| 1. |
- Miglio, A., et al.
(författare)
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PLATO as it is : A legacy mission for Galactic archaeology
- 2017
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : WILEY-V C H VERLAG GMBH. - 0004-6337 .- 1521-3994. ; 338:6, s. 644-661
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Tidskriftsartikel (refereegranskat)abstract
- Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but it will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental prerequisite to then reach the more ambitious goal of a similar level of accuracy, which will be possible only if we have at hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal that conveniently falls within the main aims of PLATO's core science. We therefore strongly endorse PLATO's current design and proposed observational strategy, and conclude that PLATO, as it is, will be a legacy mission for Galactic archaeology.
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| 2. |
- Barbuy, B., et al.
(författare)
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Light elements Na and Al in 58 bulge spheroid stars from APOGEE
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 526:2, s. 2365-2376
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Tidskriftsartikel (refereegranskat)abstract
- We identified a sample of 58 candidate stars with metallicity [Fe/H]-0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20 per cent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H]-1.0. For the lower-metallicity end ([Fe/H <-2.5), hypernovae are assumed to be the main contributor to yields.
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| 3. |
- Bonifacio, P., et al.
(författare)
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First stars XII. Abundances in extremely metal-poor turnoff stars, and comparison with the giants
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 501:2, s. 519-530
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Tidskriftsartikel (refereegranskat)abstract
- Context. The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. Aims. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turno. stars. Methods. VLT/UVES spectra at R similar to 45 000 and S/N similar to 130 per pixel (lambda lambda 330-1000 nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. Results. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are similar to 0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are similar to 0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again similar to 0.4 dex higher than in giants of similar [Fe/H] (6 stars only). Conclusions. For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.
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| 4. |
- Cayrel, R., et al.
(författare)
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Determination of [O/Fe] in BD +23 3130 from ESO VLT-UVES observations
- 2001
-
Ingår i: New Astronomy Reviews. - 1872-9630. ; 45:8, s. 533-535
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Tidskriftsartikel (refereegranskat)abstract
- We report a new determination of [O/Fe, the relative logarithmicabundance of O/Fe with respect to the Sun, for the very metal-poor starBD+23 3130 ([Fe/H=-2.6). The value was derived from the forbidden line[O I at 630 nm and from six weak Fe II lines, with a S/N ratiosubstantially larger than those obtained before, thanks to theefficiency of the VLT-UVES instrument at Paranal. We obtain[O/Fe=0.71+/-0.25, a value 0.36 dex higher than the value obtained fromthe same lines by Fulbright and Kraft [AJ 118 (1999) 527, but 0.46lower than the one derived by Israelian et al. [ApJ 507 (1998) 805 fromthe UV OH bands.
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| 5. |
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| 6. |
- Cayrel, R., et al.
(författare)
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First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
- 2004
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 416:3, s. 1117-1138
