Context. NGC 6558 is a bulge globular cluster with a blue horizontal branch (BHB), combined with a metallicity of Fe/H ≈ −1.0. It is similar to HP 1 and NGC 6522, which could be among the oldest ...objects in the Galaxy. Element abundances in these clusters could reveal the nature of the first supernovae. Aims. We aim to carry out detailed spectroscopic analysis for four red giants of NGC 6558, in order to derive the abundances of the light elements C, N, O, Na, Al, the α-elements Mg, Si, Ca, Ti, and the heavy elements Y, Ba, and Eu. Methods. High-resolution spectra of four stars with FLAMES-UVES at VLT UT2-Kueyen were analysed. Spectroscopic parameter-derivation was based on excitation and ionization equilibrium of Fe I and Fe II. Results. This analysis results in a metallicity of Fe/H = − 1.17 ± 0.10 for NGC 6558. We find the expected α-element enhancements in O and Mg with O/Fe = +0.40, Mg/Fe = +0.33, and low enhancements in Si and Ca. Ti has a moderate enhancement of Ti/Fe = +0.22. The r-element Eu appears very enhanced with a mean value of Eu/Fe = +0.63. The first peak s-elements Y and Sr are also enhanced, these results have however to be treated with caution, given the uncertainties in the continuum definition; the use of neutral species (Sr I, Y I), instead of the dominant ionized species is another source of uncertainty. Ba appears to have a solar abundance ratio relative to Fe. Conclusions. NGC 6558 shows an abundance pattern that could be typical of the oldest inner bulge globular clusters, together with the pattern in the similar clusters NGC 6522 and HP 1. They show low abundances of the odd-Z elements Na and Al, and of the explosive nucleosynthesis α-elements Si, Ca, and Ti. The hydrostatic burning α-elements O and Mg are normally enhanced as expected in old stars enriched with yields from core-collapse supernovae, and the iron-peak elements Mn, Cu, Zn show low abundances, which is expected for Mn and Cu, but not for Zn. Finally, the cluster trio NGC 6558, NGC 6522, and HP 1 have relatively high abundances of first-peak heavy elements, variable second-peak element Ba, and the r-element Eu is enhanced. The latter is particularly high in NGC 6558.
The all-sky PLATO input catalogue Montalto, M.; Piotto, G.; Marrese, P. M. ...
Astronomy and astrophysics (Berlin),
09/2021, Letnik:
653
Journal Article
Recenzirano
Odprti dostop
Context.
The ESA PLAnetary Transits and Oscillations of stars (PLATO) mission will search for terrestrial planets in the habitable zone of solar-type stars. Because of telemetry limitations, PLATO ...targets need to be pre-selected.
Aims.
In this paper, we present an all sky catalogue that will be fundamental to selecting the best PLATO fields and the most promising target stars, deriving their basic parameters, analysing the instrumental performances, and then planing and optimising follow-up observations. This catalogue also represents a valuable resource for the general definition of stellar samples optimised for the search of transiting planets.
Methods.
We used
Gaia
Data Release 2 astrometry and photometry and 3D maps of the local interstellar medium to isolate FGK (
V
≤ 13) and M (
V
≤ 16) dwarfs and subgiant stars.
Results.
We present the first public release of the all-sky PLATO input catalogue (asPIC1.1) containing a total of 2 675 539 stars including 2 378 177 FGK dwarfs and subgiants and 297 362 M dwarfs. The median distance in our sample is 428 pc for FGK stars and 146 pc for M dwarfs, respectively. We derived the reddening of our targets and developed an algorithm to estimate stellar fundamental parameters (
T
eff
, radius, mass) from astrometric and photometric measurements.
Conclusions.
We show that the overall (internal+external) uncertainties on the stellar parameter determined in the present study are ∼230 K (4%) for the effective temperatures, ∼0.1
R
⊙
(9%) for the stellar radii, and ∼0.1
M
⊙
(11%) for the stellar mass. We release a special target list containing all known planet hosts cross-matched with our catalogue.
