Intrinsic iron spread and a new metallicity scale for globular clusters

By E. Carretta, A. Bragaglia, R. Gratton, V. D’Orazi, S. L. I. Bologna, Inaf - Padova, Excellence Cluster Universe, Garching. 2009

495 citations recorded by the source corpus.

We have collected spectra of about 2000 red giant branch (RGB) stars in 19 Galactic globular clusters (GC) using FLAMES@VLT (about 100 stars with GIRAFFE and about 10 with UVES, respectively, in each GC). These observations provide an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We use it to study the cosmic scatter of iron and find that, as far as Fe is concerned, most GCs can still be considered mono-metallic, since the upper limit to the scatter of iron is less than 0.05 dex, meaning that the degree of homogeneity is better than 12%. The scatter in Fe we find seems to have a dependence on luminosity, possibly due to the well-known inadequacies of stellar atmospheres for upper-RGB stars and/or to intrinsic variability. It also seems to be correlated with cluster properties, like the mass, indicating a larger scatter in more massive GCs which is likely a (small) true intrinsic scatter. The 19 GCs, covering the metallicity range of the bulk of Galactic GCs, define an accurate and updated metallicity scale. We provide transformation equations for a few existing scales. We also provide new values of [Fe/H], on our scale, for all GCs in the Harris catalogue.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8ab93186faf4dec15e0316cd6d832b236abe727e

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. R. Gratton
2. E. Carretta
3. A. Bragaglia
4. Timothy C. Beers
5. Jay Anderson
6. Jo Bovy
7. G. Piotto
8. A. Milone

In Instrumentation

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

Citations in the corpus

• Target Selection for the SDSS-IV APOGEE-2 Survey (2017, background): “…Calibration A subset of stars in many of the targeted open and globular clusters have existing multi-element abundance, stellar parameter, and radial velocity derivations from high resolution optical spectroscopy, in many cases homogeneously observed and analyzed (e.g., Carretta et al. 2009b,c).”
• The SUMO project: a SUrvey of Multiple pOpulations in globular clusters (2013, methodology): “In case of NGC 6121, stars with available spectroscopic measurements of Na and O from Marino et al. (2008) and Carretta et al. (2009) are plotted as circles and triangles respectively, while the Na-O nticorrelation determined by these authors is shown in the two insets.”
• Abundance patterns of multiple populations in globular clusters: a chemical evolution model based on yields from AGB ejecta (2010, methodology): “Carretta et al. (2009a) find that the upper limit to the scatter of iron is less than 0.05 dex in the 19 clusters they examine.”
• Multiple populations in globular clusters (2012, methodology): “…al. 2011); NGC 288, NGC 362 (Smith et al. 2009; Carretta et al. 2009a,b); 47 Tuc, NGC 1904, NGC 3201, NGC 4590, NGC 6171, NGC 6254, NGC 6809, NGC 6838, NGC 7078, NGC 7099 (Carretta et al. 2009a,b: these papers present results on the first 19 globular clusters of a survey with FLAMES@VLT, see Fig.”
• THE SEGUE STELLAR PARAMETER PIPELINE. IV. VALIDATION WITH AN EXTENDED SAMPLE OF GALACTIC GLOBULAR AND OPEN CLUSTERS (2010, methodology): “…procedure adopts the following metallicities: M92 ([Fe/H] = −2.35), M15 ([Fe/H] = −2.33), M13 ([Fe/H] = −1.58), and M2 ([Fe/H] = −1.66) from Table A1 in Carretta et al. (2009), NGC 2420 ([Fe/H] = −0.37) from Anthony-Twarog, et al. (2006), M67 ([Fe/H] = +0.05) from Randich et al. (2006), and NGC…”
• THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS (2011, background): “…behaviors of globulars include star-to-star scatter of light element [el/Fe] ratios (for C, N, O, Na, Mg, and Al) in both main sequence and giant stars (this is in contrast to the abundance trends of halo field stars; e.g. Carretta et al. 2009a(18) and Gratton, Sneden, & Carretta 2004(36))1.”
• The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, background): “Most GCs are mono-metallic (Carretta et al. 2009a) , i.e. they have no detectable dispersion in [Fe/H].1 But all clusters studied to date with substantial stellar samples exhibit star-to-star variations in the light elements C, N, O, Na, Mg, and Al.”
• The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “…differences in metallicity and abundance scales adopted by various studies reporting GC ages (e.g. Carretta & Gratton 1997; Kraft & Ivans 2003; Carretta et al. 2009), which in turn affect the GC age measurements (e.g. VandenBerg et al. 2016).21 These may be improved by better measurements of…”
• Synthetic stellar photometry – I. General considerations and new transformations for broad-band systems (2014, methodology): “Interestingly, recent F110W and F160W photometry of two globular clusters (namely, NGC 2808 and M 4, which both have [Fe/H] ' −1.2, e.g., Carretta et al. 2009, making them about 0.4 dex more metal-poor than the isochrones considered here) has revealed that they have split lower main sequences…”
• N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes (2016, methodology): “…al. (2013) LOS Lardo et al. (2015) LOS Watkins et al. (2015a) PM NGC 6809 Carretta et al. (2009b) LOS Lane et al. (2011) LOS NGC 6838 Peterson & Latham (1986) LOS Carretta et al. (2009b) LOS Smolinski et al. (2011) LOS Kimmig et al. (2015) LOS Cordero et al. (2015) LOS Drukier, Fahlman & Richer…”
• Properties of stellar generations in globular clusters and relations with global parameters (2010, methodology): “In summary, in this paper we combine the results of our extensive survey of abundances in RGB stars in 19 GCs (Carretta et al. 2009a,b,c) with previous knowledge of a GC, in order to discuss scenarios for their formation.”
• The second and third parameters of the horizontal branch in globular clusters (2010, methodology): “…magnitude diagrams (CMD) and accurate ages provided by ground (Rosenberg et al. 2000a,b) and space observations (e.g., Piotto et al. 2002), and the extensive data on the Na-O anticorrelation from our FLAMES survey (Carretta et al. 2009a,b and references therein), complemented by literature data.”
• THE SEGUE STELLAR PARAMETER PIPELINE. V. ESTIMATION OF ALPHA-ELEMENT ABUNDANCE RATIOS FROM LOW-RESOLUTION SDSS/SEGUE STELLAR SPECTRA (2010, background): “This statement also holds true for Na and Al, which exhibit star-to-star variations in the GCs (e.g., Carretta et al. 2009a, 2009b; references therein), as the wavelength window for measuring [α/Fe] does not include any strong lines of these two elements.”
• The bifurcated age–metallicity relation of Milky Way globular clusters and its implications for the accretion history of the galaxy (2013, methodology): “Although some studies (e.g., Brown, Wallerstein & Zucker 1997, Pritzl, Venn & Irwin 2005) found [α/Fe] ' 0.0 for Ruprecht 106, they also reported [Fe/H] values that are 0.3–0.4 dex higher than the value ([Fe/H] = −1.78) given by Carretta et al. (2009a).”
• THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. IX. HORIZONTAL BRANCH MORPHOLOGY AND THE SECOND PARAMETER PHENOMENON (2009, background): “However, the recent results from Carretta et al. (2009b, 2009c) lend some insight into the problem of deriving GC ages in the presence of light element abundance variations.”