A new look at the kinematics of the bulge from an N-body model

(Abridged) By using an N-body simulation of a bulge that was formed via a bar instability mechanism, we analyse the imprints of the initial (i.e. before bar formation) location of stars on the bulge kinematics, in particular on the heliocentric radial velocity distribution of bulge stars. Four different latitudes were considered: $b=-4^\circ$, $-6^\circ$, $-8^\circ$, and $-10^\circ$, along the bulge minor axis as well as outside it, at $l=\pm5^\circ$ and $l=\pm10^\circ$. The bulge X-shaped structure comprises stars that formed in the disk at different locations. Stars formed in the outer disk, beyond the end of the bar, which are part of the boxy peanut-bulge structure may show peaks in the velocity distributions at positive and negative heliocentric radial velocities with high absolute values that can be larger than 100 $\rm km$ $\rm s^{-1}$, depending on the observed direction. In some cases the structure of the velocity field is more complex and several peaks are observed. Stars formed in the inner disk, the most numerous, contribute predominantly to the X-shaped structure and present different kinematic characteristics. Our results may enable us to interpret the cold high-velocity peak observed in the APOGEE commissioning data, as well as the excess of high-velocity stars in the near and far arms of the X-shaped structure at $l$=$0^\circ$ and $b$=$-6^\circ$. When compared with real data, the kinematic picture becomes more complex due to the possible presence in the observed samples of classical bulge and/or thick disk stars. Overall, our results point to the existence of complex patterns and structures in the bulge velocity fields, which are generated by the bar. This suggests that caution should be used when interpreting the bulge kinematics: the presence of substructures, peaks and clumps in the velocity fields is not necessarily a sign of past accretion events.Comment: 21 pages, 18 figures. Accepted for publication in A&

The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude

High resolution (R$\sim$22,500) spectra for 400 red clump giants, in four fields within $\rm -4.8^{\circ} \lesssim b \lesssim -3.4^{\circ}$ and $\rm -10^{\circ} \lesssim l \lesssim +10^{\circ}$, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another $\sim$ 400 stars in Baade's Window, observed with the identical instrumental configuration. We constructed the metallicity distributions for the entire sample, as well as for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is well fitted by two Gaussians. The metal poor component is rather broad, with a mean at $\rm =-0.31$ dex and $\sigma=0.31$ dex. The metal-rich one is narrower, with mean $\rm =+0.26$ and $\sigma=0.2$ dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime, similar to the one observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at $\rm [Fe/H]=-0.44$ dex. This \textit{knee} is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the one reported for the Bulge micro lensed dwarf and sub-giant stars. We found no variation in $\alpha$-element abundance distributions between different fields.Comment: Accepted for publication in A&

The GIRAFFE Inner Bulge Survey (GIBS). I. Survey Description and a kinematical map of the Milky Way bulge

The Galactic bulge is a massive, old component of the Milky Way. It is known to host a bar, and it has recently been demonstrated to have a pronounced boxy/peanut structure in its outer region. Several independent studies suggest the presence of more than one stellar populations in the bulge, with different origins and a relative fraction changing across the bulge area. This is the first of a series of papers presenting the results of the Giraffe Inner Bulge Survey, carried out at the ESO-VLT with the multifibre spectrograph FLAMES. Spectra of ~5000 red clump giants in 24 bulge fields have been obtained at resolution R=6500, in the infrared Calcium triplet wavelength region at 8500 {\AA}. They are used to derive radial velocities and metallicities, based on new calibration specifically devised for this project. Radial velocities for another ~1200 bulge red clump giants, obtained from similar archive data, have been added to the sample. Higher resolution spectra have been obtained for 450 additional stars at latitude b=-3.5, with the aim of investigating chemical abundance patterns variations with longitude, across the inner bulge. In total we present here radial velocities for 6392 RC stars. We derive a radial velocity, and velocity dispersion map of the Milky Way bulge, useful to be compared with similar maps of external bulges, and to infer the expected velocities and dispersion at any line of sight. The K-type giants kinematics is consistent with the cylindrical rotation pattern of M-giants from the BRAVA survey. Our sample enables to extend this result to latitude b=-2, closer to the Galactic plane than probed by previous surveys. Finally, we find strong evidence for a velocity dispersion peak at (0,-1) and (0,-2), possibly indicative of a high density peak in the central 250 pc of the bulgeComment: A&A in pres

Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants

We obtained FLAMES-GIRAFFE spectra (R=22,500) at the ESO Very Large Telescope for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b=-4, b=-6, b=-12. Another 176 stars belong to a field containing the globular cluster NGC 6553, located at b=-3 and 5 degrees away from the other three fields along the major axis. Our results confirm, with large number statistics, the chemical similarity between the Galactic bulge and thick disk, which are both enhanced in alpha elements when compared to the thin disk. In the same context, we analyze [alpha/Fe] vs. [Fe/H] trends across different bulge regions. The most metal rich stars, showing low [alpha/Fe] ratios at b=-4 disappear at higher Galactic latitudes in agreement with the observed metallicity gradient in the bulge. Metal-poor stars ([Fe/H]<-0.2) show a remarkable homogeneity at different bulge locations. We have obtained further constrains for the formation scenario of the Galactic bulge. A metal-poor component chemically indistinguishable from the thick disk hints for a fast and early formation for both the bulge and the thick disk. Such a component shows no variation, neither in abundances nor kinematics, among different bulge regions. A metal-rich component showing low [alpha/Fe] similar to those of the thin disk disappears at larger latitudes. This allows us to trace a component formed through fast early mergers (classical bulge) and a disk/bar component formed on a more extended timescale.Comment: 13 pages, 17 figures. Accepted for publication in Astronomy and Astrophysic