Aims. We present the analysis of the α/Fe abundance ratios for a large number of stars at several locations in the Milky Way bulge with the aim of constraining its formation scenario. Methods. We ...obtained FLAMES-GIRAFFE spectra (R = 22 500) at the ESO Very Large Telescope for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b = −4°, b = −6°, b = −12°. Another 176 stars belong to a field containing the globular cluster NGC 6553, located at b = −3° and 5° away from the other three fields along the major axis. Stellar parameters and metallicities for these stars were presented in Zoccali et al. (2008, A&A, 486, 177). We have also re-derived stellar parameters and abundances for the sample of thick and thin disk red giants analyzed in Alves-Brito et al. (2010, A&A, 513, A35). Therefore using a homogeneous abundance database for the bulge, thick and thin disk, we have performed a differential analysis minimizing systematic errors, to compare the formation scenarios of these Galactic components. Results. Our results confirm, with large number statistics, the chemical similarity between the Galactic bulge and thick disk, which are both enhanced in alpha elements when compared to the thin disk. In the same context, we analyze α/Fe vs. Fe/H trends across different bulge regions. The most metal rich stars, showing low α/Fe ratios at b = −4° disappear at higher Galactic latitudes in agreement with the observed metallicity gradient in the bulge. Metal-poor stars (Fe/H < −0.2) show a remarkable homogeneity at different bulge locations. Conclusions. We have obtained further constrains for the formation scenario of the Galactic bulge. A metal-poor component chemically indistinguishable from the thick disk hints for a fast and early formation for both the bulge and the thick disk. Such a component shows no variation, neither in abundances nor kinematics, among different bulge regions. A metal-rich component showing low α/Fe similar to those of the thin disk disappears at larger latitudes. This allows us to trace a component formed through fast early mergers (classical bulge) and a disk/bar component formed on a more extended timescale.
Abstract In this paper we investigate the correlation between the atmospheric perturbations at Paranal Observatory and the Chilean coast tides, which are mostly modulated by the 14-d syzygy ...solar–lunar tidal cycle. To this aim, we downloaded 15 yr (2003–2017) of cloud coverage data from the Aqua satellite, in a matrix that includes also Armazones, the site of the European Extremely Large Telescope. By applying the Fast Fourier transform to these data we detected a periodicity peak of about 14 d. We studied the tide cycle at Chanaral De Las Animas, on the ocean coast, for the year 2017, and we correlated it with the atmospheric perturbations at Paranal and the lunar phases. We found a significant correlation ($96{\rm {per\, cent}}$) between the phenomena of short duration and intensity (1–3 d) and the tidal cycle at Chanaral. We then show that an atmospheric perturbation occurs at Paranal in concomitance with the low tide, which anticipates the full (or the new) moon by 3–4 d. This result allows to improve current weather forecasting models for astronomical observatories by introducing a lunar variable.
Context.
Palomar 6 (Pal6) is a moderately metal-poor globular cluster projected towards the Galactic bulge. A full analysis of the cluster can give hints on the early chemical enrichment of the ...Galaxy and a plausible origin of the cluster.
Aims.
The aim of this study is threefold: a detailed analysis of high-resolution spectroscopic data obtained with the UVES spectrograph at the Very Large Telescope (VLT) at ESO, the derivation of the age and distance of Pal6 from
Hubble
Space Telescope (HST) photometric data, and an orbital analysis to determine the probable origin of the cluster.
Methods.
High-resolution spectra of six red giant stars in the direction of Pal6 were obtained at the 8 m VLT UT2-Kueyen telescope equipped with the UVES spectrograph in FLAMES+UVES configuration. Spectroscopic parameters were derived through excitation and ionisation equilibrium of Fe
I
and Fe
II
lines, and the abundances were obtained from spectrum synthesis. From HST photometric data, the age and distance were derived through a statistical isochrone fitting. Finally, a dynamical analysis was carried out for the cluster assuming two different Galactic potentials.
Results.
