The Besancon Galaxy Model, a Population Synthesis Tool
           for Galactic Structure and Evolution Studies

© Annie C. Robin                                © Céline Reylé                                 © Bernard Debray
Institut UTINA                                   OSU THETA                           Université de Franche-Comté
                                                Besançon, France
annie.robin@obs-besancon.fr



                                                                   scale length, scale heights, bar structure, halo
                      Abstract                                     shape, and evolution parameters such as the
        Understanding the Milky Way structure and                  star formation history [5] in the solar
    evolution is a major objective in astrophysics.                neighborhood. It is also a useful tool to
    Our Galaxy is an object of highest interest for                prepare future surveys, in particular the Gaia
    learning about galaxy formation and evolution                  mission launched by the European Space
    in general. Many data of different kinds                       Agency in December 2013, or further projects
    (photometry, astrometry, spectroscopy) are                     like PLATO and EUCLID.
    available for millions of stars in the Milky                       The model simulator is available through a
    Way, which interpretation in terms of evolution                dedicated web interface, which allows the
    is not easy. Stars in the Milky Way have been                  users to run the model and prepare their own
    recognized to be part of several populations                   simulations for direct comparisons with real
    with typical characteristics and spatial                       data. The simulations are computed on the
    distributions, such as the disc, the halo and the              cluster of the Institut UTINAM and deposited
    bulge, which shape the overall Galaxy and                      on the ftp server. VOTable and ascii format
    classify it as a barred spiral galaxy.                         are available for these simulations. Further
        We present here an approach for                            developments are envisaged for the web
    understanding the Galaxy by simulating stars in                service, such as a data base of simulations, and
    these various populations. The population                      a service for bayesian stellar classification. We
    synthesis scheme is used to simulate a scenario                shall present various applications of the
    of formation of the Galaxy. It allows to                       simulations in the different astrophysical
    confront such scenario with real data. It is used              domains.
    to prepare new observations (define the best
    protocole of observations to answer a given
                                                                References
    question) and to interpret observations in terms             [1] Aihara, H., Allende Prieto, C., An, D., et al. 2011.
    of Galaxy structure and evolution. The main                      The Eighth Data Release of the Sloan Digital Sky
    hypotheses to build the model are based on up-                   Survey: First Data from SDSS-III. Astrophys. J.
    to-date knowledge on stellar evolution models,                   Suppl, 193, 29.
    grids of atmosphere models, and galactic                     [2] Skrutskie, M. F., Cutri, R. M., Stiening, R., et al.
    dynamics. Many parameters are needed, but the                    2006. The Two Micron All Sky Survey (2MASS).
    availability of many sources of data allow to                    Astronomical J., 131, 1163.
    constraint step by step theses parameters. The
                                                                 [3] Robin, A. C., Reyle, C., Derriere, S., & Picaud, S.
    model produces simulations at a variety of
                                                                     2003. A synthetic view on structure and evolution
    wavelengths from X rays to mid infrared. It has
                                                                     of the Milky Way. Astron. Astrophys., 409, 523.
    been confronted to large scale surveys, ground
    based (Sloan Digital Sky Survey [1], 2MASS                   [4] Robin, A. C., Marshall, D. J., Schultheis, M., &
    near-infrared sky survey [2], among others),                     Reyle, C. 2012. Stellar populations in the Milky
    and space based surveys (GALEX UV                                Way bulge region: towards solving the Galactic
    telescope, Hubble Space Telescope, etc.). It has                 bulge and bar shapes using 2MASS data. Astron.
    been successfully used to constrain galactic                     Astrophys., 538, A106.
    structure parameters [3, 4], such as the disc                [5] Czekaj, M. A., Robin, A. C., Figueras, F., Luri, X.,
                                                                     & Haywood, M. 2014. The Besancon Galaxy
Proceedings of the 16th All-Russian Conference “Digital              model renewed. I. Constraints on the local star
Libraries: Advanced Methods and Technologies, Digital                formation history from Tycho data. Astron.
Collections” — RCDL-2014, Dubna, Russia, October                     Astrophys., 564, A102.
13–16, 2014.




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