Gaia Data Release 2: Summary of the contents and survey properties

© ESO, 2018. This is the accepted version of the article published by EDP Sciences at: https://doi.org/10.1051/0004-6361/201833051[Abstract]: Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330-680 nm) and GRP (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia Archive website is http://gea.esac.esa.int/archive/. The Gaia mission and data processing have financially been supported by, in alphabetical order by country: the Algerian Centre de Recherche en Astronomie, Astrophysique et Géophysique of Bouzareah Observatory; the Austrian Fonds zur Förderung der wissenschaftlichen Forschung (FWF) Hertha Firnberg Programme through grants T359, P20046, and P23737; the BELgian federal Science Policy Office (BELSPO) through various PROgramme de Développement d’EXpériences scientifiques (PRODEX) grants and the Polish Academy of Sciences - Fonds Wetenschappelijk Onderzoek through grant VS.091.16N; the Brazil-France exchange programmes Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Coordenação de Aperfeicoamento de Pessoal de Nível Superior (CAPES) - Comité Français d’Evaluation de la Coopération Universitaire et Scientifique avec le Brésil (COFECUB); the Chilean Dirección de Gestión de la Investigación (DGI) at the University of Antofagasta and the Comité Mixto ESO-Chile; the National Science Foundation of China (NSFC) through grants 11573054 and 11703065; the Czech-Republic Ministry of Education, Youth, and Sports through grant LG 15010, the Czech Space Office through ESA PECS contract 98058, and Charles University Prague through grant PRIMUS/SCI/17; the Danish Ministry of Science; the Estonian Ministry of Education and Research through grant IUT40-1; the European Commission’s Sixth Framework Programme through the European Leadership in Space Astrometry (ELSA) Marie Curie Research Training Network (MRTN-CT-2006-033481), through Marie Curie project PIOF-GA-2009-255267 (Space AsteroSeismology & RR Lyrae stars, SAS-RRL), and through a Marie Curie Transfer-of-Knowledge (ToK) fellowship (MTKD-CT-2004-014188); the European Commission’s Seventh Framework Programme through grant FP7-606740 (FP7-SPACE-2013-1) for the Gaia European Network for Improved data User Services (GENIUS) and through grant 264895 for the Gaia Research for European Astronomy Training (GREAT-ITN) network; the European Research Council (ERC) through grants 320360 and 647208 and through the European Union’s Horizon 2020 research and innovation programme through grants 670519 (Mixing and Angular Momentum tranSport ofmassIvE stars – MAMSIE) and 687378 (Small Bodies: Near and Far); the European Science Foundation (ESF), in the framework of the Gaia Research for European Astronomy Training Research Network Programme (GREAT-ESF); the European Space Agency (ESA) in the framework of the Gaia project, through the Plan for European Cooperating States (PECS) programme through grants for Slovenia, through contracts C98090 and 4000106398/12/NL/KML for Hungary, and through contract 4000115263/15/NL/IB for Germany; the European Union (EU) through a European Regional Development Fund (ERDF) for Galicia, Spain; the Academy of Finland and the Magnus Ehrnrooth Foundation; the French Centre National de la Recherche Scientifique (CNRS) through action “Défi MASTODONS”, the Centre National d’Etudes Spatiales (CNES), the L’Agence Nationale de la Recherche (ANR) “Investissements d’avenir” Initiatives D’EXcellence (IDEX) programme Paris Sciences et Lettres (PSL*) through grant ANR-10-IDEX-0001-02, the ANR “Défi de tous les savoirs” (DS10) programme through grant ANR-15-CE31-0007 for project “Modelling the Milky Way in the Gaia era” (MOD4Gaia), the Région Aquitaine, the Université de Bordeaux, and the Utinam Institute of the Université de Franche-Comté, supported by the Région de Franche-Comté and the Institut des Sciences de l’Univers (INSU); the German Aerospace Agency (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) through grants 50QG0501, 50QG0601, 50QG0602, 50QG0701, 50QG0901, 50QG1001, 50QG1101, 50QG1401, 50QG1402, 50QG1403, and 50QG1404 and the Centre for Information Services and High Performance Computing (ZIH) at the Technische Universität (TU) Dresden for generous allocations of computer time; the Hungarian Academy of Sciences through the Lendület Programme LP2014-17 and the János Bolyai Research Scholarship (L. Molnár and E. Plachy) and the Hungarian National Research, Development, and Innovation Office through grants NKFIH K-115709, PD-116175, and PD-121203; the Science Foundation Ireland (SFI) through a Royal Society - SFI University Research Fellowship (M. Fraser); the Israel Science Foundation (ISF) through grant 848/16; the Agenzia Spaziale Italiana (ASI) through contracts I/037/08/0, I/058/10/0, 2014-025-R.0, and 2014-025-R.1.2015 to the Italian Istituto Nazionale di Astrofisica (INAF), contract 2014-049-R.0/1/2 to INAF dedicated to the Space Science Data Centre (SSDC, formerly known as the ASI Science Data Centre, ASDC), and contracts I/008/10/0, 2013/030/I.0, 2013-030-I.0.1-2015, and 2016-17-I.0 to the Aerospace Logistics Technology Engineering Company (ALTEC S.p.A.), and INAF; the Netherlands Organisation for Scientific Research (NWO) through grant NWO-M-614.061.414 and through a VICI grant (A. Helmi) and the Netherlands Research School for Astronomy (NOVA); the Polish National Science Centre through HARMONIA grant 2015/18/M/ST9/00544 and ETIUDA grants 2016/20/S/ST9/00162 and 2016/20/T/ST9/00170; the Portugese Fundação para a Ciência e a Tecnologia (FCT) through grant SFRH/BPD/74697/2010; the Strategic Programmes UID/FIS/00099/2013 for CENTRA and UID/EEA/00066/2013 for UNINOVA; the Slovenian Research Agency through grant P1-0188; the Spanish Ministry of Economy (MINECO/FEDER, UE) through grants ESP2014-55996-C2-1-R, ESP2014-55996-C2-2-R, ESP2016-80079-C2-1-R, and ESP2016-80079-C2-2-R, the Spanish Ministerio de Economía, Industria y Competitividad through grant AyA2014-55216, the Spanish Ministerio de Educación, Cultura y Deporte (MECD) through grant FPU16/03827, the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia “María de Maeztu”) through grant MDM-2014-0369, the Xunta de Galicia and the Centros Singulares de Investigación de Galicia for the period 2016-2019 through the Centro de Investigación en Tecnologías de la Información y las Comunicaciones (CITIC), the Red Española de Supercomputación (RES) computer resources at MareNostrum, and the Barcelona Supercomputing Centre - Centro Nacional de Supercomputación (BSC-CNS) through activities AECT-2016-1-0006, AECT-2016-2-0013, AECT-2016-3-0011, and AECT-2017-1-0020; the Swedish National Space Board (SNSB/Rymdstyrelsen); the Swiss State Secretariat for Education, Research, and Innovation through the ESA PRODEX programme, the Mesures d’Accompagnement, the Swiss Activités Nationales Complémentaires, and the Swiss National Science Foundation; the United Kingdom Rutherford Appleton Laboratory, the United Kingdom Science and Technology Facilities Council (STFC) through grant ST/L006553/1, the United Kingdom Space Agency (UKSA) through grant ST/N000641/1 and ST/N001117/1, as well as a Particle Physics and Astronomy Research Council Grant PP/C503703/1. The GBOT programme (Gaia Collaboration 2016b; Altmann et al. 2014) uses observations collected at (i) the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) with the VLT Survey Telescope (VST), under ESO programmes 092.B-0165, 093.B-0236, 094.B-0181, 095.B-0046, 096.B-0162, 097.B-0304, 098.B-0034, 099.B-0030, 0100.B-0131, and 0101.B-0156, and (ii) the Liverpool Telescope, which is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias with financial support from the United Kingdom Science and Technology Facilities Council, and (iii) telescopes of the Las Cumbres Observatory Global Telescope Network. In this work we made use of the Set of Identifications, Measurements, and Bibliography for Astronomical Data (SIMBAD; Wenger et al. 2000), the “Aladin sky atlas” (Bonnarel et al. 2000; Boch & Fernique 2014), and the VizieR catalogue access tool (Ochsenbein et al. 2000), all operated at the Centre de Données astronomiques de Strasbourg (CDS). We additionally made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2018), IPython (Pérez & Granger 2007), Matplotlib (Hunter 2007), and TOPCAT (Taylor 2005, http://www.starlink.ac.uk/topcat/)

