昴星团天体测量标准区域441颗星的高精度位置和自行

HIGH-PRECISION POSITIONS AND PROPER MOTIONS OF 441 STARS IN THE PLEIADES ASTROMETRIC STANDARD REGION

本文利用由ＰＰＭ和ＡＣＲＳ星表以及Ｅｉｃｈｈｏｒｎ等、Ｊｏｎｅｓ和Ｈｅｒｔｚｓｐｒｕｎｇ的星表综合而成的初始参考星表，对佘山４０厘米折射望远镜拍摄的历元间隔８６年１１张底片上３３次露光按中心重叠法进行归算，得出了昂星团天体测量标准区域４４１颗星的高精度位置和自行，这些位置的标准误差均小于±０．″０５，接近百分之九十恒星的自行标准误差小于±０〃．００１／年．

Based on a preliminary reference catalogue, constructed by a combination of the catalogues PPM and ACRS, and those in Eichhorn et al. (1970),Jones (1973 ), and Hertzsprung (1947 ), 33 exposures on 11 plates taken with the Zo- se 40 cm refractor (f= 6895 mm) in 86 years are reduced. by the central overlapping technique, and high-precision positions and proper motions of 441 stars in the Pleiades astrometric standard region are obtained. After a test with the Eichhorn and Williams' (1963 ) criterion, in the reduction, we adopted the plate constant model Eq. 1. The weight described in Wang et al. (1987 ) is assigned to each image in the plate reduction of every loop of iteration. The images with residuals in the plate reduction of the first two loops greater than 3 times unit weight standard error, are rejected in further reductions, so assigned as zero weight. The positions and proper motions from the preliminary catalogue are included in the position and proper motion reductions of all loops with the weights in Eqs. 2 and 3. The nOImal equation system which involves the positions and proper motions is given in Eq .6 and the weights of standard Coordinates obtained from the plate measurements are calculated with Eqs .4 and 5. The results are listed in Table 2 which contains our and Hertzsprung's (1947) numerations (Columns 1 and 2, respectively), R. A. (Column 3) and Decl. (Column 8 ) at the J2000. 0 epoch for the J2000. 0 equator and equinox, their standard errors (Columns 4 and 9, respectively), their central epochs (Columns 7 and 12,respectively), proper motion components in R. A. and Decl. (Columns 5 and 10, respectively ), and their standard errors (Columns 6 and 11, respectively ). The standard errors of positions for the stars in Table 2 are less than ± 0.〃05 and the standard errors of proper motions for 90 per cent of those stars less than ±0 .〃001/yr., A comparison for stars in common with the catalogues PPM and ACRS is shown in Table 3, and we found that the external errors are close to the internal standard errors.