Towards absolute scales for the radii and masses of open clusters^*

¹ Astronomisches Rechen-Institut, Mönchhofstraße 12-14, 69120 Heidelberg, Germany e-mail: [apiskunov;elena;nkhar;roeser]@ari.uni-heidelberg.de
² Institute of Astronomy of the Russian Acad. Sci., 48 Pyatnitskaya Str., 109017 Moscow, Russia e-mail: piskunov@inasan.rssi.ru
³ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: [apiskunov;nkharchenko;rdscholz]@aip.de
⁴ Main Astronomical Observatory, 27 Academica Zabolotnogo Str., 03680 Kiev, Ukraine e-mail: nkhar@mao.kiev.ua

Received: 10 January 2007
Accepted: 19 February 2007

Abstract

Aims. In this paper we derive tidal radii and masses of open clusters in the nearest kiloparsecs around the Sun.

Methods.For each cluster, the mass is estimated from tidal radii determined from a fitting of three-parameter King profiles to the observed integrated density distribution. Different samples of members are investigated.

Results.For 236 open clusters, all contained in the catalogue ASCC-2.5, we obtain core and tidal radii, as well as tidal masses. The distributions of the core and tidal radii peak at about 1.5 pc and 7–10 pc, respectively. A typical relative error of the core radius lies between 15% and 50%, whereas, for the majority of clusters, the tidal radius was determined with a relative accuracy better than 20%. Most of the clusters have tidal masses between 50 and 1000 , and for about half of the clusters, the masses were obtained with a relative error better than 50%.