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

Zheng, Zihao; Peng, Q. Y.; Lin, F. R.

doi:10.1093/mnras/stab406

Cited by 3 publications

(4 citation statements)

References 21 publications

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“…As shown in Appendix A, the cubic terms of the two GD solutions are similar, and larger differences are found in quadratic terms and linear terms. Similar discrepancies between the two GD solutions are also found in our previous paper (Zheng et al 2021). Although Anderson & King (2003) stated that the observations at the same orientation are unable to constrain the linear distortion terms, we think there are also some quadratic distortion terms in the constructed master frame.…”

Section: Gd2 Procedures By Means Of Differential Astrometrysupporting

confidence: 87%

“…As a result, there might be a degeneracy between low-order terms (order≤2) in the fitted distortion polynomial and the translation in the conformal transformation. By introducing observations at various orientations, the discrepancy between the two GD solutions will become much smaller (Zheng et al 2021). Unlike many ground-based telescopes with rigid mounting of the telescope itself and of its detectors, the CSST and other space telescopes are able to obtain this type of observations.…”

Section: Gd2 Procedures By Means Of Differential Astrometrymentioning

confidence: 99%

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A deeper solution to the actual geometry of CCD mosaic chips

Zheng

Peng

Vienne

et al. 2022

A&A

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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...

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Section: Gd2 Procedures By Means Of Differential Astrometrysupporting

confidence: 87%

Section: Gd2 Procedures By Means Of Differential Astrometrymentioning

confidence: 99%

A deeper solution to the actual geometry of CCD mosaic chips

Zheng

Peng

Vienne

et al. 2022

A&A

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“…But it is indeed fortunate that the CSST is able to attain the observations at different orientations. And the GD2 solution derived from observations taken at different orientations have been proven to be able to recover the linear terms and quadratic terms of the distortion (see Table .4 in Zheng et al 2021). The determination of gap by differential astrometry has an apparent advantage over photographic astrometry due to its high precision and stable performance.…”

Section: Resultsmentioning

confidence: 99%

“…As the distortion of the optical system is dominated by cubic terms, the patterns derived from the two types of astrometry are similar. But there is a little difference still for the marginal GD vectors, and it is mainly due to the difference of the linear terms and quadratic terms between the two GD solutions according to the work of Zheng et al (2021). The median (MED) of GD1 solutions is about 0.30 pixel smaller than Wang et al (2019) for Obs16, and 0.17 pixel smaller than Wang et al (2019) for Obs17.…”

Section: Gd Solutionmentioning

confidence: 99%

A Deeper Solution to the Actual Geometry of CCD Mosaic Chips

Zheng,

Peng,

Vienne

et al. 2021

Preprint

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Context. For 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 (Platais et al. 2006) or construction for deeper images that can also seamlessly cover a larger area of the sky. A key part of the reduction involved the accurate geometric distortion (GD) correction and the precise determination of the relative positions of the CCD chips. Also the short-term and long-term stabilities of them are important for 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, rather than determine their relative positions directly from the distortion-free coordinate. We verify the applicability of this solution from two types of astrometry. One is to make use of the astrometric catalog -Gaia DR2 (Gaia Collaboration et al. 2018) to compute stars' celestial positions. We refer to the practice as photographic astrometry in this paper. And the other practice is to compute stars' relative positions by only using their pixel coordinates. We refer to it as differential astrometry. Meanwhile, we also aim to test the consistency between two types of astrometry from the results. Methods. By taking advantage of the GD solutions derived from observations, we relate the physical positions of the adjacent pixel edges of two CCD chips to each other and estimate the actual relative positions between chips. We implement the technique for two epochs of observations, which are taken from the CCD mosaic chips of the Bok 2.3-m telescope at Kitt Peak. Results. There is a good agreement between the two types of astrometry for the relative positions between chips. And the results provide us with more confidence in the differential astrometry of the planned Chinese Space Station Telescope (CSST). Since the CSST can observe much fainter stars (e.g. 26 mag in g band) than the Gaia satellite, of which we only have the pixel positions rather than their astrometric parameters (e.g. J2000.0 positions, proper motions, parallaxes and etc), differential astrometry is expected to be more suitable for measurements. We achieved a 0.04 pixel uncertainty for the relative positions between chips on average, at least the factor of two improvement over the method which is used to monitor the progress of the interchip offset of CCD mosaic chips in the Hubble Space Telescope (HS T ). For the first-epoch observations, although suffered from possible variations in the non-linear parts of distortion, we still achieved a better uncertainty, 0.02 pixel on average. Conclusions. We think there are two definite advantages for 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 alleviate the propagated error of residual distortions of each observation deviating from the average solution throughout ...

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A Geometric Distortion Solution Specifically for Historical Observations and its Implementation

Lin,

Peng,

Zheng

et al. 2024

Res. Astron. Astrophys.

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Geometric distortion (GD) critically constrains the precision of astrometry. Using well-established methods to correct GD requires calibration observations, which can only be obtained using a special dithering strategy during the observation period. Unfortunately, this special observation mode is not often used, especially for the historical observations before those GD correction methods presented. As a result, some telescopes have no GD calibration observations for a long period, making it impossible to accurately determine the GD effect. This limits the value of the telescope observations in certain astrometric scenarios, such as using historical observations of moving targets in the solar system to improve their orbits. We investigated a method for handling GD that does not rely on the calibration observations. With this advantage, it can be used to solve the GD models of telescopes which were intractable in the past. The method was implemented in Python and released on GitHub. It was then applied to solve GD in the observations taken with the 1-m and 2.4-m telescopes at Yunnan Observatory. The resulting GD models were compared with those obtained using well-established methods to demonstrate the accuracy. Furthermore, the method was applied in the reduction of observations for two targets, the moon of Jupiter (Himalia) and the binary GSC2038-0293, to show its effectiveness. After GD correction, the astrometric results for both targets show improvements. Notably, the mean residual between observed and computed position (O-C) for the binary GSC2038-0293 decreased from 36 mas to 5 mas.

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

Cited by 3 publications

References 21 publications

A deeper solution to the actual geometry of CCD mosaic chips

A deeper solution to the actual geometry of CCD mosaic chips

A Deeper Solution to the Actual Geometry of CCD Mosaic Chips

A Geometric Distortion Solution Specifically for Historical Observations and its Implementation

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