Four stars that are members of Pal 6 were identified in the sample, which gives a mean radial velocity of 174.3 ± 1.6 km s
−1
and a mean metallicity of Fe/H = −1.10 ± 0.09 for the cluster. We found an enhancement of
α
-elements (O, Mg, Si, and Ca) of 0.29< X/Fe < 0.38 and the iron-peak element Ti of Ti/Fe ∼ +0.3. The odd-
Z
elements (Na and Al) show a mild enhancement of X/Fe ∼ +0.25. The abundances of both first- (Y and Zr) and second-peak (Ba and La) heavy elements are relatively high, with +0.4 < X/Fe < +0.60 and +0.4 < X/Fe < +0.5, respectively. The r-element Eu is also relatively high with Eu/Fe ∼ +0.6. One member star presents enhancements in N and Al, with Al/Fe > +0.30, this being evidence of a second stellar population, further confirmed with the NaON-Al (anti)correlations. For the first time, we derived the age of Pal 6, which resulted to be 12.4 ± 0.9 Gyr. We also found a low extinction coefficient
R
V
= 2.6 for the Pal 6 projection, which is compatible with the latest results for the highly extincted bulge populations. The derived extinction law results in a distance of 7.67 ± 0.19 kpc from the Sun with an
A
V
= 4.21 ± 0.05. The chemical and photometric analyses combined with the orbital-dynamical analyses point out that Pal 6 belongs to the bulge component probably formed in the main-bulge progenitor.
Conculsions.
The present analysis indicates that the globular cluster Pal 6 is located in the bulge volume and that it was probably formed in the bulge in the early stages of the Milky Way formation, sharing the chemical properties with the family of intermediate metallicity very old clusters M 62, NGC 6522, NGC 6558, and HP 1.
We present the abundance analysis of a sample of more than 120 red giants in the globular cluster (GC) NGC 1851, based on FLAMES spectra. We find a small but detectable metallicity spread. This ...spread is compatible with the presence of two different groups of stars with a metallicity difference of 0.06-0.08 dex, in agreement with earlier photometric studies. If stars are divided into these two groups according to their metallicity, both components show Na-O anticorrelation (signature of a genuine GC nature) of moderate extension. The metal-poor stars are more concentrated than the metal-rich ones. We tentatively propose the hypothesis that NGC 1851 formed from a merger of two individual GCs with a slightly different Fe and {alpha}-element content and possibly an age difference up to 1 Gyr. This is also supported by number ratios of stars on the split subgiant and on the bimodal horizontal branches. The distribution of n-capture process elements in the two components also supports the idea that the enrichment must have occurred in each of the structures separately and not as a continuum of events in a single GC. The most probable explanation is that the proto-clusters formed into a (now dissolved) dwarf galaxy and later merged to produce the present GC.
In this paper, we analyse three sites of great astronomical importance: Mt Graham, Paranal and La Silla. In recent years, with the development of new telescopes, the study of cloud cover is getting ...more and more important for the selection of new sites as well as for the development of existing telescopes. At the moment there is discussion on the techniques used to study climatic conditions. We have mainly two large data sets: satellite data and ground data. The two sets have advantages and disadvantages. We study in detail the various data available and we compare these data and analyse the correlations between them. In particular, we focus on the long-term statistics for the trends in climate change. We use two satellites: GOES (Geostationary Operational Environmental Satellite) and Aqua. In particular, we use the GOES camera data and MODIS (Moderate Resolution Imaging Spectroradiometer) data, which is a key instrument aboard the Aqua satellite. Finally, we use the heliograph ground data of the Columbine weather station to validate the two families of satellite data. The use of such data allows a mutual validation of the results, which allows the analysis to be extended to other sites. We obtained a mean night cloud cover for the 10 yr analysed (2003–2012) of 12 per cent at Paranal, 22 per cent at La Silla and 37 per cent at Mt Graham. We also get a punctual correlation of 96 per cent between the two satellites and of 92 per cent between the satellite and the heliograph data at Mt Graham for 2009.
Context. The globular cluster HP 1 is projected at only 3.̊33 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. Aims. 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. Methods. High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP 1 were obtained with the 8 m 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 Fe i and Fe ii. Results. 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 ≲ +0.35 dex, while Ca and Ti show lower values of −0.04 ≲ Ca,Ti/Fe ≲ +0.28 dex. 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 < +0.43 dex 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.
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 4°.12 4 . ° 12 $ ...4{{\overset{\circ}{.}}}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 −2.0 < Fe/H < −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 v r h = 58.1 ± 1.1 $ {v}^{\mathrm{h}}_{\mathrm{r}} = 58.1 \pm 1.1 $ km s−1, 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.
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