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Session 54 - Star Clusters, Kinematics and the Galactic Center.
Display session, Wednesday, June 10
Atlas Ballroom,
In order to investigate the large discrepancy between the companion star fraction (csf) of young T Tauri stars and older field stars and to study the role of binarity in stellar rotational evolution, we have conducted a 2.2 \mum speckle imaging survey of 106 members of the young (50-70 Myr) open cluster \alpha Persei. The stars in the sample all have K magnitudes brighter than K=10.0mag. Based on a preliminary analysis of this data set, 10 binaries are detected within the separation range 0\farcs20 to 1\farcs70 (33 AU - 282 AU) and the magnitude difference range \DeltaK \le 3mag; the limited number of binaries detected thus far prevents a significant comparison of the csf of the slow and rapid rotators in \alpha Persei. The initial assesment of the observed csf is csf_\alpha Per=0.09 \pm 0.03. This value of the cluster multiplicity is more than 2 times lower than the observed csf, measured over the same separation range, for nearby T Tauri stars (csf_T T=0.24 \pm 0.03), but is consistent with the results from surveys of the slightly older (\sim125 Myr) Pleiades cluster (csf_Pl=0.13 \pm 0.03) and the much older (\sim5 Gyr) field G-dwarfs (csf_field=0.13 \pm 0.03). Contrary to the results of a recent speckle survey of the Hyades (sensitive to a closer separation range), the initial results of the \alpha Persei study do not support the idea that multiple systems are disrupted over time, and instead support explanations for the high value of csf_T T that involve environmental factors such as density and temperature or different distributions of binary separations. Further analysis of the \alpha Persei data will cover a wider separation range, allowing an investigation of the distribution of binary separations.
