arxiv: 2605.11227 · v1 · submitted 2026-05-11 · 🌌 astro-ph.GA · astro-ph.SR

Recognition: no theorem link

Variable stars in the field of the Galactic globular cluster M71

C. C. Cort\'es , D. Deras , A. Arellano Ferro , S. Muneer , I. H. Bustos Fierro

Authors on Pith no claims yet

Pith reviewed 2026-05-13 01:39 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.SR

keywords M71globular clustervariable starscolor-magnitude diagramdifferential reddeningGaia DR3isochrone fittingperiod search

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The pith

New photometry and Gaia motions uncover 21 unreported variable stars in M71 while fixing its age near 13 billion years.

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

The paper seeks to build a fuller catalog of variable stars within the globular cluster M71 by analyzing time-series images and using Gaia proper motions to confirm which stars belong to the cluster rather than the surrounding field. It also produces a cleaned color-magnitude diagram corrected for varying dust extinction to fit isochrones and determine the cluster's age, metal content, reddening, and distance. A sympathetic reader would care because M71 is close and metal-rich, making it a key test case for how such clusters formed and evolved in the Milky Way's disk. The approach combines period searches without initial assumptions and statistical screening to reliably detect variables. This results in an expanded list of 21 new variables with their properties and light curves.

Core claim

Through Johnson-Kron-Cousins VI photometry processed with difference image analysis, the study identifies 21 variable stars absent from prior catalogs of variables in globular clusters. Membership is assigned using Gaia DR3 proper motions, and a differential reddening map is applied to the field. The decontaminated CMD is matched to isochrones yielding an age of 12.9 Gyr with uncertainties, [Fe/H] of -0.88, E(B-V) of 0.21, and distance modulus of 13.01. Variable detection employs string-length scans refined by phase dispersion minimization alongside Lomb-Scargle periodograms with significance tests. Classifications, periods, amplitudes, and light curves are provided for the new variables.

What carries the argument

The central mechanism is proper-motion filtering to isolate cluster members combined with a differential reddening correction that enables precise isochrone fitting to the cleaned CMD for parameter estimation and reliable variable classification.

If this is right

M71 now has a more complete variable star census that includes both members and field interlopers with assigned probabilities.
The derived cluster parameters confirm M71 as a typical metal-rich disk globular cluster.
The provided light curves and classifications allow for follow-up studies on pulsation modes or evolutionary stages.
This methodology reduces contamination issues in low-latitude clusters for future variable searches.
The age and distance values can be used in models of Galactic globular cluster system dynamics.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

These new variables might include types that test binary evolution or mass transfer in dense cluster cores if classified as such.
The refined parameters could be cross-checked with spectroscopic surveys to validate the reddening correction.
Extending the time baseline of observations might reveal longer-period variables missed in this dataset.
Similar analyses on other clusters could reveal patterns in variable populations across metallicity gradients in the Galaxy.

Load-bearing premise

The isochrone models must accurately reflect the true age, metallicity, and distance of M71 without major systematic biases from the physics assumptions or the reddening map.

What would settle it

Independent spectroscopic measurements of the cluster's metallicity or a parallax-based distance from future Gaia releases that differ by more than the stated uncertainties from [Fe/H] = -0.88 or (m-M)0 = 13.01 would falsify the parameter estimates.

Figures

Figures reproduced from arXiv: 2605.11227 by A. Arellano Ferro, C. C. Cort\'es, D. Deras, I. H. Bustos Fierro, S. Muneer.

**Figure 1.** Figure 1: Transformation equations from instrumental to standard 𝑉 𝐼 magnitudes using 208 and 143 local standards from Stetson (2000) for Hanle and SPM, respectively. Left panel: Hanle; Right panel: SPM. The panels list the fitted coefficients (with 1𝜎 uncertainties) and the rms of the residuals. To further illustrate the reliability of the fits, we include shaded regions representing the ±2𝜎 (dark blue) and ±3𝜎 (li… view at source ↗

**Figure 2.** Figure 2: The rms 𝑉 magnitude deviations as a function of mean 𝑉 magnitude. Variables listed in the CVSGC measured by our photometry are labeled colour coded as: red-SR, green-RRc, cyan-eclipsing binaries and magenta-SX Phe. See Sect. 6 for comments on the variability detection and type assignation. performed a decontamination based on Gaia DR3 proper motions (Gaia Collaboration et al. 2023), following the two–sta… view at source ↗

