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  • 1
    Electronic Resource
    Electronic Resource
    Carbon stars in infrared surveys (1994)
    Springer
    Astrophysics and space science 217 (1994), S. 141-142 
    Details
    ISSN: 1572-946X
    Keywords: AGB stars ; Infrared surveys ; Galactic structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In order to prepare the analysis of the forthcoming near-IR surveys (DENIS, 2MASS) and to interpret them in terms of galactic structure and AGB evolution, we present model predictions of AGB distributions in K, in 12μm and in (J-K, [12–25]) space, as they will be obtained from these surveys, cross-correlated with IRAS Catalog. The simulations have been made by adding the AGB to the Besançon model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00990041
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    Paper (German National Licenses)
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  • 2
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    Close encounters involving RAVE stars beyond the 47 Tucanae tidal radius (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-07
    Description: The most accurate six-dimensional (6D) phase-space information from the Radial Velocity Experiment (RAVE) was used to integrate the orbits of 105 stars around the galactic globular cluster 47 Tucanae, to look for close encounters between them in the past with a minimum distance approach less than the cluster tidal radius. The stars are currently spread over the distance range 3.0 kpc 〈 d  〈 5.5 kpc. Using the uncertainties in the current position and velocity vector for both stars and cluster, 105 pairs of star–cluster orbits were generated in a Monte Carlo numerical scheme, integrated over 2 Gyr and considering an axisymmetric and non-axisymmetric Milky-Way-like Galactic potential, respectively. In this scheme, we identified 20 potential cluster members that had close encounters with the globular cluster 47 Tucanae, all of which have a relative velocity distribution ( V rel ) less than 200 km s –1 at the minimum distance approach. Among these potential members, nine had close encounters with the cluster with velocities less than the escape velocity of 47 Tucanae; therefore a scenario of tidal stripping seems likely. These stars have been classified with a 93 per cent confidence level, leading to the identification of extratidal cluster stars. For the other 11 stars, V rel exceeds the escape velocity of the cluster; therefore likely they were ejected or are unassociated interlopers.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    ExELS: an exoplanet legacy science proposal for the ESA Euclid mission - II. Hot exoplanets and sub-stellar systems (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-06
    Description: The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the frequency of cold exoplanets down to Earth mass from host separations of ~1 au out to the free-floating regime by detecting microlensing events in Galactic bulge. We show that ExELS can also detect large numbers of hot, transiting exoplanets in the same population. The combined microlensing+transit survey would allow the first self-consistent estimate of the relative frequencies of hot and cold sub-stellar companions, reducing biases in comparing ‘near-field’ radial velocity and transiting exoplanets with ‘far-field’ microlensing exoplanets. The age of the bulge and its spread in metallicity further allows ExELS to better constrain both the variation of companion frequency with metallicity and statistically explore the strength of star–planet tides. We conservatively estimate that ExELS will detect ~4100 sub-stellar objects, with sensitivity typically reaching down to Neptune-mass planets. Of these, ~600 will be detectable in both Euclid's VIS (optical) channel and Near Infrared Spectrometer and Photometer (NISP)- H -band imager, with ~90 per cent of detections being hot Jupiters. Likely scenarios predict a range of 2900–7000 for VIS and 400–1600 for H band. Twice as many can be expected in VIS if the cadence can be increased to match the 20-min H -band cadence. The separation of planets from brown dwarfs via Doppler boosting or ellipsoidal variability will be possible in a handful of cases. Radial velocity confirmation should be possible in some cases, using 30 m-class telescopes. We expect secondary eclipses, and reflection and emission from planets to be detectable in up to ~100 systems in both VIS and NISP- H . Transits of ~500 planetary-radius companions will be characterized with two-colour photometry and ~40 with four-colour photometry (VIS, YJH ), and the albedo of (and emission from) a large sample of hot Jupiters in the H band can be explored statistically.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Besancon Galactic model analysis of MOA-II microlensing: evidence for a mass deficit in the inner bulge (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-26
