Photometric signatures of multiple stellar populations in galactic globular clusters

By L. Sbordone, Maurizio Salaris, A. Weiss, S. C. M. F. Astrophysik, G. B. Muenchen, Heidelberg · Germany, G. Paris, Cnrs, U. Diderot, France. and 6 more. 2011

165 citations recorded by the source corpus.

We calculated synthetic spectra for typical chemical element mixtures (i.e., a standard α-enhanced distribution, and distributions displaying CN and ONa anticorrelations) found in the various subpopulations harboured by individual Galactic globular clusters. From the spectra we determined bolometric corrections to the standard Johnson-Cousins and Stromgren filters and finally predicted colours. These bolometric corrections and colour-transformations, coupled to our theoretical isochrones with the appropriate chemical composition, provided us with a complete and self-consistent set of theoretical predictions for the effect of abundance variations on the observed cluster colour–magnitude diagrams. CNO abundance variations affect mainly wavelengths shorter than ∼400 nm owing to the rise of molecular absorption bands in cooler atmospheres. As a consequence, colour and magnitude changes are largest in the blue filters, independently of using broad or intermediate bandpasses. Colour–magnitude diagrams involving uvy and UB filters (and their various possible colour combinations) are therefore best suited to infer photometrically the presence of multiple stellar generations in individual clusters. They are particularly sensitive to variations in the N abundance, with the largest variations affecting the red giant branch (RGB) and lower main sequence (MS). BVI diagrams are expected to display multiple sequences only if the different populations are characterized by variations of the C+N+ Os um and/or helium abundance that lead to changes in luminosity and effective temperature, but leave the flux distribution above 400 nm practically unaffected. A variation of just the helium abundance up to the level we investigate here exclusively affects the interior structure of stars, and is largely irrelevant for the atmospheric structure and the resulting flux distribution in the whole wavelength range spanned by our analysis.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/87d6607e2b3ce80bc4b1d14ebbd2331f9f8e0368

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Jay Anderson
2. G. Piotto
3. A. Milone
4. L. Bedin
5. C. Conroy
6. Aaron Dotter
7. R. Gratton
8. E. Carretta

In Instrumentation

1. Jay Anderson
2. G. Piotto
3. F. D’Antona
4. L. Bedin
5. A. Milone
6. R. Gratton
7. E. Carretta
8. A. Bragaglia

Citations in the corpus

• The ACS survey of Galactic globular clusters. XII. Photometric binaries along the main sequence (2011, background): “In general the MSs cor- responding to the different stellar populations observed in the majority of GCs (and hence formed by stars that could have dif- ferent overall CNO abundance, and light elements variations) are almost overimposed when observed in themF606W−mF814W color (Sbordone et al. 2011).”
• Multiple populations in globular clusters (2012, methodology): “Sbordone et al. (2011) used theoretical computations to show the effects of different chemical compositions in the observed colour-magnitude diagrams in the Johnson and Strömgren systems.”
• The SUMO project: a SUrvey of Multiple pOpulations in globular clusters (2013, background): “…range; v) a self-consistent study of the HB morphology; vi) identification of spectroscopic targets for future follow-ups; vii) new theoretical models will have to be developed, with ad-hoc chemical mixtures and the proper model atmospheres, following the pioneering work of Sbordone et al. (2011).”
• Synthetic stellar photometry – I. General considerations and new transformations for broad-band systems (2014, background): “We defer to a future investigation a more detailed exploration of the effects of chemical abundances on colours, in particular accounting for the anti-correlations observed in many globular clusters (e.g., Sbordone et al. 2011).”
• A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752 (2013, methodology): “It is worth noting that the observed light-element difference among the three stellar populations have a negligible effect for filters redder than ∼4000Åas already shown by Sbordone et al. (2011).”
• Evolutionary stellar population synthesis with MILES – II. Scaled-solar and α-enhanced models (2015, background): “Due to the impact on the SED of molecular bands associated with both C and N (see the detailed discussion made by Sbordone et al. 2011 and Cassisi et al. 2013), one might anticipate that the light-element (anti) correlations characteristic of the second generation stars in GGCs will affect the…”
• MULTIPLE STELLAR POPULATIONS IN 47 Tucanae (2011, background): “…attributed to differences in helium content (e.g., Norris 2004; D’Antona et al. 2005; Piotto et al. 2005, 2007) or in lightelement abundances (e.g., Sbordone et al. 2011), so we will explore both of these possibilities by making three different (A color version of this figure is available in the…”
• A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808 (2019, background): “This population has been considered as the most He-enhanced population in NGC 2808 (Milone et al. 2015) and stars having different helium content also have different Teff and log g at a given luminosity (Sbordone et al. 2011).”
• THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS (2014, background): “The photometric appearance of multiple populations strongly depends on the adopted photometric bands (Sbordone et al. 2011, Cassisi et al. 2013).”
• THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED METHOD ALONG WITH COLOR–MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES (2013, background): “…elements affect the H-R diagram locations and morphologies of isochrones, but uv photometry (preferably narrow-band, perhaps centered on a suitable spectral feature) appears to be needed to detect CMD splittings due to O–Na or Mg–Al anticorrelations (see Sbordone et al. 2011, Cassisi et al. 2013).”