High-resolution spectroscopy of RGB stars  in the Sagittarius
streams

Monaco, L.; Bellazzini, M.; Bonifacio, P.; Buzzoni, A.; Ferraro, F. R.; Marconi, G.; Sbordone, L.; Zaggia, S.

doi:10.1051/0004-6361:20066228

Cited by 81 publications

(151 citation statements)

References 45 publications

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“…RR Lyrae are generally old Pop II stars, which is consistent with them being stripped from a dwarf galaxy (e.g., Sgr) in an early merger event because the age (>10 Gyr) would allow the star to have been stripped early on. In addition to this, the earlier study by Monaco et al (2007) showed that there is a southern and a northern stream that peak around Last, we consider that m176 is a normal RR Lyrae star located toward the direction of the bulge, which is on the tail of the RR Lyrae star velocity distribution. Its spectroscopic [Fe/H] is expected for a RR Lyrae stars located toward the bulge (e.g., Walker & Terndrup 1991;Pietrukowicz et al 2015), as is its distance from the Galactic center.…”

Section: Chemical Inferences On the Birthplace Of M176mentioning

confidence: 76%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high-or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s −1 . In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ∼-400 km s −1 . Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] = −0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.

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Section: Chemical Inferences On the Birthplace Of M176mentioning

confidence: 76%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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“…What fraction of the stellar population in the Galaxy halo could have been built-up by this mechanism is still, however, a matter of debate. The chemical composition of the oldest, most metalpoor stars in the Milky Way dwarf satellites indeed provides conflicting evidence in this respect (Monaco et al 2007;Aoki et al 2009;Frebel et al 2010).…”

Section: Discussionmentioning

confidence: 99%

The lithium content ofω Centauri

Monaco

Bonifacio

Sbordone

et al. 2010

A&A

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Context.A discrepancy has emerged between the cosmic lithium abundance inferred by the WMAP satellite measurement coupled with the prediction of the standard big-bang nucleosynthesis theory, and the constant Li abundance measured in metal-poor halo dwarf stars (the so-called Spite plateau). Several models are being proposed to explain this discrepancy, involving either new physics, in situ depletion, or the efficient depletion of Li in the pristine Galaxy by a generation of massive first stars. The realm of possibilities may be narrowed considerably by observing stellar populations in different galaxies, which have experienced different evolutionary histories. Aims. The ω Centauri stellar system is commonly considered as the remnant of a dwarf galaxy accreted by the Milky Way. We investigate the lithium content of a conspicuous sample of unevolved stars in this object. Methods. We obtained moderate resolution (R = 17 000) spectra for 91 main-sequence/early sub-giant branch (MS/SGB) ω Cen stars using the FLAMES-GIRAFFE/VLT spectrograph. Lithium abundances were derived by matching the equivalent width of the Li i resonance doublet at 6708 Å to the prediction of synthetic spectra computed with different Li abundances. Synthetic spectra were computed using the SYNTHE code along with ATLAS-9 model atmospheres. The stars effective temperatures are derived by fitting the wings of the H α line with synthetic profiles. Results. We obtain a mean content of A(Li) = 2.19 ± 0.14 dex for ω Centauri MS/SGB stars. This is comparable to what is observed in Galactic halo field stars of similar metallicities and temperatures. Conclusions. The Spite plateau seems to be an ubiquitous feature of old, warm metal-poor stars. It exists also in external galaxies, if we accept the current view about the origin of ω Cen. This implies that the mechanism(s) that causes the "cosmological lithium problem" may be the same in the Milky Way and other galaxies.

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“…Stars in the Sgr dSph stream appear to be slightly less metal rich than those in the main body, with metallicity gradients along the stream (Bellazzini et al 2006b;Clewley & Jarvis 2006;Monaco et al 2007;Chou et al 2007). This would not be unexpected if the most metal poor stars were located in the outskirts of Sgr dSph and then subject to the tidal interaction with the MW.…”

Section: Introductionmentioning

confidence: 99%

A wide angle view of the Sagittarius dwarf spheroidal galaxy

Giuffrida

Sbordone

Zaggia

et al. 2010

A&A

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Context. The Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) provides us with a unique possibility of studying a dwarf galaxy merging event while still in progress. Moving along a short-period, quasi-polar orbit in the Milky Way Halo, Sgr dSph is being tidally dispersed along a huge stellar stream. Due to its low distance (25 kpc), the main body of Sgr dSph covers a vast area in the sky (roughly 15 × 7 degrees). Available photometric and spectroscopic studies have concentrated either on the central part of the galaxy or on the stellar stream, but the overwhelming majority of the galaxy body has never been probed. Aims. The aim of the present study is twofold. On the one hand, to produce color magnitude diagrams across the extension of Sgr dSph to study its stellar populations, searching for age and/or composition gradients (or lack thereof). On the other hand, to derive spectroscopic low-resolution radial velocities for a subsample of stars to determine membership to Sgr dSph for the purpose of high resolution spectroscopic follow-up. Methods. We used VIMOS@VLT to produce V and I photometry on 7 fields across the Sgr dSph minor and major axis, plus 3 more centered on the associated globular clusters Terzan 7, Terzan 8 and Arp 2. A last field has been centered on M 54, lying in the center of Sgr dSph. VIMOS high resolution spectroscopic mode has then been used to derive radial velocities for a subsample of the observed stars, concentrating on objects having colors and magnitudes compatible with the Sgr dSph red giant branch. Results. We present photometry for 320 000 stars across the main body of Sgr dSph, one of the richest, and safely the most wide-angle sampling ever produced for this fundamental object. We also provide robust memberships for more than one hundred stars, whose high resolution spectroscopic analysis will be the object of forthcoming papers. Sgr dSph appears remarkably uniform among the observed fields. We confirm the presence of a main Sgr dSph population characterized roughly by the same metallicity of 47 Tuc, but we also found the presence of multiple populations on the peripheral fields of the galaxy, with a metallicity spanning from [Fe/H] = -2.3 to a nearly solar value.

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High-resolution spectroscopy of RGB stars in the Sagittarius streams

Cited by 81 publications

References 45 publications

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Chemical abundances in a high-velocity RR Lyrae star near the bulge

The lithium content ofω Centauri

A wide angle view of the Sagittarius dwarf spheroidal galaxy

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