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Heiter, Ulrike
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Publications (10 of 98) Show all publications
Baratella, M., D'Orazi, V., Carraro, G., Desidera, S., Randich, S., Magrini, L., . . . Lewis, J. (2020). The Gaia-ESO Survey: a new approach to chemically characterising young open clusters I. Stellar parameters, and iron-peak, alpha-, and proton-capture elements. Astronomy and Astrophysics, 634, Article ID A34.
Open this publication in new window or tab >>The Gaia-ESO Survey: a new approach to chemically characterising young open clusters I. Stellar parameters, and iron-peak, alpha-, and proton-capture elements
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2020 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 634, article id A34Article in journal (Refereed) Published
Abstract [en]

Context: Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than less than or similar to 150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements.

Aims: In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques.

Methods: We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (tau < 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe I, Fe II, Tit, Tin,Na I, Mg I, Al I,Sit, Ca I, Cr I, and Ni I.

Results: Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated.

Conclusions: Our clusters display a metallicity [Fe/H] between +0.04 +/- 0.01 and +0.12 +/- 0.02; they are not more metal poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2020
Keywords
stars: abundances, stars: fundamental parameters, stars: solar-type, open clusters and associations: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-406733 (URN)10.1051/0004-6361/201937055 (DOI)000510742100003 ()
Funder
EU, FP7, Seventh Framework Programme, 320360Knut and Alice Wallenberg FoundationSwedish National Space Board
Available from: 2020-03-19 Created: 2020-03-19 Last updated: 2020-03-19Bibliographically approved
Jofre, P., Heiter, U. & Soubiran, C. (2019). Accuracy and Precision of Industrial Stellar Abundances. Annual Review of Astronomy and Astrophysics, 57, 571-616
Open this publication in new window or tab >>Accuracy and Precision of Industrial Stellar Abundances
2019 (English)In: Annual Review of Astronomy and Astrophysics, ISSN 0066-4146, E-ISSN 1545-4282, Vol. 57, p. 571-616Article in journal (Refereed) Published
Abstract [en]

There has been an incredibly large investment in obtaining high-resolution stellar spectra for determining chemical abundances of stars. This information is crucial to answer fundamental questions in astronomy by constraining the formation and evolution scenarios of the Milky Way as well as the stars and planets residing in it. We have just entered a new era, in which chemical abundances of FGK-type stars are being produced at industrial scales, and in which the observations, reduction, and analysis of the data are automatically performed by machines. Here, we review the latest human efforts to assess the accuracy and precision of such industrial abundances by providing insights into the steps and uncertainties associated with the process of determining stellar abundances. We also provide a description of current and forthcoming spectroscopic surveys, focusing on their reported abundances and uncertainties. This allows us to identify which elements and spectral lines are best and why. Finally, we make a brief selection of main scientific questions the community is aiming to answer with abundances. Uncertainties in abundances need to be disentangled into random and systematic components. Precision can be increased by applying differential or data-driven methods based on accurate data. High-resolution and signal-to-noise spectra provide fundamental data that can be used to calibrate lower-resolution and signal-to-noise spectra of millions of stars. Different survey calibration strategies must agree on a common set of reference stars to create data products that are consistent. Data products provided by individual groups must be published using standard formats to ensure straightforward applicability.

Place, publisher, year, edition, pages
ANNUAL REVIEWS, 2019
Keywords
stellar spectroscopy, Milky Way, catalogs
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-394726 (URN)10.1146/annurev-astro-091918-104509 (DOI)000483964100015 ()978-0-8243-0957-2 (ISBN)
Available from: 2019-10-11 Created: 2019-10-11 Last updated: 2019-10-11Bibliographically approved
Bossini, D., Vallenari, A., Bragaglia, A., Cantat-Gaudin, T., Sordo, R., Balaguer-Nunez, L., . . . Heiter, U. (2019). Age determination for 269 Gaia DR2 open clusters. Astronomy and Astrophysics, 623, Article ID A108.
Open this publication in new window or tab >>Age determination for 269 Gaia DR2 open clusters
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 623, article id A108Article in journal (Refereed) Published
Abstract [en]

Context

The Gaia Second Data Release provides precise astrometry and photometry for more than 1.3 billion sources. This catalog opens a new era concerning the characterization of open clusters and test stellar models, paving the way for better understanding of the disk properties.

