Authors: Tadashi Nakajima & Jun-Ichi Morino
Purpose: Identify kinematic groups from their XYZ positions and UVW space velocities.
Background:
- Why find kinematic groups?
- ages of individual stars are difficult to determine
- it is easier to find the age of a system of stars using their bulk properties
- we are interested in finding young stars because their giant planets may be warm enough to be detectable with direct imaging
- within 30 pc, groups are distributed over a wider range of 3D spatial coordinates
- cannot JUST use their positions to identify groups
Method:
- The sample
- WEB catalog of radial velocities
- Hipparcos catalog of parallaxes (distances)
- distance + radial velocity will give you 3D space velocity (UVWs)
- choose V<45km/s for the youngest stars
- should be no kinematic bias since the highest velocity stars are excluded
- choose d>30pc for the most nearby stars
- 966 stars made this initial cut
- 383 within 20 pc
- 265 between 20-25 pc
- 318 between 25-30 pc
- kinematic groups
- IC 2391, Castor, Ursa Major, Hyades, Pleiades, beta Pic, TW Hya, AB Dor, Eta Cha, Cha-Near, and Tuc-Hor (from Zuckerman & Song 2004 and Montes et al. 2001)
- groups centers:
- IC 2391, Castor, Ursa Major, Hyades - centered on Sun
- centers of other groups taken from Z&S 2004
- require that the candidate members of a SKG must have a 3D velocity within 8km/s of the group mean
- calculate the birth position of the candidates in relation to the birth position of the SKG
- use the epicyclic approximation, the 3D velocity vectors, 3D positions, and group age
- use only in tie-breakers between two possible group memberships
Results:
- 137 (of 966) were selected as candidate members of SGKs
- comparison with other works (Maldonado et al. 2010, Lopez-Santiago et al. 2006, Zuckerman 7 Song 2004:
- 43 stars in common
- 8 of 43 are determined (in this work) to be non-members
- 102 new members of SKGs not listed in other works
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