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of the ESO Large Programme ``First Stars'', veryhigh-quality spectra of some 70 very metal-poor dwarfs and giants wereobtained with the ESO VLT and UVES spectrograph. These stars are likelyto have descended from the first generation(s) of stars formed after theBig Bang, and their detailed composition provides constraints on issuessuch as the nature of the first supernovae, the efficiency of mixingprocesses in the early Galaxy, the formation and evolution of the haloof the Galaxy, and the possible sources of reionization of the Universe.This paper presents the abundance analysis of an homogeneous sample of35 giants selected from the HK survey of Beers et al. (cite{BPS92},cite{Be99}), emphasizing stars of extremely low metallicity: 30 of our35 stars are in the range -4.1 <[Fe/H]< -2.7, and 22 stars have[Fe/H] < -3.0. Our new VLT/UVES spectra, at a resolving power ofR∼45 000 and with signal-to-noise ratios of 100-200 per pixel overthe wavelength range 330-1000 nm, are greatly superior to those of theclassic studies of McWilliam et al. (cite{MPS95}) and Ryan et al.(cite{RNB96}).The immediate objective of the work is to determine precise,comprehensive, and homogeneous element abundances for this large sampleof the most metal-poor giants presently known. In the analysis wecombine the spectral line modeling code ``Turbospectrum'' with OSMARCSmodel atmospheres, which treat continuum scattering correctly and thusallow proper interpretation of the blue regions of the spectra, wherescattering becomes important relative to continuous absorption (λ< 400 nm). We obtain detailed information on the trends of elementalabundance ratios and the star-to-star scatter around those trends,enabling us to separate the relative contributions of cosmic scatter andobservational/analysis errors.Abundances of 17 elements from C to Zn have been measured in all stars,including K and Zn, which have not previously been detected in starswith [Fe/H] < -3.0. Among the key results, we discuss the oxygenabundance (from the forbidden [OI] line), the different and sometimescomplex trends of the abundance ratios with metallicity, the very tightrelationship between the abundances of certain elements (e.g., Fe andCr), and the high [Zn/Fe] ratio in the most metal-poor stars. Within theerror bars, the trends of the abundance ratios with metallicity areconsistent with those found in earlier literature, but in many cases thescatter around the average trends is much smaller than found in earlierstudies, which were limited to lower-quality spectra. We find that thecosmic scatter in several element ratios may be as low as 0.05 dex.The evolution of the abundance trends and scatter with decliningmetallicity provides strong constraints on the yields of the firstsupernovae and their mixing into the early ISM. The abundance ratiosfound in our sample do not match the predicted yields frompair-instability hypernovae, but are consistent with element productionby supernovae with progenitor masses up to 100 M⊙.Moreover, the composition of the ejecta that have enriched the matterBased on observations obtained in the frame of the ESO programme ID165.N-0276(A).Full Tables 3 and 8 are available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/1117 This work hasmade use of the SIMBAD database.
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| 7. |
- Cayrel, R., et al.
(författare)
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Measurement of stellar age from uranium decay
- 2001
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 409:6821, s. 691-692
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Tidskriftsartikel (refereegranskat)abstract
- The ages of the oldest stars in the Galaxy indicate when star formationbegan, and provide a minimum age for the Universe. Radioactive dating ofmeteoritic material and stars relies on comparing the present abundanceratios of radioactive and stable nuclear species to the theoreticallypredicted ratios of their production. The radioisotope 232Th(half-life 14Gyr) has been used to date Galactic stars, but it decays byonly a factor of two over the lifetime of the Universe. 238U(half-life 4.5Gyr) is in principle a more precise age indicator, buteven its strongest spectral line, from singly ionized uranium at awavelength of 385.957nm, has previously not been detected in stars. Herewe report a measurement of this line in the very metal-poor starCS31082-0018, a star which is strongly overabundant in itsheavy elements. The derived uranium abundance, log(U/H) = -13.7 +/- 0.14+/- 0.12 yields an age of 12.5 +/- 3Gyr, though this is still modeldependent. The observation of this cosmochronometer gives the mostdirect age determination of the Galaxy. Also, with improved theoreticaland laboratory data, it will provide a highly precise lower limit to theage of the Universe.
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| 8. |
- Depagne, E., et al.
