Science Rationale
Reconstructing the Milky Way’s history: Spectroscopic surveys, Asteroseismology and chemodynamical models
The mechanisms of the formation and evolution of the Milky Way are encoded in the kinematics, chemistry and ages of its stars. Deciphering the assembly history of our Galaxy requires large-scale ground-based spectroscopic surveys able to map large portions of the Galaxy (Galactic Archaeology). An enourmous effort is ongoing with large spectrosopic surveys such as RAVE, SEGUE, LAMOST, Gaia-ESO, APOGEE and GALAH, from which stellar parameters, radial velocities and the abundances of several chemical elements can be measured. However, the difficulties associated with estimating ages and distances of individual field stars has long been major obstacle for Galactic Archeology. In addition the large uncertainties in key stellar parameters, such as the stellar gravity, has also been a major problem.
The detection of radial and non-radial solar-like oscillations in a large number of giants with CoRoT and Kepler and their use into studies of stellar populations in the Galaxy offered a breakthrough in the field. Indeed, seismic constraints are now available for thousands of stars, sampling different regions of the Milky Way. Asteroseismology allows largely model-independent determination of stellar radii and masses, which in turn can be used to determine the position and age (model dependent) of field and open clusters stars, and a much more precise estimate of their gravity.
The availability of asteroseismic constraints for populations of stars calls for a novel scientific collaboration that combines expertise from diverse areas of astrophysics, such as models of Galactic and stellar evolution, model atmospheres, asteroseismology and spectroscopy. A first conference entitled “Red Giants as Probes of the Structure and Evolution of the Milky Way”, aimed at bringing experts from these different fields together, took place in 2010 (see proceedings). A second conference, entitled “Asteroseismology of Stellar Populations in the Milky Way” took place in 2013 (see proceedings). There the first results achieved by combining photometric/spectroscopic and seismic constraints on populations of stars observed by CoRoT and Kepler were presented and a roadmap for further follow-up of the seismic targets by spectroscopic facilities was discussed.
During 2013/2014 several important steps were taken, such as the follow-up of many Kepler and CoRoT targets by APOGEE and the Gaia-ESO Survey, as well as the Collaborations such as APOKASC (between APOGEE and Kepler members), and CoRoGEE (between CoRoT and APOGEE members) were set, and the first scientific results are being now published. The K2 (new Kepler campaign) being observed this year not only overlaps with some of the RAVE targets, but will also be followed-up by APOGEE. The future for this area also starts taking shape with the launch of Gaia, the recommendation of extended wide-field multi-objects spectroscopic facilities such as 4MOST and WEAVE for further development, and the choice of PLATO 2.0 as the third medium class mission in ESA’s Cosmic Vision 2015-2025 programme.
Time is now ripe to bring again the representatives from the extensive ground-based surveys, as well as asteroseismology, Galaxy formation and stellar evolution experts to set our roadmap for future endeavors in this field. The participation of PhD students and young postdocs is greatly encouraged as they will be the main users of the future ground based and space facilities in the horizon of 2020. The involvement of young generations in frontier science topics is one of the main goals of the “Wilhelm und Else Heraeus-Stiftung”, and we greatly acknowledge their support.