    Description: Galactic bulge microlensing surveys provide a probe of Galactic structure. We present the first field-by-field comparison between microlensing observations and the Besancon population synthesis Galactic model. Using an updated version of the model we provide maps of optical depth, average event duration and event rate for resolved source populations and for difference imaging analysis (DIA) events. We also compare the predicted event time-scale distribution to that observed. The simulation follows the selection criteria of the MOA-II survey. We modify the Besancon model to include M dwarfs and brown dwarfs. Our best-fitting model requires a brown dwarf mass function slope of –0.4. The model provides good agreement with the observed average duration, and respectable consistency with the shape of the time-scale distribution (reduced 2 ~= 2.2). The DIA and resolved source limiting yields bracket the observed number of events by MOA-II (2.17 x and 0.83 x the number observed, respectively). We perform a two-dimensional fit to the event spatial distribution to predict the optical depth and event rate across the Galactic bulge. The most serious difficulty for the model is that it provides only ~50 per cent of the measured optical depth and event rate per star at low Galactic latitude around the inner bulge (| b | 〈 3°). This discrepancy most likely is associated with known underestimated extinction and star counts in the innermost regions and therefore provides additional support for a missing inner stellar population.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    N-body simulation insights into the X-shaped bulge of the Milky Way: kinematics and distance to the Galactic Centre (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-20
    Description: Using simulations of box/peanut- (B/P-) shaped bulges, we explore the nature of the X-shape of the Milky Way's bulge. An X-shape can be associated with a B/P-shaped bulge driven by a bar. By comparing in detail the simulations and the observations we show that the principal kinematic imprint of the X-shape is a minimum in the difference between the near and far side mean line-of-sight velocity along the minor axis. This minimum occurs at around | b | = 4°, which is close to the lower limit at which the X-shape can be detected. No coherent signature of an X-shape can be found in Galactocentric azimuthal velocities, vertical velocities or any of the dispersions. After scaling our simulations, we find that a best fit to the Bulge Radial Velocity Assay data leads to a bar angle of 15°. We also explore a purely geometric method for determining the distance to the Galactic Centre by tracing the arms of the X-shape. We find that we are able to determine this ill-known distance to an accuracy of about 5 per cent with sufficiently accurate distance measurements for the red clump stars in the arms.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Constraining the Galactic structure parameters with the XSTPS-GAC and SDSS photometric surveys (2016)
    Oxford University Press
    Details
    Publication Date: 2016-11-05
    Description: Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are used to derive the global structure parameters of the smooth components of the Milky Way. The data, which cover nearly 11 000 deg 2 sky area and the full range of Galactic latitude, allow us to construct a globally representative Galactic model. The number density distribution of Galactic halo stars is fitted with an oblate spheroid that decays by power law. The best fitting yields an axis ratio and a power-law index = 0.65 and p = 2.79, respectively. The r -band differential star counts of three dwarf samples are then fitted with a Galactic model. The best-fitting model yielded by a Markov Chain Monte Carlo analysis has thin and thick disc scale heights and lengths of H 1 = 322 pc and L 1 = 2343 pc, H 2 = 794 pc and L 2 = 3638 pc, a local thick-to-thin disc density ratio of f 2 = 11 per cent, and a local density ratio of the oblate halo to the thin disc of f h = 0.16 per cent. The measured star count distribution, which is in good agreement with the above model for most of the sky area, shows a number of statistically significant large-scale overdensities, including some of the previously known substructures, such as the Virgo overdensity and the so-called ‘north near structure’, and a new feature between $150^\circ 〈 l 〈 240^\circ$ and $-1^\circ 〈 b 〈 -5^\circ$ , at an estimated distance between 1.0 and 1.5 kpc. The Galactic North–South asymmetry in the anticentre is even stronger than previously thought.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-01
    Description: Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general is an important unsolved problem in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE (Apache Point Observatory Galactic Evolution Experiment) of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe] and anticorrelated with [C/Fe]. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars within the same volume. Their metallicity distribution is seemingly unimodal, peaking at [Fe/H] ~ –1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of ~8. In that scenario, the total mass contained in so-called ‘first-generation’ stars cannot be larger than that in ‘second-generation’ stars by more than a factor of ~9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between ‘second-generation’ stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    ExELS: an exoplanet legacy science proposal for the ESA Euclid mission - I. Cold exoplanets (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-08
