arXiv subjects

Teresa Antoja

Publications and source records attributed to Teresa Antoja.

31 records · Page 2Linked to original sources

arXiv2020

The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities

The Radial Velocity Experiment (RAVE) is a magnitude-limited (9<I<12) spectroscopic survey of Galactic stars randomly selected in the southern hemisphere. The RAVE medium-resolution spectra (R~7500) cover the Ca-triplet region (8410-8795A). The 6th and final data release (DR6 or FDR) is based on 518387 observations of 451783 unique stars. RAVE observations were taken between 12 April 2003 and 4 April 2013. Here we present the genesis, setup and data reduction of RAVE as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in RAVE DR6. Furthermore, we present derived spectral classification and radial velocities for the RAVE targets, complemented by cross matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km/s, while 95% of the objects have radial velocities better than 4.0 km/s. Stellar atmospheric parameters, abundances and distances are presented in subsequent publication. The data can be accessed via the RAVE Web (http://rave-survey.org) or the Vizier database.

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arXiv2019

Gaia DR2 white dwarfs in the Hercules stream

We analyzed the velocity space of the thin and thick-disk Gaia white dwarf population within 100 pc looking for signatures of the Hercules stellar stream. We aimed to identify those objects belonging to the Hercules stream and, by taking advantage of white dwarf stars as reliable cosmochronometers, to derive a first age distribution. We applied a kernel density estimation to the $UV$ velocity space of white dwarfs. For the region where a clear overdensity of stars was found, we created a 5-D space of dynamic variables. We applied a hierarchichal clustering method, HDBSCAN, to this 5-D space, identifying those white dwarfs that share similar kinematic characteristics. Finally, under general assumptions and from their photometric properties, we derived an age estimate for each object. The Hercules stream was firstly revealed as an overdensity in the $UV$ velocity space of the thick-disk white dwarf population. Three substreams were then found: Hercules $a$ and Hercules $b$, formed by thick-disk stars with an age distribution peaked $4\,$Gyr in the past and extended to very old ages; and Hercules $c$, with a ratio of 65:35 thin:thick stars and a more uniform age distribution younger than 10 Gyr.

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arXiv2018

Correlations between age, kinematics, and chemistry as seen by the RAVE survey

We explore the connections between stellar age, chemistry, and kinematics across a Galactocentric distance of $7.5 < R\,(\mathrm{kpc}) < 9.0$, using a sample of $\sim 12\,000$ intermediate-mass (FGK) turnoff stars observed with the RAdial Velocity Experiment (RAVE) survey. The kinematics of this sample are determined using radial velocity measurements from RAVE, and parallax and proper motion measurements from the Tycho-Gaia Astrometric Solution (TGAS). In addition, ages for RAVE stars are determined using a Bayesian method, taking TGAS parallaxes as a prior. We divide our sample into young ($0 < τ< 3$ Gyr) and old ($8 < τ< 13$ Gyr) populations, and then consider different metallicity bins for each of these age groups. We find significant differences in kinematic trends of young and old, metal-poor and metal-rich, stellar populations. In particular, we find a strong metallicity dependence in the mean Galactocentric radial velocity as a function of radius ($\partial {V_{\rm R}}/\partial R$) for young stars, with metal-rich stars having a much steeper gradient than metal-poor stars. For $\partial {V_ϕ}/\partial R$, young, metal-rich stars significantly lag the LSR with a slightly positive gradient, while metal-poor stars show a negative gradient above the LSR. We interpret these findings as correlations between metallicity and the relative contributions of the non-axisymmetries in the Galactic gravitational potential (the spiral arms and the bar) to perturb stellar orbits.

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arXiv2018

Dynamical Ages of the Young Local Associations with $\textit{Gaia}$

The Young Local Associations constitute an excellent sample for the study of a variety of astrophysical topics, especially the star formation process in low-density environments. Data from the Gaia mission allows us to undertake studies of the YLAs with unprecedented accuracy. We determine the dynamical age and place of birth of a set of associations in a uniform and dynamically consistent manner. There are nine YLAs in our sample $ε$ Chamaeleontis, TW Hydrae, $β$ Pictoris, Octans, Tucana-Horologium, Columba, Carina, Argus and AB Doradus. We designed a method for deriving the dynamical age of the YLAs based on the orbital integration. It involves a strategy to account for the effect of observational errors and we tested it using mock YLAs. Finally, we applied it to our set of nine YLAs with astrometry from the first Gaia data release and complementary on-ground radial velocities from the literature. Our orbital analysis yields a first estimate of the dynamical age of 3$^{+9}_{-0}$ Myr, 13$^{+7}_{-0}$ Myr and 5$^{+23}_{-0}$ Myr for $ε$ Cha, $β$ Pict and Tuc-Hor, respectively. For four other associations (Oct, Col, Car and Arg), we provide a lower limit for the dynamical age. Our rigorous error treatment indicates that TW Hya and AB Dor deserve further study. Our dynamical ages are compatible spectroscopic and isochrone fitting ages obtained elsewhere. From the orbital analysis, we suggest a scenario with two episodes of star formation: one ~40 Myr ago in the first quadrant that gave birth to $ε$ Cha, TW Hya and $β$ Pic, and another 5-15 Myr ago close to the Sun that formed Tuc-Hor, Col, and Car. Future Gaia data will provide the necessary accuracy to improve the present results, especially for the controversial age determinations, and additional evidence for the proposed scenario, once a complete census of YLAs and better membership can be obtained.

