Multiple populations in massive star clusters under the magnifying glass of photometry: theory and tools

Abstract

The existence of star-to-star light-element abundance variations in massive Galactic and extragalactic star clusters has fairly recently superseded the traditional paradigm of individual clusters hosting stars with the same age, and uniform chemical composition. Several scenarios have been put forward to explain the origin of this multiple stellar population phenomenon, but so far all have failed to reproduce the whole range of key observations. Complementary to high-resolution spectroscopy, which has first revealed and characterized chemically the presence of multiple populations in Galactic globular clusters, photometry has been instrumental in investigating this phenomenon in much larger samples of stars—adding a number of crucial observational constraints and correlations with global cluster properties—and in the discovery and characterization of multiple populations also in Magellanic Clouds’ intermediate-age clusters. The purpose of this review is to present the theoretical underpinning and application of the photometric techniques devised to identify and study multiple populations in resolved star clusters. These methods have played and continue to play a crucial role in advancing our knowledge of the cluster multiple population phenomenon, and promise to extend the scope of these investigations to resolved clusters even beyond the Local Group, with the launch of the James Webb Space Telescope.

This is a preview of subscription content, log in to check access.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
Fig. 14
Fig. 15
Fig. 16
Fig. 17
Fig. 18
Fig. 19
Fig. 20
Fig. 21
Fig. 22
Fig. 23
Fig. 24
Fig. 25
Fig. 26
Fig. 27
Fig. 28
Fig. 29
Fig. 30
Fig. 31
Fig. 32

Notes

  1. 1.

    Interestingly, it has been found that within these ‘peculiar’ clusters C–N, O–Na anticorrelations are present among stars with the same Fe abundance (see, e.g.Marino et al. 2011).

  2. 2.

    In the interiors of low-mass models, \({\log {R}}\) reaches values on the order of \(\sim 0.5\) only during the RGB advanced evolutionary phases. However in this regime the electron conduction opacity is the dominant contributor to the opacity in the He-core.

  3. 3.

    In case of complete ionisation, the mean molecular weight is given by \(\mu =\frac{1}{2X+\frac{3}{4}Y+\frac{Z}{2}}\).

  4. 4.

    We recall that, as long as the CNO sum (and initial Y) is the same, P1 and P2 theoretical isochrones are identical.

  5. 5.

    Lee (2017) has introduced the \(\mathrm{cn}_\mathrm{JWL}\) index, defined as \(\mathrm{cn}_\mathrm{JWL}=JWL39-\mathrm{Ca}_\mathrm{new}\), where JWL39 and \(\mathrm{Ca}_\mathrm{new}\) are two filters in the wavelength range between 3800 and 4050 Å. The \(\mathrm{cn}_{JWL}\) index is sensitive to the absorption of the CN band at 3883 Å, and the V-\(cn_{JWL}\) diagram is very similar to the V-\(c_y\) counterpart, but with a better MP resolving power.

  6. 6.

    The \(\delta _4\)index is also almost insensitive to reddening, given that \(E(\delta _4) \sim 0.01 E(B-V)\).

  7. 7.

    See also Milone et al. (2015) for a first discussion of this map for the Galactic GC NGC 2808, and alternative versions of chromosome maps. Zennaro et al. (2019) has very recently used another version of chromosome maps to study the Galactic GC NGC 2419, employing the pseudocolour \(C_{\mathrm{F275W}, \mathrm{F343N}, \mathrm{F438W}}=(\mathrm{F275W}-\mathrm{F343N})-(\mathrm{F343N}-\mathrm{F438W})\) and the colour \((\mathrm{F438W}-\mathrm{F814W})\). The construction and general properties of this map are the same as for Milone et al. (2017b) maps. For the same cluster, Larsen et al. (2019) have devised an analogous type of chromosome map, but based on the (F438W–F814W) and (F336W–F343N) pair of colours.

References

  1. Bastian N, Lardo C (2018) Multiple stellar populations in globular clusters. Annu Rev Astron Astrophys 56:83–136. https://doi.org/10.1146/annurev-astro-081817-051839. arxiv:1712.01286

    ADS  Article  Google Scholar 

  2. Bastian N, Lamers HJGLM, de Mink SE, Longmore SN, Goodwin SP, Gieles M (2013) Early disc accretion as the origin of abundance anomalies in globular clusters. Mon Not R Astron Soc 436(3):2398–2411. https://doi.org/10.1093/mnras/stt1745. arxiv:1309.3566

    ADS  Article  Google Scholar 

  3. Bedin LR, Piotto G, Anderson J, Cassisi S, King IR, Momany Y, Carraro G (2004) \({\omega }\) Centauri: the population puzzle goes deeper. Astrophys J Lett 605(2):L125–L128. https://doi.org/10.1086/420847. arxiv:astro-ph/0403112

    ADS  Article  Google Scholar 

  4. Bellini A, Renzini A, Anderson J, Bedin LR, Piotto G, Soto M, Brown TM, Milone AP, Sohn ST, Sweigart AV (2015) UV Insights into the complex populations of M87 globular clusters. Astrophys J 805(2):178. https://doi.org/10.1088/0004-637X/805/2/178. arxiv:1504.01742

    ADS  Article  Google Scholar 

  5. Böhm-Vitense E (1958) Über die Wasserstoffkonvektionszone in Sternen verschiedener Effektivtemperaturen und Leuchtkräfte. Z Astrophys 46:108

    ADS  Google Scholar 

  6. Bragaglia A, Carretta E, Gratton R, D’Orazi V, Cassisi S, Lucatello S (2010) Helium in first and second-generation stars in globular clusters from spectroscopy of red giants. Astron Astrophys 519:A60. https://doi.org/10.1051/0004-6361/201014702. arxiv:1005.2659

    ADS  Article  Google Scholar 

  7. Brott I, Hauschildt PH (2005) A PHOENIX model atmosphere grid for Gaia. In: Turon C, O’Flaherty KS, Perryman MAC (eds) The three-dimensional universe with Gaia, ESA Special Publication, vol 576, p 565. arxiv:astro-ph/0503395

  8. Busso G, Cassisi S, Piotto G, Castellani M, Romaniello M, Catelan M, Djorgovski SG, Recio Blanco A, Renzini A, Rich MR, Sweigart AV, Zoccali M (2007) The peculiar horizontal branch morphology of the Galactic globular clusters NGC 6388 and NGC 6441: new insights from UV observations. Astron Astrophys 474:105–119. https://doi.org/10.1051/0004-6361:20077806. arxiv:0708.1736

    ADS  Article  Google Scholar 

  9. Cabrera-Ziri I, Lardo C, Mucciarelli A (2019) Constant light element abundances suggest that the extended P1 in NGC 2808 is not a consequence of CNO-cycle nucleosynthesis. Mon Not R Astron Soc 485(3):4128–4133. https://doi.org/10.1093/mnras/stz707. arxiv:1903.03621

