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Barklem, Paul
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Publications (10 of 96) Show all publications
Roederer, I. U. & Barklem, P. (2018). A New Test of Copper and Zinc Abundances in Late-type Stars Using Ultraviolet Cu II and Zn II Lines. Astrophysical Journal, 857(1), Article ID 2.
Open this publication in new window or tab >>A New Test of Copper and Zinc Abundances in Late-type Stars Using Ultraviolet Cu II and Zn II Lines
2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 857, no 1, article id 2Article in journal (Refereed) Published
Abstract [en]

We present new abundances derived from Cu I, Cu II, Zn I, and Zn II lines in six warm (5766 <= T-eff <= 6427 K), metal-poor (-2.50 <= [Fe/H] <= -0.95) dwarf and subgiant (3.64 <= log g <= 4.44) stars. These abundances are derived from archival high-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope and ground-based optical spectra from several observatories. Ionized Cu and Zn are the majority species, and abundances derived from Cu II and Zn II lines should be largely insensitive to departures from local thermodynamic equilibrium (LTE). We find good agreement between the [Zn/H] ratios derived separately from Zn I and Zn II lines, suggesting that departures from LTE are, at most, minimal (less than or similar to 0.1 dex). We find that the [Cu/H] ratios derived from Cu II lines are 0.36 +/- 0.06 dex larger than those derived from Cu I lines in the most metal-poor stars ([Fe/H] < 1.8), suggesting that LTE underestimates the Cu abundance derived from Cu I lines. The deviations decrease in more metal-rich stars. Our results validate previous theoretical non-LTE calculations for both Cu and Zn, supporting earlier conclusions that the enhancement of [Zn/Fe] in metal-poor stars is legitimate, and the deficiency of [Cu/Fe] in metal-poor stars may not be as large as previously thought.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
nuclear reactions, nucleosynthesis, abundances, stars: abundances, stars: atmospheres, stars: individual, stars: population II, ultraviolet: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-352482 (URN)10.3847/1538-4357/aab71f (DOI)000429348600002 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-06-08Bibliographically approved
Yakovleva, S. A., Barklem, P. S. & Belyaev, A. K. (2018). Data on inelastic processes in low-energy potassium-hydrogen and rubidium-hydrogen collisions. Monthly notices of the Royal Astronomical Society, 473(3), 3810-3817
Open this publication in new window or tab >>Data on inelastic processes in low-energy potassium-hydrogen and rubidium-hydrogen collisions
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, no 3, p. 3810-3817Article in journal (Refereed) Published
Abstract [en]

Two sets of rate coefficients for low-energy inelastic potassium-hydrogen and rubidium-hydrogen collisions were computed for each collisional system based on two model electronic structure calculations, performed by the quantum asymptotic semi-empirical and the quantum asymptotic linear combinations of atomic orbitals (LCAO) approaches, followed by quantum multichannel calculations for the non-adiabatic nuclear dynamics. The rate coefficients for the charge transfer (mutual neutralization, ion-pair formation), excitation and de-excitation processes are calculated for all transitions between the five lowest lying covalent states and the ionic states for each collisional system for the temperature range 1000–10 000 K. The processes involving higher lying states have extremely low rate coefficients and, hence, are neglected. The two model calculations both single out the same partial processes as having large and moderate rate coefficients. The largest rate coefficients correspond to the mutual neutralization processes into the K(5s 2S) and Rb(4d 2D) final states and at temperature 6000 K have values exceeding 3 × 10−8 cm3 s−1 and 4 × 10−8 cm3 s−1, respectively. It is shown that both the semi-empirical and the LCAO approaches perform equally well on average and that both sets of atomic data have roughly the same accuracy. The processes with large and moderate rate coefficients are likely to be important for non-LTE modelling in atmospheres of F, G and K-stars, especially metal-poor stars.