Aims

The aim of the paper is to improve the knowledge of cluster parameters, using only the unprecedented quality of the Gaia photometry and astrometry.

Methods

We have made use of the membership determination based on the precise Gaia astrometry and photometry. We applied an automated Bayesian tool, BASE-9, to fit stellar isochrones on the observed G, G(BP), G(RP) magnitudes of the high probability member stars.

Results

We derive parameters such as age, distance modulus, and extinction for a sample of 269 open clusters, selecting only low reddening objects and discarding very young clusters, for which techniques other than isochrone-fitting are more suitable for estimating ages.

Keywords
methods: statistical, open clusters and associations: general, Galaxy: stellar content, catalogs
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-380453 (URN)10.1051/0004-6361/201834693 (DOI)000460892200001 ()
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-03-28Bibliographically approved
Eyer, L., Korn, A. J., Barklem, P. S., Edvardsson, B., Eriksson, K., Gavel, A., . . . Zwitter, T. (2019). Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram. Astronomy and Astrophysics, 623, Article ID A110.
Open this publication in new window or tab >>Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 623, article id A110Article in journal (Refereed) Published
Abstract [en]

Context

The ESA Gaia mission provides a unique time-domain survey for more than 1.6 billion sources with G less than or similar to 21 mag.

Aims

We showcase stellar variability in the Galactic colour-absolute magnitude diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses.

Methods

We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce "motions". To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric Gaia data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched Gaia sources with known variable stars. We also used the statistics and variability detection modules of the Gaia variability pipeline. Corrections for interstellar extinction are not implemented in this article.

Results

Gaia enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of Gaia. Finally, we report the most complete description of variability-induced motion within the CaMD to date.

Conclusions

Gaia enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future Gaia data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars.

Keywords
stars: general, stars: variables: general, stars: oscillations, binaries: eclipsing, surveys, methods: data analysis
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-380450 (URN)10.1051/0004-6361/201833304 (DOI)000461008700002 ()
Funder
EU, Horizon 2020, 670519
Note

For complete list of authors see http://dx.doi.org/10.1051/0004-6361/201833304

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-03-29Bibliographically approved
Casali, G., Magrini, L., Tognelli, E., Jackson, R., Jeffries, R. D., Lagarde, N., . . . Bayo, A. (2019). The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters. Astronomy and Astrophysics, 629, Article ID A62.
Open this publication in new window or tab >>The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 629, article id A62Article in journal (Refereed) Published
Abstract [en]

Context: In the era of large high-resolution spectroscopic surveys such as Gaia-ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive astrophysical quantities: stellar age.

Aims: Some abundance ratios, such as [C/N], have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using open star clusters, observed by the Gaia-ESO and APOGEE surveys, as calibrators.

Methods: We used stellar parameters and abundances from the Gaia-ESO Survey and APOGEE Survey of the Galactic field and open cluster stars. Ages of star clusters were retrieved from the literature sources and validated using a common set of isochrones. We used the same isochrones to determine for each age and metallicity the surface gravity at which the first dredge-up and red giant branch bump occur. We studied the effect of extra-mixing processes in our sample of giant stars, and we derived the mean [C/N] in evolved stars, including only stars without evidence of extra mixing. By combining the Gaia-ESO and APOGEE samples of open clusters, we derived a linear relationship between [C/N] and (logarithmic) cluster ages.

Results: We apply our relationship to selected giant field stars in the Gaia-ESO and APOGEE surveys. We find an age separation between thin-and thick-disc stars and age trends within their populations, with an increasing age towards lower metallicity populations.