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arXiv2017

Tails and streams around the Galactic globular clusters NGC1851, NGC1904, NGC2298 and NGC2808

We present DECam imaging for the peculiar Galactic globular clusters NGC1851, NGC1904 (M79), NGC2298 and NGC2808. Our deep photometry reveals that all the clusters have an important contribution of stars beyond their King tidal radii and present tails with different morphologies. We have also explored the surroundings of the clusters where the presence of the Canis Major overdensity and/or the low Galactic latitude Monoceros ring at d~8kpc is evident. A second stellar system is found at d~17kpc and spans at least 18deg x 15deg in the sky. As one of the possible scenarios to explain that feature, we propose that the unveiled system is part of Monoceros explained as a density wave moving towards the outer Milky Way. Alternatively, the unveiled system might be connected with other known halo substructures or associated with the progenitor dwarf galaxy of NGC1851 and NGC1904, which are widely considered accreted globular clusters.

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arXiv2016

The Radial Velocity Experiment (RAVE): Fifth Data Release

Data Release 5 (DR5) of the Radial Velocity Experiment (RAVE) is the fifth data release from a magnitude-limited (9< I < 12) survey of stars randomly selected in the southern hemisphere. The RAVE medium-resolution spectra ($R\sim7500$) covering the Ca-triplet region (8410-8795Å) span the complete time frame from the start of RAVE observations in 2003 to their completion in 2013. Radial velocities from 520,781 spectra of 457,588 unique stars are presented, of which 255,922 stellar observations have parallaxes and proper motions from the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. For our main DR5 catalog, stellar parameters (effective temperature, surface gravity, and overall metallicity) are computed using the RAVE DR4 stellar pipeline, but calibrated using recent K2 Campaign 1 seismic gravities and Gaia benchmark stars, as well as results obtained from high-resolution studies. Also included are temperatures from the Infrared Flux Method, and we provide a catalogue of red giant stars in the dereddened color $(J-Ks)_0$ interval (0.50,0.85) for which the gravities were calibrated based only on seismology. Further data products for sub-samples of the RAVE stars include individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and distances found using isochrones. Each RAVE spectrum is complemented by an error spectrum, which has been used to determine uncertainties on the parameters. The data can be accessed via the RAVE Web site or the Vizier database.

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arXiv2015

Detection of satellite remnants in the Galactic Halo with Gaia III. Detection limits for Ultra Faint Dwarf Galaxies

We present a method to identify Ultra Faint Dwarf Galaxy (UFDG) candidates in the halo of the Milky Way using the future Gaia catalogue and we explore its detection limits and completeness. The method is based on the Wavelet Transform and searches for over-densities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time. We test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot (GUMS) as a background, and use a library of around 30 000 UFDGs simulated as Plummer spheres with a single stellar population. For the UFDGs we use a wide range of structural and orbital parameters that go beyond the range spanned by real systems, where some UFDGs may remain undetected. We characterize the detection limits as function of the number of observable stars by Gaia in the UFDGs with respect to that of the background and their apparent sizes in the sky and proper motion planes. We find that the addition of proper motions in the search improves considerably the detections compared to a photometric survey at the same magnitude limit. Our experiments suggest that Gaia will be able to detect UFDGs that are similar to some of the known UFDGs even if the limit of Gaia is around 2 magnitudes brighter than that of SDSS, with the advantage of having a full-sky catalogue. We also see that Gaia could even find some UFDGs that have lower surface brightness than the SDSS limit.

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arXiv2014

The analysis of realistic Stellar Gaia mock catalogues. I. Red Clump Stars as tracers of the central bar

In this first paper we simulate the population of disc Red Clump stars to be observed by Gaia. We generate a set of test particles and we evolve it in a 3D barred Milky Way like galactic potential. We assign physical properties of the Red Clump trace population and a realistic 3D interstellar extinction model. We add Gaia observational constraints and an error model according to the pre-commissioning scientific performance assessments. We present and analyse two mock catalogues, offered to the community, that are an excellent test bed for testing tools being developed for the future scientific exploitation of Gaia data. The first catalogue contains stars up to Gaia G 20, while the second is the subset containing Gaia radial velocity data with a maximum error of sigmaVr=10 kms. Here we present first attempts to characterise the density structure of the Galactic bar in the Gaia space of observables. The Gaia large errors in parallax and the high interstellar extinction in the inner parts of the Galactic disc prevent us to model the bar overdensity. This result suggests the need to combine Gaia and IR data to undertake such studies. We find that IR photometric distances for this Gaia sample allow us to recover the Galactic bar orientation angle with an accuracy of approximately 5 degrees.