    ADS  Article  Google Scholar 

  10. Caloi V, D’Antona F (2005) Helium self-enrichment in globular clusters and the second parameter problem in M 3 and M 13. Astron Astrophys 435:987–993. https://doi.org/10.1051/0004-6361:20041773. arxiv:astro-ph/0502195

    ADS  Article  Google Scholar 

  11. Caloi V, D’Antona F (2007) NGC 6441: another indication of very high helium content in globular cluster stars. Astron Astrophys 463:949–955. https://doi.org/10.1051/0004-6361:20066074. arxiv:astro-ph/0610406

    ADS  Article  Google Scholar 

  12. Carretta E, Gratton RG, Lucatello S, Bragaglia A, Bonifacio P (2005) Abundances of C, N, O in slightly evolved stars in the globular clusters NGC 6397, NGC 6752 and 47 Tuc. Astron Astrophys 433:597–611. https://doi.org/10.1051/0004-6361:20041892. arxiv:astro-ph/0411241

    ADS  Article  Google Scholar 

  13. Carretta E, Bragaglia A, Gratton R, Lucatello S (2009a) Na-O anticorrelation and HB. VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra. Astron Astrophys 505:139–155. https://doi.org/10.1051/0004-6361/200912097. arxiv:0909.2941

    ADS  Article  Google Scholar 

  14. Carretta E, Bragaglia A, Gratton RG, Lucatello S, Catanzaro G, Leone F, Bellazzini M, Claudi R, D’Orazi V, Momany Y, Ortolani S, Pancino E, Piotto G, Recio-Blanco A, Sabbi E (2009b) Na-O anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra. Astron Astrophys 505:117–138. https://doi.org/10.1051/0004-6361/200912096. arxiv:0909.2938

    ADS  Article  Google Scholar 

  15. Carretta E, Bragaglia A, Gratton R, D’Orazi D’Orazi V, Lucatello S (2011) A Strömgren view of the multiple populations in globular clusters. Astron Astrophys 535:A121. https://doi.org/10.1051/0004-6361/201117180. arxiv:1109.3199

    ADS  Article  Google Scholar 

  16. Casagrande L, VandenBerg DA (2014) Synthetic stellar photometry-I. General considerations and new transformations for broad-band systems. Mon Not R Astron Soc 444:392–419. https://doi.org/10.1093/mnras/stu1476. arxiv:1407.6095

    ADS  Article  Google Scholar 

  17. Cassisi S, Salaris M, Bono G (2002) The shape of the red giant branch bump as a diagnostic of partial mixing processes in low-mass stars. Astrophys J 565(2):1231–1238. https://doi.org/10.1086/324695. arxiv:astro-ph/0110247

    ADS  Article  Google Scholar 

  18. Cassisi S, Salaris M (2013) Old stellar populations: how to study the fossil record of galaxy formation. Wiley-VCH, Weinheim

    Google Scholar 

  19. Cassisi S, Salaris M (2014) The main sequences of NGC 2808: constraints on the early disc accretion scenario. Astron Astrophys 563:A10. https://doi.org/10.1051/0004-6361/201323185. arxiv:1312.6363

    ADS  Article  Google Scholar 

  20. Cassisi S, Salaris M, Pietrinferni A, Piotto G, Milone AP, Bedin LR, Anderson J (2008) The double subgiant branch of NGC 1851: the role of the CNO abundance. Astrophys J Lett 672:L115–L118. https://doi.org/10.1086/527035. arxiv:0711.3823

    ADS  Article  Google Scholar 

  21. Cassisi S, Mucciarelli A, Pietrinferni A, Salaris M, Ferguson J (2013) Photometric properties of stellar populations in Galactic globular clusters: the role of the Mg-Al anticorrelation. Astron Astrophys 554:A19. https://doi.org/10.1051/0004-6361/201321311. arxiv:1303.5222

    ADS  Article  Google Scholar 

  22. Cassisi S, Salaris M, Pietrinferni A, Hyder D (2017) On the determination of the He abundance distribution in globular clusters from the width of the main sequence. Mon Not R Astron Soc 464(2):2341–2348. https://doi.org/10.1093/mnras/stw2579. arxiv:1610.01755

    ADS  Article  Google Scholar 

  23. Chantereau W, Salaris M, Bastian N, Martocchia S (2019) Helium enrichment in intermediate-age Magellanic Clouds clusters: towards an ubiquity of multiple stellar populations? Mon Not R Astron Soc 484(4):5236–5244. https://doi.org/10.1093/mnras/stz378. arxiv:1902.01806

    ADS  Article  Google Scholar 

  24. Charbonnel C, Lagarde N (2010) Thermohaline instability and rotation-induced mixing. I. Low- and intermediate-mass solar metallicity stars up to the end of the AGB. Astron Astrophys 522:A10. https://doi.org/10.1051/0004-6361/201014432. arxiv:1006.5359

    ADS  Article  Google Scholar 

  25. Cohen JG (1978) Abundances in globular cluster red giants. I. M3 and M13. Astrophys J 223:487–508. https://doi.org/10.1086/156284

    ADS  Article  Google Scholar 

  26. Dalessandro E, Salaris M, Ferraro FR, Cassisi S, Lanzoni B, Rood RT, Fusi Pecci F, Sabbi E (2011) The peculiar horizontal branch of NGC 2808. Mon Not R Astron Soc 410(1):694–704. https://doi.org/10.1111/j.1365-2966.2010.17479.x. arxiv:1008.4478

    ADS  Article  Google Scholar 

  27. Dalessandro E, Salaris M, Ferraro FR, Mucciarelli A, Cassisi S (2013) The horizontal branch in the UV colour-magnitude diagrams-II. The case of M3, M13 and M79. Mon Not R Astron Soc 430(1):459–471. https://doi.org/10.1093/mnras/sts644. arxiv:1212.4419

    ADS  Article  Google Scholar 

  28. Dalessandro E, Massari D, Bellazzini M, Miocchi P, Mucciarelli A, Salaris M, Cassisi S, Ferraro FR, Lanzoni B (2014) First evidence of fully spatially mixed first and second generations in globular clusters: the case of NGC 6362. Astrophys J Lett 791(1):L4. https://doi.org/10.1088/2041-8205/791/1/L4. arxiv:1407.0484

    ADS  Article  Google Scholar 

  29. Dalessandro E, Lapenna E, Mucciarelli A, Origlia L, Ferraro FR, Lanzoni B (2016) Multiple Populations in the old and massive small magellanic cloud globular cluster NGC 121. Astrophys J 829(2):77. https://doi.org/10.3847/0004-637X/829/2/77. arxiv:1607.05736