(författare)
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First Stars. II. Elemental abundances in the extremely metal-poor star CS 22949--037. A diagnostic of early massive supernovae
- 2002
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 390:1, s. 187-198
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Tidskriftsartikel (refereegranskat)abstract
- CS 22949-037 is one of the most metal-poor giants known ([Fe/H]~-4.0),and it exhibits large overabundances of carbon and nitrogen (Norris etal.). Using VLT-UVES spectra of unprecedented quality, regardingresolution and S/N ratio, covering a wide wavelength range (from lambda= 350 to 900 nm), we have determined abundances for 21 elements in thisstar over a wide range of atomic mass. The major new discovery is anexceptionally large oxygen enhancement, [O/Fe] = 1.97+/-0.1, as measuredfrom the [O I] line at 630.0 nm. We find an enhancement of [N/Fe] of2.56+/- 0.2, and a milder one of [C/Fe] = 1.17+/-0.1, similar to thosealready reported in the literature. This implies Zstar =0.01Zsun. We also find carbon isotopic ratios12C/13C =4+/-2.0 and 13C/14N=0.03 +0.035-0.015, close to the equilibrium valueof the CN cycle. Lithium is not detected. Na is strongly enhanced([Na/Fe] = +2.1 +/- 0.2), while S and K are not detected. Thesilicon-burning elements Cr and Mn are underabundant, while Co and Znare overabundant ([Zn/Fe]=+0.7). Zn is measured for the first time insuch an extremely metal-poor star. The abundances of the neutron-captureelements Sr, Y, and Ba are strongly decreasing with the atomic number ofthe element: [Sr/Fe] ~ +0.3, [Y/Fe] ~ -0.1, and [Ba/Fe] ~ -0.6. Amongpossible progenitors of CS 22949-037, we discuss the pair-instabilitysupernovae. Such very massive objects indeed produce large amounts ofoxygen, and have been found to be possible sources of primary nitrogen.However, the predicted odd/even effect is too large, and the predictedZn abundance much too low. Other scenarios are also discussed. Inparticular, the yields of a recent model (Z35Z) from Heger and Woosleyare shown to be in fair agreement with the observations. The onlydiscrepant prediction is the very low abundance of nitrogen, possiblycurable by taking into account other effects such as rotationallyinduced mixing. Alternatively, the absence of lithium in our star, andthe values of the isotopic ratios 12C/13C and13C/14N close to the equilibrium value of the CNcycle, suggest that the CNO abundances now observed might have beenaltered by nuclear processing in the star itself. A 30-40Msun supernova, with fallback, seems the most likelyprogenitor for CS 22949-037. Based on observations made with the ESOVery Large Telescope at Paranal Observatory, Chile (programme ID165.N-0276(A)).
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| 9. |
- Ernandes, H., et al.
(författare)
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Reanalysis of neutron-capture elements in the benchmark r-rich star CS 31082-001
- 2023
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 524:1, s. 656-677
-
Tidskriftsartikel (refereegranskat)abstract
- We revisit the abundances of neutron-capture elements in the metal-poor ([Fe/H] = -2.9) r-process-rich halo star CS 31082-001. Partly motivated by the development of the new near-ultraviolet Cassegrain U-band Efficient Spectrograph for the Very Large Telescope, we compiled an expanded line list for heavy elements over the range 3000-4000 Å, including hyperfine structure for several elements. Combining archival near-ultraviolet spectra of CS 31082-001 from the Hubble Space Telescope and the Very Large Telescope, we investigate the abundances and nucleosynthesis of 35 heavy elements (Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Os, Ir, Pt, Pb, Bi, Th, and U). Our analysis includes the first abundance estimates for tin, holmium, and ytterbium from these data, and the first for lutetium from ground-based data, enabling a more complete view of the abundance pattern of this important reference star. In general, the r-process-dominated elements are as enhanced as those in the Sun, particularly for elements with Z ≥ 56 (Ba and heavier). However, the abundances for the lighter elements in our sample, from Ge to Sn (31 ≤ Z ≤ 50), do not scale with the solar abundance pattern. Moreover, the Ge abundance is deficient relative to solar, indicating that it is dominantly an iron-peak rather than neutron-capture element. Our results (or upper limits) on Sn, Pt, Au, Pb, and Bi all pose further questions, prompting further study on the origin and evolution of the known r-rich and actinide-rich, metal-poor stars.
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| 10. |
- François, P., et al.
