Context. Data-driven methods play an increasingly important role in the field of astrophysics. In... more Context. Data-driven methods play an increasingly important role in the field of astrophysics. In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general). Aims. We test whether it is possible to transfer the labels derived from a high-resolution stellar survey to intermediate-resolution spectra of another survey by using a CNN. Methods. We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R = 22 500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R ∼ 7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and ...
The second Gaia data release has published high-precision astrometric measurements for over a bil... more The second Gaia data release has published high-precision astrometric measurements for over a billion sources. In the coming years, Gaia data will make fundamental contributions to numerous open questions on the evolution of our Galaxy. We here focus on the long-standing debate on the origin and dynamical nature of the warp of our Galaxy, with particular attention to the warp-induced motions in stellar kinematics. Taking advantage of Gaia DR2 data, we detect the kinematic signature of the Galactic warp out to a distance of 7 kpc from the Sun. The signature manifests itself as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius, with a signal-to-noise larger than 10. The signal is present in two samples of intrinsically young and old stellar populations, selected via a probabilistic approach. Based on our results, we argue that the warp is principally a gravitational phenomenon, thus placing an important constraint on the possible formation scenario....
Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun fro... more Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the Gaia Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. Methods. Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue. Re...
Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using ... more Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using a sample of Sloan Extension for Galactic Understanding and Exploration (SEGUE) G-dwarfs. We investigate the rotation curve shape for the presence of any peculiarities just outside the solar radius as has been reported by some authors. Methods. Using the modified Strömberg relation and the most recent data from the RAdial Velocity Experiment (RAVE), we determine the solar peculiar velocity and the radial scale lengths for the three populations of different metallicities representing the Galactic thin disc. Subsequently, with the same binning in metallicity for the SEGUE G-dwarfs, we construct the rotation curve for a range of Galactocentric distances from 7 to 10 kpc. We approach this problem in a framework of classical Jeans analysis and derive the circular velocity by correcting the mean tangential velocity for the asymmetric drift in each distance bin. With SEGUE data we also calculate...
Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (po... more Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (positions, proper motions, and parallaxes) for an unprecedented number of sources (more than 1.3 billion, mostly stars). This new wealth of data will enable the undertaking of statistical analysis of many astrophysical problems that were previously infeasible for lack of reliable astrometry, and in particular because of the lack of parallaxes. However, the use of this wealth of astrometric data comes with a specific challenge: how can the astrophysical parameters of interest be properly inferred from these data?Aims.The main focus of this paper, but not the only focus, is the issue of the estimation of distances from parallaxes, possibly combined with other information. We start with a critical review of the methods traditionally used to obtain distances from parallaxes and their shortcomings. Then we provide guidelines on how to use parallaxes more efficiently to estimate distances by usi...
Proceedings of the International Astronomical Union, 2015
Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in t... more Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in the infra-red calcium triplet (CaII) spectral region. In this study we extended the analysis of RAVE very metal-poor stars ([Fe/H]…
Proceedings of the International Astronomical Union, 2013
We present a qualitative characterization of activity levels of a large database of ~44,000 candi... more We present a qualitative characterization of activity levels of a large database of ~44,000 candidate RAVE stars (unbiased, magnitude limited medium resolution survey) that show chromospheric emission in the Ca II infrared triplet and this vastly enlarges previously known samples. Our main motivation to study these stars is the anti-correlation of chromospheric activity and stellar ages that could be calibrated using stellar clusters with known ages. Locally linear embedding used for a morphological classification of spectra revealed 53,347 cases with a suggested emission component in the calcium lines. We analyzed a subsample of ~44,000 stars with S/N>20 using a spectral subtraction technique where observed reference spectra of inactive stars were used as templates instead of synthetic ones. Both the equivalent width of the excess emission for each calcium line and their sum is derived for all candidate active stars with no respect to the origin of their emission flux. ~17,800 s...