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arXiv2014

The Galactic bar and the large scale velocity gradients in the Galactic disk

Aims: We investigate whether the cylindrical (galactocentric) radial velocity gradient of ~ -3 km/s/kpc, directed radially from the Galactic center and recently observed in the stars of the solar neighborhood with the RAVE survey, can be explained by the resonant effects of the bar near the solar neighborhood. Methods: We compared the results of test particle simulations of the Milky Way with a potential that includes a rotating bar with observations from the RAVE survey. To this end we applied the RAVE selection function to the simulations and convolved these with the characteristic RAVE errors. We explored different "solar neighborhoods" in the simulations, as well as different bar models Results: We find that the bar induces a negative radial velocity gradient at every height from the Galactic plane, outside the outer Lindblad resonance and for angles from the long axis of the bar compatible with the current estimates. The selection function and errors do not wash away the gradient, but often make it steeper, especially near the Galactic plane, because this is where the RAVE survey is less radially extended. No gradient in the vertical velocity ispresent in our simulations, from which we may conclude that this cannot be induced by the bar.

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arXiv2014

A novel method to bracket the corotation radius in galaxy disks: vertex deviation maps

We map the kinematics of stars in simulated galaxy disks with spiral arms using the velocity ellipsoid vertex deviation (l$_v$). We use test particle simulations, and for the first time, fully self-consistent high resolution N-body models. We compare our maps with the Tight Winding Approximation model analytical predictions. We see that for all barred models spiral arms rotate closely to a rigid body manner and the vertex deviation values correlate with the density peaks position bounded by overdense and underdense regions. In such cases, vertex deviation sign changes from negative to positive when crossing the spiral arms in the direction of disk rotation, in regions where the spiral arms are in between corotation (CR) and the Outer Lindblad Resonance (OLR). By contrast, when the arm sections are inside the CR and outside the OLR, l$_v$ changes from negative to positive.We propose that measurements of the vertex deviations pattern can be used to trace the position of the main resonances of the spiral arms. We propose that this technique might exploit future data from Gaia and APOGEE surveys. For unbarred N-body simulations with spiral arms corotating with disk material at all radii, our analysis suggests that no clear correlation exists between l$_v$ and density structures.

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arXiv2013

3D test particle simulations of the Galactic disks. The kinematical effects of the bar

Aims: To study the imprints of a rotating bar on the kinematics of stars in the thin and thick disks throughout the Galaxy. Methods: We perform test particle numerical simulations of the thin and thick disks in a 3D Galactic potential that includes a halo, a bulge, thin and thick disks, and a Ferrers bar. We analyze the resulting velocity distributions of populations corresponding to both disks, for different positions in the Galaxy and for different structural parameters of the bar. Results: We find that the velocity distributions of the disks are affected by the bar, and that strong transient effects are present for approximately 10 bar rotations after this is introduced adiabatically. On long (more realistic) timescales, the effects of the bar are strong on the kinematics of thin disk stars, and weaker on those in the thick disk, but in any case significant. Furthermore, we find that it is possible to trace the imprints of the bar also vertically and at least up to z ~ 1 kpc for the thin disk and z ~ 2 kpc for the thick disk.

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arXiv2013

On the galaxy spiral arms' nature as revealed by rotation frequencies

High resolution N-body simulations using different codes and initial condition techniques reveal two different behaviours for the rotation frequency of transient spiral arms like structures. Whereas unbarred disks present spiral arms nearly corotatingwith disk particles, strong barred models (bulged or bulge-less) quickly develop a bar-spiral structure dominant in density, with a pattern speed almost constant in radius. As the bar strength decreases the arm departs from bar rigid rotation and behaves similar to the unbarred case. In strong barred models we detect in the frequency space other subdominant and slower modes at large radii, in agreement with previous studies, however we also detect them in the configuration space. We propose that the distinctive behaviour of the dominant spiral modes can be exploited in order to constraint the nature of Galactic spiral arms by the astrometric survey GAIA and by 2-D spectroscopic surveys like CALIFA and MANGA in external galaxies.

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arXiv2011

Constraining the Milky Way potential using the dynamical kinematic substructures

We present a method to constrain the potential of the non-axisymmetric components of the Galaxy using the kinematics of stars in the solar neighborhood. The basic premise is that dynamical substructures in phase-space (i.e. due to the bar and/or spiral arms) are associated with families of periodic or irregular orbits, which may be easily identified in orbital frequency space. We use the "observed" positions and velocities of stars as initial conditions for orbital integrations in a variety of gravitational potentials. We then compute their characteristic frequencies, and study the structure present in the frequency maps. We find that the distribution of dynamical substructures in velocity- and frequency-space is best preserved when the integrations are performed in the "true" gravitational potential.

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