Conclusions: With this empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. For giant stars, the isochrone fitting method is indeed less sensitive than for dwarf stars at the turn-off. Our method can therefore be considered as an additional tool to give an independent estimate of the age of giant stars. The uncertainties in their ages is similar to those obtained using isochrone fitting for dwarf stars.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
Galaxy: abundances, open clusters and associations: general, Galaxy: disk
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-394198 (URN)10.1051/0004-6361/201935282 (DOI)000483925600007 ()
Funder
EU, FP7, Seventh Framework Programme, 320360Knut and Alice Wallenberg FoundationAustralian Research Council, 170100521Swedish National Space Board
Available from: 2019-10-08 Created: 2019-10-08 Last updated: 2019-10-08Bibliographically approved
Gavel, A., Gruyters, P., Heiter, U., Korn, A., Lind, K. & Nordlander, T. (2019). The LUMBA UVES stellar parameter pipeline. Astronomy and Astrophysics, 629, Article ID A74.
Open this publication in new window or tab >>The LUMBA UVES stellar parameter pipeline
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 629, article id A74Article in journal (Refereed) Published
Abstract [en]

Context. The Gaia-ESO Survey has taken high-quality spectra of a subset of 100 000 stars observed with the Gaia spacecraft. The goal for this subset is to derive chemical abundances for these stars that will complement the astrometric data collected by Gaia. Deriving the chemical abundances requires that the stellar parameters be determined. Aims. We present a pipeline for deriving stellar parameters from spectra observed with the FLAMES-UVES spectrograph in its standard fibre-fed mode centred on 580 nm, as used in the Gaia-ESO Survey. We quantify the performance of the pipeline in terms of systematic offsets and scatter. In doing so, we present a general method for benchmarking stellar parameter determination pipelines. Methods. Assuming a general model of the errors in stellar parameter pipelines, together with a sample of spectra of stars whose stellar parameters are known from fundamental measurements and relations, we use a Markov chain Monte Carlo method to quantitatively test the pipeline. Results. We find that the pipeline provides parameter estimates with systematic errors on effective temperature below 100 K, on surface gravity below 0.1 dex, and on metallicity below 0.05 dex for the main spectral types of star observed in the Gaia-ESO Survey and tested here. The performance on red giants is somewhat lower. Conclusions. The pipeline performs well enough to fulfil its intended purpose within the Gaia-ESO Survey. It is also general enough that it can be put to use on spectra from other surveys or other spectrographs similar to FLAMES-UVES.

Keywords
methods: numerical, stars: atmospheres, stars: statistics
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-394967 (URN)10.1051/0004-6361/201935937 (DOI)000484658100007 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2015-00415_3Swedish National Space Board
Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
Piskunov, N., Stempels, E., Lavail, A., Escuti, M., Snik, F., Dolgopolov, A., . . . Valenti, E. (2018). A unique infrared spectropolarimetric unit for CRIRES+. In: Evans, CJ Simard, L Takami, H (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, USA. SPIE-INT SOC OPTICAL ENGINEERING, Article ID 1070234.
Open this publication in new window or tab >>A unique infrared spectropolarimetric unit for CRIRES+
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2018 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII / [ed] Evans, CJ Simard, L Takami, H, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 1070234Conference paper, Published paper (Refereed)
Abstract [en]

High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully-and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polarization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polarization. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT.

Place, publisher, year, edition, pages
SPIE-INT SOC OPTICAL ENGINEERING, 2018
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
Spectroscopy, Spectropolarimetry, Polarisation gratings, Stokes parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373550 (URN)10.1117/12.2313512 (DOI)000452664300275 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, USA
Funder
Knut and Alice Wallenberg Foundation
Available from: 2019-01-17 Created: 2019-01-17 Last updated: 2019-01-17Bibliographically approved
Karovicova, I., White, T. R., Nordlander, T., Lind, K., Casagrande, L., Ireland, M. J., . . . Asplund, M. (2018). Accurate effective temperatures of the metal-poor benchmark stars HD140283, HD122563, and HD103095 from CHARA interferometry. Monthly notices of the Royal Astronomical Society, 475(1), L81-L85
Open this publication in new window or tab >>Accurate effective temperatures of the metal-poor benchmark stars HD140283, HD122563, and HD103095 from CHARA interferometry
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 475, no 1, p. L81-L85Article in journal (Refereed) Published
Abstract [en]

