Revised Distances, Kinematics, and Classifications of the Nearest Stellar Groups within 100 pc

Details Revised Distances, Kinematics, and Classifications of the Nearest Stellar Groups within 100 pc Revised Distances, Kinematics, and Classifications of the Nearest Stellar Groups within 100 pc

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21545505m&link_type=abstract

American Astronomical Society, AAS Meeting #215, #455.05; Bulletin of the American Astronomical Society, Vol. 42, p.473

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Given the recent interest in assigning membership of low-mass or substellar field objects to clusters of "known" age, a modern analysis of the distances, kinematics, memberships, and physicality of purported nearby young stellar groups is needed. Van Leeuwen (2007) recently published a new astrometric analysis of data from the Hipparcos mission. Here I use the revised Hipparcos astrometry to estimate updated distances and parameters for the young stellar groups with obvious nuclei previously reported to lie within 100 pc of the Sun (except for the Hyades and Coma Ber, which were reported by van Leeuwen). Among the highlights of the results reported are: (1) the revised mean distances to the nuclei of the following groups: AB Dor (20.1+-1.5 pc), Ursa Major (25.2+-0.3 pc), Carina-Near (32.7+-1.2 pc), Tucana (43.0+-1.0 pc), TW Hya (52.7+-3.0 pc), 32 Ori (92.9+-2.4 pc), and eta Cha (94.3+-1.2 pc), (2) the 5-Myr-old epsilon Cha group appears to be the nearest known group associated with molecular gas (117+-4 pc), (3) the 8 Myr-old eta Cha cluster is the densest cluster within 100 pc ( 36 Msun/pc3), (4) the convergent point for the AB Dor group nucleus appears to be near its geometric center, a phenomena unique among nearby kinematic groups, and (5) the intrinsic 1D velocity dispersions of the nuclei are all remarkably similar (all 1 km/s), and are larger than that predicted assuming the nuclei are virialized (typically <0.5 km/s). This discrepancy is likely to be due to stellar multiplicity affecting the projected photocentric motions of the nuclear members. I present evidence suggesting that the purported clusters Chereul 2, Chereul 3, Latyshev 2, and Polaris are probably unphysical. With refined kinematic parameters for the nearby stellar groups, one can now conduct a more refined membership analysis for others stars purported to be distant ``members'' of these groups.

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