9 Summary

  We have successfully used digitised sky survey data of the Palomar Schmidt telescope for a new proper motion study for about 1400 stars with R < 18 mag in a one square degree region around the young open cluster IC348. An overall accuracy of about 3mas/yr for the stellar proper motions allowed to separate the cluster stars from both foreground and background stars. Whereas the foreground stars could obviously be separated due to their large proper motion dispersion, the separation of the cluster from background stars was supported by the direction of the standard antapex and an increase of mean proper motion cluster membership probabilities with smaller cluster radii. A cluster membership probability of more than 80% was found for 240 stars of our sample.

We have compared our results with the highly accurate proper motion study of Fredrick (1956) and with other catalogues (PPM, ACT, Hipparcos), all containing only bright stars. On the basis of Hipparcos data we calculate a mean distance of 261_-23⁺²⁷pc for the cluster. Hipparcos proper motions and parallaxes do also allow the separation of foreground stars, cluster stars and background stars in a somewhat larger region around IC348. The mean proper motion of the cluster IC 348 obtained in our study is in good agreement with that of the highly probable members of the Per OB 2 association according to de Zeeuw et al. (1999). Together with the above mentioned Hipparcos distance estimate, which is also in agreement with de Zeeuw et al. (1999) data for Per OB 2, this confirms that IC 348 is embedded in the Per OB 2 association.

From our proper motion membership probabilities we found a cluster radius of 10-15arcmin. There is a concentration of Fredrick's highly probable cluster stars just in between our cluster stars and the distant field stars proper motion distributions. On the other hand, two groups of stars in the proper motion diagram of Fredrick (1956) also seem to be indicated if all his possible cluster members are considered.

In addition to the proper motion study we have also carried out UBVR photographic photometry using standard stars from Trullols & Jordi (1997). Since the standards cover only the very central region of the one square degree field, the variation in extinction over the field lead to a large scatter in the photographic colours, particularly in (B-V).

The X-ray sources from Preibisch et al. (1996) identified with optical counterparts from our proper motion sample show a strong concentration in the proper motion diagram. For these objects which are likely T Tauri stars we obtained high membership probabilities so that we conclude that they belong to the cluster IC 348 and to the Per OB 2 association. The proper motion foreground stars and cluster members which are counterparts of near-infrared (NIR) sources (Lada & Lada 1995) are located in different parts of the (J-H)-(H-K) two colour diagram, respectively.

Acknowledgements

This research is based on data from the Digitized Sky Surveys and from the Tautenburg Schmidt telescope. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain. We would like to thank the Palomar and Tautenburg observatories for supplying the plates used in this investigation.

This study has also made use of the APM catalogues (Irwin et al. 1994). The APM is a national astronomy facility financed by the Particle Physics and Astronomy Research Council.

We would also like to thank H.-J. Tucholke and R. Ungruhe for their support with the Münster (MRSP) software.

We are grateful to E. Lada, who provided us with the data of her NIR survey of IC348, and to S. Röser for providing us with his Starnet catalogue data.

GI and NK thank the Deutsche Forschungsgemeinschaft (DFG) for financial support. JB gratefully acknowledges financial support from the DFG under grant Me1350/3-2.

We thank the anonymous referee for useful comments and suggestions.