| 1. |
- Anguiano, B., et al.
(författare)
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Comprehensive comparison between APOGEE and LAMOST Radial velocities and atmospheric stellar parameters
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
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Tidskriftsartikel (refereegranskat)abstract
- Context. In the era of massive spectroscopy surveys, automated stellar parameter pipelines and their validation are extremely important for an efficient scientific exploitation of the spectra. Aims. We undertake a critical and comprehensive comparison of the radial velocities and the main stellar atmosphere parameters for stars in common between the latest data releases from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE) and the Large sky Area Multi-Object Spectroscopic Telescope (LAMOST) surveys. Methods. APOGEE is a high-resolution (R = 22500) spectroscopic survey with high signal-to-noise ratio that is part of the Sloan Digital Sky Survey (SDSS). The latest data release, SDSS DR14, comprises APOGEE spectra for 263 444 stars, together with main stellar parameters and individual abundances for up to 20 chemical species. LAMOST is a low-resolution (R = 1800) optical spectroscopic survey also in the Northern Hemisphere, where 4000 fibers can be allocated simultaneously. LAMOST DR3 contains 3 177 995 stars. Results. A total of 42 420 dwarfs and giants stars are in common between the APOGEE DR14 - LAMOST DR3 stellar catalogs. A comparison between APOGEE and LAMOST RVs shows a clear offset of 4.54 +/- 0.03 km s(-1), with a dispersion of 5.8 km s(-1), in the sense that APOGEE radial velocities are higher. We observe a small offset in the effective temperatures of about 13 K, with a scatter of 155 K. A small offset in [Fe/H] of about 0.06 dex together with a scatter of 0.13 dex is also observed. We note that the largest offset between the surveys occurs in the surface gravities. Using only surface gravities in calibrated red giants from APOGEE DR14, with which there are 24 074 stars in common, a deviation of 0.14 dex is found with substantial scatter (0.25 dex). There are 17 482 red giant stars in common between APOGEE DR14 and those in LAMOST tied to APOGEE DR12 via the code called the Cannon. There is generally good agreement between the two data-sets. However, we find that the differences in the stellar parameters depend on effective temperature. For metal-rich stars, a different trend for the [Fe/H] discrepancies is found. Surprisingly, we see no correlation between the internal APOGEE DR14 - DR12 differences in T-eff and those in DR14 - LAMOST tied to DR12, where a correlation should be expected since LAMOST has been calibrated to APOGEE DR12. We find no correlation either between the [Fe/H] discrepancies, suggesting that LAMOST/Cannon is not well coupled to the APOGEE DR12 stellar parameter scale. An [Fe/H] dependence between the stellar parameters in APOGEE DR12 and those in DR14 is reported. We find a weak correlation in the differences between APOGEE DR14 - DR12 and LAMOST on DR12 surface gravity for stars hotter than 4800 K and in the log g range between 2.0 and 2.8 dex. We do not observe an [Fe/H] dependency in the gravity discrepancies.
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| 2. |
- Atalay, B., et al.
(författare)
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MCDHF and RCI calculations of energy levels, lifetimes, and transition rates in Si III and Si IV
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- We present extensive multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations including 106 states in doubly ionized silicon (Si III) and 45 states in triply ionized silicon (Si IV), which are important for astrophysical determination of plasma properties in different objects. These calculations represents an important extension and improvement of earlier calculations especially for Si III. The calculations are in good agreement with available experiments for excitation energies, transition properties, and lifetimes. Important deviations from the NIST-database for a selection of perturbed Rydberg series are discussed in detail.
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| 3. |
- Blackwell-Whitehead, Richard, et al.
(författare)
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Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool dwarfs
- 2011
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 525
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 angstrom, 15 of which are in the infrared. The transitions at 12 899 angstrom and 12 975 angstrom are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 +/- 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 +/- 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 +/- 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150.
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| 4. |
- Burheim, Madeleine, et al.
(författare)
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Experimental oscillator strengths of Al I lines for near-infrared astrophysical spectroscopy
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 672
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Tidskriftsartikel (refereegranskat)abstract
- Context. Elemental abundances can be determined from stellar spectra, making it possible to study galactic formation and evolution. Accurate atomic data is essential for the reliable interpretation and modeling of astrophysical spectra. In this work, we perform laboratory studies on neutral aluminium. This element is found, for example, in young, massive stars and it is a key element for tracing ongoing nucleosynthesis throughout the Galaxy. The near-infrared (NIR) wavelength region is of particular importance, since extinction in this region is lower than for optical wavelengths. This makes the NIR wavelength region a better probe for highly obscured regions, such as those located close to the Galactic center.Aims. We investigate the spectrum of neutral aluminium with the aim to provide oscillator strengths (f-values) of improved accuracy for lines in the NIR and optical regions (670–4200 nm).Methods. Measurements of high-resolution spectra were performed using a Fourier transform spectrometer and a hollow cathode discharge lamp. The f-values were derived from experimental line intensities combined with published radiative lifetimes.Results. We report oscillator strengths for 12 lines in the NIR and optical spectral regions, with an accuracy between 2 and 11%, as well as branching fractions for an additional 16 lines.
