Open Clusters in All-Sky Catalogue ASCC- 2.5 N.V.Kharchenko 1, A.E.Piskunov 2, S.Röser 3, E.Schilbach 3, & R.-D.Scholz 4 1 Main Astronomical Observatory, Kiev, Ukraine 2 Institute of Astronomy, Moscow, Russia 3 Astronomisches Rechen-Institut, Heidelberg, Germany 4 Astrophysikalisches Institut Potsdam, Germany

All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5, I/280A) Hipparcos family: Tycho1/2+TRC+ ACT RC + …. PPM, CMC11 Systems: Hipparcos coordinates, PM Johnson B,V ASCC-2.5 Accurate positions and proper motions, B-V,V for 2,501,304 stars + parallaxes, RV,Sp, ids for many of them

Aims of the study: Identify in ASCC-2.5 all known open clusters and associations; Select a uniform over the sky list of proper motion and photometric members; Based on this membership, derive a uniform set of parameters of these clusters (cluster coordinates, radii, proper motions, radial velocities, ages and optionally reddenings and distances); Search of new (unknown) clusters with the aim of establishing their membership and determining their parameters

Cluster sample About 1700 open clusters and about 100 associations are known currently Catalogues of Lyng ₢ and Dias et al. were cross-correlated with ASCC-2.5 in search of open clusters Catalogue of Ruprecht et. al. was browsed in looking for compact associations; 520 cluster/association areas were identified in the ASCC-2.5 containing 160,000 stars

Galactic coordinates

Equatorial coodinates

Member selection scheme 1  -member: P >61% 2  -member: P =14-61% 3  -member: P >=1-14% Coordinate selection Photometric selection Proper motion selection 1  -member list changed ? Final member list No Yes

Proper motion membership Vector Point Diagram

Photometric membership To filter off co-moving field stars influencing PM-selection Used: sequences of Unresolved Binaries Post-MS isochrones Pre-MS isochrones Stars 1,3  P=100 % Stars 2,4,5  P>0 % Stars 6,7  P=0 % Post-MS Pre-MS q=0.8 q=1  bars

Example of open cluster well determined in 6-D parameter space

A cluster with strongly revised parameters (position, size, distance)

New nearby cluster discovered by Alessi+2003 from Tycho-2 PM

Difficult case of cluster identification. 1.Previous View (from literature)

Difficult case of cluster identification. 2. Final view

Example of previously rejected cluster with newly defined parameters

Example of a classical young open cluster Pre-MS

A cluster in Orion Belt

How Trapezium looks like in ASCC-2.5: difficult !