    ADS  Article  Google Scholar 

  30. Dalessandro E, Lardo C, Cadelano M, Saracino S, Bastian N, Mucciarelli A, Salaris M, Stetson P, Pancino E (2018) IC 4499 revised: spectro-photometric evidence of small light-element variations. Astron Astrophys 618:A131. https://doi.org/10.1051/0004-6361/201833650. arxiv:1807.07618

    ADS  Article  Google Scholar 

  31. D’Antona F, Caloi V, Montalbán J, Ventura P, Gratton R (2002) Helium variation due to self-pollution among Globular Cluster stars. Consequences on the horizontal branch morphology. Astron Astrophys 395:69–75. https://doi.org/10.1051/0004-6361:20021220. arxiv:astro-ph/0209331

    ADS  Article  Google Scholar 

  32. D’Antona F, Bellazzini M, Caloi V, Pecci FF, Galleti S, Rood RT (2005) A helium spread among the main-sequence stars in NGC 2808. Astrophys J 631(2):868–878. https://doi.org/10.1086/431968. arxiv:astro-ph/0505347

    ADS  Article  Google Scholar 

  33. di Criscienzo M, Ventura P, D’Antona F, Milone A, Piotto G (2010) The helium spread in the globular cluster 47 Tuc. Mon Not R Astron Soc 408(2):999–1005. https://doi.org/10.1111/j.1365-2966.2010.17168.x. arxiv:1006.2024

    ADS  Article  Google Scholar 

  34. Dotter A, Ferguson JW, Conroy C, Milone AP, Marino AF, Yong D (2015) Stellar models of multiple populations in globular clusters-I. The main sequence of NGC 6752. Mon Not R Astron Soc 446(2):1641–1656. https://doi.org/10.1093/mnras/stu2170. arxiv:1410.4570

    ADS  Article  Google Scholar 

  35. Dupree AK, Avrett EH (2013) Direct evaluation of the helium abundances in omega centauri. Astrophys J Lett 773(2):L28. https://doi.org/10.1088/2041-8205/773/2/L28. arxiv:1307.5860

    ADS  Article  Google Scholar 

  36. Ferguson JW, Alexander DR, Allard F, Barman T, Bodnarik JG, Hauschildt PH, Heffner-Wong A, Tamanai A (2005) Low-temperature opacities. Astrophys J 623(1):585–596. https://doi.org/10.1086/428642. arxiv:astro-ph/0502045

    ADS  Article  Google Scholar 

  37. Forbes DA, Bastian N, Gieles M, Crain RA, Kruijssen JMD, Larsen SS, Ploeckinger S, Agertz O, Trenti M, Ferguson AMN, Pfeffer J, Gnedin OY (2018) Globular cluster formation and evolution in the context of cosmological galaxy assembly: open questions. Proc R Soc Lond Ser A 474:20170616. https://doi.org/10.1098/rspa.2017.0616. arxiv:1801.05818

    ADS  MathSciNet  Article  MATH  Google Scholar 

  38. Gilligan CK, Chaboyer B, Cummings JD, Mackey D, Cohen RE, Geisler D, Grocholski AJ, Parisi MC, Sarajedini A, Ventura P, Villanova S, Yang SC, Wagner-Kaiser R (2019) Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud-IV. Evidence for multiple populations in Hodge 11 and NGC 2210. Mon Not R Astron Soc 486(4):5581–5599. https://doi.org/10.1093/mnras/stz1174. arxiv:1904.01434

    ADS  Article  Google Scholar 

  39. Girardi L, Castelli F, Bertelli G, Nasi E (2007) On the effect of helium enhancement on bolometric corrections and Teff-colour relations. Astron Astrophys 468(2):657–662. https://doi.org/10.1051/0004-6361:20077129. arxiv:astro-ph/0703094

    ADS  Article  Google Scholar 

  40. Gratton R, Bragaglia A, Carretta E, D’Orazi V, Lucatello S, Sollima A (2019) What is a globular cluster? An observational perspective. Astron Astrophys Rev 27:8. https://doi.org/10.1007/s00159-019-0119-3. arxiv:1911.02835

    ADS  Article  Google Scholar 

  41. Gratton RG, Sneden C, Carretta E, Bragaglia A (2000) Mixing along the red giant branch in metal-poor field stars. Astron Astrophys 354:169–187

    ADS  Google Scholar 

  42. Gratton RG, Carretta E, Bragaglia A (2012) Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters. Astron Astrophys Rev 20:50. https://doi.org/10.1007/s00159-012-0050-3. arxiv:1201.6526

    ADS  Article  Google Scholar 

  43. Gratton RG, Lucatello S, Sollima A, Carretta E, Bragaglia A, Momany Y, D’Orazi V, Cassisi S, Pietrinferni A, Salaris M (2013) The Na-O anticorrelation in horizontal branch stars. III. 47 Tucanae and M 5. Astron Astrophys 549:A41. https://doi.org/10.1051/0004-6361/201219976. arxiv:1210.4069

    ADS  Article  Google Scholar 

  44. Grundahl F, Briley M, Nissen PE, Feltzing S (2002) Abundances of RGB stars in NGC 6752. Astron Astrophys 385:L14–L17. https://doi.org/10.1051/0004-6361:20020264

    ADS  Article  Google Scholar 

  45. Hollyhead K, Martocchia S, Lardo C, Bastian N, Kacharov N, Niederhofer F, Cabrera-Ziri I, Dalessandro E, Mucciarelli A, Salaris M, Usher C (2019) Spectroscopic detection of multiple populations in the 2 Gyr old cluster Hodge 6 in the LMC. Mon Not R Astron Soc 484:4718–4725. https://doi.org/10.1093/mnras/stz317. arxiv:1902.02297

    ADS  Article  Google Scholar 

  46. Iglesias CA, Rogers FJ (1996) Updated opal opacities. Astrophys J 464:943. https://doi.org/10.1086/177381

    ADS  Article  Google Scholar 

  47. Johnson CI, Pilachowski CA (2010) Chemical abundances for 855 giants in the globular cluster omega centauri (NGC 5139). Astrophys J 722:1373–1410. https://doi.org/10.1088/0004-637X/722/2/1373. arxiv:1008.2232

    ADS  Article  Google Scholar 

  48. Kamann S, Giesers B, Bastian N, Brinchmann J, Dreizler S, Göttgens F, Husser TO, Latour M, Weilbacher PM, Wisotzki L (2020) The binary content of multiple populations in NGC 3201. Astron Astrophys 635:A65. https://doi.org/10.1051/0004-6361/201936843. arxiv:1912.01627