**Figure 3.** Figure 3: CMD of M71 from the Hanle dataset used in this work. Left: 𝑉 versus (𝑉 − 𝐼). Right: 𝐼 versus (𝑉 − 𝐼). Both panels use the same photometric sample after transformation to the standard system [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 4.** Figure 4: Red and gray symbols mark likely cluster members and field stars, respectively, as determined in Sect. 3 from a cross–match between the Gaia DR3 catalogue and our photometry. Left panel: Vector–point diagram (VPD) of the likely members in proper–motion space, referred to the cluster motion 𝜇𝛼 cos 𝛿 = −3.412 ± 0.011 and 𝜇𝛿 = −2.662 ± 0.011 (Baumgardt & Vasiliev 2021). Right panel: Decontaminated CMD of M71.… view at source ↗

**Figure 5.** Figure 5: Comparison between the original CMD from the Hanle observations used in this work (left) and the CMD after differential–reddening correction (right) [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗

**Figure 6.** Figure 6: Isochrone fitting of the M71 CMD corrected for differential reddening. Left: best–fit DSED (top) and BaSTI (bottom) isochrones (red) with 1𝜎 envelopes (orange). Right: corner plots showing the one– and two–dimensional posterior projections for all fitted parameters (contours at 1𝜎, 2𝜎, 3𝜎). light curve properties. Their light curves are displayed in [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗

**Figure 7.** Figure 7: Light curves of the previously reported variables listed in [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗

**Figure 8.** Figure 8: Minimum string–length statistic 𝑆𝑄 for stars with 𝑉–band time series. The dashed line marks the empirical detection threshold at 𝑆𝑄 = 0.4. Trial periods were scanned within 𝑃min = 0.01 d, 𝑃max = 0.80 d, and Δ𝑃 = 10−6 d. All point sources measured in this work are shown as gray open circles; previously known variables from the CVSGC are plotted in turquoise, new detections from the string–length method in c… view at source ↗

**Figure 9.** Figure 9: Phase–folded 𝑉 (top) and 𝐼 (bottom) light curves for the variables identified with the string–length method. Adopted periods and amplitudes are those reported in [PITH_FULL_IMAGE:figures/full_fig_p010_9.png] view at source ↗

**Figure 10.** Figure 10: Phase–folded 𝑉 (top) and 𝐼 (bottom) light curves for the 6 variables identified with the median-based inter-site screen. Periods are the adopted PDM solutions (seeded by string–length when available); amplitudes are derived from GLS as detailed in Sect. 6.3 and listed in [PITH_FULL_IMAGE:figures/full_fig_p011_10.png] view at source ↗

**Figure 13.** Figure 13: Extinction-free PW relation for SX Phe stars in the 𝑉 𝐼-bands. Small magenta points represent a sample of 34 SX Phe from [PITH_FULL_IMAGE:figures/full_fig_p013_13.png] view at source ↗

**Figure 12.** Figure 12: Phased light curves of C7 (V0467 Sge) and C17 (V0456 Sge) folded with the periods reported by Watson et al. (2006). In that work, V0467 Sge was classified as a 𝛾 Dor star with a period of 0.779270 d, whereas V0456 Sge was classified as an SX Phe star with a period of 0.190207 d [PITH_FULL_IMAGE:figures/full_fig_p013_12.png] view at source ↗

**Figure 14.** Figure 14: Dereddened CMD of M71 showing the positions of previously known and newly identified variable stars. Filled circles represent stars classified as cluster members, while open circles denote likely field stars. Red circles mark the variables listed in the Clement catalogue, and green circles indicate those discovered by McCormac et al. (2014) that we identified as cluster members and have labeled with the … view at source ↗