(författare)
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First Stars. III. A detailed elemental abundance study of four extremely metal-poor giant stars
- 2003
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 403:3, s. 1105-1114
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports detailed abundance analyses for four extremelymetal-poor (XMP) giant stars with [Fe/H]<-3.8, based onhigh-resolution, high-S/N spectra from the ESO VLT (Kueyen/UVES) and LTEmodel atmosphere calculations. The derived [alpha /Fe] ratios in oursample exhibit a small dispersion, confirming previous findings in theliterature, i.e. a constant overabundance of the alpha -elements with avery small (if any) dependence on [Fe/H]. In particular, the very smallscatter we determine for [Si/Fe] suggests that this element shows aconstant overabundance at very low metallicity, a conclusion which couldnot have been derived from the widely scattered [Si/Fe] values reportedin the literature for less metal-poor stars. For the iron-peak elements,our precise abundances for the four XMP stars in our sample confirm thedecreasing trend of Cr and Mn with decreasing [Fe/H], as well as theincreasing trend for Co and the absence of any trend for Sc and Ni. Incontrast to the significant spread of the ratios [Sr/Fe] and [Ba/Fe], wefind [Sr/Ba] in our sample to be roughly solar, with a much lowerdispersion than previously found for stars in the range -3.5 < [Fe/H]< -2.5.Based on observations made with the ESO Very Large Telescope at ParanalObservatory, Chile (Large Programme ID 165.N-0276(A)).The complete version of Table 5 is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp:/ /cdsweb.u-strasbg.fr/cgi-bin/qcat?J /A+A/403/1105
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| 11. |
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| 12. |
- Geisler, D., et al.
(författare)
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CAPOS : The bulge Cluster APOgee Survey I. Overview and initial ASPCAP results
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools. Aims. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [alpha/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods. CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results. We derive mean [Fe/H] values of -0.85 +/- 0.04 (Terzan 2), -1.40 +/- 0.05 (Terzan 4), -1.20 +/- 0.10 (HP 1), -1.40 +/- 0.07 (Terzan 9), -1.07 +/- 0.09 (Djorg 2), -1.06 +/- 0.06 (NGC 6540), and -1.11 +/- 0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [alpha/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances of the iron-peak elements Mn and Ni and compare their trends with field populations. Conclusions. CAPOS is proving to be an unprecedented resource for greatly improving our knowledge of the formation and evolution of BGCs and the bulge itself.
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| 13. |
- Hill, V., et al.
(författare)
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First stars. I. The extreme r-element rich, iron-poor halo giant CS31082-001. Implications for the r--process site(s) and radioactive cosmochronology
- 2002
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 387:2, s. 560-579
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Forskningsöversikt (refereegranskat)abstract
- We present a high-resolution ( R= 75 000, S/ N ) spectroscopic analysis of the bright ( V= 11.7), extreme halo giant CS 31082-001([Fe/H] = -2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We find CS 31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS 22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the first time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements (44 counting Hydrogen) are reported in CS 31082-001, almost half of the entire periodic table. The main atmospheric parameters of CS 31082-001 are as follows: K, (cgs), [Fe/H] = -2.9 (in LTE), and microturbulence 1.8 0.2 km s -1. Carbon and nitrogen are not significantly enhanced relative to iron. As usual in giant stars, Li is depleted by dilution ( (Li/H) = 0.85). The -elements show the usual enhancements with respect to iron, with [O/Fe] (from [O I] 6300 Å), [Mg/Fe] , [Si/Fe] , and [Ca/Fe] , while [Al/Fe] is near -0.5. The r-process elements show unusual patterns: among the lightest elements ( 40), Sr and Zr follow the Solar r-element distribution, but Ag is down by 0.8 dex. All elements with 56 Z 72 follow the Solar r-element pattern, reduced by about 1.25 dex. Accordingly, the [ r/Fe] enhancement is about +1.7 dex (a factor of 50), very similar to that of CS 22892-052. Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. In CS 31082-001, log(Th/Eu) is , higher than in the Solar System (-0.46) or in CS 22892-052 (-0.66). If CS 31082-001 and CS 22892-052 have similar ages, as expected for two extreme halo stars, this implies that the production ratios were different by about 0.4 dex for the two objects. Conversely, if the Th/Eu production ratio were universal, an age of 15 Gyr for CS 22892-052 would imply a negative age for CS 31082-001. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 Z 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating, for two reasons: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238U and 232Th is more robustly predicted than the 151Eu/ 232Th ratio. Our current best estimate for the age of CS 31082-001 is Gyr. However, the computed actinide production ratios should be verified by observations of daughter elements such as Pb and Bi in the same star, which are independent of the subsequent history of star formation and nucelosynthesis in the Galaxy.
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| 14. |
- Plez, B., et al.