    ADS  Article  Google Scholar 

  49. King IR, Bedin LR, Cassisi S, Milone AP, Bellini A, Piotto G, Anderson J, Pietrinferni A, Cordier D (2012) Hubble space telescope observations of an outer field in omega centauri: a definitive helium abundance. Astron J 144:5. https://doi.org/10.1088/0004-6256/144/1/5. arxiv:1205.3760

    ADS  Article  Google Scholar 

  50. Krishna Swamy KS (1966) Profiles of strong lines in K-Dwarfs. Astrophys J 145:174. https://doi.org/10.1086/148752

    ADS  Article  Google Scholar 

  51. Kruijssen JMD (2015) Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies. Mon Not R Astron Soc 454(2):1658–1686. https://doi.org/10.1093/mnras/stv2026. arxiv:1509.02163

    ADS  Article  Google Scholar 

  52. Lagioia EP, Milone AP, Marino AF, Cassisi S, Aparicio AJ, Piotto G, Anderson J, Barbuy B, Bedin LR, Bellini A, Brown T, D’Antona F, Nardiello D, Ortolani S, Pietrinferni A, Renzini A, Salaris M, Sarajedini A, van der Marel R, Vesperini E (2018) The Hubble space telescope UV legacy survey of galactic globular clusters-XII. The RGB bumps of multiple stellar populations. Mon Not R Astron Soc 475(3):4088–4103. https://doi.org/10.1093/mnras/sty083. arxiv:1801.03395

    ADS  Article  Google Scholar 

  53. Lagioia EP, Milone AP, Marino AF, Cordoni G, Tailo M (2019a) The role of cluster mass in the multiple populations of galactic and extragalactic globular clusters. Astron J 158(5):202. https://doi.org/10.3847/1538-3881/ab45f2. arxiv:1909.08439

    ADS  Article  Google Scholar 

  54. Lagioia EP, Milone AP, Marino AF, Dotter A (2019b) Helium variation in four small magellanic cloud globular clusters. Astrophys J 871(2):140. https://doi.org/10.3847/1538-4357/aaf729

    ADS  Article  Google Scholar 

  55. Lardo C, Salaris M, Bastian N, Mucciarelli A, Dalessandro E, Cabrera-Ziri I (2018) Chemical inhomogeneities amongst first population stars in globular clusters. Evidence for He variations. Astron Astrophys 616:A168. https://doi.org/10.1051/0004-6361/201832999. arxiv:1805.09599

    ADS  Article  Google Scholar 

  56. Larsen SS, Brodie JP, Grundahl F, Strader J (2014) Nitrogen Abundances and multiple stellar populations in the globular clusters of the fornax dSph. Astrophys J 797:15. https://doi.org/10.1088/0004-637X/797/1/15. arxiv:1409.0541

    ADS  Article  Google Scholar 

  57. Larsen SS, Baumgardt H, Bastian N, Hernandez S, Brodie J (2019) Hubble Space Telescope photometry of multiple stellar populations in the inner parts of NGC 2419. Astron Astrophys 624:A25. https://doi.org/10.1051/0004-6361/201834494. arxiv:1902.01416

    ADS  Article  Google Scholar 

  58. Lattanzio JC, Siess L, Church RP, Angelou G, Stancliffe RJ, Doherty CL, Stephen T, Campbell SW (2015) On the numerical treatment and dependence of thermohaline mixing in red giants. Mon Not R Astron Soc 446(3):2673–2688. https://doi.org/10.1093/mnras/stu2238. arxiv:1410.6517

    ADS  Article  Google Scholar 

  59. Lee JW (2017) Multiple stellar populations of globular clusters from homogeneous Ca-CN photometry. II. M5 (NGC 5904) and a new filter system. Astrophys J 844(1):77. https://doi.org/10.3847/1538-4357/aa7b8c. arxiv:1706.07969

    ADS  Article  Google Scholar 

  60. Lee YW, Joo SJ, Han SI, Chung C, Ree CH, Sohn YJ, Kim YC, Yoon SJ, Yi SK, Demarque P (2005) Super-helium-rich populations and the origin of extreme horizontal-branch stars in globular clusters. Astrophys J Lett 621(1):L57–L60. https://doi.org/10.1086/428944. arxiv:astro-ph/0501500

    ADS  Article  Google Scholar 

  61. Madau P, Dickinson M (2014) Cosmic star-formation history. Annu Rev Astron Astrophys 52:415–486. https://doi.org/10.1146/annurev-astro-081811-125615. arxiv:1403.0007

    ADS  Article  Google Scholar 

  62. Magic Z, Weiss A, Asplund M (2015) The Stagger-grid: a grid of 3D stellar atmosphere models. III. The relation to mixing length convection theory. Astron Astrophys 573:A89. https://doi.org/10.1051/0004-6361/201423760. arxiv:1403.1062

    ADS  Article  Google Scholar 

  63. Marino AF, Villanova S, Piotto G, Milone AP, Momany Y, Bedin LR, Medling AM (2008) Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4). Astron Astrophys 490:625–640. https://doi.org/10.1051/0004-6361:200810389. arxiv:0808.1414

    ADS  Article  Google Scholar 

  64. Marino AF, Milone AP, Piotto G, Villanova S, Gratton R, D’Antona F, Anderson J, Bedin LR, Bellini A, Cassisi S, Geisler D, Renzini A, Zoccali M (2011) Sodium-oxygen anticorrelation and neutron-capture elements in omega centauri stellar populations. Astrophys J 731:64. https://doi.org/10.1088/0004-637X/731/1/64. arxiv:1102.1653

    ADS  Article  Google Scholar 

  65. Marino AF, Milone AP, Piotto G, Cassisi S, D’Antona F, Anderson J, Aparicio A, Bedin LR, Renzini A, Villanova S (2012a) The C+N+O Abundance of \({\omega }\) Centauri giant stars: implications for the chemical-enrichment scenario and the relative ages of different stellar populations. Astrophys J 746(1):14. https://doi.org/10.1088/0004-637X/746/1/14. arxiv:1111.1891

    ADS  Article  Google Scholar 

  66. Marino AF, Milone AP, Sneden C, Bergemann M, Kraft RP, Wallerstein G, Cassisi S, Aparicio A, Asplund M, Bedin RL, Hilker M, Lind K, Momany Y, Piotto G, Roederer IU, Stetson PB, Zoccali M (2012b) The double sub-giant branch of NGC 6656 (M 22): a chemical characterization. Astron Astrophys 541:A15. https://doi.org/10.1051/0004-6361/201118381. arxiv:1202.2825