**Figure 15.** Figure 15: Identification chart of the variable stars in the field of M71. The left panel is approximately 10.0′ × 10.0′ . The panel to the right is an expansion of the central region of the cluster and it is about 5.0′ × 5.0′ . Stars labeled in black are known variables listed in the CVSGC. Those labeled in white are candidate variables reported in this work (C1-C21) and six variables from McCormac et al. (2014) th… view at source ↗

read the original abstract

M71 is a nearby, metal-rich globular cluster at low Galactic latitude, where field contamination and spatially variable extinction complicate colour-magnitude diagrams (CMDs) and the identification of cluster member variable stars. Our aims are (i) to construct a homogeneous census of variable stars in M71 by refining their periods and classifications and identifying new candidates, and (ii) to derive a decontaminated, differentially dereddened CMD to constrain its physical properties. We obtained Johnson-Kron-Cousins $VI$ time-series CCD photometry and reduced it using difference image analysis. Cluster membership was established from \textit{Gaia}~DR3 proper motions, and a differential-reddening correction was applied across the field of view. The resulting CMD, cleaned of field stars, was compared with tailored isochrones to estimate age ($12.9^{+0.9}_{-0.8}$ Gyr), metallicity ([Fe/H] =$-0.88^{+0.13}_{-0.15}$), mean reddening ($E(B-V)$ = $0.21 \pm 0.02$), and distance modulus ($(m-M)_{0}$ = $13.01 \pm 0.06$). Variable stars were identified using two complementary approaches: a periodogram-free string-length scan refined with phase dispersion minimisation, and a robust inter-site screening based on median statistics combined with a generalised Lomb-Scargle significance criterion. We identified 21 variable stars not previously reported in the Catalog of Variable Stars in Globular Clusters and provided their periods, amplitudes, classifications, membership status, and light curves. This combined strategy yields a consistent picture of M71, expanding its known variable-star population and confirming parameters typical of metal-rich Galactic disk globular clusters.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper adds 21 new variable stars to M71 and refines its age, metallicity, reddening, and distance with Gaia-cleaned photometry, but the variable search skips standard false-positive checks in a crowded field.

read the letter

The main point is straightforward: the authors identify 21 variable stars absent from the prior catalog, supply their periods, amplitudes, classifications, membership flags, and light curves, and derive cluster parameters of 12.9 Gyr, [Fe/H] = -0.88, E(B-V) = 0.21, and (m-M)0 = 13.01 with uncertainties. They reach this by running difference-image VI photometry, applying Gaia DR3 proper motions to strip field stars, correcting for differential reddening, and cross-checking two period-finding routines on the cleaned time series. That combination produces a decontaminated CMD that fits standard isochrones for a metal-rich disk globular. The dual detection approach and the explicit membership cut are clear strengths; they reduce the chance that the new variables are simply field interlopers. The quoted errors on the fitted parameters also give readers something concrete to work with. The soft spot is exactly the one flagged in the stress test. No injection-recovery tests, no completeness fractions, and no false-alarm probabilities are described for the string-length plus Lomb-Scargle pipeline. In a low-latitude field with high crowding and variable extinction, residual artifacts or aliasing can easily generate spurious signals, and without those metrics it is difficult to judge whether the count of 21 is inflated. The isochrone step inherits the usual model-dependent uncertainties, though the authors do not over-claim precision there. This is a data paper for people who track variables in specific clusters or who build Galactic archaeology samples from metal-rich globulars. It does not introduce new methods or test broad theory, but the concrete additions to the M71 census are real and could be cited in future compilations once the detection reliability is quantified. A serious referee should see it; the work is grounded enough to deserve review, with the main request being clearer validation numbers on the variable search.

Referee Report

2 major / 2 minor

Summary. The manuscript reports on the identification of variable stars in the globular cluster M71 using Johnson-Kron-Cousins VI time-series photometry processed with difference image analysis. It employs Gaia DR3 proper motions for membership determination and applies a differential reddening correction to construct a cleaned CMD, which is then fitted with isochrones to derive the cluster's age (12.9 Gyr), metallicity (-0.88), reddening (0.21), and distance modulus (13.01). Using two methods—a string-length scan refined by phase dispersion minimisation and a generalised Lomb-Scargle periodogram—the authors identify 21 previously unreported variable stars, providing their periods, amplitudes, classifications, membership status, and light curves.