    Description: The Euclid mission is the second M-class mission of the ESA Cosmic Vision programme, with the principal science goal of studying dark energy through observations of weak lensing and baryon acoustic oscillations. Euclid is also expected to undertake additional Legacy Science programmes. One such proposal is the Exoplanet Euclid Legacy Survey (ExELS) which will be the first survey able to measure the abundance of exoplanets down to Earth mass for host separations from ~1 au out to the free-floating (unbound) regime. The cold and free-floating exoplanet regimes represent a crucial discovery space for testing planet formation theories. ExELS will use the gravitational microlensing technique and will detect 1000 microlensing events per month over 1.6 deg 2 of the Galactic bulge. We assess how many of these events will have detectable planetary signatures using a detailed multiwavelength microlensing simulator – the Manchester–Besançon microLensing Simulator (MABμLS) – which incorporates the Besançon Galactic model with 3D extinction. MABμLS is the first theoretical simulation of microlensing to treat the effects of point spread function (PSF) blending self-consistently with the underlying Galactic model. We use MABμLS, together with current numerical models for the Euclid PSFs, to explore a number of designs and de-scope options for ExELS, including the exoplanet yield as a function of filter choice and slewing time, and the effect of systematic photometry errors. Using conservative extrapolations of current empirical exoplanet mass functions determined from ground-based microlensing and radial velocity surveys, ExELS can expect to detect a few hundred cold exoplanets around mainly G-, K- and M-type stellar hosts, including ~45 Earth-mass planets and ~6 Mars-mass planets for an observing programme totalling 10 months. ExELS will be capable of measuring the cold exoplanet mass function down to Earth mass or below, with orbital separations ranging from ~1 au out to infinity (i.e. the free-floating regime). Recent ground-based microlensing measurements indicate a significant population of free-floating Jupiters, in which case ExELS will detect hundreds of free-floating planets. ExELS will also be sensitive to hot exoplanets and sub-stellar companions through their transit signatures and this is explored in a companion paper.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Chemical composition of planet building blocks as predicted by stellar population synthesis (2019)
    EDP Sciences
    Details
    Publication Date: 2019-01-24
    Description: Context. Future space missions (TESS, CHEOPS, PLATO, and the JWST) will considerably improve our understanding of the formation and history of planetary systems by providing accurate constraints on planetary radius, mass, and atmospheric composition. Currently, observations show that the presence of planetary companions is closely linked to the metallicity and the chemical abundances of the host stars. Aims. We aim to build an integrated tool for predicting the planet building blocks (PBBs) composition as a function of the stellar populations to interpret ongoing and future large surveys. The different stellar populations we observe in our Galaxy are characterized by different metallicities and α-element abundances. We here investigate the trends of the expected PBBs composition with the chemical abundance of the host star in different parts of the Galaxy. Methods. We synthesized stellar populations with the Besançon galaxy model, which includes stellar evolutionary tracks that are computed with the stellar evolution code STAREVOL. We integrated a previously published simple stoichiometric model into this code to determine the expected composition of the PBBs. Results. We determine the expected PBB composition around FGK stars for the four galactic populations (thin and thick disks, halo, and bulge) within the Milky Way. Our solar neighborhood simulations are in good agreement with the recent results obtained with the HARPS survey for firon, fw, and the heavy element mass fraction fZ. We present evidence of a clear dependence of firon and fw on the initial alpha abundances [α/Fe] of the host star. We find that the different initial [α/Fe] distributions in the different galactic populations lead to a bimodal distribution of PBB composition. Our simulations show an iron valley that separates PBBs with high and low iron mass fractions and a water valley that separates PBBs with high and low water mass fractions. Conclusions. We linked host star abundances and expected PBB composition in an integrated model of the Galaxy. The trends we derive are an important step for statistical analyses of expected planet properties. In particular, internal structure models may use these results to derive statistical trends of rocky planet properties, constrain habitability, and prepare an interpretation of ongoing and future large-scale surveys of exoplanets.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 10
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    New nearby stars in the Liverpool-Edinburgh high proper motion survey selected by DENIS photometry (2004)
    EDP Sciences
    Details
    Publication Date: 2004-06-22
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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