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Barklem, Paul
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Publications (10 of 106) Show all publications
Allende Prieto, C., Koesterke, L., Hubeny, I., Bautista, M. A., Barklem, P. & Nahar, S. N. (2018). A collection of model stellar spectra for spectral types B to early-M. Astronomy and Astrophysics, 618, Article ID A25.
Open this publication in new window or tab >>A collection of model stellar spectra for spectral types B to early-M
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A25Article in journal (Refereed) Published
Abstract [en]

Context: Models of stellar spectra are necessary for interpreting light from individual stars, planets, integrated stellar populations, nebulae, and the interstellar medium.

Aims: We provide a comprehensive and homogeneous collection of synthetic spectra for a wide range of atmospheric parameters and chemical compositions.

Methods: We compile atomic and molecular data from the literature. We adopt the largest and most recent set of ATLAS9 model atmospheres, and use the radiative code ASS epsilon T.

Results: The resulting collection of spectra is made publicly available at medium and high-resolution (R lambda/delta lambda = 10 000, 100 000 and 300 000) spectral grids, which include variations in effective temperature between 3500K and 30 000 K, surface gravity (0 <= log g <= 5), and metallicity (-5 <= [Fe/H] <= +0 : 5), spanning the wavelength interval 120-6500 nm. A second set of denser grids with additional dimensions, [alpha/ Fe] and micro-turbulence, are also provided (covering 200-2500 nm). We compare models with observations for a few representative cases.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
radiative transfer, atlases, stars: atmospheres
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-367029 (URN)10.1051/0004-6361/201732484 (DOI)000446750800003 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2018-11-28Bibliographically approved
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: 2018-12-11
Nandakumar, G., Ryde, N., Schultheis, M., Thorsbro, B., Jönsson, H., Barklem, P., . . . Fragkoudi, F. (2018). Chemical characterization of the inner Galactic bulge: North-South symmetry. Monthly notices of the Royal Astronomical Society, 478(4), 4374-4389
Open this publication in new window or tab >>Chemical characterization of the inner Galactic bulge: North-South symmetry
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 4, p. 4374-4389Article in journal (Refereed) Published
Abstract [en]

While the number of stars in the Galactic bulge with detailed chemical abundance measurements is increasing rapidly, the inner Galactic bulge (vertical bar b vertical bar < 2 degrees) remains poorly studied, due to heavy interstellar absorption and photometric crowding. We have carried out a high-resolution IR spectroscopic study of 72 M giants in the inner bulge using the CRIRES (ESO/VLT) facility. Our spectra cover the wavelength range of 2.0818-2.1444 mu m with the resolution of R similar to 50 000 and have signal-to-noise ratio of 50: 100. Our stars are located along the bulge minor axis at l = 0 degrees, b= +/- 0 degrees, +/- 1 degrees, +/- 2 degrees, and + 3 degrees. Our sample was analysed in a homogeneous way using the most current K-band line list. We clearly detect a bimodal metallicity distribution function with a metal-rich peak at similar to + 0.3 dex and a metal-poor peak at similar to -0.5 dex and no stars with [Fe/H] > + 0.6 dex. The Galactic Centre field reveals in contrast a mainly metal-rich population with a mean metallicity of + 0.3 dex. We derived [Mg/Fe] and [Si/Fe] abundances that are consistent with trends from the outer bulge. We confirm for the supersolar metallicity stars the decreasing trend in [Mg/Fe] and [Si/Fe] as expected from chemical evolution models. With the caveat of a relatively small sample, we do not find significant differences in the chemical abundances between the Northern and the Southern fields; hence, the evidence is consistent with symmetry in chemistry between North and South.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
stars: abundances, stars: late-type, Galaxy: bulge
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-362839 (URN)10.1093/mnras/sty1255 (DOI)000441288300008 ()
Funder
Swedish Research Council, 621-2014-5640Knut and Alice Wallenberg FoundationThe Crafoord FoundationStiftelsen Olle Engkvist Byggmästare
Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-10-12Bibliographically 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
Amarsi, A. M., Nordlander, T., Barklem, P., Asplund, M., Collet, R. & Lind, K. (2018). Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation. Astronomy and Astrophysics, 615, Article ID A139.
Open this publication in new window or tab >>Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A139Article in journal (Refereed) Published
Abstract [en]

Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H alpha, H beta, and H gamma we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H gamma, while the inner wings can be weaker in 3D models, particularly for H alpha. For H alpha, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (T-eff approximate to 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (T-eff approximate to 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H alpha, H beta, and H gamma; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1 sigma uncertainties. For H alpha, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H alpha can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.