    ADS  Article  Google Scholar 

  67. Marino AF, Milone AP, Przybilla N, Bergemann M, Lind K, Asplund M, Cassisi S, Catelan M, Casagrande L, Valcarce AAR, Bedin LR, Cortés C, D’Antona F, Jerjen H, Piotto G, Schlesinger K, Zoccali M, Angeloni R (2014) Helium enhanced stars and multiple populations along the horizontal branch of NGC 2808: direct spectroscopic measurements. Mon Not R Astron Soc 437(2):1609–1627. https://doi.org/10.1093/mnras/stt1993. arxiv:1310.4527

    ADS  Article  Google Scholar 

  68. Marino AF, Milone AP, Sills A, Yong D, Renzini A, Bedin LR, Cordoni G, D’Antona F, Jerjen H, Karakas A, Lagioia E, Piotto G, Tailo M (2019) Chemical abundances along the 1G sequence of the chromosome maps: the globular cluster NGC 3201. Astrophys J 887(1):91. https://doi.org/10.3847/1538-4357/ab53d9. arxiv:1910.02892

    ADS  Article  Google Scholar 

  69. Martins F, Morin J, Charbonnel C, Lardo C, Chantereau W (2020) Impact of a companion and of chromospheric emission on the shape of chromosome maps for globular clusters. Astron Astrophys 635:A52. https://doi.org/10.1051/0004-6361/201937212. arxiv:2001.07581

    ADS  Article  Google Scholar 

  70. Martocchia S, Bastian N, Usher C, Kozhurina-Platais V, Niederhofer F, Cabrera-Ziri I, Dalessandro E, Hollyhead K, Kacharov N, Lardo C, Larsen S, Mucciarelli A, Platais I, Salaris M, Cordero M, Geisler D, Hilker M, Li C, Mackey D (2017) The search for multiple populations in Magellanic Cloud Clusters-III. No evidence for multiple populations in the SMC cluster NGC 419. Mon Not R Astron Soc 468(3):3150–3158. https://doi.org/10.1093/mnras/stx660. arxiv:1703.04631

    ADS  Article  Google Scholar 

  71. Martocchia S, Cabrera-Ziri I, Lardo C, Dalessandro E, Bastian N, Kozhurina-Platais V, Usher C, Niederhofer F, Cordero M, Geisler D, Hollyhead K, Kacharov N, Larsen S, Li C, Mackey D, Hilker M, Mucciarelli A, Platais I, Salaris M (2018a) Age as a major factor in the onset of multiple populations in stellar clusters. Mon Not R Astron Soc 473:2688–2700. https://doi.org/10.1093/mnras/stx2556. arxiv:1710.00831

    ADS  Article  Google Scholar 

  72. Martocchia S, Niederhofer F, Dalessandro E, Bastian N, Kacharov N, Usher C, Cabrera-Ziri I, Lardo C, Cassisi S, Geisler D, Hilker M, Hollyhead K, Kozhurina-Platais V, Larsen S, Mackey D, Mucciarelli A, Platais I, Salaris M (2018b) The search for multiple populations in Magellanic Cloud clusters-IV. Coeval multiple stellar populations in the young star cluster NGC 1978. Mon Not R Astron Soc 477(4):4696–4705. https://doi.org/10.1093/mnras/sty916. arxiv:1804.04141

    ADS  Article  Google Scholar 

  73. Martocchia S, Dalessandro E, Lardo C, Cabrera-Ziri I, Bastian N, Kozhurina-Platais V, Salaris M, Chantereau W, Geisler D, Hilker M, Kacharov N, Larsen S, Mucciarelli A, Niederhofer F, Platais I, Usher C (2019) The search for multiple populations in Magellanic Clouds clusters-V. Correlation between cluster age and abundance spreads. Mon Not R Astron Soc. https://doi.org/10.1093/mnras/stz1596. arxiv:1906.03273

    Article  Google Scholar 

  74. Milone AP, Marino AF, Cassisi S, Piotto G, Bedin LR, Anderson J, Allard F, Aparicio A, Bellini A, Buonanno R, Monelli M, Pietrinferni A (2012a) The Infrared eye of the wide-field camera 3 on the hubble space telescope reveals multiple main sequences of very low mass stars in NGC 2808. Astrophys J 754:L34. https://doi.org/10.1088/2041-8205/754/2/L34. arxiv:1206.5529

    ADS  Article  Google Scholar 

  75. Milone AP, Piotto G, Bedin LR, Cassisi S, Anderson J, Marino AF, Pietrinferni A, Aparicio A (2012b) Luminosity and mass functions of the three main sequences of the globular cluster NGC 2808. Astron Astrophys 537:A77. https://doi.org/10.1051/0004-6361/201116539. arxiv:1108.2391

    ADS  Article  Google Scholar 

  76. Milone AP, Piotto G, Bedin LR, King IR, Anderson J, Marino AF, Bellini A, Gratton R, Renzini A, Stetson PB, Cassisi S, Aparicio A, Bragaglia A, Carretta E, D’Antona F, Di Criscienzo M, Lucatello S, Monelli M, Pietrinferni A (2012c) Multiple stellar populations in 47 Tucanae. Astrophys J 744:58. https://doi.org/10.1088/0004-637X/744/1/58. arxiv:1109.0900

    ADS  Article  Google Scholar 

  77. Milone AP, Marino AF, Bedin LR, Piotto G, Cassisi S, Dieball A, Anderson J, Jerjen H, Asplund M, Bellini A, Brogaard K, Dotter A, Giersz M, Heggie DC, Knigge C, Rich RM, van den Berg M, Buonanno R (2014) The M 4 Core Project with HST-II. Multiple stellar populations at the bottom of the main sequence. Mon Not R Astron Soc 439(2):1588–1595. https://doi.org/10.1093/mnras/stu030. arxiv:1401.1091

    ADS  Article  Google Scholar 

  78. Milone AP, Marino AF, Piotto G, Renzini A, Bedin LR, Anderson J, Cassisi S, D’Antona F, Bellini A, Jerjen H, Pietrinferni A, Ventura P (2015) The hubble space telescope UV legacy survey of galactic globular clusters. III. A quintuple stellar population in NGC 2808. Astrophys J 808(1):51. https://doi.org/10.1088/0004-637X/808/1/51. arxiv:1505.05934

    ADS  Article  Google Scholar 

  79. Milone AP, Marino AF, Bedin LR, Anderson J, Apai D, Bellini A, Bergeron P, Burgasser AJ, Dotter A, Rees JM (2017a) The HST large programme on \({\omega }\) Centauri-I. Multiple stellar populations at the bottom of the main sequence probed in NIR-Optical. Mon Not R Astron Soc 469(1):800–812. https://doi.org/10.1093/mnras/stx836. arxiv:1704.00418

