Abstract
The kinematic properties of the different classes of objects in a given association hold important clues about its member's history, and offer a unique opportunity to test the predictions of the various models of stellar formation and evolution. DANCe (standing for Dynamical Analysis of Nearby ClustErs) is a survey program aimed at deriving a comprehensive and homogeneous census of the stellar and substellar content of a number of nearby (<1kpc) young (<500Myr) associations. Whenever possible, members will be identified based on their kinematics properties, ensuring little contamination from background and foreground sources. Otherwise, the dynamics of previously confirmed members will be studied using the proper motion measurements. We present here the method used to derive precise proper motion measurements, using the Pleiades cluster as a test bench. Combining deep wide field multi-epoch panchromatic images obtained at various obervatories over up to 14 years, we derive accurate proper motions for the sources present in the field of the survey. The datasets cover ~80 square degrees, centered around the Seven Sisters. Using new tools, we have computed a catalog of 6116907 unique sources, including proper motion measurements for 3577478 of them. The catalogue covers the magnitude range between i=12~24mag, achieving a proper motion accuracy <1mas/yr for sources as faint as i=22.5mag. We estimate that our final accuracy reaches 0.3mas/yr in the best cases, depending on magnitude, observing history, and the presence of reference extragalactic sources for the anchoring onto the ICRS.
Highlights
The Milky Way galaxy includes large scale structures such as clusters, star forming regions, and OB associations
Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii
Selecting members based on their kinematics offers several advantages: it is completely independant of evolutionary models; it rejects the majority of unrelated foreground and background sources; it is insensitive to variability or flux excess and deficiency related to e.g circumstellar material or accretion; it can disentangle coincident or neighboring associations provided that they have differing mean motions
Summary
The Milky Way galaxy includes large scale structures such as clusters, star forming regions, and OB associations. Following the advent of sensitive wide-field instruments over the past two decades, a large number of photometric studies have been performed in stellar associations and clusters (e.g Knodlseder 2000; Barrado y Navascues et al 2004; Bejar et al 2001; Lodieu et al 2006; Torres et al 2008; Eiroa & Casali 1992) These surveys dramatically improved our knowledge of the luminosity function, and extended it. The most succesful and efficient spectroscopic surveys to date (e.g RAVE, WOCS, APOGEE, MARVELS, ESOGAIA, Steinmetz et al 2006; Mathieu 2000; Majewski et al 2007; Mahadevan et al 2007; Gilmore et al 2012) are producing libraries including several hundreds of thousands of high quality spectra and radial velocity measurements over areas as large as several thousands square degrees They are still limited to the brightest sources and do not reach the substellar luminosity range. We present a similar method designed to automatically process and analyse vast amounts of images (several thousands) originating from multiple instruments and sites and covering large (>10 deg2) areas of the sky
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