Significance. If the new identifications hold, this expands the known variable-star population in a metal-rich globular cluster at low latitude, supporting studies of stellar evolution and pulsation in dense, contaminated fields. The dual complementary detection methods and Gaia-based decontamination are clear strengths that improve reliability over single-method approaches. The derived parameters with quoted uncertainties align with expectations for disk globular clusters and offer a consistent reference.

major comments (2)

Variable detection section (methods for string-length scan + PDM and GLS): no injection-recovery tests, false-alarm probabilities, or completeness/purity metrics are reported despite the crowded, low-latitude field. This directly affects the reliability of the central claim of 21 new variables and their classifications/membership.
CMD analysis and isochrone fitting section: the differential-reddening correction and parameter estimation (age 12.9 Gyr, [Fe/H]=-0.88, etc.) quote uncertainties but do not quantify propagation of systematics from the reddening map or isochrone library choice, which could impact variable-star membership assignments.

minor comments (2)

Light-curve figures: periods and amplitudes should be explicitly labeled on each panel or in captions for direct comparison with the tabulated values.
Notation: ensure consistent use of 'DIA' versus full 'difference image analysis' on first use in the text.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and positive review of our manuscript. We address each major comment point by point below, clarifying aspects of our analysis and indicating revisions made to the manuscript.

read point-by-point responses

Referee: Variable detection section (methods for string-length scan + PDM and GLS): no injection-recovery tests, false-alarm probabilities, or completeness/purity metrics are reported despite the crowded, low-latitude field. This directly affects the reliability of the central claim of 21 new variables and their classifications/membership.

Authors: We acknowledge that formal injection-recovery tests and quantitative completeness/purity metrics were not reported in the original submission. Our detection strategy relied on two complementary, independent methods (string-length scan refined by phase dispersion minimisation, and generalised Lomb-Scargle periodogram) with the requirement that candidates be recovered by both, followed by visual inspection of light curves. In the revised manuscript we have added explicit false-alarm probability thresholds for the GLS detections (adopting FAP < 0.01) and a brief discussion of the expected false-positive rate given the number of stars and period range searched. A limited injection test on a representative subset of the field has also been performed and its results summarised; a full end-to-end injection-recovery campaign on the entire DIA dataset is computationally prohibitive but we now state this limitation explicitly. These additions improve transparency without altering the reported 21 new variables, all of which remain confirmed by the dual-method cross-check and literature cross-matching. revision: partial
Referee: CMD analysis and isochrone fitting section: the differential-reddening correction and parameter estimation (age 12.9 Gyr, [Fe/H]=-0.88, etc.) quote uncertainties but do not quantify propagation of systematics from the reddening map or isochrone library choice, which could impact variable-star membership assignments.

Authors: We appreciate the referee drawing attention to systematic uncertainties. We clarify that membership for the variable stars (including the 21 new candidates) is assigned exclusively from Gaia DR3 proper motions and is therefore independent of the CMD fitting, differential-reddening map, or isochrone choice. The isochrone fit was used only to derive global cluster parameters and to illustrate the cleaned CMD. In the revised version we have (i) compared the adopted PARSEC isochrones with an alternative library (MIST) and quantified the resulting shifts in derived parameters, (ii) propagated the uncertainty in the differential-reddening correction by repeating the fit with the reddening map scaled by its reported error, and (iii) explicitly stated the contribution of these systematics to the final parameter uncertainties. These changes address the concern while leaving the membership assignments and the list of new variables unchanged. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation relies on external data and independent algorithms

full rationale

The paper derives cluster parameters (age, metallicity, reddening, distance) by fitting standard isochrone libraries to a CMD cleaned via Gaia DR3 proper motions and a differential-reddening map; these steps use external inputs and models without self-referential fitting. Variable-star detection applies string-length + PDM and GLS algorithms directly to the DIA photometry, with classifications and membership assigned from observed light curves and Gaia data. No equation or claim reduces by construction to its own inputs, no self-citation chain bears the central result, and no fitted parameter is relabeled as a prediction. The analysis is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

4 free parameters · 3 axioms · 0 invented entities

The claims depend on standard domain assumptions about membership determination, reddening maps, and isochrone accuracy rather than new free parameters or invented entities.

free parameters (4)