    ADS  Article  Google Scholar 

  80. Milone AP, Piotto G, Renzini A, Marino AF, Bedin LR, Vesperini E, D’Antona F, Nardiello D, Anderson J, King IR, Yong D, Bellini A, Aparicio A, Barbuy B, Brown TM, Cassisi S, Ortolani S, Salaris M, Sarajedini A, van der Marel RP (2017b) The Hubble Space Telescope UV legacy survey of galactic globular clusters-IX. The Atlas of multiple stellar populations. Mon Not R Astron Soc 464:3636–3656. https://doi.org/10.1093/mnras/stw2531. arxiv:1610.00451

    ADS  Article  Google Scholar 

  81. Milone AP, Marino AF, Renzini A, D’Antona F, Anderson J, Barbuy B, Bedin LR, Bellini A, Brown TM, Cassisi S, Cordoni G, Lagioia EP, Nardiello D, Ortolani S, Piotto G, Sarajedini A, Tailo M, van der Marel RP, Vesperini E (2018) The Hubble Space Telescope UV legacy survey of galactic globular clusters-XVI. The helium abundance of multiple populations. Mon Not R Astron Soc 481:5098–5122. https://doi.org/10.1093/mnras/sty2573. arxiv:1809.05006

    ADS  Article  Google Scholar 

  82. Monelli M, Milone AP, Stetson PB, Marino AF, Cassisi S, del Pino Molina A, Salaris M, Aparicio A, Asplund M, Grundahl F, Piotto G, Weiss A, Carrera R, Cebrián M, Murabito S, Pietrinferni A, Sbordone L (2013) The SUMO project I. A survey of multiple populations in globular clusters. Mon Not R Astron Soc 431:2126–2149. https://doi.org/10.1093/mnras/stt273. arxiv:1303.5187

    ADS  Article  Google Scholar 

  83. Mucciarelli A, Origlia L, Ferraro FR, Pancino E (2009) Looking outside the galaxy: the discovery of chemical anomalies in three old large magellanic cloud clusters. Astrophys J Lett 695(2):L134–L139. https://doi.org/10.1088/0004-637X/695/2/L134. arxiv:0902.4778

    ADS  Article  Google Scholar 

  84. Mucciarelli A, Lovisi L, Lanzoni B, Ferraro FR (2014) The helium abundance in the metal-poor globular clusters M30 and NGC 6397. Astrophys J 786(1):14. https://doi.org/10.1088/0004-637X/786/1/14. arxiv:1403.0595

    ADS  Article  Google Scholar 

  85. Mucciarelli A, Lapenna E, Massari D, Ferraro FR, Lanzoni B (2015) The origin of the spurious iron spread in the globular cluster NGC 3201. Astrophys J 801(1):69. https://doi.org/10.1088/0004-637X/801/1/69. arxiv:1501.01968

    ADS  Article  Google Scholar 

  86. Mucciarelli A, Dalessandro E, Massari D, Bellazzini M, Ferraro FR, Lanzoni B, Lardo C, Salaris M, Cassisi S (2016) NGC 6362: the least massive globular cluster with chemically distinct multiple populations. Astrophys J 824(2):73. https://doi.org/10.3847/0004-637X/824/2/73. arxiv:1604.04151

    ADS  Article  Google Scholar 

  87. Nardiello D, Piotto G, Milone AP, Marino AF, Bedin LR, Anderson J, Aparicio A, Bellini A, Cassisi S, D’Antona F, Hidalgo S, Ortolani S, Pietrinferni A, Renzini A, Salaris M, Marel RPvd, Vesperini E (2015) The Hubble Space Telescope UV legacy survey of galactic globular clusters-IV. Helium content and relative age of multiple stellar populations within NGC 6352. Mon Not R Astron Soc 451(1):312–322. https://doi.org/10.1093/mnras/stv971. arxiv:1504.07876

    ADS  Article  Google Scholar 

  88. Nardiello D, Piotto G, Milone AP, Rich RM, Cassisi S, Bedin LR, Bellini A, Renzini A (2019) Hubble Space Telescope analysis of stellar populations within the globular cluster G1 (Mayall II) in M 31. Mon Not R Astron Soc 485:3076–3087. https://doi.org/10.1093/mnras/stz629 arxiv:1903.00488

    ADS  Article  Google Scholar 

  89. Nataf DM, Gould A, Pinsonneault MH, Stetson PB (2011a) The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are consistent with a centrally concentrated. Helium-enriched second stellar generation. Astrophys J 736(2):94. https://doi.org/10.1088/0004-637X/736/2/94. arxiv:1102.3916

    ADS  Article  Google Scholar 

  90. Nataf DM, Udalski A, Gould A, Pinsonneault MH (2011b) OGLE-III detection of the anomalous galactic bulge red giant branch bump: evidence of enhanced helium enrichment. Astrophys J 730:118. https://doi.org/10.1088/0004-637X/730/2/118. arxiv:1011.4293

    ADS  Article  Google Scholar 

  91. Niederhofer F, Bastian N, Kozhurina-Platais V, Larsen S, Salaris M, Dalessandro E, Mucciarelli A, Cabrera-Ziri I, Cordero M, Geisler D, Hilker M, Hollyhead K, Kacharov N, Lardo C, Li C, Mackey D, Platais I (2017) The search for multiple populations in Magellanic Cloud clusters-I. Two stellar populations in the Small Magellanic Cloud globular cluster NGC 121. Mon Not R Astron Soc 464(1):94–103. https://doi.org/10.1093/mnras/stw2269. arxiv:1609.01595

    ADS  Article  Google Scholar 

  92. Origlia L, Massari D, Rich RM, Mucciarelli A, Ferraro FR, Dalessandro E, Lanzoni B (2013) The Terzan 5 puzzle: Discovery of a third. Metal-poor component. Astrophys J Lett 779:L5. https://doi.org/10.1088/2041-8205/779/1/L5. arxiv:1311.1706

    ADS  Article  Google Scholar 

  93. Pasquini L, Mauas P, Käufl HU, Cacciari C (2011) Measuring helium abundance difference in giants of NGC 2808. Astron Astrophys 531:A35. https://doi.org/10.1051/0004-6361/201116592. arxiv:1105.0346

    ADS  Article  Google Scholar 

  94. Pietrinferni A, Cassisi S, Salaris M, Castelli F (2004) A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones. Astrophys J 612(1):168–190. https://doi.org/10.1086/422498. arxiv:astro-ph/0405193

    ADS  Article  Google Scholar 

  95. Pietrinferni A, Cassisi S, Salaris M, Castelli F (2006) A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an \(\alpha \)-enhanced Metal Distribution. Astrophys J 642:797–812. https://doi.org/10.1086/501344. arxiv:astro-ph/0603721