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| 5. |
- Eriksson, M, et al.
(författare)
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Modeling of C IV pumped fluorescence of Fe II in symbiotic stars
- 2008
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 477:1, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We describe how the C IV lambda 1548.18 line pumps the 1548.20 and 1548.41 angstrom channels of Fe II in symbiotic stars through the process known as photo-ionization by accidental resonance (PAR). We describe where and why Fe II fluorescence arises in symbiotic stars and whether the Fe II lambda 1548.41 channel can only be activated when there is a white-dwarf wind present in the system. Further, we aim to show how an analysis of the PAR-pumped lines helps to understand the phyisical conditions that they manifest. Methods. We calculate intensities of the C IV-pumped Fe II fluorescence lines in symbiotic stars, corresponding to the y(4)H(11/)2 and w(2)D(3/2) levels, based on a simple geometrical model of the emitting regions. We apply the model to seven symbiotic stars, known to have Fe II fluorescence lines pumped by C IV in their spectra. We compare the predicted intensities to the observed intensities of the selected symbiotic stars. Results. We find that we can reproduce the observed fluorescence intensities of the seven symbiotic stars in our sample, using parameters that are consistent with their known properties. We show that PAR-produced lines can be used as a diagnostic tool to derive important physical parameters of a stellar system. We suggest that the detection of Fe II lines corresponding to the w2D3/2 level in certain symbiotic stars provide evidence of hot shells expanding with velocities of at least hundreds km s(-1) in those systems.
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| 6. |
- Forsberg, R., et al.
(författare)
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Abundances of disk and bulge giants from high-resolution optical spectra IV. Zr, La, Ce, Eu
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- Context. Observations of the Galactic bulge suggest that the disk formed through secular evolution rather than gas dissipation and/or mergers, as previously believed. This would imply very similar chemistry in the disk and bulge. Some elements, such as the alpha-elements, are well studied in the bulge, but others like the neutron-capture elements are much less well explored. Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for Galactic chemical evolution. Aims. In this work, we make a differential comparison of neutron-capture element abundances determined in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis, with the aim of finding possible differences/similarities between the populations. Methods. Abundances are determined for Zr, La, Ce, and Eu in 45 bulge giants and 291 local disk giants, from high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin- and thick-disk components using a combination of abundances and kinematics. Results. We find flat Zr, La, and Ce trends in the bulge, with a similar to 0.1 dex higher La abundance compared with the disk, possibly indicating a higher s-process contribution for La in the bulge. [Eu/Fe] decreases with increasing [Fe/H], with a plateau at around [Fe/H] similar to -0.4, pointing at similar enrichment to alpha-elements in all populations. Conclusions. We find that the r-process dominated the neutron-capture production at early times both in the disks and bulge. Further, [La/Eu] ratios for the bulge are systematically higher than for the thick disk, pointing to either a) a different amount of SN II or b) a different contribution of the s-process in the two populations. Considering [(La+Ce)/Zr], the bulge and the thick disk follow each other closely, suggesting a similar ratio of high-to-low-mass asymptotic giant branch stars.
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| 7. |
- Forsberg, R., et al.
(författare)
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First r-process enhanced star confirmed as a member of the Galactic bulge
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Stars with strong enhancements of r-process elements are rare and tend to be metal-poor, generally with [Fe/H] < -2 dex, and located in the halo. In this work, we aim to investigate a candidate r-process enriched bulge star with a relatively high metallicity of [Fe/H] similar to - 0.65 dex and to compare it with a previously published r-rich candidate star in the bulge. Methods. We reconsidered the abundance analysis of a high-resolution optical spectrum of the red-giant star 2MASS J18082459-2548444 and determined its europium (Eu) and molybdenum (Mo) abundance, using stellar parameters from five different previous studies. Applying 2MASS photometry, Gaia astrometry, and kinematics, we estimated the distance, orbits, and population membership of 2MASS J18082459-2548444 and a previously reported r-enriched star 2MASS J18174532-3353235. Results. We find that 2MASS J18082459-2548444 is a relatively metal-rich, enriched r-process star that is enhanced in Eu and Mo, but not substantially enhanced in s-process elements. There is a high probability that it has a Galactic bulge membership, based on its distance and orbit. We find that both stars show r-process enhancement with elevated [Eu/Fe]-values, even though 2MASS J18174532-3353235 is 1 dex lower in metallicity. Additionally, we find that the plausible origins of 2MASS J18174532-3353235 to be either that of the halo or the thick disc. Conclusions. We conclude that 2MASS J18082459-2548444 represents the first example of a confirmed r-process enhanced star confined to the inner bulge. We assume it is possibly a relic from a period of enrichment associated with the formation of the bar.
