Resumen
We analyze spectra of 18 stars belonging to the faintest subgiant branch in ω Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution of R 17 000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have [Fe/H] =-0.73 ± 0.14 dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure [α/Fe] = + 0.40 ± 0.16 dex, and [Ba/Fe] = + 0.87 ± 0.23 dex, in general agreement with past studies. It is very interesting to note that we found a uniform Al abundance, [Al/Fe] = + 0.32 ± 0.14 dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of ω Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory. It has also been suggested that the most metal-rich population in ω Cen is significantly enriched in helium. If this is true, the traditional abundance analysis techniques, based on model atmospheres with normal helium content, might lead to errors. We have computed helium enhanced atmospheres for three stars in our sample and verified that the abundance errors due to the use of non-enhanced atmospheres are negligible. Additional, indirect support to the enhanced helium content of the SGB-a population comes from our Li upper limits.
| Idioma original | English |
|---|---|
| Número de artículo | A53 |
| Publicación | Astronomy and Astrophysics |
| Volumen | 534 |
| DOI | |
| Estado | Published - 11 oct 2011 |
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ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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The subgiant branch of ω Centauri seen through high-resolution spectroscopy : II. the most metal-rich population. / Pancino, E.; Mucciarelli, A.; Bonifacio, P.; Monaco, L.; Sbordone, L.
En: Astronomy and Astrophysics, Vol. 534, A53, 11.10.2011.Resultado de la investigación: Article
TY - JOUR
T1 - The subgiant branch of ω Centauri seen through high-resolution spectroscopy
T2 - II. the most metal-rich population
AU - Pancino, E.
AU - Mucciarelli, A.
AU - Bonifacio, P.
AU - Monaco, L.
AU - Sbordone, L.
PY - 2011/10/11
Y1 - 2011/10/11
N2 - We analyze spectra of 18 stars belonging to the faintest subgiant branch in ω Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution of R 17 000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have [Fe/H] =-0.73 ± 0.14 dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure [α/Fe] = + 0.40 ± 0.16 dex, and [Ba/Fe] = + 0.87 ± 0.23 dex, in general agreement with past studies. It is very interesting to note that we found a uniform Al abundance, [Al/Fe] = + 0.32 ± 0.14 dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of ω Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory. It has also been suggested that the most metal-rich population in ω Cen is significantly enriched in helium. If this is true, the traditional abundance analysis techniques, based on model atmospheres with normal helium content, might lead to errors. We have computed helium enhanced atmospheres for three stars in our sample and verified that the abundance errors due to the use of non-enhanced atmospheres are negligible. Additional, indirect support to the enhanced helium content of the SGB-a population comes from our Li upper limits.
AB - We analyze spectra of 18 stars belonging to the faintest subgiant branch in ω Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution of R 17 000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have [Fe/H] =-0.73 ± 0.14 dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure [α/Fe] = + 0.40 ± 0.16 dex, and [Ba/Fe] = + 0.87 ± 0.23 dex, in general agreement with past studies. It is very interesting to note that we found a uniform Al abundance, [Al/Fe] = + 0.32 ± 0.14 dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of ω Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory. It has also been suggested that the most metal-rich population in ω Cen is significantly enriched in helium. If this is true, the traditional abundance analysis techniques, based on model atmospheres with normal helium content, might lead to errors. We have computed helium enhanced atmospheres for three stars in our sample and verified that the abundance errors due to the use of non-enhanced atmospheres are negligible. Additional, indirect support to the enhanced helium content of the SGB-a population comes from our Li upper limits.
KW - Globular clusters: individual:ωCentauri
KW - Stars: abundances
UR - http://www.scopus.com/inward/record.url?scp=80053520383&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201117378
DO - 10.1051/0004-6361/201117378
M3 - Article
AN - SCOPUS:80053520383
VL - 534
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
M1 - A53
ER -