Cosmography of nearby OB associations with HIPPARCOS

ESO’s VLT reveals the Carina Nebula's hidden secrets(ESA press release:) Astronomers have used modern techniques to visualise data from ESA’s Hipparcos space astrometry mission in three dimensions. The treatment of the data has offered insights into the distribution of nearby stars and uncovered new groupings of stars in the solar neighbourhood, shedding light on the origins of the stars in Orion and calling into question the existence of the Gould Belt – an iconic ring-shaped structure of stars in the Milky Way. The results show the potential of 3D visualisation of the solar neighbourhood, an approach which is of particular relevance to ESA’s Gaia mission which will map the Milky Way and Local Group in 3D with unprecedented sensitivity and accuracy. The above image is the Carina Nebula, imaged using VLT/HAWK-I and roughly centred on the extremely young (~0.3 – 0.5 Myr) cluster Trumpler 14 (right), part of the Carina OB1 association. The paper is “Cosmography of OB stars in the solar neighbourhood” H. Bouy & J. Alves, 2015 A&A, 584, 13 and I reproduce in part the abstract. The must-view visualisation is here (screenshot below).ESO-Trumpler14-cluster

We construct a 3D map of the spatial density of OB stars within 500 pc from the Sun using the Hipparcos  catalogue and find three large-scale stream-like structures that allow a new view on the solar neighbourhood. The spatial coherence of these blue streams and the monotonic age sequence over hundreds of parsecs suggest that they are made of young stars, similar to the young streams that are conspicuous in nearby spiral galaxies. The three streams are 1) the Scorpius to Canis Majoris stream, covering 350 pc and 65 Myr of star formation history; 2) the Vela stream, encompassing at least 150 pc and 25 Myr of star formation history; and 3) the Orion stream, including not only the well-known Orion OB1abcd associations, but also a large previously unreported foreground stellar group lying only 200 pc from the Sun. The map also reveals a remarkable and previously unknown nearby OB association, between the Orion stream and the Taurus molecular clouds, which might be responsible for the observed structure and star formation activity in this cloud complex. This new association also appears to be the birthplace of Betelgeuse, as indicated by the proximity and velocity of the red giant. If this is confirmed, it would solve the long-standing puzzle of the origin of Betelgeuse. The well-known nearby star-forming low-mass clouds, including the nearby T and R associations Lupus, Cha, Oph, CrA, Taurus, Vela R1, and various low-mass cometary clouds in Vela and Orion, appear in this new view of the local neighbourhood to be secondary star formation episodes that most likely were triggered by the feedback from the massive stars in the streams. We also recover well-known star clusters of various ages that are currently cruising through the solar neighbourhood. Finally, we find no evidence of an elliptical structure such as the Gould belt, a structure we suggest is a 2D projection effect, and not a physical ring.Screen Shot 2015-11-28 at 10.16.01

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