Context. Data-driven methods play an increasingly important role in the field of astrophysics. In... more Context. Data-driven methods play an increasingly important role in the field of astrophysics. In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general). Aims. We test whether it is possible to transfer the labels derived from a high-resolution stellar survey to intermediate-resolution spectra of another survey by using a CNN. Methods. We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R = 22 500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R ∼ 7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and ...
The second Gaia data release has published high-precision astrometric measurements for over a bil... more The second Gaia data release has published high-precision astrometric measurements for over a billion sources. In the coming years, Gaia data will make fundamental contributions to numerous open questions on the evolution of our Galaxy. We here focus on the long-standing debate on the origin and dynamical nature of the warp of our Galaxy, with particular attention to the warp-induced motions in stellar kinematics. Taking advantage of Gaia DR2 data, we detect the kinematic signature of the Galactic warp out to a distance of 7 kpc from the Sun. The signature manifests itself as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius, with a signal-to-noise larger than 10. The signal is present in two samples of intrinsically young and old stellar populations, selected via a probabilistic approach. Based on our results, we argue that the warp is principally a gravitational phenomenon, thus placing an important constraint on the possible formation scenario....
Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun fro... more Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the Gaia Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. Methods. Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue. Re...
Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using ... more Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using a sample of Sloan Extension for Galactic Understanding and Exploration (SEGUE) G-dwarfs. We investigate the rotation curve shape for the presence of any peculiarities just outside the solar radius as has been reported by some authors. Methods. Using the modified Strömberg relation and the most recent data from the RAdial Velocity Experiment (RAVE), we determine the solar peculiar velocity and the radial scale lengths for the three populations of different metallicities representing the Galactic thin disc. Subsequently, with the same binning in metallicity for the SEGUE G-dwarfs, we construct the rotation curve for a range of Galactocentric distances from 7 to 10 kpc. We approach this problem in a framework of classical Jeans analysis and derive the circular velocity by correcting the mean tangential velocity for the asymmetric drift in each distance bin. With SEGUE data we also calculate...
Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (po... more Context.The secondGaiadata release (GaiaDR2) provides precise five-parameter astrometric data (positions, proper motions, and parallaxes) for an unprecedented number of sources (more than 1.3 billion, mostly stars). This new wealth of data will enable the undertaking of statistical analysis of many astrophysical problems that were previously infeasible for lack of reliable astrometry, and in particular because of the lack of parallaxes. However, the use of this wealth of astrometric data comes with a specific challenge: how can the astrophysical parameters of interest be properly inferred from these data?Aims.The main focus of this paper, but not the only focus, is the issue of the estimation of distances from parallaxes, possibly combined with other information. We start with a critical review of the methods traditionally used to obtain distances from parallaxes and their shortcomings. Then we provide guidelines on how to use parallaxes more efficiently to estimate distances by usi...
Proceedings of the International Astronomical Union, 2015
Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in t... more Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in the infra-red calcium triplet (CaII) spectral region. In this study we extended the analysis of RAVE very metal-poor stars ([Fe/H]…
Proceedings of the International Astronomical Union, 2013
We present a qualitative characterization of activity levels of a large database of ~44,000 candi... more We present a qualitative characterization of activity levels of a large database of ~44,000 candidate RAVE stars (unbiased, magnitude limited medium resolution survey) that show chromospheric emission in the Ca II infrared triplet and this vastly enlarges previously known samples. Our main motivation to study these stars is the anti-correlation of chromospheric activity and stellar ages that could be calibrated using stellar clusters with known ages. Locally linear embedding used for a morphological classification of spectra revealed 53,347 cases with a suggested emission component in the calcium lines. We analyzed a subsample of ~44,000 stars with S/N>20 using a spectral subtraction technique where observed reference spectra of inactive stars were used as templates instead of synthetic ones. Both the equivalent width of the excess emission for each calcium line and their sum is derived for all candidate active stars with no respect to the origin of their emission flux. ~17,800 s...
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Papers by G. Seabroke