| 41. |
- San Roman, I., et al.
(författare)
-
The Gaia-ESO Survey : Detailed abundances in the metal-poor globular cluster NGC 4372
- 2015
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 579
-
Tidskriftsartikel (refereegranskat)abstract
- We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high-resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 +/- 0.03 and find no evidence of any metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor Galactic globular clusters. We also find an a-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular, we find a Na-O anticorrelation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present that spans a range of more than 0.5 dex in Al abundances. Na is correlated with Al and Mg abundances at a lower significance level. This pattern suggests that the Mg-Al burning cycle is active. This behavior can also be seen in giant stars of other massive, metal-poor clusters. A relation between light and heavy s-process elements has been identified.
|
|
| 42. |
- Tinetti, G., et al.
(författare)
-
A chemical survey of exoplanets with ARIEL
- 2018
-
Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 46:1, s. 135-209
-
Tidskriftsartikel (refereegranskat)abstract
- Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.
|
|
| 43. |
- Koposov, Sergey E., et al.
(författare)
-
Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
- 2015
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 811:1
-
Tidskriftsartikel (refereegranskat)abstract
- We report on VLT/GIRAFFE spectra of stars in two recently discovered ultra-faint satellites, Reticulum 2 and Horologium 1, obtained as part of the Gaia-ESO Survey. We identify 18 members in Reticulum 2 and five in Horologium 1. We find Reticulum 2 to have a velocity dispersion of 3.22(-0.49)(+1.64) km s(-1) , implying a mass-to-light ratio (M/L) of similar to 500. The mean metallicity of Reticulum 2 is [Fe/H] = -2.46, with an intrinsic dispersion of similar to 0.3 dex and alpha-enhancement of similar to 0.4 dex. We conclude that Reticulum 2 is a dwarf galaxy. We also report on the serendipitous discovery of four stars in a previously unknown stellar substructure near Reticulum 2 with [Fe/H] similar to -2 and V-hel similar to 220 km s(-1), far from the systemic velocity of Reticulum 2. For Horologium 1 we infer a velocity dispersion of sigma (V) = 4.9(-0.9)(+2.8) km s(-1) and a M/L ratio of similar to 600, leading us to conclude that Horologium 1 is also a dwarf galaxy. Horologium 1 is slightly more metal-poor than Reticulum 2 ([Fe/H] = -2.76) and is similarly alpha-enhanced: [alpha/Fe] similar to 0.3 dex with a significant spread of metallicities of 0.17 dex. The line-of-sight velocity of Reticulum 2 is offset by 100 km s(-1) from the prediction of the orbital velocity of the Large Magellanic Cloud (LMC), thus making its association with the Cloud uncertain. However, at the location of Horologium 1, both the backward-integrated orbit of the LMC and its halo are predicted to have radial velocities similar to that of the dwarf. Therefore, it is possible that Horologium 1 is or once was a member of the Magellanic family.
|
|
| 44. |
- Ruchti, Gregory, et al.
(författare)
-
The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc
- 2015
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 450:3, s. 2874-2887
-
Tidskriftsartikel (refereegranskat)abstract
- According to our current cosmological model, galaxies like the Milky Way are expected to experience many mergers over their lifetimes. The most massive of the merging galaxies will be dragged towards the disc plane, depositing stars and dark matter into an accreted disc structure. In this work, we utilize the chemodynamical template developed in Ruchti et al. to hunt for accreted stars. We apply the template to a sample of 4675 stars in the third internal data release from the Gaia-ESO Spectroscopic Survey. We find a significant component of accreted halo stars, but find no evidence of an accreted disc component. This suggests that the Milky Way has had a rather quiescent merger history since its disc formed some 8-10 billion years ago and therefore possesses no significant dark matter disc.
|
|
| 45. |
- Schultheis, M., et al.