Large stellar surveys of the MilkyWay require validation with reference to a set of 'benchmark' stars whose fundamental properties are well determined. For metal-poor benchmark stars, disagreement between spectroscopic and interferometric effective temperatures has called the reliability of the temperature scale into question. We present new interferometric measurements of three metal-poor benchmark stars, HD140283, HD122563, and HD103095, from which we determine their effective temperatures. The angular sizes of all the stars were determined from observations with the PAVO beam combiner at visible wavelengths at the CHARA array, with additional observations of HD103095 made with the VEGA instrument, also at the CHARA array. Together with photometrically derived bolometric fluxes, the angular diameters give a direct measurement of the effective temperature. For HD140283, we find theta(LD) = 0.324 +/- 0.005 mas, T-eff = 5787 +/- 48 K; for HD122563,theta(LD) = 0.926 +/- 0.011 mas, T-eff = 4636 +/- 37 K; and for HD103095,theta(LD) = 0.595 +/- 0.007 mas, T-eff = 5140 +/- 49 K. Our temperatures for HD140283 and HD103095 are hotter than the previous interferometric measurements by 253 and 322 K, respectively. We find good agreement between our temperatures and recent spectroscopic and photometric estimates. We conclude some previous interferometric measurements have been affected by systematic uncertainties larger than their quoted errors.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
standards, techniques: interferometric, surveys, stars: individual: HD103095, stars: individual: HD122563, stars: individual: HD140283
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-360553 (URN)10.1093/mnrasl/sly010 (DOI)000438222600018 ()
Funder
Australian Research Council, DP150100250Australian Research Council, FT160100402Australian Research Council, DE140101364EU, European Research Council, 320360Swedish Research Council, 2015 - 004153Swedish National Space Board
Available from: 2018-09-20 Created: 2018-09-20 Last updated: 2018-09-20Bibliographically approved
Brucalassi, A., Dorn, R. J., Follert, R., Hatzes, A., Bristow, P., Seemann, U., . . . Umlauf, T. (2018). Full System Test and early Preliminary Acceptance Europe results for CRIRES. In: Evans, CJ, Simard, L, Takami, H (Ed.), Ground-Based And Airborne Instrumentation For Astronomy VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX. , Article ID UNSP 1070239.
Open this publication in new window or tab >>Full System Test and early Preliminary Acceptance Europe results for CRIRES
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2018 (English)In: Ground-Based And Airborne Instrumentation For Astronomy VII / [ed] Evans, CJ, Simard, L, Takami, H, 2018, article id UNSP 1070239Conference paper, Published paper (Refereed)
Abstract [en]

CRIRES+ is the new high-resolution NIR echelle spectrograph intended to be operated at the platform B of VLT Unit telescope UT3. It will cover from Y to M bands (0.95-5.3um) with a spectral resolution of R = 50000 or R = 100000. The main scientific goals are the search of super-Earths in the habitable zone of low-mass stars, the characterisation of transiting planets atmosphere and the study of the origin and evolution of stellar magnetic fields. Based on the heritage of the old adaptive optics (AO) assisted VLT instrument CRIRES, the new spectrograph will present improved optical layout, a new detector system and a new calibration unit providing optimal performances in terms of simultaneous wavelength coverage and radial velocity accuracy (a few m/s). The total observing efficiency will be enhanced by a factor of 10 with respect to CRIRES. An innovative spectro-polarimetry mode will be also offered and a new metrology system will ensure very high system stability and repeatability. Fiinally, the CRIRES+ project will also provide the community with a new data reduction software (DRS) package. CRIRES+ is currently at the initial phase of its Preliminary Acceptance in Europe (PAE) and it will be commissioned early in 2019 at VLT. This work outlines the main results obtained during the initial phase of the full system test at ESO HQ Garching.

Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
CRIRES, VLT, high resolution spectroscopy, echelle spectrograph, infrared instrumentation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373093 (URN)10.1117/12.2313743 (DOI)000452664300080 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX
Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically 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
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