Keywords
atomic data, atomic processes, stars: atmospheres
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-346361 (URN)10.1093/mnras/stx2580 (DOI)000423809400074 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-03-16Bibliographically approved
Barklem, P. S. (2018). Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron. Astronomy and Astrophysics, 612, Article ID A90.
Open this publication in new window or tab >>Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A90Article in journal (Refereed) Published
Abstract [en]

Data for inelastic processes due to hydrogen atom collisions with iron are needed for accurate modelling of the iron spectrum in late-type stars. Excitation and charge transfer in low-energy Fe+H collisions is studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau-Zener model. An extensive calculation including 166 covalent states and 25 ionic states is presented and rate coefficients are calculated for temperatures in the range 1000-20 000 K. The largest rates are found for charge transfer processes to and from two clusters of states around 6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p electrons undergoing transfer. Excitation and de-excitation processes among these two sets of states are also significant.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
atomic data, atomic processes, line: formation, Sun: abundances, stars: abundances
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-356398 (URN)10.1051/0004-6361/201732365 (DOI)000431338900001 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-07-25Bibliographically approved
Barklem, P. (2018). Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen. Astronomy and Astrophysics, 610, Article ID A57.
Open this publication in new window or tab >>Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 610, article id A57Article in journal (Refereed) Published
Abstract [en]

Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000-20000 K, and charge transfer and (de) excitation processes involving the first excited S-states, 4s.S-5(0) and 4s.S-3(0), are found to have the highest rates.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
atomic data, atomic processes, line: formation, Sun: abundances, stars: abundances
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-350901 (URN)10.1051/0004-6361/201731968 (DOI)000427137600002 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-05-17Bibliographically approved
Nordlander, T., Amarsi, A. M., Lind, K., Asplund, M., Barklem, P. S., Casey, A. R., . . . Leenaarts, J. (2017). 3D NLTE Analysis of the Most Iron-Deficient Star, SMSS0313-6708. Astronomy and Astrophysics, 597, Article ID A6.
Open this publication in new window or tab >>3D NLTE Analysis of the Most Iron-Deficient Star, SMSS0313-6708
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 597, article id A6Article in journal (Refereed) Published
Abstract [en]

Context. Models of star formation in the early universe require a detailed understanding of accretion, fragmentation and radiative feedback in metal-free molecular clouds. Different simulations predict different initial mass functions of the first stars, ranging from predominantly low-mass (0.1-10 Msol), to massive (10-100 Msol), or even supermassive (100-1000 Msol). The mass distribution of the first stars should lead to unique chemical imprints on the low-mass second and later generation metal-poor stars still in existence. The chemical composition of SMSS0313-6708, which has the lowest abundances of Ca and Fe of any star known, indicates it was enriched by a single massive supernova.

Aims. The photospheres of metal-poor stars are relatively transparent in the UV, which may lead to large three-dimensional (3D) effects as well as departures from local thermodynamical equilibrium (LTE), even for weak spectral lines. If 3D effects and departures from LTE (NLTE) are ignored or treated incorrectly, errors in the inferred abundances may significantly bias the inferred properties of the polluting supernovae. We redetermine the chemical composition of SMSS0313-6708 by means of the most realistic methods available, and compare the results to predicted supernova yields.

Methods. A 3D hydrodynamical Stagger model atmosphere and 3D NLTE radiative transfer were applied to obtain accurate abundances for Li, Na, Mg, Al, Ca and Fe. The model atoms employ realistic collisional rates, with no calibrated free parameters.

Results. We find significantly higher abundances in 3D NLTE than 1D LTE by 0.8 dex for Fe, and 0.5 dex for Mg, Al and Ca, while Li and Na are unaffected to within 0.03 dex. In particular, our upper limit for [Fe/H] is now a factor ten larger, at [Fe/H] < -6.53 (3 sigma), than previous estimates based on <3D> NLTE (i.e., using averaged 3D models). This higher estimate is due to a conservative upper limit estimation, updated NLTE data, and 3D-<3D> NLTE differences, all of which lead to a higher abundance determination.

Conclusions. We find that supernova yields for models in a wide range of progenitor masses reproduce the revised chemical composition. In addition to massive progenitors of 20-60 Msol exploding with low energies (1-2 B, where 1 B = 10^51 erg), we also find good fits for progenitors of 10 Msol, with very low explosion energies (<1 B). We cannot reconcile the new abundances with supernovae or hypernovae with explosion energies above 2.5 B, nor with pair-instability supernovae. 