(författare)
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Lead abundance in the uranium star CS 31082-001
- 2004
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 428:1, s. 9-12
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Tidskriftsartikel (refereegranskat)abstract
- In a previous paper we were able to measure the abundance of uranium andthorium in the very-metal poor halo giant BPS CS31082-001, but only obtained an upper limit for the abundanceof lead (Pb). We have got from ESO 17 h of additional exposure on thisstar in order to secure a detection of the minimum amount of leadexpected to be present in CS 31082-001, the amountarising from the decay of the original content of Th and U in the star.We report here this successful detection. We find an LTE abundancelog(Pb/H)+12=-0.55 ± 0.15 dex, one dex below the upper limitsgiven by other authors for the similar stars CS22892-052 and BD +17°3248, alsoenhanced in r-process elements. From the observed present abundances ofTh and U in the star, the expected amount of Pb produced by the decay of232Th, and 238U alone, over 12-15 Gyr is-0.73± 0.17 dex. The decay of 235U is more difficultto estimate, but is probably slightly below the contribution of238U, making the contribution of the 3 actinides onlyslightly below, or even equal to, the measured abundance. Thecontribution from the decay of 234U has was not included, forlack of published data. In this sense our determination is a lower limitto the contribution of actinides to lead production. We comment thisresult, and we note that if a NLTE analysis, not yet possible, doublesour observed abundance, the decay of the 3 actinides will stillrepresent 50 per cent of the total lead, a proportion higher than thevalues considered so far in the literature.Based on observations obtained with the Very Large Telescope of theEuropean Southern Observatory at Paranal, Chile.
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| 15. |
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| 16. |
- Sivarani, T., et al.
(författare)
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First stars IV. CS 29497-030: Evidence for operation of the s-process at very low metallicity
- 2004
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 413:3, s. 65-1073
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Forskningsöversikt (refereegranskat)abstract
- We present an abundance analysis of the very metal-poor, carbon-enhancedstar CS 29497-030. Our results indicate that this unusually hot turnoffstar (Teff = 6650 K, log g = 3.5) has a metallicity [Fe/H] =-2.8, and exhibits large overabundances of carbon ([C/Fe] = +2.38),nitrogen ([N/Fe] = +1.88), and oxygen ([O/Fe] = +1.67). This star alsoexhibits a large enhancement in its neutron-capture elements; thepattern follows that expected to arise from the s-process. Inparticular, the Pb abundance is found to be very high with respect toiron ([Pb/Fe] = +3.5), and also with respect to the second peaks-process elements (e.g., Ba, La, Ce, Nd), which fits into the newlyintroduced classification of lead (Pb) stars. The known spectroscopicbinary status of this star, along with the observed s-process abundancepattern, suggest that it has accreted matter from a companion, whichformerly was an Asymptotic Giant-Branch (AGB) star. In a preliminaryanalysis, we have also identified broad absorption lines of metallicspecies that suggest a large axial rotational velocity for this star,which may be the result of spin-up associated with the accretion ofmaterial from its previous AGB companion. In addition, this star isclearly depleted in the light element Li. When considered along with itsrather high inferred temperature, these observations are consistent withthe expected properties of a very low metallicity halo blue straggler.Based on observations made with the ESO Very Large Telescope at ParanalObservatory, Chile (program ID 165.N-0276(A)).Table ef{tab6} is only available in electronic form athttp://www.edpsciences.org
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| 17. |
- Sivarani, T., et al.
(författare)
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First stars X. The nature of three unevolved carbon-enhanced metal-poor stars
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 459:1, s. 125-135
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Tidskriftsartikel (refereegranskat)abstract
- Context. On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population. Aims. We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis. Methods. From high-resolution VLT/UVES spectra (R similar to 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as C-12/C-13 isotopic ratios. Results. All three stars have -3.30 <= [Fe/H]<= -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([O/Fe] = +2.35) and in CS 22958-042 ([O/Fe] = +1.35). All three stars exhibit [Sr/Fe] < 0; Ba is not detected in CS 22958-042 ([Ba/Fe] < -0.53),but it is moderately enhanced ([Ba/Fe] similar to 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([Na/Fe] = +2.8). CS 22958-042 has C-12/C-13 = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while C-12/C-13 = 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) similar to 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042. Conclusions. CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars.
