Our view of Globular Clusters has deeply changed in the last decade. Modern spectroscopic and photometric data have
conclusively established that globulars are neither coeval nor monometallic, reopening the issue of the formation of such systems.
Their formation is now schematized as a two-step process, during which the polluted matter from the more massive
stars of a first generation gives birth, in the cluster innermost regions, to a second generation of stars with the characteristic signature of
fully CNO-processed matter.
To date, star-to-star variations in abundances of the light elements (C, N, O, Na) have been observed in stars of all evolutionary phases in
all properly studied Galactic globular clusters. Multiple or broad evolutionary sequences have also been observed in nearly all the clusters that have been observed with good signal-to-noise in the appropriate photometric bands.
The body of evidence suggests that spreads in light-element abundances can be fairly well traced by photometric indices including near
ultraviolet passbands, as CNO abundance variations affect mainly wavelengths shorter than ~400 nm owing to the rise of some NH and CN molecular
absorption bands. Here, we exploit this property of near ultraviolet photometry to trace internal chemical variations and combined it with low resolution spectroscopy aimed to derive carbon and nitrogen abundances in order to maximize the information on the multiple populations.
This approach has been proven to be very effective in (i) detecting multiple population,
(ii) characterizing their global properties (i.e., relative fraction of stars, location in the color-magnitude diagram, spatial distribution, and trends with cluster parameters) and (iii) precisely tagging their chemical properties (i.e., extension of the C-N anticorrelation, bimodalities in the N content).
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:5204 |
| Date | 25 February 2013 |
| Creators | Lardo, Carmela <1984> |
| Contributors | Marano, Bruno |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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