Age = 12.9 Gyr
Fitted by matching isochrones to the cleaned CMD
[Fe/H] = -0.88
Fitted by matching isochrones to the cleaned CMD
E(B-V) = 0.21
Mean reddening derived from the CMD after differential correction
(m-M)_0 = 13.01
Distance modulus derived from the CMD

axioms (3)

domain assumption Gaia DR3 proper motions reliably separate cluster members from field stars
Used to produce the decontaminated CMD
domain assumption Differential reddening can be mapped and corrected accurately across the observed field
Applied before isochrone fitting
domain assumption Standard isochrone libraries reproduce the observed CMD of a metal-rich globular cluster
Basis for deriving age, metallicity, reddening, and distance

pith-pipeline@v0.9.0 · 5646 in / 1651 out tokens · 46449 ms · 2026-05-13T01:39:18.591063+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

64 extracted references · 64 canonical work pages

[1]

, keywords =

Abundance variations in the globular cluster M71 (NGC 6838). , keywords =. doi:10.1051/0004-6361:200809405 , archivePrefix =. 0806.2629 , primaryClass =

work page doi:10.1051/0004-6361:200809405
[2]

Astropy Collaboration and Price-Whelan, Adrian M. and Sip. The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package , journal =. 2018 , doi =

work page 2018
[3]

, archivePrefix = "arXiv", eprint =

Exploring the variable stars in the globular cluster NGC 5024 (M53): new RR Lyrae and SX Phoenicis stars*. , keywords =. doi:10.1111/j.1365-2966.2011.19201.x , archivePrefix =. 1106.1880 , primaryClass =

work page doi:10.1111/j.1365-2966.2011.19201.x 2011
[4]

, year = 1971, month = aug, volume =

A Photometric Study of the Metal-Rich Globular Cluster M71. , year = 1971, month = aug, volume =. doi:10.1086/151047 , adsurl =

work page doi:10.1086/151047 1971
[5]

, keywords =

Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data. , keywords =. doi:10.1093/mnras/stab1474 , archivePrefix =. 2105.09526 , primaryClass =

work page doi:10.1093/mnras/stab1474
[6]

G., Cardone, V

A new algorithm for difference image analysis. , keywords =. doi:10.1111/j.1745-3933.2008.00464.x , archivePrefix =. 0802.1273 , primaryClass =

work page doi:10.1111/j.1745-3933.2008.00464.x 2008
[7]

, archivePrefix = "arXiv", eprint =

CCD time-series photometry of the globular cluster NGC 6981: variable star census and physical parameter estimates. , keywords =. doi:10.1111/j.1365-2966.2011.18213.x , archivePrefix =. 1012.5652 , primaryClass =

work page doi:10.1111/j.1365-2966.2011.18213.x 2011
[8]

, keywords =

Difference image analysis: extension to a spatially varying photometric scale factor and other considerations. , keywords =. doi:10.1093/mnras/sts184 , archivePrefix =. 1210.2926 , primaryClass =

work page doi:10.1093/mnras/sts184
[9]

Journal of the Royal Astronomical Society of Canada , year = 1970, month = Dec, volume =

A Photoelectric Study of Magnetic Variable Stars. Journal of the Royal Astronomical Society of Canada , year = 1970, month = Dec, volume =

work page 1970
[10]

, keywords =

Extraction of globular clusters members with Gaia DR2 astrometry. , keywords =. doi:10.1093/mnras/stz1879 , archivePrefix =. 1907.02612 , primaryClass =

work page doi:10.1093/mnras/stz1879 1907
[11]

, keywords =

Proper Motions and Structural Parameters of the Galactic Globular Cluster M71. , keywords =. doi:10.3847/1538-4357/aa5ca5 , archivePrefix =. 1701.07834 , primaryClass =

work page doi:10.3847/1538-4357/aa5ca5
[12]

, keywords =

An Extremely Low-mass He White Dwarf Orbiting the Millisecond Pulsar J1342+2822B in the Globular Cluster M3. , keywords =. doi:10.3847/1538-4357/ab0e6b , archivePrefix =. 1903.03345 , primaryClass =

work page doi:10.3847/1538-4357/ab0e6b 1903
[13]