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| 8. |
- Gilmore, G., et al.
(författare)
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The Gaia-ESO Public Spectroscopic Survey : Motivation, implementation, GIRAFFE data processing, analysis, and final data products star
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100 000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for the homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. Aims. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper introduces the survey results. Methods. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus, all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. Results. The Gaia-ESO Survey obtained 202 000 spectra of 115 000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. Conclusions. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022. A companion article reviews the survey implementation, scientific highlights, the open cluster survey, and data products.
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| 9. |
- Gurell, Jonas, 1981-, et al.
(författare)
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The FERRUM project : Transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 508:1, s. 525-529
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Tidskriftsartikel (refereegranskat)abstract
- Context. Accurate transition probabilities for forbidden lines are important diagnostic parameters for low-density astrophysical plasmas. In this paper we present experimental atomic data for forbidden [Fe II] transitions that are observed as strong features in astrophysical spectra. Aims. We measure lifetimes for the 3d(6)((3)G)4s a (4)G(11/2) and 3d(6)((3)D)4s b (4)D(1/2) metastable levels in Fe II and experimental transition probabilities for the forbidden transitions 3d(7) a (4)F(7/2,9/2)-3d(6)((3)G)4s a (4)G(11/2). Methods. The lifetimes were measured at the ion storage ring facility CRYRING using a laser probing technique. Astrophysical branching fractions were obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching fractions were combined to yield absolute transition probabilities. Results. The lifetimes of the a (4)G(11/2) and the b (4)D(1/2) levels have been measured and have the following values, tau = 0.75 +/- 0.10 s and tau = 0.54 +/- 0.03 s respectively. Furthermore, we have determined the transition probabilities for two forbidden transitions of a (4)F(7/2,9/2)-a (4)G(11/2) at 4243.97 and 4346.85 angstrom. Both the lifetimes and the transition probabilities are compared to calculated values in the literature.
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| 10. |
- Hansen, C. J., et al.
(författare)
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Silver and palladium help unveil the nature of a second r-process
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 545
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Tidskriftsartikel (refereegranskat)abstract
- Context. The rapid neutron-capture process, which created about half of the heaviest elements in the solar system, is believed to have been unique. Many recent studies have shown that this uniqueness is not true for the formation of lighter elements, in particular those in the atomic number range 38 < Z < 48. Among these, palladium (Pd) and especially silver (Ag) are expected to be key indicators of a possible second r-process, but until recently they have been studied only in a few stars. We therefore target Pd and Ag in a large sample of stars and compare these abundances to those of Sr, Y, Zr, Ba, and Eu produced by the slow (s-) and rapid (r-) neutron-capture processes. Hereby we investigate the nature of the formation process of Ag and Pd. Aims. We study the abundances of seven elements (Sr, Y, Zr, Pd, Ag, Ba, and Eu) to gain insight into the formation process of the elements and explore in depth the nature of the second r-process. Methods. By adopting a homogeneous one-dimensional local thermodynamic equilibrium (1D LTE) analysis of 71 stars, we derive stellar abundances using the spectral synthesis code MOOG, and the MARCS model atmospheres. We calculate abundance ratio trends and compare the derived abundances to site-dependent yield predictions (low-mass O-Ne-Mg core-collapse supernovae and parametrised high-entropy winds), to extract characteristics of the second r-process. Results. The seven elements are tracers of different (neutron-capture) processes, which in turn allows us to constrain the formation process(es) of Pd and Ag. The abundance ratios of the heavy elements are found to be correlated and anti-correlated. These trends lead to clear indications that a second/weak r-process, is responsible for the formation of Pd and Ag. On the basis of the comparison to the model predictions, we find that the conditions under which this process takes place differ from those for the main r-process in needing lower neutron number densities, lower neutron-to-seed ratios, and lower entropies, and/or higher electron abundances. Conclusions. Our analysis confirms that Pd and Ag form via a rapid neutron-capture process that differs from the main r-process, the main and weak s- processes, and charged particle freeze-outs. We find that this process is efficiently working down to the lowest metallicity sampled by our analysis ([Fe/H] = -3.3). Our results may indicate that a combination of these explosive sites is needed to explain the variety in the observationally derived abundance patterns.
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