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| 18. |
- Souza, S. O., et al.
(författare)
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Chrono-chemodynamical analysis of the globular cluster NGC 6355 : Looking for the fundamental bricks of the Bulge
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- The information on Galactic assembly time is imprinted on the chemodynamics of globular clusters. This makes them important probes that help us to understand the formation and evolution of the Milky Way. Discerning between in-situ and ex-situ origin of these objects is difficult when we study the Galactic bulge, which is the most complex and mixed component of the Milky Way. To investigate the early evolution of the Galactic bulge, we analysed the globular cluster NGC 6355. We derived chemical abundances and kinematic and dynamic properties by gathering information from high-resolution spectroscopy with FLAMES-UVES, photometry with the Hubble Space Telescope, and Galactic dynamic calculations applied to the globular cluster NGC 6355. We derive an age of 13:2 ± 1:1 Gyr and a metallicity of [Fe/H] =-1:39 ± 0:08 for NGC 6355, with α-enhancement of [α/Fe] = +0:37 ± 0:11. The abundance pattern of the globular cluster is compatible with bulge field RR Lyrae stars and in-situ well-studied globular clusters. The orbital parameters suggest that the cluster is currently confined within the bulge volume when we consider a heliocentric distance of 8:54 ± 0:19 kpc and an extinction coefficient of RV = 2:84 ± 0:02. NGC 6355 is highly likely to come from the main bulge progenitor. Nevertheless, it still has a low probability of being formed from an accreted event because its age is uncertain and because of the combined [Mg/Mn] [Al/Fe] abundance. Its relatively low metallicity with respect to old and moderately metal-poor inner Galaxy clusters may suggest a low-metallicity floor for globular clusters that formed in-situ in the early Galactic bulge.
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| 19. |
- Spite, M., et al.
(författare)
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First stars IX - Mixing in extremely metal-poor giants. Variation of the C-12/C-13, [Na/Mg] and [Al/Mg] ratios
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 455:1, s. 291-301
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Tidskriftsartikel (refereegranskat)abstract
- Context. Extremely metal-poor (EMP) stars preserve a fossil record of the composition of the ISM when the Galaxy formed. It is crucial, however, to verify whether internal mixing has modified their surface composition, especially in the giants where most elements can be studied. Aims. We aim to understand the CNO abundance variations found in some, but not all EMP field giants analysed earlier. Mixing beyond the first dredge-up of standard models is required, and its origin needs clarification. Methods. The C-12/C-13 ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters and should be uniformly high in near-primordial gas. We have measured C-12 and C-13 abundances in 35 EMP giants (including 22 with [Fe/H] < -3.0) from high-quality VLT/UVES spectra analysed with LTE model atmospheres. Correlations with other abundance data are used to study the depth of mixing. Results. The C-12/C-13 ratio is found to correlate with [C/Fe] (and Li/H), and clearly anti-correlate with [N/Fe], as expected if the surface abundances are modified by CNO processed material from the interior. Evidence for such deep mixing is observed in giants above log L/L-circle dot = 2.6, brighter than in less metal-poor stars, but matching the bump in the luminosity function in both cases. Three of the mixed stars are also Na- and Al-rich, another signature of deep mixing, but signatures of the ON cycle are not clearly seen in these stars. Conclusions. Extra mixing processes clearly occur in luminous RGB stars. They cannot be explained by standard convection, nor in a simple way by rotating models. The Na- and Al-rich giants could be AGB stars themselves, but an inhomogeneous early ISM or pollution from a binary companion remain possible alternatives.
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| 20. |
- Spite, M, et al.
