80 research outputs found
Iron-peak elements Sc, V, Mn, Cu and Zn in Galactic bulge globular clusters
Globular clusters are tracers of the history of star formation and chemical
enrichment in the early Galaxy. Their abundance pattern can help understanding
their chemical enrichment processes. In particular, the iron-peak elements have
been relatively little studied so far in the Galactic bulge. The abundances of
iron-peak elements are derived for the sample clusters, and compared with bulge
field, and thick disk stars. We derive abundances of the iron-peak elements Sc,
V, Mn, Cu, and Zn in individual stars of five bulge globular clusters (NGC
6528, NGC 6553, NGC 6522, NGC 6558, HP1), and of the reference thick disk/inner
halo cluster 47 Tucanae (NGC 104). High resolution spectra were obtained with
the UVES spectrograph at the Very Large Telescope over the years. The sample
globular clusters studied span metallicities in the range -1.2<Fe/H]<0.0. V and
Sc appear to vary in lockstep with Fe, indicating that they are produced in the
same supernovae as Fe. We find that Mn is deficient in metal-poor stars,
confirming that it is underproduced in massive stars; Mn-over-Fe steadily
increases at the higher metallicities due to a metallicity-dependent enrichment
by supernovae of type Ia. Cu behaves as a secondary element, indicating its
production in a weak-s process in massive stars. Zn has an alpha-like behaviour
at low metallicities, which can be explained in terms of nucleosynthesis in
hypernovae. At the metal-rich end, Zn decreases with increasing metallicity,
similarly to the alpha-elements.Comment: article resubmitted to Astronomy & Astrophysics, taking into account
referee's comment
High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1
The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic
center. Together with its distance, this makes it one of the most central
globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a
metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest
objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern
of the first stars as well as the early chemical enrichment and early formation
of stellar populations. High-resolution spectra obtained for six stars were
analyzed to derive the abundances of the light elements C, N, O, Na, and Al,
the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba,
La, and Eu.} High-resolution spectra of six red giants that are confirmed
members of the bulge globular cluster HP~1 were obtained with the 8m VLT
UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration.
The spectroscopic parameter derivation was based on the excitation and
ionization equilibrium of FeI and FeII. We confirm a mean metallicity of [Fe/H]
= -1.06~0.10, by adding the two stars that were previously analyzed in HP~1.
The alpha-elements O and Mg are enhanced by about +0.3<[O,Mg/Fe]<+0.5 dex, Si
is moderately enhanced with +0.15<[Si/Fe]<+0.35dex, while Ca and Ti show lower
values of -0.04<[Ca,Ti/Fe]<+0.28dex. The r-element Eu is also enhanced with
[Eu/Fe]~+0.4, which together with O and Mg is indicative of early enrichment by
type II supernovae. Na and Al are low, but it is unclear if Na-O are
anticorrelated. The heavy elements are moderately enhanced, with
-0.20<[La/Fe]<+0.43dex and 0.0<[Ba/Fe]<+0.75~dex, which is compatible with
r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other
hand, appears to be compatible with the spinstar scenario or other additional
mechanisms such as the weak r-process.Comment: 15 pages, 8 figures In press in Astronomy & Astrophysics (2016
A MUSE study of the inner bulge globular cluster Terzan 9: a fossil record in the Galaxy
Context. Moderately metal-poor inner bulge globular clusters are relics of a
generation of long-lived stars that formed in the early Galaxy. Terzan 9,
projected at 4d 12 from the Galactic center, is among the most central globular
clusters in the Milky Way, showing an orbit which remains confined to the inner
1 kpc. Aims. Our aim is the derivation of the cluster's metallicity, together
with an accurate measurement of the mean radial velocity. In the literature,
metallicities in the range between have been estimated for Terzan 9 based on
color-magnitude diagrams and CaII triplet (CaT) lines. Aims. Our aim is the
derivation of the cluster's metallicity, together with an accurate measurement
of the mean radial velocity. In the literature, metallicities in the range
between -2.0 and -1.0 have been estimated for Terzan 9 based on color-magnitude
diagrams and CaII triplet (CaT) lines.
Methods. Given its compactness, Terzan 9 was observed using the Multi Unit
Spectroscopic Explorer (MUSE) at the Very Large Telescope. The extraction of
spectra from several hundreds of individual stars allowed us to derive their
radial velocities, metallicities, and [Mg/Fe]. The spectra obtained with MUSE
were analysed through full spectrum fitting using the ETOILE code.
Results. We obtained a mean metallicity of [Fe/H] -1.10 0.15, a heliocentric
radial velocity of vhr = 58.1 1.1 km/s , and a magnesium-to-iron [Mg/Fe] = 0.27
0.03. The metallicity-derived character of Terzan 9 sets it among the family of
the moderately metal-poor Blue Horizontal Branch clusters HP 1, NGC 6558, and
NGC 6522
CUBES: a UV spectrograph for the future
In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000, although a lower-resolution, sky-limited mode of R ~ 7,000 is also planned. CUBES will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the Phase B dedicated to detailed design and construction. First science operations are planned for 2028. In this paper, we briefly describe the CUBES project development and goals, the main science cases, the instrument design and the project organization and management
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