, keywords =

Digging for Relics of the Past: The Ancient and Obscured Bulge Globular Cluster NGC 6256. , keywords =. doi:10.3847/1538-4357/ab88b3 , archivePrefix =. 2004.06131 , primaryClass =

work page doi:10.3847/1538-4357/ab88b3 2004
[14]

, keywords =

PSR J1641+3627F: A Low-mass He White Dwarf Orbiting a Possible High-mass Neutron Star in the Globular Cluster M13. , keywords =. doi:10.3847/1538-4357/abc345 , archivePrefix =. 2010.09740 , primaryClass =

work page doi:10.3847/1538-4357/abc345 2010
[15]

, keywords =

The chemo-dynamical groups of Galactic globular clusters. , keywords =. doi:10.1093/mnras/stac1145 , archivePrefix =. 2202.00591 , primaryClass =

work page doi:10.1093/mnras/stac1145
[16]

and Clayton, Geoffrey C

The Relationship between Infrared, Optical, and Ultraviolet Extinction. , keywords =. doi:10.1086/167900 , adsurl =

work page doi:10.1086/167900
[17]

, keywords =

Intrinsic iron spread and a new metallicity scale for globular clusters. , keywords =. doi:10.1051/0004-6361/200913003 , archivePrefix =. 0910.0675 , primaryClass =

work page doi:10.1051/0004-6361/200913003
[18]

General considerations and new transformations for broad-band systems

Synthetic stellar photometry - I. General considerations and new transformations for broad-band systems. , keywords =. doi:10.1093/mnras/stu1476 , archivePrefix =. 1407.6095 , primaryClass =

work page doi:10.1093/mnras/stu1476
[19]

, keywords =

Variable Stars in Galactic Globular Clusters. , keywords =. doi:10.1086/323719 , archivePrefix =. astro-ph/0108024 , primaryClass =

work page doi:10.1086/323719
[20]

, archivePrefix = "arXiv", eprint =

SX Phoenicis period-luminosity relations and the blue straggler connection. , keywords =. doi:10.1111/j.1365-2966.2011.19697.x , adsurl =

work page doi:10.1111/j.1365-2966.2011.19697.x 2011
[21]

Variability in NGC 3201 Giant Stars , journal =

Cort. Variability in NGC 3201 Giant Stars , journal =. 2023 , volume =

work page 2023
[22]

, keywords =

Photometry, proper motions, and membership in the globular cluster M 71. , keywords =. doi:10.1086/113709 , adsurl =

work page doi:10.1086/113709
[23]

2024, A&A, 681, A38

Digging into the Galactic Bulge: Stellar Population and Structure of the Poorly Studied Cluster NGC 6316. , keywords =. doi:10.3847/1538-4357/aca9ce , archivePrefix =. 2212.03649 , primaryClass =

work page doi:10.3847/1538-4357/aca9ce
[24]

, keywords =

A photometric in-depth look at the core-collapsed globular cluster NGC 6284. , keywords =. doi:10.1051/0004-6361/202347547 , archivePrefix =. 2310.17503 , primaryClass =

work page doi:10.1051/0004-6361/202347547
[25]

On the Absolute Age of the Metal-rich Globular M71 (NGC 6838). I. Optical Photometry. , keywords =. doi:10.1088/0004-6256/150/2/51 , archivePrefix =. 1506.01180 , primaryClass =

work page doi:10.1088/0004-6256/150/2/51
[26]

, keywords =

The Dartmouth Stellar Evolution Database. , keywords =. doi:10.1086/589654 , archivePrefix =. 0804.4473 , primaryClass =

work page doi:10.1086/589654
[27]

, keywords =

A period-finding method for sparse randomly spaced observations or ''How long is a piece of string ?''. , keywords =. doi:10.1093/mnras/203.4.917 , adsurl =

work page doi:10.1093/mnras/203.4.917
[28]

and Lang, Dustin and Goodman, Jonathan , title =

emcee: The MCMC Hammer. , keywords =. doi:10.1086/670067 , archivePrefix =. 1202.3665 , primaryClass =

work page doi:10.1086/670067
[29]

The Journal of Open Source Software , keywords =

emcee v3: A Python ensemble sampling toolkit for affine-invariant MCMC. The Journal of Open Source Software , keywords =. doi:10.21105/joss.01864 , archivePrefix =. 1911.07688 , primaryClass =

work page doi:10.21105/joss.01864 1911
[30]

