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LOW-RESOLUTION SPECTROSCOPIC STUDIES OF GLOBULAR CLUSTERS WITH MULTIPLE POPULATIONS

  • LIM, DONGWOOK (Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University) ;
  • HAN, SANG-IL (Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University) ;
  • ROH, DONG-GOO (Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University) ;
  • LEE, YOUNG-WOOK (Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University)
  • Received : 2014.11.30
  • Accepted : 2015.06.30
  • Published : 2015.09.30
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Abstract

Recent narrow-band Ca photometry discovered two distinct red giant branch (RGB) populations in some massive globular clusters (GCs) including M22, NGC 1851, and NGC 288. In order to investigate the differences in light/heavy elements abundances between the two subpopulations, we have performed low-resolution spectroscopy for stars on the two RGBs in these GCs. We find a significant difference (more than $4{\sigma}$) in calcium abundance from the spectroscopic HK' index for both M22 and NGC 1851. We also find a more than $8{\sigma}$ difference in CN band strength between the Ca-strong and Ca-weak subpopulations. For NGC 288, however, we detect the presence of a large difference only in the CN strength. The calcium abundances of the two subpopulations in this GC are identical within errors. We also find interesting differences in CN-CH relations among these GCs. While CN and CH indices are correlated in M22, they show an anti-correlation in NGC 288. However, NGC 1851 shows no difference in CH between two groups of stars having different CN strengths. The CN bimodality in these GCs could be explained by pollution from intermediate-mass asymptotic giant branch stars and/or fast-rotating massive stars. For the presence or absence of calcium bimodality and the differences in CN-CH relations, we suggest these would be best explained by how strongly type II supernovae enrichment has contributed to the chemical evolutions of these GCs.

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References

  1. Anthony-Twarog, B. J., Twarog, B. A., Laird, J. B., & Payne, D., 1991, Ca II H and K Filter Photometry on the UVBY System. I - The Standard System, AJ, 101, 1902 https://doi.org/10.1086/115815
  2. Baumgardt, H., Kroupa, P., & Parmentier, G., 2008, The Influence of Residual Gas Expulsion on the Evolution of the Galactic Globular Cluster System and the Origin of the Population II halo, MNRAS, 384, 1231 https://doi.org/10.1111/j.1365-2966.2007.12811.x
  3. Bekki, K. & Yong, D., 2012, On the Origin of the Stellar Halo and Multiple Stellar Populations in the Globular Cluster NGC 1851, MNRAS, 419, 2063 https://doi.org/10.1111/j.1365-2966.2011.19856.x
  4. Carretta, E., Gratton, R. G., & Lucatello, S., et al., 2010, Abundances for a Large Sample of Red Giants in NGC 1851: Hints for a Merger of Two Clusters?, ApJ, 722, L1 https://doi.org/10.1088/2041-8205/722/1/L1
  5. Da Costa, G. S., Held, E. V., Saviane, I., & Gullieuszik, M., 2009, M22: An [Fe/H] Abundance Range Revealed, ApJ, 705, 1481 https://doi.org/10.1088/0004-637X/705/2/1481
  6. Decressin, T., Meynet, G., Charbonnel, C., Prantzos, N., & Ekstrom, S., 2007, Fast Rotating Massive Stars and the Origin of the Abundance Patterns in Galactic Globular Clusters, A&A, 464, 1029 https://doi.org/10.1051/0004-6361:20066013
  7. Harbeck, D., Smith, G. H., & Grebel, E. K., 2003, CN Abundance Variations on the Main Sequence of 47 Tucanae, AJ, 125, 197 https://doi.org/10.1086/345570
  8. Hsyu, T., Johnson, C. I., Lee, Y.-W., & Rich, R. M., 2014, Light-Element Chemistry and the Double Red Giant Branch in the Galactic Globular Cluster NGC 288, PASP, 126, 597
  9. Joo, S. -J. & Lee, Y. -W., 2013, Star Formation Histories of Globular Clusters with Multiple Populations. I. $\omega$ CEN, M22, and NGC 1851, ApJ, 762, 36 https://doi.org/10.1088/0004-637X/762/1/36
  10. Lee, J. -W., Kang, Y. -W., Lee, J., & Lee, Y. -W., 2009, Enrichment by Supernovae in Globular Clusters with Multiple Populations, Nature, 462, 480 https://doi.org/10.1038/nature08565
  11. Lee, Y. -W., Han, S. -I., & Joo, S. -J., et al., 2013, Two Distinct Red Giant Branch Populations in the Globular Cluster NGC 2419 as Tracers of a Merger Event in the Milky Way, ApJ, 778, L13 https://doi.org/10.1088/2041-8205/778/1/L13
  12. Lee, Y. -W., Joo, J. -M., & Sohn, Y. -J., et al., 1999, Multiple Stellar Populations in the Globular Cluster $\omega$ Centauri as tracers of a merger event, Nature, 402, 55 https://doi.org/10.1038/46985
  13. Lim, D., Han, S. -I., & Lee, Y. -W., et al., 2014, Low-Resolution Spectroscopy for the Globular Clusters with Multiple Red Giant Branches: M22, NGC 1851 and NGC 288, ApJS, submitted
  14. Marino, A. F., Milone, A. P., & Piotto, G., et al., 2011, Sodium-Oxygen Anticorrelation and Neutron-capture Elements in Omega Centauri Stellar Populations, ApJ, 731, 64 https://doi.org/10.1088/0004-637X/731/1/64
  15. Norris, J. E., Freeman, K. C., & Mighell, K. J., 1996, The Giant Branch of omega Centauri. V. The Calcium Abundance Distribution, ApJ, 462, 241 https://doi.org/10.1086/177145
  16. Prochaska, J. X., Weiner, B. J., Chen, H. -W., & Mulchaey, J. S., 2006, Probing the Intergalactic Medium-Galaxy Connection toward PKS 0405-123. III. The Galaxy Survey and Correlations with O VI Absorbers, ApJ, 643, 680 https://doi.org/10.1086/503184
  17. Roh, D. -G., Lee, Y. -W., & Joo, S. -J., et al., 2011, ApJ, Two Distinct Red Giant Branches in the Globular Cluster NGC 288, 733, L45 https://doi.org/10.1088/2041-8205/733/2/L45
  18. Siegel, M. H., Dotter, A., & Majewski, S. R., et al., 2007, The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy, ApJ, 667, L57 https://doi.org/10.1086/522003
  19. Timmes, F. X., Woosley, S. E., & Weaver, T. A., 1995, Galactic chemical evolution: Hydrogen through zinc, ApJS, 98, 617 https://doi.org/10.1086/192172
  20. Ventura, P. & D'Antona, F., 2008, Self-enrichment by Asymptotic Giant Branch Stars in Globular Clusters:Comparison Between Intermediate and High Metallicities, MNRAS, 385, 2034 https://doi.org/10.1111/j.1365-2966.2008.12970.x