Accurate positions and proper motions of H{alpha} emission-line objects in the Chamaeleon star-forming region

Helena Relke, Werner Pfau, Jena

Complete text (abstract only):

The present investigation aims at the kinematics of pre-main sequence (PMS) stars in one of the most thoroughly investigated regions with low-mass star formation: the star-forming complex in Chamaeleon. The kinematics of PMS stars gives important clues to the membership in stellar associations and places of origin. The latter point is especially important for the widely distributed PMS stars and might give insight into dynamic processes related to star formation (Hoff et al. 1998). Our surveys on 1995 and 1997 ESO-Schmidt objective-prism plates revealed the presence of H{alpha} emission line objects (B magnitudes from 14 to 20 mag) even between the regions of the dark clouds Cha I, II, and III. These objects are probably low-mass YSOs, part of them being well outside the three known star-forming regions in Chamaeleon.

With ESO-Schmidt astrometric plates (= second epoch plates) we cover the whole Chamaeleon region. Up to now the field around the Cha I cloud was digitized on the measuring machine (scanner) of the Thüringer Landessternwarte Tautenburg and for a total of 157 H{alpha} emission line objects accurate positions (epoch 1997) were determined. Plates of the Digitized Sky Survey (DSS), taken with the UK-Schmidt telescope at Siding Spring Observatory in 1976, served for the first epoch. Positions were measured with the MIDAS software, the rms accuracy of the x, y coordinates on the ESO and DSS plates is 0.4 and 0.6 µm, resp. For the reduction, a polynomial with 10 coefficients was applied (60 stars per plate from ESO and the DSS), reference catalogue is the Hipparcos catalogue. The finally achieved accuracy of the proper motions is 2.5 and 2.0 mas/yr for µRAcos(Dec) and µDec, resp.

The proper motion diagram of the ChaI field shows that as a mean the PMS stars move in the direction of the galactic plane. There are positional subgroups showing common proper motion vectors, however (see also Frink et al., 1998). The stars with the largest proper motions have a tendency to move in the direction of the Cha I cloud. Our up to now restricted results are not conclusive as to the different hypotheses trying to explain the kinematics of low-mass PMS stars.


We are grateful to the Thüringer Landessternwarte Tautenburg and Dipl.-Phys. J. Brunzendorf for scanning the Schmidt plates. One of the authors (H. R.) is funded by the Otto Benecke Stiftung e.V. Bonn.



Frink S., Röser S., Alcalá J.M., Covino E., Brandner W., 1998: Kinematics of T Tauri stars in Chamaeleon. A&A 338, 442F

Hoff W., Henning Th., Pfau W., 1998: The nature of isolated T Tauri stars. A&A 336, 242

Bibliographical details:

Helena Relke, Werner Pfau: Accurate positions and proper motions of H emission-line objects in the Chamaeleon star-forming region. In: Peter Brosche, Wolfgang R. Dick, Oliver Schwarz, Roland Wielen (Eds.): The Message of the Angles - Astrometry from 1798 to 1998. Proceedings of the International Spring Meeting of the Astronomische Gesellschaft, Gotha, May 11-15, 1998. (Acta Historica Astronomiae ; 3). Thun ; Frankfurt am Main : Deutsch, 1998, p. 196-197.