摘要
对于用佘山40厘米折射望远镜拍摄的10组底片,用底片常数法和中心重叠法分别重新作了归算; 对于包含大时角底片的组,归算中使用在恒星常数中加进折射项的办法计入了大气色散改正。给出了 15颗星的相对视差和自行,以及由重叠解换算的绝对视差。对视差测定值的精度作了讨论。
As a preparation for the trigonometric parallax program with φ 1.56-m astrometric reflector of the Shanghai Observatory, since 1980 an experimental program has been performed with the Zo-Se φ 40-cm refractor(f= 6.9 m, scale being 29'.89/mm,λ= - 8b04m44:75, φ = + 31° 05'. 47' .6). Kodak 103 a-O spectroscopic emulsions are used without any filter for all exposures. As a general rule, three exposures for each plate are made with 4-15 minutes per exposure. The observational hour angles are not restricted within narrow limits and for a few plates the hour angles are excess 2h (east or west). All the plates are automatically measured on the PDS-1010 MS microdensitometer at the Purple Mountain Observatory. The digital image centering (DIC) of PDS measurements is done by means of a circular Gaussian distribution fitting. The weighting system of star images is based on fitting errors of DIC and plate errors, which are found from comparison of various exposures on the same plate (Eq. 1).
Differences between the coordinates of reference stars and those of the central star in R. A. and Decl. are both limited within ±20' and differences between the photographic magnitudes of different reference stars in the brighter side are usually not greater than 1 mag. The magnitudes of reference stars are found from fitting a function (Eq. 2) to density peak values, which are obtained from DIC. The mean colour index of reference .stars are adopted as +0.8 mag to reduce the average photographic magnitudes to the Vref. Various sources of errors being taken account of, the total uncertainty of the corrections to absolute parallaxes, which are quoted from the van Altena's table, is about ±0'.001. Each exposure, as an independent observation, is reduced with the plate constant method (Eqs. 3 and 4). The standard frame is taken from an arbitrary exposure and orientated in the J 2000.0 system. The initial values of star constants are found with the non-overlapping solutions (Eq. 5). The rigorous non-iterative central overlapping technique, which is used by Murray and Corben (Eqs. 7 and 8), is applied to obtain the resulting values. The normal equations are solved by means of an iterative scheme suggested by one of authors (W). For the series of plates, where the correlation coefficients between Rζand Rζ(Eq. 6) are greater than 0.5 and the mean ranges of Rζ at about the same epochs are greater than 0.4, the refraction terms are included in star constants for non-overlapping and overlapping solutions both.
The detailed results of 15 stars are given in Tables 1 to 4. The external standard-errors of our parallaxes, found from common star comparisons, visual pair comparisons and reference star parallax dispersions, are ±0'0105, ±'0110 and ±0''.0078, respectively.
出处
《中国科学院上海天文台年刊》
1989年第10期57-65,共9页
Annals Shanghai Astronomical Observatory Chinese Academy of Sciences