(författare)
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First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
- 2005
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 430:2, s. 655-668
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances from the NH band at 336 nm in 35 extremely metal-poor halo giants, with carbon and oxygen abundances from Cayrel et al. (2004, A&A, 416, 1117), using high-quality ESO VLT/UVES spectra (30 of our 35 stars are in the range -4.1 <[Fe/H] < -2.7 and 22 stars have [Fe/H] < -3.0). N abundances derived both from the NH band and from the CN band at 389 nm for 10 stars correlate well, but show a systematic difference of 0.4 dex, which we attribute to uncertainties in the physical parameters of the NH band (line positions, gf values, dissociation energy, etc.). Because any dredge-up of CNO processed material to the surface may complicate the interpretation of CNO abundances in giants, we have also measured the surface abundance of lithium in our stars as a diagnostic of such mixing. Our sample shows a clear dichotomy between two groups of stars. The first group shows evidence of C to N conversion through CN cycling and strong Li dilution, a signature of mixing; these stars are generally more evolved and located on the upper Red Giant Branch (RGB) or Horizontal Branch (HB). The second group has [N/Fe] < 0.5, shows no evidence for C to N conversion, and Li is only moderately diluted; these stars belong to the lower RGB and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy, they are called "unmixed stars". The [O/Fe] and [(C+N)/Fe] ratios are the same in the two groups, confirming that the differences between them are caused by dredge-up of CN-processed material in the first group, with negligible contributions from the O-N cycle. The "unmixed" stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about + 0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massive zero-metal supernovae. The [N/Fe] and [N/Mg] ratios scatter widely. Their mean values in each metallicity bin decrease with increasing metallicity, but this trend could be a statistical effect. The larger values of these ratios define a flat upper plateau ([N/Mg] = 0.0, [N/Fe] = + 0.1), which could reflect higher values within a wide range of yields of zero-metal SNe II. Alternatively, by analogy with the DLAs, the lower abundances ([N/Mg] = -1.1, [N/Fe] = -0.7) could reflect generally low yields from the first SNe II, the other stars being N enhanced by winds of massive Asymptotic Giant Branch (AGB) stars. Since all the stars show clear [alpha/Fe] enhancements, they were formed before any significant enrichment of the Galactic gas by SNe Ia, and their composition should reflect the yields of the first SNe II. However, if massive AGB stars or AGB supernovae evolved more rapidly than SNe Ia and contaminated the ISM, our stars would also reflect the yields of these AGB stars. At present it cannot be decided whether primary N is produced primarily in SNe II or in massive AGB stars, or in both. The stellar N abundances and [N/O] ratios are compatible with those found in Damped Lyman-alpha (DLA) systems. They extend the well-known DLA "plateau" at [N/O] approximate to -0.8 to lower metallicities, albeit with more scatter; no star is found below the putative "low [N/alpha] plateau" at [N/O] approximate to -1.55 in DLAs.
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| 21. |
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| 22. |
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| 23. |
- Morris, Simon, et al.
(författare)
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The ELT-MOS (MOSAIC) : towards the construction phase
- 2018
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Ingår i: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510619586 ; 10702
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Konferensbidrag (refereegranskat)abstract
- When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.
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| 24. |
- Ryde, Nils, et al.
(författare)
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Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 509:1, s. A20-
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Tidskriftsartikel (refereegranskat)abstract
- Context. It is debated whether the Milky Way bulge has characteristics more similar to those of a classical bulge than those of a pseudobulge. Detailed abundance studies of bulge stars are important when investigating the origin, history, and classification of the bulge. These studies provide constraints on the star-formation history, initial mass function, and differences between stellar populations. Not many similar studies have been completed because of the large distance and high variable visual extinction along the line-of-sight towards the bulge. Therefore, near-IR investigations can provide superior results. Aims. To investigate the origin of the bulge and study its chemical abundances determined from near-IR spectra for bulge giants that have already been investigated with optical spectra. The optical spectra also provide the stellar parameters that are very important to the present study. In particular, the important CNO elements are determined more accurately in the near-IR. Oxygen and other alpha elements are important for investigating the star-formation history. The C and N abundances are important for determining the evolutionary stage of the giants and the origin of C in the bulge. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer mounted on the Very Large Telescope. The CNO abundances are determined from the numerous molecular lines in the wavelength range observed. Abundances of the alpha elements Si, S, and Ti are also determined from the near-IR spectra. Results. The abundance ratios [O/Fe], [Si/Fe], and [S/Fe] are enhanced to metallicities of at least [Fe/H] = -0.3, after which they decline. This suggests that the Milky Way bulge experienced a rapid and early burst of star formation similar to that of a classical bulge. However, a similarity between the bulge trend and the trend of the local thick disk seems to be present. This similarity suggests that the bulge could have had a pseudobulge origin. The C and N abundances suggest that our giants are first-ascent red-giants or clump stars, and that the measured oxygen abundances are those with which the stars were born. Our [C/Fe] trend does not show any increase with [Fe/H], which is expected if W-R stars contributed substantially to the C abundances. No "cosmic scatter" can be traced around our observed abundance trends: the measured scatter is expected, given the observational uncertainties.