3D kinematics through the X-shaped Milky Way bulge

Context. It has recently been discovered that the Galactic bulge is X-shaped, with the two southern arms of the X both crossing the lines of sight at l = 0 and | b| > 4, hence producing a double red clump in the bulge color magnitude diagram. Dynamical models predict the formation of X-shaped bulges as extreme cases of boxy-peanut bulges. However, since X-shaped bulges were known to be present only in external galaxies, models have never been compared to 3D kinematical data for individual stars. Aims. We study the orbital motion of Galactic bulge stars in the two arms (overdensities) of the X in the southern hemisphere. The goal is to provide observational constraints to bulge formation models that predict the formation of X-shapes through bar dynamical instabilities. Methods. Radial velocities have been obtained for a sample of 454 bulge giants, roughly equally distributed between the bright and the faint red clump, in a field at (l,b) = (0, −6). Proper motions were derived for all red clump stars in the same field by combining images from two epochs, which were obtained 11 years apart, with WFI at the 2.2 m at La Silla. The observed field contains the globular cluster NGC 6558, whose member stars were used to assess the accuracy of the proper motion measurement. At the same time, as a by-product, we provide the first proper motion measurement of NGC 6558. The proper motions for the spectroscopic subsample are analyzed for a subsample of 352 stars, taking into account the radial velocities and metallicities measured from near-infrared calcium triplet lines. Results. The radial velocity distribution of stars in the bright red clump, which traces the closer overdensity of bulge stars, shows an excess of stars moving towards the Sun. Similarly, an excess of stars receding from the Sun is seen in the far overdensity, which is traced by faint red clump stars. This is explained by the presence of stars on elongated orbits, which are most likely streaming along the arms of the X-shaped bulge. Proper motions for these stars are consistent with qualitative predictions of dynamical models of peanut-shaped bulges. Surprisingly, stars on elongated orbits have preferentially metal-poor (subsolar) metallicities, while the metal rich ones, in both overdensities, are preferentially found in more axisymmetric orbits. The observed proper motion of NGC 6558 has been measured as (μlcos   (b),μb) = (0.30   ±   0.14, −0.43 ± 0.13), with a velocity dispersion of (σlcos(b),σb) = (1.8,1.7) mas/yr. This is the first proper motion measurement for this cluster

GYES, a multifibre spectrograph for the CFHT

We have chosen the name of GYES, one of the mythological giants with one hundred arms, offspring of Gaia and Uranus, for our instrument study of a multifibre spectrograph for the prime focus of the Canada-France-Hawaii Telescope. Such an instrument could provide an excellent ground-based complement for the Gaia mission and a northern complement to the HERMES project on the AAT. The CFHT is well known for providing a stable prime focus environment, with a large field of view, which has hosted several imaging instruments, but has never hosted a multifibre spectrograph. Building upon the experience gained at GEPI with FLAMES-Giraffe and X-Shooter, we are investigating the feasibility of a high multiplex spectrograph (about 500 fibres) over a field of view 1 degree in diameter. We are investigating an instrument with resolution in the range 15000 to 30000, which should provide accurate chemical abundances for stars down to 16th magnitude and radial velocities, accurate to 1 km/s for fainter stars. The study is led by GEPI-Observatoire de Paris with a contribution from Oxford for the study of the positioner. The financing for the study comes from INSU CSAA and Observatoire de Paris. The conceptual study will be delivered to CFHT for review by October 1st 2010.Comment: Contributed talk at the Gaia ELSA conference 2010, S\`evres 7-11 June 2010, to be published on the EAS Series, Editors: C. Turon, F. Arenou & F. Meynadie

Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Bulge studies

We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J-Ks) color of red clump giants in small subfields of 2' to 6' in the following bulge area: -10.3<b<+5.1 and -10<l<+10.4. To determine the reddening values E(J-Ks) for each region, we measure the RC color and compare it to the (J-Ks) color of RC stars measured in Baade's window, for which we adopt E(B-V)=0.55. This allows us to construct a reddening map sensitive to small scale variations minimizing the problems arising from differential extinction. The significant reddening variations are clearly observed on spatial scales as small as 2'. We find a good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are not reliable for regions within |b| < 6. In the inner regions we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map has better quality due to both higher resolution and a more complete spatial coverage in the Bulge. We investigate the importance of differential reddening and demonstrate the need for high resolution extinction maps for detailed studies of Bulge stellar populations and structure. The extinction variations on scales of up to 2'-6', must be taken into account when analysing the stellar populations of the Bulge.Comment: Accepted for publication in A&

Reddening and metallicity maps of the Milky Way Bulge from VVV and 2MASS. I.The method and minor axis maps

We present a method to obtain reddening maps and to trace structure and metallicity gradients of the bulge using data from the recently started ESO public survey Vista Variables in the Via Lactea (VVV). We derive the mean J-Ks color of the red clump (RC) giants in 1835 subfields in the Bulge region with -8<b<-0.4 and 0.2<l<1.7, and compare it to the color of RC stars in Baade's Window for which we adopt E(B-V)=0.55. This allows us to derive the reddening map on a small enough scale to minimize the problems arising from differential extinction. The dereddened magnitudes are then used to build the bulge luminosity function in regions of 0.4 x 0.4 deg to obtain the mean RC magnitudes. These are used as distance indicator in order to trace the bulge structure. Finally, for each subfield we derive photometric metallicities through interpolation of red giant branch colors on a set of empirical ridge lines. The photometric metallicity distributions are compared to metallicity distributions obtained from high resolution spectroscopy in the same regions. The reddening determination is sensitive to small scale variations which are clearly visible in our maps. The luminosity function clearly shows the double RC recently discovered in 2MASS and OGLE III datasets, hence allowing to trace the X-shape morphology of the bulge. Finally, the mean of the derived photometric metallicity distributions are in remarkable agreement with those obtained from spectroscopy. The VVV survey presents a unique tool to map the bulge properties by means of the consistent method presented here. The remarkable agreement between our results and those presented in literature for the minor axis allows us to safely extend our method to the whole region covered by the survey.Comment: Accepted for publication in A&

Astrometric orbits of SB9 stars

Hipparcos Intermediate Astrometric Data (IAD) have been used to derive astrometric orbital elements for spectroscopic binaries from the newly released Ninth Catalogue of Spectroscopic Binary Orbits (SB9). Among the 1374 binaries from SB9 which have an HIP entry, 282 have detectable orbital astrometric motion (at the 5% significance level). Among those, only 70 have astrometric orbital elements that are reliably determined (according to specific statistical tests discussed in the paper), and for the first time for 20 systems, representing a 10% increase relative to the 235 DMSA/O systems already present in the Hipparcos Double and Multiple Systems Annex. The detection of the astrometric orbital motion when the Hipparcos IAD are supplemented by the spectroscopic orbital elements is close to 100% for binaries with only one visible component, provided that the period is in the 50 - 1000 d range and the parallax is larger than 5 mas. This result is an interesting testbed to guide the choice of algorithms and statistical tests to be used in the search for astrometric binaries during the forthcoming ESA Gaia mission. Finally, orbital inclinations provided by the present analysis have been used to derive several astrophysical quantities. For instance, 29 among the 70 systems with reliable astrometric orbital elements involve main sequence stars for which the companion mass could be derived. Some interesting conclusions may be drawn from this new set of stellar masses, like the enigmatic nature of the companion to the Hyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but the companion remains elusive.Comment: Astronomy & Astrophysics, in press (16 pages, 12 figures); also available at http://www.astro.ulb.ac.be/Html/ps.html#Astrometr