Keywords
radiative transfer, stars: abundances, Stars: Population III, techniques: spectroscopic, stars: individual: SMSS J031300.36, supernovae: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-313591 (URN)10.1051/0004-6361/201629202 (DOI)000392392900095 ()
Funder
Swedish National Space BoardAustralian Research Council, FL110100012Swedish Research Council, 2015-00415_3The Royal Swedish Academy of SciencesWenner-Gren FoundationsGöran Gustafsson Foundation for Research in Natural Sciences and MedicineKnut and Alice Wallenberg FoundationSwedish National Infrastructure for Computing (SNIC), p2013234
Available from: 2017-01-22 Created: 2017-01-22 Last updated: 2017-11-29Bibliographically approved
Barklem, P., Osorio, Y., Fursa, D. V., Bray, I., Zatsarinny, O., Bartschat, K. & Jerkstrand, A. (2017). Inelastic e plus Mg collision data and its impact on modelling stellar and supernova spectra. Astronomy and Astrophysics, 606, Article ID A11.
Open this publication in new window or tab >>Inelastic e plus Mg collision data and its impact on modelling stellar and supernova spectra
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 606, article id A11Article in journal (Refereed) Published
Abstract [en]

Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg I (up to 3s6p P-1), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, similar to 5000 K, the results of the two calculations differ on average by only 4%,with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988, ApJ, 330, 1008), covering 25 transitions among 12 states, suggests the Mauas et al. data are on average similar to 57% too low, and with a very large scatter of a factor of similar to 6.5. In particular the collision strength for the transition corresponding to the Mg I intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by similar to 0.1 dex (similar to 25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations.

Keywords
atomic data, atomic processes
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-337751 (URN)10.1051/0004-6361/201730864 (DOI)000412874000002 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-01-04 Created: 2018-01-04 Last updated: 2018-01-04Bibliographically approved
Lind, K., Amarsi, A. M., Asplund, M., Barklem, P. S., Bautista, M., Bergemann, M., . . . Pereira, T. M. (2017). Non-LTE line formation of Fe in late-type stars - IV. Modelling of the solar centre-to-limb variation in 3D. Monthly notices of the Royal Astronomical Society, 468(4), 4311-4322
Open this publication in new window or tab >>Non-LTE line formation of Fe in late-type stars - IV. Modelling of the solar centre-to-limb variation in 3D
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 468, no 4, p. 4311-4322Article in journal (Refereed) Published
Abstract [en]

Our ability to model the shapes and strengths of iron lines in the solar spectrum is a critical test of the accuracy of the solar iron abundance, which sets the absolute zero-point of all stellar metallicities. We use an extensive 463-level Fe atom with new photoionization cross-sections for Fe I and quantum mechanical calculations of collisional excitation and charge transfer with neutral hydrogen; the latter effectively remove a free parameter that has hampered all previous line formation studies of Fe in non-local thermodynamic equilibrium (NLTE). For the first time, we use realistic 3D NLTE calculations of Fe for a quantitative comparison to solar observations. We confront our theoretical line profiles with observations taken at different viewing angles across the solar disc with the Swedish 1-m Solar Telescope. We find that 3D modelling well reproduces the observed centre-to-limb behaviour of spectral lines overall, but highlight aspects that may require further work, especially cross-sections for inelastic collisions with electrons. Our inferred solar iron abundance is log(epsilon(Fe)) = 7.48 +/- 0.04 dex.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
atomic data, line: formation, methods: numerical, methods: observational, Sun: abundances, Sun: atmosphere
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-327363 (URN)10.1093/mnras/stx673 (DOI)000402819700043 ()
Funder
Swedish Research Council, 2015-00415 3Swedish National Infrastructure for Computing (SNIC), p2013234The Royal Swedish Academy of SciencesWenner-Gren FoundationsGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyKnut and Alice Wallenberg FoundationEU, European Research Council, 291058
Available from: 2017-08-18 Created: 2017-08-18 Last updated: 2017-08-18Bibliographically approved
Hill, V., Christlieb, N., Beers, T. C., Barklem, P. S., Kratz, K.-L. -., Nordstrom, B., . . . Farouqi, K. (2017). The Hamburg/ESO R-process Enhanced Star survey (HERES). Astronomy and Astrophysics, 607, Article ID A91.
Open this publication in new window or tab >>The Hamburg/ESO R-process Enhanced Star survey (HERES)
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 607, article id A91Article in journal (Refereed) Published
Abstract [en]

