## Kinematic Tracebacks

2014-01-05T21:28:15Z (GMT)
<p>Kinematic tracebacks of IC2391 and the IC 2391 supercluster (Eggen 1991) and the Argus Association (Torres et al. 2008, Zuckerman et al. 2011, Riedel et al. 2011, and others; sample is restricted to only the stars considered "bona-fide" by Malo et al. (2013))</p> <p>Also: A kinematic traceback of AB Doradus, for comparison.  Data is again restricted to the "bona-fide" sample from Malo et al. (2013).</p> <p> </p> <p>The point of a kinematic traceback is this: Our current definition of a moving group is a group of stars that formed from a single burst of star formation.  Because they are not gravitationally bound to each other, they are not clusters, but they should still be young enough that their motions are essentially undisturbed.  Therefore, we can use their motions and an approximation of galactic orbits (here, an epicyclic approximation from Makarov et al. (2004) with updated Oort constants from Bobylev et al. (2013)) to find out where they were in the past.  For a true moving group, all of the stars should have been fairly close to each other at the time of formation.</p> <p> </p> <p>Eggen's IC 2391 supercluster was thought to be the dissolving remains of the IC 2391 cluster, whose reality Lopez-Santiago et al. (2006) disputed.  Torres et al. (2006) proposed an Argus association that was also linked to IC 2391.  We see here that the two end up very far apart (and very spread out) in the past, which makes it difficult for both of them to be actually related to IC 2391 at the same time.</p> <p> </p> <p>Note that both movies go back before the formation of both groups- IC 2391 and Argus are supposed to be 40-50 Myr old; AB Doradus is either 50 or 120 Myr old depending on who you talk to.</p>