    ADS  Article  Google Scholar 

  96. Pietrinferni A, Cassisi S, Salaris M, Percival S, Ferguson JW (2009) A large stellar evolution database for population synthesis studies. V. Stellar models and isochrones with CNONa abundance anticorrelations. Astrophys J 697:275–282. https://doi.org/10.1088/0004-637X/697/1/275. arxiv:0903.0825

    ADS  Article  Google Scholar 

  97. Piotto G, Villanova S, Bedin LR, Gratton R, Cassisi S, Momany Y, Recio-Blanco A, Lucatello S, Anderson J, King IR, Pietrinferni A, Carraro G (2005) Metallicities on the double main sequence of \(\omega \) Centauri imply large helium enhancement. Astrophys J 621:777–784. https://doi.org/10.1086/427796. arxiv:astro-ph/0412016

    ADS  Article  Google Scholar 

  98. Piotto G, Bedin LR, Anderson J, King IR, Cassisi S, Milone AP, Villanova S, Pietrinferni A, Renzini A (2007) A triple main sequence in the globular cluster NGC 2808. Astrophys J Lett 661:L53–L56. https://doi.org/10.1086/518503. arxiv:astro-ph/0703767

    ADS  Article  Google Scholar 

  99. Piotto G, Milone AP, Marino AF, Bedin LR, Anderson J, Jerjen H, Bellini A, Cassisi S (2013) Multi-wavelength Hubble Space telescope photometry of stellar populations in NGC 288. Astrophys J 775(1):15. https://doi.org/10.1088/0004-637X/775/1/15. arxiv:1306.5795

    ADS  Article  Google Scholar 

  100. Piotto G, Milone AP, Bedin LR, Anderson J, King IR, Marino AF, Nardiello D, Aparicio A, Barbuy B, Bellini A, Brown TM, Cassisi S, Cool AM, Cunial A, Dalessandro E, D’Antona F, Ferraro FR, Hidalgo S, Lanzoni B, Monelli M, Ortolani S, Renzini A, Salaris M, Sarajedini A, van der Marel RP, Vesperini E, Zoccali M (2015) The Hubble Space Telescope UV legacy survey of galactic globular clusters. I. Overview of the project and detection of multiple stellar populations. Astron J 149(3):91. https://doi.org/10.1088/0004-6256/149/3/91. arxiv:1410.4564

    ADS  Article  Google Scholar 

  101. Renzini A, D’Antona F, Cassisi S, King IR, Milone AP, Ventura P, Anderson J, Bedin LR, Bellini A, Brown TM, Piotto G, van der Marel RP, Barbuy B, Dalessandro E, Hidalgo S, Marino AF, Ortolani S, Salaris M, Sarajedini A (2015) The Hubble Space Telescope UV legacy survey of galactic globular clusters-V. Constraints on formation scenarios. Mon Not R Astron Soc 454:4197–4207. https://doi.org/10.1093/mnras/stv2268. arxiv:1510.01468

    ADS  Article  Google Scholar 

  102. Salaris M, Cassisi S (2008) Stellar models with the ML2 theory of convection. Astron Astrophys 487:1075–1080. https://doi.org/10.1051/0004-6361:200810253. arxiv:0807.0863

    ADS  Article  Google Scholar 

  103. Salaris M, Cassisi S (2014) Lithium and oxygen in globular cluster dwarfs and the early disc accretion scenario. Astron Astrophys 566:A109. https://doi.org/10.1051/0004-6361/201423722. arxiv:1404.6123

    ADS  Article  Google Scholar 

  104. Salaris M, Weiss A (2002) Homogeneous age dating of 55 Galactic globular clusters. Clues to the galaxy formation mechanisms. Astron Astrophys 388:492–503. https://doi.org/10.1051/0004-6361:20020554. arxiv:astro-ph/0204410

    ADS  Article  Google Scholar 

  105. Salaris M, Chieffi A, Straniero O (1993) The \({\alpha }\)-enhanced isochrones and their impact on the FITS to the galactic globular cluster system. Astrophys J 414:580. https://doi.org/10.1086/173105

    ADS  Article  Google Scholar 

  106. Salaris M, Weiss A, Ferguson JW, Fusilier DJ (2006) On the primordial scenario for abundance variations within globular clusters: the Isochrone test. Astrophys J 645:1131–1137. https://doi.org/10.1086/504520. arxiv:astro-ph/0604137

    ADS  Article  Google Scholar 

  107. Salaris M, Cassisi S, Pietrinferni A (2008) The Horizontal Branch of NGC 1851: constraints on the cluster subpopulations. Astrophys J Lett 678:L25–L28. https://doi.org/10.1086/588467. arxiv:0803.3546

    ADS  Article  Google Scholar 

  108. Salaris M, Pietrinferni A, Piersimoni AM, Cassisi S (2015) Post first dredge-up [C/N] ratio as age indicator. Theoretical calibration. Astron Astrophys 583:A87. https://doi.org/10.1051/0004-6361/201526951. arxiv:1509.06904

    ADS  Article  Google Scholar 

  109. Salaris M, Cassisi S, Pietrinferni A (2016) On the red giant branch mass loss in 47 Tucanae: constraints from the horizontal branch morphology. Astron Astrophys 590:A64. https://doi.org/10.1051/0004-6361/201628181. arxiv:1604.02874

    ADS  Article  Google Scholar 

  110. Salaris M, Cassisi S, Schiavon RP, Pietrinferni A (2018) Effective temperatures of red giants in the APOKASC catalogue and the mixing length calibration in stellar models. Astron Astrophys 612:A68. https://doi.org/10.1051/0004-6361/201732340. arxiv:1801.09441

    ADS  Article  Google Scholar 

  111. Salaris M, Cassisi S, Mucciarelli A, Nardiello D (2019) Detection of multiple stellar populations in extragalactic massive clusters with JWST. Astron Astrophys 629:A40. https://doi.org/10.1051/0004-6361/201936252. arxiv:1908.02229

    ADS  Article  Google Scholar 

  112. Salaris M, Usher C, Martocchia S, Dalessandro E, Bastian N, Saracino S, Cassisi S, Cabrera-Ziri I, Lardo C (2020) Photometric characterization of multiple populations in star clusters: the impact of the first dredge-up. Mon Not R Astron Soc 492(3):3459–3464. https://doi.org/10.1093/mnras/staa089. arxiv:2001.04145

    ADS  Article  Google Scholar 

  113. Saracino S, Bastian N, Kozhurina-Platais V, Cabrera-Ziri I, Dalessandro E, Kacharov N, Lardo C, Larsen SS, Mucciarelli A, Platais I, Salaris M (2019) An extragalactic chromosome map: the intermediate-age SMC cluster Lindsay 1. Mon Not R Astron Soc 489(1):L97–L101. https://doi.org/10.1093/mnrasl/slz135. arxiv:1909.02138

