blue filled diamonds the young MC GCs. NGC 2257 is shown with a big red diamond. The thick dark green lin…

**Figure 19.** Figure 19: Plots of ∆WCF336W,F438W,F814W vs. logM/M⊙ vs. NFG/Ntot. fect, we showed that the ∆σ[C,N/Fe] and ∆σ[C+N/Fe] of the Galactic GCs are correlated with the GC mass (see also Milone et al. 2017). Similar to the σ[C,N/Fe] and σ[C+N/Fe] versus [Fe/H] relations, NGC 2257 is in…

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Pith tools

Reviewed August 10, 2026 · model on record in the stance chip above.

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