Keywords
radiative transfer, line: formation, line: profiles, stars: atmospheres, stars: late-type
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-361994 (URN)10.1051/0004-6361/201732546 (DOI)000440220000006 ()
Funder
Swedish Research Council, 2015004153Australian Research Council, DP150100250Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-03Bibliographically 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
Helmi, A., van Leeuwen, F., McMillan, P. J., Massari, D., Antoja, T., Robin, A. C., . . . Zwitter, T. (2018). Gaia Data Release 2 Kinematics of globular clusters and dwarf galaxies around the Milky Way. Astronomy and Astrophysics, 616, Article ID A12.
Open this publication in new window or tab >>Gaia Data Release 2 Kinematics of globular clusters and dwarf galaxies around the Milky Way
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A12Article in journal (Refereed) Published
Abstract [en]

Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Methods. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Results. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (i v) derive a lower limit for the mass of the Milky Way of 9.1(-2.6)(+6.2) x 10(11) M-circle dot based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (v i) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. Conclusions. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.

Keywords
Galaxy: kinematics and dynamics, astrometry, globular clusters: general, galaxies: dwarf, Local Group, Magellanic Clouds
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-363114 (URN)10.1051/0004-6361/201832698 (DOI)000441203000012 ()
Funder
EU, European Research Council, 320360EU, European Research Council, 647208EU, Horizon 2020, 670519EU, Horizon 2020, 687378Swedish National Space Board
Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-10-12Bibliographically approved
Katz, D., Antoja, T., Romero-Gomez, M., Drimmel, R., Reyle, C., Seabroke, G. M., . . . Zwitter, T. (2018). Gaia Data Release 2 Mapping the Milky Way disc kinematics. Astronomy and Astrophysics, 616, Article ID A11.
Open this publication in new window or tab >>Gaia Data Release 2 Mapping the Milky Way disc kinematics
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A11Article in journal (Refereed) Published
Abstract [en]

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar <= 20%), and precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4 km s(-1) and 20% of the stars with uncertainties smaller than 1 km s(-1) on all three components). From this sample, we extracted a sub-sample of 3.2 million giant stars to map the velocity field of the Galactic disc from similar to 5 kpc to similar to 13 kpc from the Galactic centre and up to 2 kpc above and below the plane. We also study the distribution of 0.3 million solar neighbourhood stars (r < 200 pc), with median velocity uncertainties of 0.4 km s(-1), in velocity space and use the full sample to examine how the over-densities evolve in more distant regions. Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.

Keywords
Galaxy: kinematics and dynamics, Galaxy: disk, solar neighborhood
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-363115 (URN)10.1051/0004-6361/201832865 (DOI)000441203000011 ()
Funder
EU, European Research Council, 320360EU, European Research Council, 647208EU, Horizon 2020, 670519EU, Horizon 2020, 687378Swedish National Space Board
Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-10-12Bibliographically approved
Spoto, F., Tanga, P., Mignard, F., Berthier, J., Carry, B., Cellino, A., . . . Zwitter, T. (2018). Gaia Data Release 2: Observations of solar system objects. Astronomy and Astrophysics, 616, Article ID A13.
Open this publication in new window or tab >>Gaia Data Release 2: Observations of solar system objects
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A13Article in journal (Refereed) Published
Abstract [en]

Context: The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations.

Aims: We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality.

Methods: To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP).

Results: The overall astrometric performance is close to the expectations, with an optimal range of brightness G similar to 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G similar to 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
astrometry, minor planets, asteroids: general, methods: data analysis, space vehicles: instruments
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-364977 (URN)10.1051/0004-6361/201832900 (DOI)000441203000013 ()
Funder
Swedish National Space Board
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-08Bibliographically approved
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