Precise CCD positions of Triton in 2014–2016 using the newest Gaia DR1 star catalogue

Monthly Notices of the Royal Astronomical Society

Zhou

et al. 2019

The Beijing-Arizona Sky Survey (BASS) is an imaging survey and uses the 2.3 m Bok telescope at Kitt Peak. In order to tap the astrometric potential of the Bok telescope and improve the astrometry of BASS, a distortion solution for the Bok telescope is made. In the past, we used a single lookup table to correct all the positional errors. However, this method can not be applied to the reduction of the observation for the Bok telescope where four CCD chips are equipped with. Then quite different from our previous method, two third-order polynomials were used to fit the lookup table. By using the polynomial Geometric Distortion (called GD hereafter) correction the astrometry of BASS is improved greatly. Moreover, an additional lookup table correction is found to be more effective to obtain a final GD. The results show that the positional measurement precision of the appropriate bright stars is estimated at about 20 mas and even better in each direction. Besides, the relative positions of the chips are measured. The change of the inter-chip gaps in horizontal or vertical is no more than 5 pixel between 2016 and 2017 and the change of the roll angle is no more than 0.1 degree.

Section: )mentioning

confidence: 99%

Section: )mentioning

confidence: 99%

A distortion solution for the Bok telescope with four CCD chips

Wang

Monthly Notices of the Royal Astronomical Society

Zhou

et al. 2019

“…The solution has been successfully applied for the astrometry of HST and several ground-based telescopes (Anderson et al 2006;Libralato et al 2014). For photographic astrometry, we proposed an alternative GD solution, taking an astrometric catalog as reference (Peng et al 2012) and the solution is also successfully applied for the astrometry of some natural satellites (Peng et al 2015(Peng et al , 2017Wang et al 2017). However, if derived from the same observations, are the two GD solutions in agreement with each other?…”

Section: Introductionmentioning

confidence: 99%

Using Gaia DR2 to make a systematic comparison between two geometric distortion solutions

Zheng

Monthly Notices of the Royal Astronomical Society

Lin

2021

Gaia Data Release 2 (Gaia DR2) provides high accuracy and precision astrometric parameters (position, parallax, and proper motion) for more than 1 billion sources and is revolutionising astrometry. For a fast-moving target such as an asteroid, with many stars in the field of view that are brighter than the faint limit magnitude of Gaia (21 Gmag), its measurement accuracy and precision can be greatly improved by taking advantage of Gaia reference stars. However, if we want to study the relative motions of cluster members, we could cross-match them in different epochs based on pixel positions. For both types of targets, the determination of optical field-angle distortion or called geometric distortion (GD) in this paper is important for image calibration especially when there are few reference stars to build a high-order plate model. For the former, the GD solution can be derived based on the astrometric catalog’s position, while for the latter, a reference system called ‘master frame’ is constructed from these observations in pixel coordinates, and then the GD solution is derived. But are the two GD solutions in agreement with each other? In this paper, two types of GD solutions, which are derived either from the Gaia DR2 catalog or from the self-constructed master frame, are applied respectively for the observations taken by 1-m telescope at Yunnan Observatory. It is found that two GD solutions enable the precision to achieve a comparable level (∼10 mas) but their GD patterns are different. Synthetic distorted positions are generated for further investigation into the discrepancy between the two GD solutions. We aim to find the correlation and distinction between the two types of GD solutions, and their applicability in high precision astrometry.

“…Finally, we obtain about 3,000 Gaia stars for Obs16 and about 120,000 for Obs17. The above processings are based on the software developed by us (Peng et al 2012(Peng et al , 2015(Peng et al , 2017Wang et al 2017).…”

Section: Data Pre-processingmentioning

confidence: 99%

A deeper solution to the actual geometry of CCD mosaic chips

Zheng

Vienne

et al. 2022

A&A

Self Cite

Context. For charge-coupled device (CCD) mosaic chips in the focal plane of a large telescope, the unification for all the measurements of each chip is vital to some scientific projects, such as deep astrometric standards or construction for deeper images that can also seamlessly cover a larger area of the sky. A key part of the reduction involves the accurate geometric distortion (GD) correction and the precise determination of the relative positions of the CCD chips. The short-term and long-term stabilities of them are also important when it comes to studying whether there are systematic variations in the optical system of the telescope. Aims. We present a solution to determine the actual or physical relative positions between CCD chips. Due to the limited depth of the Gaia catalogue, there may be few stars identified from the Gaia catalogue for astrometric calibration on the deep observation of a large, ground-based or space-based telescope, such as the planned two-metre Chinese Space Station Telescope (CSST). For this reason, we referred to the idea from the Hubble Space Telescope (HST) astrometry to only use stars' pixel positions to derive the relative positions between chips. We refer to the practice as differential astrometry in this paper. In order to ensure the results are reliable, we took advantage of Gaia EDR3 to derive the relative positions between chips, to provide a close comparison. We refer to the practice as photographic astrometry. Methods. By taking advantage of the GD solution and the common distortion-free frame derived from the observations, we related the physical positions of the adjacent pixel edges of two CCD chips and estimated the actual relative positions between chips. We implemented the technique for the CCD mosaic chips of the Bok 2.3-m telescope at Kitt Peak based on two epochs of observations (Jan 17,2016 and Mar 5,2017). Results. There is a good agreement between the two types of astrometry for the relative positions between chips. For the two epochs of observations, the averages of the gaps derived from photographic astrometry and differential astrometry differ to about 0.046 pixels (∼0.021 arcsec) and 0.001 pixels (<0.001 arcsec), respectively, while the average precisions of the gaps are about 0.018 pixel (∼0.008 arcsec) and 0.028 pixels (∼0.013 arcsec), respectively. The results provide us with more confidence in applying this solution for the CCD mosaic chips of the CSST by means of differential astrometry. Compared with the solution described by Anderson & King, which has been used to determine the interchip offset of Wide Field Planetary Camera 2 (WFPC2) chips and Wide Field Camera 3 (WFC3) chips at the HST, the solution proposed in this paper shows at least a factor of two improvement in precision, on average. Conclusions. We think there are two definite advantages of our method. On one hand, we perform the measurements for two adjacent edges instead of two individual chips, allowing the results to be as local as possible, and meanwhile we alleviate the propagated err...