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| 25. |
- Ryde, Nils, et al.
(författare)
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CNO abundances in the Galactic bulge
- 2010
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Ingår i: Proceedings of the International Astronomical Union. ; 265, s. 285-288
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Konferensbidrag (refereegranskat)
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| 26. |
- Sales-Silva, J. V., et al.
(författare)
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A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE
- 2024
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 965:2
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Tidskriftsartikel (refereegranskat)abstract
- This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of similar to 2000 stars in the Galactic bulge bar spatially contained within divided by X-Gal divided by < 5 kpc, divided by Y-Gal divided by < 3.5 kpc, and divided by Z(Gal)divided by < 1 kpc, and spanning metallicities between -2.0 less than or similar to [Fe/H] less than or similar to +0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd] < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magnetorotational supernovae.
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| 27. |
- Trevisan, M., et al.
(författare)
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Analysis of old very metal rich stars in the solar neighbourhood
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 535, s. A42-
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Tidskriftsartikel (refereegranskat)abstract
- Context. A sample of mostly old metal-rich dwarf and turn-off stars with high eccentricity and low maximum height above the Galactic plane has been identified. From their kinematics, it was suggested that the inner disk is their most probable birthplace. Their chemical imprints may therefore reveal important information about the formation and evolution of the still poorly understood inner disk.Aims. To probe the formation history of these stellar populations, a detailed analysis of a sample of very metal-rich stars is carried out. We derive the metallicities, abundances of a elements, ages, and Galactic orbits.Methods. The analysis of 71 metal-rich stars is based on optical high-resolution echelle spectra obtained with the FEROS spectrograph at the ESO 1.52-m Telescope at La Silla, Chile. The metallicities and abundances of C, O, Mg, Si, Ca, and Ti were derived based on LTE detailed analysis, employing the MARCS model atmospheres.Results. We confirm the high metallicity of these stars reaching up to [Fe(I)/H] = 0.58, and the sample of metal-rich dwarfs can be kinematically subclassified in samples of thick disk, thin disk, and intermediate stellar populations. All sample stars show solar alpha-Fe ratios, and most of them are old and still quite metal rich. The orbits suggest that the thin disk, thick disk and intermediate populations were formed at Galactocentric distances of similar to 8 kpc, similar to 6 kpc, and similar to 7 kpc, respectively. The mean maximum height of the thick disk subsample of Z(max) similar to 380 pc, is lower than for typical thick disk stars. A comparison of a-element abundances of the sample stars with bulge stars shows that the oxygen is compatible with a bulge or inner thick disk origin. Our results suggest that models of radial mixing and dynamical effects of the bar and bar/spiral arms might explain the presence of these old metal-rich dwarf stars in the solar neighbourhood.
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| 28. |
- Trevisan, M., et al.
(författare)
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Metal rich stars in solar neighbourhood (Trevisan+, 2011)
- 2011
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Ingår i: VizieR Online Data Catalog. ; 353
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Tidskriftsartikel (refereegranskat)abstract
- Spectroscopic stellar parameters and abundances of C, O, Mg, Si, Ca, Ti and Ni for 71 stars. U, V, W velocities and orbital parameters derived using the GRINTON integrator (Carraro et al. 2002MNRAS.332..705C, Bedin et al. 2006A\ampA...460L..27B). Atomic data for Fe I, Fe II, Si I, Ca I, and Ti I lines. (7 data files).
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