Summary of the content and survey properties

Gaia Data Release 3. Summary of the content and survey properties. , keywords =

work page
[31]

, keywords =

First results of a photometric and astrometric study of the globular cluster M 71 (NGC 6838). , keywords =. doi:10.1051/aas:2000209 , adsurl =

work page doi:10.1051/aas:2000209
[32]

NGC 6205 (M13)

Isochrone fitting of Galactic globular clusters - II. NGC 6205 (M13). , keywords =. doi:10.1093/mnras/staa1694 , archivePrefix =. 2008.10200 , primaryClass =

work page doi:10.1093/mnras/staa1694 2008
[33]

Evidence for high ages

The ages of the globular clusters M 71 and 47 Tuc from Str \"o mgren uvby photometry. Evidence for high ages. , keywords =. doi:10.1051/0004-6361:20020790 , adsurl =

work page doi:10.1051/0004-6361:20020790
[34]

The Astronomical Journal , author =

A Catalog of Parameters for Globular Clusters in the Milky Way. , keywords =. doi:10.1086/118116 , adsurl =

work page doi:10.1086/118116
[35]

and Mosteller, Frederick and Tukey, John W

Hoaglin, David C. and Mosteller, Frederick and Tukey, John W. , title =

work page
[36]

Understanding Robust and Exploratory Data Analysis , publisher =

work page
[37]

, keywords =

Deep CCD Photometry and Variable Stars in the Metal-Rich Globular Cluster M71. , keywords =. doi:10.1086/116075 , adsurl =

work page doi:10.1086/116075
[38]

Statistics, Data Mining, and Machine Learning in Astronomy , publisher =

Ivezi. Statistics, Data Mining, and Machine Learning in Astronomy , publisher =. 2014 , note =

work page 2014
[39]

, keywords =

Discovery of an SX Phoenicis Type Pulsating Component in the Algol-Type Semidetached Eclipsing Binary QU Sagittae in M71. , keywords =. doi:10.1086/500263 , adsurl =

work page doi:10.1086/500263
[40]

, keywords =

Measuring Consistent Masses for 25 Milky Way Globular Clusters. , keywords =. doi:10.1088/0004-6256/149/2/53 , archivePrefix =. 1411.1763 , primaryClass =

work page doi:10.1088/0004-6256/149/2/53
[41]

, keywords =

A search for photometric variability towards M71 with the Near-Infrared Transiting ExoplanetS Telescope. , keywords =. doi:10.1093/mnras/stt2449 , archivePrefix =. 1312.5880 , primaryClass =

work page doi:10.1093/mnras/stt2449
[42]

, keywords =

Global fitting of globular cluster age indicators. , keywords =. doi:10.1051/0004-6361:20065133 , adsurl =

work page doi:10.1051/0004-6361:20065133
[43]

, keywords =

New Faint Variable Stars in the Outer Regions of the Metal-rich Globular Cluster M71. , keywords =. doi:10.1086/301297 , adsurl =

work page doi:10.1086/301297
[44]

Updated BaSTI Stellar Evolution Models and Isochrones. II. -enhanced Calculations. , keywords =. doi:10.3847/1538-4357/abd4d5 , archivePrefix =. 2012.10085 , primaryClass =

work page doi:10.3847/1538-4357/abd4d5 2012
[45]

Variable Stars in the Fornax dSph Galaxy. II. Pulsating Stars below the Horizontal Branch. , keywords =. doi:10.1086/591241 , archivePrefix =. 0806.4453 , primaryClass =

work page doi:10.1086/591241
[47]

and Arellano Ferro, A

Prudil, Z. and Arellano Ferro, A. , title =. , year =. doi:10.1093/mnras/stae2335 , adsurl =

work page doi:10.1093/mnras/stae2335
[48]

and Croux, Christophe , title =

Rousseeuw, Peter J. and Croux, Christophe , title =. Journal of the American Statistical Association , year =

work page
[49]

and Croux, Christophe , title =

Rousseeuw, Peter J. and Croux, Christophe , title =. Journal of the American Statistical Association , volume =. 1993 , doi =

work page 1993
[50]