We report an abundance analysis for the highly r-process-enhanced (r-II) star CS 29497-004, a very metal-poor giant with solar system T-eff = 5013 K and [Fe/H] = -2 : 85, whose nature was initially discovered in the course of the HERES project. Our analysis is based on high signal-to-noise ratio, high-resolution (R similar to 75 000) VLT/UVES spectra and MARCS model atmospheres under the assumption of local thermodynamic equilibrium, and obtains abundance measurements for a total of 46 elements, 31 of which are neutron-capture elements. As is the case for the other similar to 25 r-II stars currently known, the heavy-element abundance pattern of CS 29497-004 well-matches a scaled solar system second peak r-process-element abundance pattern. We confirm our previous detection of Th, and demonstrate that this star does not exhibit an "actinide boost". Uranium is also detected (log is an element of (U) = -2 : 20 +/- 0 : 30), albeit with a large measurement error that hampers its use as a precision cosmo-chronometer. Combining the various elemental chronometer pairs that are available for this star, we derive a mean age of 12 : 2 +/- 3 : 7 Gyr using the theoretical production ratios from published waitingpoint approximation models. We further explore the high-entropy wind model (Farouqi et al. 2010, ApJ, 712, 1359) production ratios arising from different neutron richness of the ejecta (Y-e), and derive an age of 13 : 7 +/- 4 : 4 Gyr for a best-fitting Y-e = 0 : 447. The U/Th nuclei-chronometer is confirmed to be the most resilient to theoretical production ratios and yields an age of 16 : 5 +/- 6 : 6 Gyr. Lead (Pb) is also tentatively detected in CS 29497-004, at a level compatible with a scaled solar r-process, or with the theoretical expectations for a pure r-process in this star.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2017
Keywords
stars: abundances, stars: individual: CS 29497-004, stars: Population II, stars: chemically peculiar, Galaxy: halo
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-356350 (URN)10.1051/0004-6361/201629092 (DOI)000415863500002 ()
Funder
German Research Foundation (DFG), Sonderforschungsbereich SFB 881Knut and Alice Wallenberg Foundation
Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-07-24Bibliographically approved
Barklem, P. S. (2016). Accurate abundance analysis of late-type stars: advances in atomic physics. The Astronomy and Astrophysics Review, 24, Article ID 9.
Open this publication in new window or tab >>Accurate abundance analysis of late-type stars: advances in atomic physics
2016 (English)In: The Astronomy and Astrophysics Review, ISSN 0935-4956, E-ISSN 1432-0754, Vol. 24, article id 9Article, review/survey (Refereed) Published
Abstract [en]

The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.

Keywords
Abundances, Chemical composition, Stellar atmospheres, Atomic processes and interactions, Atomic and molecular data
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-299647 (URN)10.1007/s00159-016-0095-9 (DOI)000376780100001 ()
Funder
The Royal Swedish Academy of SciencesWenner-Gren FoundationsGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologySwedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-07-25 Created: 2016-07-25 Last updated: 2017-11-28Bibliographically approved
Barklem, P. S. (2016). Excitation and charge transfer in low-energy hydrogen-atom collisions with neutral atoms: Theory, comparisons, and application to Ca. PHYSICAL REVIEW A, 93(4), Article ID 042705.
Open this publication in new window or tab >>Excitation and charge transfer in low-energy hydrogen-atom collisions with neutral atoms: Theory, comparisons, and application to Ca
2016 (English)In: PHYSICAL REVIEW A, ISSN 2469-9926, Vol. 93, no 4, article id 042705Article in journal (Refereed) Published
Abstract [en]

A theoretical method is presented for the estimation of cross sections and rates for excitation and charge-transfer processes in low-energy hydrogen-atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen-atom system. The calculation of potentials and nonadiabatic radial couplings using the method is demonstrated. The potentials are used together with the multichannel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wave functions, which can be determined from known atomic parameters. The method is applied to Li + H, Na + H, and Mg + H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca + H collisions, and rate coefficients are calculated for temperatures in the range 1000-20 000 K.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-297904 (URN)10.1103/PhysRevA.93.042705 (DOI)000374523500005 ()
Funder
The Royal Swedish Academy of SciencesWenner-Gren FoundationsGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologySwedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-06-29 Created: 2016-06-28 Last updated: 2016-06-29Bibliographically approved
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