Accurate positions for radio stars as determined from CCD observations in the extragalactic reference frame

被引:6
作者
Stone, RC
机构
[1] U.S. Naval Observatory, Flagstaff Station, Flagstaff, AZ 86002
关键词
D O I
10.1086/118598
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
This paper presents positions for 155 radio stars determined directly in the extragalactic reference system from CCD scan observations made with the Flagstaff Astrometric Scanning Transit Telescope (FASTT). All the observations were made in 1994-1997 with an accuracy of similar to+/-60 mas in each coordinate. When these positions are compared with those of 21 radio stars with well known VLBI or VLA radio positions, there is good agreement, wherein no significant zero-point differences in position were found (+/-15 mas in each coordinate), and the dispersions in (optical-radio) differences (similar to+/-72 mas in each coordinate) can be explained by the formal errors in the positional and proper motion data. Moreover, if these (optical-radio) offsets are plotted against right ascension and declination, no systematic trends are found in either coordinate. Improved optical positions for the radio stars (similar to+/-30 mas in each coordinate) can be obtained by averaging the positions presented in this paper with those determined with the CAMC and Bordeaux meridian circles. When these combined positions are compared with their radio counterparts, external errors in the radio positions of radio stars can be calculated and are <+/-10 mas and similar to+/-40 mas in each coordinate, respectively, for VLBI and VLA radio observations. The former is consistent with the errors quoted for VLBI radio star positions, while the latter is about 30% larger. None of the (combined optical-radio) offsets are significant at the >3 sigma level; but, nonetheless, several stars (HD 26337, HD 283447, b Per, and KQ Pup) have marginally significant (>2 sigma) offsets. (C) 1997 American Astronomical Society.
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页码:1679 / 1688
页数:10
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