鬼星团天体测量标准区域中部257颗星的J2000.0位置和自行

J_(2000.0)POSITIONS AND PROPER MOTIONS OF 257 STARS IN THE CENTRAL PART OF THE PRAESEPE ASTROMETRIC STANDARD REGION

本文给出了鬼星团天体测量标准区域中部15×15范围内257颗星基于FK5系统的J2000.0位置和自行,位置准确度为0.005到0.10角秒,自行准确度为0.0002到0.006角秒/年.

Seven plates of the Praesepe region were taken with the Zo-sè 40 cm refractor (f=6895 mm) in March, 1986 (Table 1) and measured on the PDS-1010MS microdensitometer of the Pnrple Mountain Observatory. 257 stars, which are in common with the Russell's (1976) catalogue and in the 1°.5×1°.5 central part of the Praespe astrometric standard region, appear at least once on the plates. This catalogue is used as the reference and the B1950.0 positions in the catalogue are the same as those at an earlier epoch. After the test based on Eichhorn and Williams'(1963) criterion, the plate constant model as Eq. 1 is adopted in the iterative reduction with the central overlapping technique. The normal equation system which involves the positions and proper motions is given in Eq. 4 and the weights of the standard coordinates obtained from the catalogue and plates, respectively, are calculated with Eqs. 2 and 3. The results are given in Table 2 which contain are the J2000.0 positions and proper motions of the 257 stars, with accuracies of 0.005～0.10 arcsec for the positions in each direction and 0.0002～0.006 arcsec per year for the proper motions in each direction.