The images of the open cluster NGC2168 are taken using the newly-fitted 2k×2k CCD attached to the 1-m telescope at the Yun-nan Observatory with two different orientations.After the catalogue position of a star fr...The images of the open cluster NGC2168 are taken using the newly-fitted 2k×2k CCD attached to the 1-m telescope at the Yun-nan Observatory with two different orientations.After the catalogue position of a star from UCAC2 is compared with its corresponding measured position,a surprising result shows that a small field of view(about 7′×7′)exhibits an obvious distortion.Spe-cifically,the polynomial between the standard coordinate(ξ,η)and its corresponding measured one(x,y)for a star in each field of view has significant terms as high as 4th order.Accordingly,the positional measurement accuracy of a bright UCAC2 star can be derived as well as~7 mas in each direction(60 s of exposure time and near the zenith).This new finding would be important for a CCD image to deliver a highly accurate position in its whole field of view.展开更多
基金supported by the National Natural Science Foundation of China and the Astronomical Joint Fund under the Chinese Academy of Sciences(Grant Nos.10573008,10778617,10973007)
文摘The images of the open cluster NGC2168 are taken using the newly-fitted 2k×2k CCD attached to the 1-m telescope at the Yun-nan Observatory with two different orientations.After the catalogue position of a star from UCAC2 is compared with its corresponding measured position,a surprising result shows that a small field of view(about 7′×7′)exhibits an obvious distortion.Spe-cifically,the polynomial between the standard coordinate(ξ,η)and its corresponding measured one(x,y)for a star in each field of view has significant terms as high as 4th order.Accordingly,the positional measurement accuracy of a bright UCAC2 star can be derived as well as~7 mas in each direction(60 s of exposure time and near the zenith).This new finding would be important for a CCD image to deliver a highly accurate position in its whole field of view.
