Chemical abundances in LMC stellar populations

Abstract

Aims. We have used FLAMES (the Fibre Large Array Multi Element Spectrograph) at the VLT-UT2 telescope to obtain spectra of a large sample of red giant stars from the inner disk of the LMC, ∼2 kpc from the center of the galaxy. We investigate the chemical abundances of key elements to understand the star formation and evolution of the LMC disk: heavy and light [s-process/Fe] and [α/Fe] give constraints on the time scales of formation of the stellar population. Cu, Na, Sc, and the iron-peak elements are also studied aiming to better understand the build up of the elements of this population and the origin of these elements. We aim to provide a more complete picture of the LMC's evolution by compiling a large sample of field star abundances. Methods. LTE abundances were derived using line spectrum synthesis or equivalent width analysis. We used OSMARCS model atmospheres and an updated line list. The [heavy-s/light-s] ratios are high, showing a slow, increasing trend with metallicity. We were surprised to find an offset for three of the iron-peak elements. We found an offset for the [iron-peak/Fe] ratios of Ni, Cr, and Co, with an underabundant pattern and subsolar values, while Vanadium ratios track the solar value. Copper shows very low abundances in our sample for all metallicities, compatible with those of the Galaxy only for the most metal-poor stars. The overall chemical distributions of this LMC sample indicates a slower star formation history relative to that of the solar neighborhood, with a higher contribution from type Ia supernovae relative to type II supernovae.

Chemical abundances of the LMC cluster Hodge 11 and its surrounding field

“…The derived metallicity is in excellent agreement with the Ca-triplet value of the FORS2 sample (Figure 3 with the results of Pompeia et al (2008) for the LMC field stars (Figure 2). The next step is to obtain high-resolution spectroscopy of a subsample of clusters.…”

“…The abundances for Fe, Ca and Ti were obtained with an LTE (local thermodynamic equilibrium) model-atmosphere analysis. Ca and Ti (α elements) abundances for Hodge 11 ([Fe/H] = −1.9 dex) and field stars are presented in comparison with Pompeia et al (2008) data for the general LMC field (see Figure 2). Black and red points are from UVES and GIRAFFE data, respectively.…”

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

“…The study by Pompéia et al (2008) (Carretta & Gratton 1997). Their RGB stars are >8 Gyr old (Sculptor) and 3−6 Gyr old (Fornax) while LMC RGB stars are mostly young (1−3 Gyr old).…”

The population of X-ray supernova remnants in the Large Magellanic Cloud

“…Abundances of Fe and Si measured with XMM-Newton are in good agreement with the results measured for a different sample of SNRs by Hughes et al (1998) 14 . More recent studies of abundances in the LMC, using large samples of field stars (Cole et al 2005;Pompéia et al 2008;Lapenna et al 2012;Van der Swaelmen et al 2013), can be used to evaluate our results. The metallicity distributions [Fe/H] 15 peak at about −0.5 dex for most field star samples (Lapenna et al 2012), corresponding to 12 + log(Fe/H) = 7.…”