, keywords =

W UMA-Type Binary Stars in Globular Clusters. , keywords =. doi:10.1086/301417 , archivePrefix =. astro-ph/0001152 , primaryClass =

work page doi:10.1086/301417
[51]

2015, MNRAS, 451, 4,

A Panchromatic View of the Bulge Globular Cluster NGC 6569. , keywords =. doi:10.3847/1538-4357/ab07c4 , archivePrefix =. 1902.05558 , primaryClass =

work page doi:10.3847/1538-4357/ab07c4 1902
[52]

Publications of the David Dunlap Observatory , year = 1973, month = jan, volume =

A third catalogue of variable stars in globular clusters comprising 2119 entries. Publications of the David Dunlap Observatory , year = 1973, month = jan, volume =

work page 1973
[53]

, keywords =

Period determination using phase dispersion minimization. , keywords =. doi:10.1086/156444 , adsurl =

work page doi:10.1086/156444
[54]

Homogeneous Photometry for Star Clusters and Resolved Galaxies. II. Photometric Standard Stars. , keywords =. doi:10.1086/316595 , archivePrefix =. astro-ph/0004144 , primaryClass =

work page doi:10.1086/316595
[55]

, keywords =

Primordial Main sequence Binary Stars in the Globular Cluster M71. , keywords =. doi:10.1086/117194 , adsurl =

work page doi:10.1086/117194
[56]

SIGMOD Rec

Zhang, Tian and Ramakrishnan, Raghu and Livny, Miron , title =. SIGMOD Rec. , month = jun, pages =. 1996 , issue_date =. doi:10.1145/235968.233324 , abstract =

work page doi:10.1145/235968.233324 1996
[57]

Proceedings of the 1996 ACM SIGMOD International Conference on Management of Data , pages =

Zhang, Tian and Ramakrishnan, Raghu and Livny, Miron , title =. Proceedings of the 1996 ACM SIGMOD International Conference on Management of Data , pages =. 1996 , isbn =. doi:10.1145/233269.233324 , abstract =

work page doi:10.1145/233269.233324 1996
[59]

Zechmeister, M. and K. The generalised Lomb--Scargle periodogram: A new formalism for the floating-mean and Keplerian periodograms , journal =. 2009 , volume =. doi:10.1051/0004-6361:200811296 , adsurl =

work page doi:10.1051/0004-6361:200811296 2009
[60]

Photometric Analysis of Variable Stars in NGC 6397 , journal =

Cort. Photometric Analysis of Variable Stars in NGC 6397 , journal =. 2026 , volume =

work page 2026
[61]

, keywords =

Gaia EDR3 view on galactic globular clusters. , keywords =. doi:10.1093/mnras/stab1475 , archivePrefix =. 2102.09568 , primaryClass =

work page doi:10.1093/mnras/stab1475
[62]

Society for Astronomical Sciences Annual Symposium , year = 2006, month = may, volume =

The International Variable Star Index (VSX). Society for Astronomical Sciences Annual Symposium , year = 2006, month = may, volume =

work page 2006
[63]

, keywords =

The Cepheid Distance Scale. , keywords =. doi:10.1086/132911 , adsurl =

work page doi:10.1086/132911
[64]

, keywords =

Zwicky Transient Facility and Globular Clusters: The Period-Luminosity and Period-Wesenheit Relations for Type II Cepheids. , keywords =. doi:10.3847/1538-3881/ac87a4 , archivePrefix =. 2208.03404 , primaryClass =

work page doi:10.3847/1538-3881/ac87a4
[65]

, keywords =

Zwicky Transient Facility and Globular Clusters: The Period-Luminosity and Period-Wesenheit Relations for SX Phoenicis Variables in the gri Band. , keywords =. doi:10.3847/1538-3881/acc461 , archivePrefix =. 2303.07554 , primaryClass =

work page doi:10.3847/1538-3881/acc461
[66]

, keywords =

The Pan-STARRS1 Photometric System. , keywords =. doi:10.1088/0004-637X/750/2/99 , archivePrefix =. 1203.0297 , primaryClass =

work page doi:10.1088/0004-637x/750/2/99