Along with stellar streams, merging galaxies may leave behind a population of globular clusters that were once hosted by the incoming galaxy. For instance, the in vivo example of a satellite accretion, the Sagittarius dwarf galaxy (Ibata, Irwin, & Gilmore 1994) currently merging with the Milky Way carries its own globular cluster system, some of which are still associated with the galaxy remnant (e.g. M54) while others are incorporated in the galactic halo (e.g. NGC 288, NGC 4147) and only traced back to their progenitor through their kinematics. The detailed chemical composition of globular clusters can provide a separate and powerful route to understanding the origin of each cluster.
On the other hand, the actual formation of globular clusters is an never ending puzzle, that took a new turn with the recent discovery that they often host multiple populations and/or signs of internal chemical enrichment (double main sequences most probably related to different He content, multiple subgiant branches that may be related to age-differences, chemical anomalies reflecting self-enrichment within the cluster, and correspondingly varied horizontal-branch morphologies). Here again, the detailed chemical characteristics of the globular cluster stars and their correlations with the cluster physical characteristics (mass, concentration, metallicity, age(s)) are the key to constrain viable scenarios for their formation.
The largest dataset of detailed chemical composition of GCs has so far been assembled by Carretta & Gratton (e.g. Carretta et al. 2007 and references therein), from a sample of FLAMES stellar spectra found in 15 galactic GC. Our group is involved in this project since its begginings. Other projects of our group involve the relative distances, reddenings and ages of the galactic globular clusters, as well as their horizontal branch morphology.
Some related articles to look at:
- “A homogenous set of globular cluster relative distances and reddenings” Recio-Blanco A., Piotto G., De Angeli F., Riello M., Bono G., Cassisi S., Zoccali M.& Aparicio A., 2005, A&A, 432, 851
- “Galactic globular cluster relative ages. II ”
De Angeli, F., Piotto, G., Cassisi, S., Busso, G., Recio-Blanco, A., Salaris, M., Aparicio,
A., Rosenberg, A., 2005, AJ, 130, 116
- “Multivariate analysis of globular cluster horizontal branch morphology: searching for the second parameter problem”
Recio-Blanco, A., Aparicio, A., Piotto, G. and De Angeli, F., Djorgovski, G., 2006, A&A, 452, 875
- “Precise Reddening and Metallicity of NGC6752 from FLAMES spectra”
Gratton, R.G., Bragaglia, A., Carretta, E., Lucatello, S., Momany, Y., Piotto, G., Recio-Blanco, A., 2005, A&A, 442, 947
- “Na-O Anticorrelation and HB I. The Na-O anticorrelation in NGC 2808”
Carretta, E., Bragaglia, A., Gratton, R.G., Leone, F., Recio-Blanco A., Lucatello, S., 2006,
A&A, 450, 523.
- “The Link between Chemical Anomalies along the Red Giant Branch and the Horizontal Branch Extension in Globular Clusters ” Carretta, E.; Recio-Blanco, A; Gratton, R. G.; Piotto, G.; Bragaglia, A., 2007, ApJL, 671, 125
- “Na-O Anticorrelation and HB. VI. The chemical composition of the peculiar bulge globular cluster NGC 6388”
Carretta, E., Bragaglia, A., Gratton, R.G., Momany, Y., Recio-Blanco, A., 2007, A&A,
- “Na-O Anticorrelation and HB. V. The Na-O anticorrelation in NGC 6441 form Giraffe
Gratton, R.G., ..., Recio-Blanco, A. et al., 2007, A&A, 464, 953
- “Metallicities on the double main sequence of Omega Centauri imply large helium enhancement” Piotto G., Villanova S., Bedin L.R., Gratton R.G., Cassisi S., Momany Y., Recio-Blanco A., Lucatello S., Anderson J., King I.R., Pietringerni A., Carraro G., 2004, ApJ, 621, 777
- “The multiplicity of the subgiant branch of ! Centauri: Evidence for prolonged star for-
Villanova, S., Piotto, G., King, I.R., Anderson, J., Bedin L.R., Gratton R.G., Cassisi, S.,
Momany, Y., Bellini, A., Cool, A.M., Recio-Blanco, A., Renzini, A., 2007, ApJ, 663, 296