(författare)
-
The Gaia-ESO Survey: Tracing interstellar extinction
- 2015
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 577
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Large spectroscopic surveys have in recent years enabled computing three-dimensional interstellar extinction maps thanks to the accurate stellar atmospheric parameters and line-of-sight distances these surveys provide. Interstellar extinction maps are complementary to 3D maps extracted from photometry and allow a more thorough studying of the dust properties. Aims. Our goal is to use the high-resolution spectroscopic survey Gaia-ESO to obtain with a good distance resolution the interstellar extinction and its dependency as a function of the environment and the Galactocentric position. Methods. We used the stellar atmospheric parameters of more than 5000 stars, obtained from the Gaia-ESO survey second internal data release, and combined them with optical (SDSS) and near-infrared (VISTA) photometry as well as different sets of theoretical stellar isochrones to calculate line-of-sight extinction and distances. The extinction coefficients were then compared with the literature to discuss their dependency on the stellar parameters and position in the Galaxy. Results. Within the errors of our method, our work does not show any dependence of the interstellar extinction coefficient on the stellar atmospheric parameters. We find no evidence of a variation of E(J - H) = E(J - K) with the angle from the Galactic centre or with Galactocentric distance. This suggests that we are dealing with a uniform extinction law in the SDSS ugriz bands and the near-IR JHKs bands. Therefore, extinction maps built from mean colour-excesses that assume a constant extinction coefficient can be used without introducing any systematic errors.
|
|
| 46. |
- Franchini, Mariagrazia, et al.
(författare)
-
Gaia-ESO Survey : INTRIGOSS-A New Library of High-resolution Synthetic Spectra
- 2018
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 862:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution synthetic spectral library, INTRIGOSS, designed for studying FGK stars. The library is based on atmosphere models computed with specified individual element abundances via ATLAS12 code. Normalized SPectra (NSPs) and surface Flux SPectra (FSP) in the wavelength range 4830-5400 angstrom were computed with the SPECTRUM code. INTRIGOSS uses the solar composition of Grevesse et al. and four [alpha/Fe] abundance ratios, and consists of 15,232 spectra. The synthetic spectra are computed with astrophysical gf-values derived by comparing synthetic predictions with a solar spectrum of very high signal-to-noise ratio and the UVES-U580 spectra of five cool giants. The validity of the NSPs is assessed by using the UVES-U580 spectra of 2212 stars observed in the framework of the Gaia-ESO (European Southern Observatory) survey and characterized by homogeneous and accurate atmospheric parameter values and by detailed chemical compositions. The greater accuracy of NSPs with respect to spectra from the synthetic spectral libraries AMBRE, GES_Grid, PHOENIX, C14, and B17 is demonstrated by evaluating the consistency of the predictions of the different libraries for stars in the UVES-U580 sample. The validity of the FSPs is checked by comparing their prediction with both the observed spectral energy distribution (SED) and spectral indices. The comparison of FSPs with SEDs derived from the libraries ELODIE, INDO-U.S., and MILES indicates that the former reproduce the observed flux distributions within a few per cent and without any systematic trend. The good agreement between observational and synthetic Lick/SDSS (Sloan Digital Sky Survey) indices shows that the predicted blanketing of FSPs well reproduces the observed one, thus confirming the reliability of INTRIGOSS FSPs.
|
|
| 47. |
- Jackson-Jones, R., et al.
(författare)
-
The Gaia-ESO Survey : alpha-abundances of metal-poor stars
- 2014
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 571, s. L5-
-
Tidskriftsartikel (refereegranskat)abstract
- We performed a detailed study of the ratio of low-alpha to high-alpha stars in the Galactic halo as observed by the Gaia-ESO Survey. Using a sample of 381 metal-poor stars from the second internal data release, we found that the value of this ratio did not show evidence of systematic trends as a function of metallicity, surface gravity, Galactic latitude, Galactic longitude, height above the Galactic plane, and Galactocentric radius. We conclude that the alpha(poor)/alpha(rich) value of 0.28 +/- 0.08 suggests that in the inner halo, the larger portion of stars were formed in a high star formation rate environment, and about 15% of the metal-poor stars originated from much lower star formation rate environments.
|
|
