The Carina Project

Abstract

We have performed a new abundance analysis of Carina red giant (RG) stars from spectroscopic data collected with UVES (high spectral resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high-resolution) and ∼800 (medium-resolution) RGs, covering a significant fraction of the galaxy's RG branch, and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins. The spectra of the stars belonging to the same gravity and temperature bin were stacked. This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit (V ≥ 20.5 mag) by at least a factor of five. We took advantage of the new photometry index c U,B,I introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean iron abundances are −2.15 ± 0.06 dex (σ = 0.28), and −1.75 ± 0.03 dex (σ = 0.21), respectively. The two iron distributions differ at the 75% level. This supports preliminary results. Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of −1.91 ± 0.05 dex (σ = 0.22) and −1.35 ± 0.03 dex (σ = 0.22); these differ at the 83% level. Carina's α-element abundances agree, within 1σ, with similar abundances for field halo stars and for cluster (Galactic and Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite different from that in the globular clusters.

On THE RR LYRAE STARS IN GLOBULARS. IV. Ω CENTAURI OPTICAL UBVRI PHOTOMETRY*

“…Note that we did not apply any selection criterion on the number of RRLs in building up this sample. We ended up with a sample of 1306RRab, 50RRd and 369RRc with iron abundances ranging from [Fe/H] = −2.6 to [Fe/H] = −1.4 (McConnachie 2012; Kirby et al 2013;Fabrizio et al 2015).…”

Inclusion of horizontal branch stars in the derivation of star formation histories of dwarf galaxies: The Carina dSph

“…This relation was determined assuming a fixed metal mixture with Several high resolution spectroscopic investigations of Carina have found a large spread in the abundance of elements like Ca and Mg, which has been explained as evidence of inhomogeneous mixing of the gas phase Lemasle et al 2012;Venn et al 2012;Fabrizio et al 2015). In particular, the bulk of the [Ca/Fe] measurements range from ∼+0.3 to slightly subsolar values.…”

The Carnegie-Chicago Hubble Program: Discovery of the Most Distant Ultra-faint Dwarf Galaxy in the Local Universe∗

“…This new system looks much fainter and smaller than any other typical dwarf galaxies in the Fornax cluster (Ferguson 1989;Mieske et al 2007;Muñoz et al 2015). This system turns out to be, indeed, a new UFD, named as Fornax UFD1, as shown below.…”

“…In Figure 2 we overlayed 12 Gyr isochrones for [α/Fe]=0.2 (Fabrizio et al 2015) and [Fe/H] = −2.4 to -0.4 in the Dartmouth model (Dotter et al 2008), which were shifted according to the distance and foreground reddening for Fornax UFD1. Although the number of stars is small, the RGB of UFD1 is, on average, bluer and narrower compared with the RGB of NGC 1316 in the control field.…”

“…We list basic parameters of Fornax UFD1 in Table 1. Ferguson (1989) published the Fornax Cluster Catalog (FCC) based on the wide field photographic survey of Fornax galaxies. Following this, several studies used CCD images to find new fainter galaxies in Fornax and investigate their properties (Kambas et al 2000;Hilker et al 2003;Mieske et al 2007;Muñoz et al 2015).…”