    ADS  Article  Google Scholar 

  114. Saracino S, Martocchia S, Bastian N, Kozhurina-Platais V, Chantereau W, Salaris M, Cabrera-Ziri I, Dalessandro E, Kacharov N, Lardo C, Larsen SS, Platais I (2020) Chromosome maps of young LMC clusters: an additional case of coeval multiple populations. Mon Not R Astron Soc 493(4):6060–6070. https://doi.org/10.1093/mnras/staa644. arxiv:2003.01780

    ADS  Article  Google Scholar 

  115. Sbordone L, Salaris M, Weiss A, Cassisi S (2011) Photometric signatures of multiple stellar populations in Galactic globular clusters. Astron Astrophys 534:A9. https://doi.org/10.1051/0004-6361/201116714. arxiv:1103.5863

    ADS  Article  Google Scholar 

  116. Schiavon RP, Caldwell N, Conroy C, Graves GJ, Strader J, MacArthur LA, Courteau S, Harding P (2013) Star clusters in M31. V. Evidence for self-enrichment in Old M31 clusters from integrated spectroscopy. Astrophys J Lett 776(1):L7. https://doi.org/10.1088/2041-8205/776/1/L7. arxiv:1308.6590

    ADS  Article  Google Scholar 

  117. Tailo M, D’Antona F, Milone AP, Bellini A, Ventura P, Di Criscienzo M, Cassisi S, Piotto G, Salaris M, Brown TM, Vesperini E, Bedin LR, Marino AF, Nardiello D, Anderson J (2017) The Hubble Space Telescope UV legacy survey of galactic globular clusters-XI. The horizontal branch in NGC 6388 and NGC 6441. Mon Not R Astron Soc 465(1):1046–1056. https://doi.org/10.1093/mnras/stw2790. arxiv:1610.08264

    ADS  Article  Google Scholar 

  118. Thomas HC (1967) Sternentwicklung. VIII. Der Helium-Flash bei einem Stern von 1. 3 Sonnenmassen. Z Astrophys 67:420

    ADS  Google Scholar 

  119. Trampedach R, Stein RF, Christensen-Dalsgaard J, Nordlund Å, Asplund M (2014) Improvements to stellar structure models, based on a grid of 3D convection simulations-II. Calibrating the mixing-length formulation. Mon Not R Astron Soc 445(4):4366–4384. https://doi.org/10.1093/mnras/stu2084 arxiv:1410.1559

    ADS  Article  Google Scholar 

  120. VandenBerg DA, Edvardsson B, Eriksson K, Gustafsson B (2008) On the use of blanketed atmospheres as boundary conditions for stellar evolutionary models. Astrophys J 675:746–763. https://doi.org/10.1086/521600. arxiv:0708.1188

    ADS  Article  Google Scholar 

  121. VandenBerg DA, Bergbusch PA, Dotter A, Ferguson JW, Michaud G, Richer J, Proffitt CR (2012) Models for metal-poor stars with enhanced abundances of C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti, in Turn, at constant helium and iron abundances. Astrophys J 755:15. https://doi.org/10.1088/0004-637X/755/1/15. arxiv:1206.1820

    ADS  Article  Google Scholar 

  122. Ventura P, Caloi V, D’Antona F, Ferguson J, Milone A, Piotto GP (2009) The C+N+O abundances and the splitting of the subgiant branch in the globular cluster NGC 1851. Mon Not R Astron Soc 399:934–943. https://doi.org/10.1111/j.1365-2966.2009.15335.x. arxiv:0907.1765

    ADS  Article  Google Scholar 

  123. Villanova S, Geisler D, Piotto G (2010) Detailed abundances of red giants in the globular cluster NGC 1851: C+N+O and the origin of multiple populations. Astrophys J Lett 722:L18–L22. https://doi.org/10.1088/2041-8205/722/1/L18. arxiv:1008.4372

    ADS  Article  Google Scholar 

  124. Villanova S, Geisler D, Piotto G, Gratton RG (2012) The helium content of globular clusters: NGC 6121 (M4). Astrophys J 748(1):62. https://doi.org/10.1088/0004-637X/748/1/62. arxiv:1201.3241

    ADS  Article  Google Scholar 

  125. Worthey G, Hc Lee (2011) An empirical UBV RI JHK color-temperature calibration for stars. Astrophys J Suppl Ser 193:1. https://doi.org/10.1088/0067-0049/193/1/1. arxiv:astro-ph/0604590

    ADS  Article  Google Scholar 

  126. Yong D, Grundahl F, Johnson JA, Asplund M (2008) Nitrogen abundances in giant stars of the globular cluster NGC 6752. Astrophys J 684:1159–1169. https://doi.org/10.1086/590658. arxiv:0806.0187

    ADS  Article  Google Scholar 

  127. Yong D, Grundahl F, D’Antona F, Karakas AI, Lattanzio JC, Norris JE (2009) A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851. Astrophys J Lett 695(1):L62–L66. https://doi.org/10.1088/0004-637X/695/1/L62. arxiv:0902.1773

    ADS  Article  Google Scholar 

  128. Zennaro M, Milone AP, Marino AF, Cordoni G, Lagioia EP, Tailo M (2019) Four stellar populations and extreme helium variation in the massive outer-halo globular cluster NGC 2419. Mon Not R Astron Soc 487(3):3239–3251. https://doi.org/10.1093/mnras/stz1477. arxiv:1902.02178

    ADS  Article  Google Scholar 

Download references

Acknowledgements

We acknowledge the anonymous referee for his/her helpful suggestions. We warmly thank Adriano Pietrinferni for interesting discussions and the fruitful collaboration over all these years. We wish to acknowledge Giampaolo Piotto for his leading role in the development of photometric studies of MPs in globular clusters. Raffaele Gratton and Alvio Renzini are also warmly acknowledged for interesting discussions and collaborations on this research topic. We thank Nate Bastian and Carmela Lardo for several comments on an early draft of the manuscript. We are grateful to Carmela Lardo also for producing some of the figures. SC acknowledges support from Premiale INAF MITiC, from Istituto Nazionale di Fisica Nucleare (INFN) (Iniziativa specifica TAsP), progetto INAF Mainstream (PI: S. Cassisi), PLATO ASI-INAF agreement n.2015-019-R.1-2018, and grant AYA2013-42781P from the Ministry of Economy and Competitiveness of Spain.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Santi Cassisi.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Cassisi, S., Salaris, M. Multiple populations in massive star clusters under the magnifying glass of photometry: theory and tools. Astron Astrophys Rev 28, 5 (2020). https://doi.org/10.1007/s00159-020-00127-y

Download citation

Keywords

  • Globular clusters: general
  • Infrared: stars
  • opacity
  • Stars: evolution
  • Stars: imaging
  • Ultraviolet: stars