EPoS Contribution
EPoS Contribution
Young Stellar Populations Towards Orion with Gaia DR2

Eleonora Zari
Leiden U, Leiden, NL
OB associations are loose groups of stars, not gravitationally bound. They are usually found near to star forming region, hence they are prime sites for large scale studies of star formation processes and of the effects of young, massive stars on the interstellar medium.
After the first data release of the Gaia mission (Gaia DR1), we explored the three dimensional arrangement and the age ordering of the many young stellar groups towards the Orion OB association, aiming at a new classification and characterization of its stellar population. We made use of the parallaxes and proper motions provided in the Tycho Gaia Astrometric Solution (TGAS) sub-set of the Gaia catalogue to estimate the distances to the different groups composing the association. By combining Gaia and 2MASS photometry we estimated the ages of these groups. Our results formed the first step toward using Gaia data to unravel the complex star formation history of the Orion region in terms of the various star formation episodes, their duration, and their effects on the surrounding interstellar medium.
With Gaia DR2 (expected for April 2018), precise parallaxes and proper motions will be available for all the sources brighter than G ~ 21 mag. G and integrated GBP and GRP photometric fluxes and magnitudes will also be released for all the sources, together with radial velocities for the sources brighter than G ~12 mag.
Only one month after Gaia DR2, we will present our results from an initial exploration of Gaia DR2 data and show how this incredibly large amount of information will revolutionise our understanding of the star formation history of Orion. The results will not just be interesting as such, but will have wider implications for the studies of other OB associations and star forming regions, and for the understanding of the entire Gould Belt.
Caption: Since the motion of the Orion OB association is mostly directed radially away from the Sun, the observed proper motions are small. For this reason a rough selection of the sources can be made by requiring the the total proper motions to be < 5 mas/yr. The figure shows the positions in the sky of the TGAS sources selected applying the condition above in three different parallax intervals. The first panel shows stars with parallax < 2 mas (d > 500 pc): the outlines of the Orion A and B molecular clouds and the lambda Ori dust ring are visible as regions with a lack of sources. The second panel shows the stars with 2 < parallax < 3.5 mas (500 < d < 285 pc). The density enhancements visible towards the centre of the field, (l,b)~(205,~18) deg are related to some known clusters. The third panel shows foreground sources, with parallax > 3.5 mas (d < 285 pc).
Collaborators:
A.G.A. Brown, Leiden O, NL
J. de Bruijne, ESTEC, NL
C.F. Manara, ESO Garching, DE
P.T. de Zeeuw, Leiden O, DE
Key publication

Suggested Session: High-mass star/star cluster formation