Astrometric Precision Tests on TESS Data

Abstract

Astrometry at or below the microarcsec level with an imaging telescope assumes that the uncertainty on the location of an unresolved source can be an arbitrarily small fraction of the detector pixel, given a sufficient photon budget. This paper investigates the geometric limiting precision, in terms of CCD pixel fraction, achieved by a large set of star field images, selected among the publicly available science data of the Transiting Exoplanet Survey Satellite (TESS) mission. The statistics of the distance between selected bright stars (G ≃ 5 mag), in pixel units, is evaluated, using the position estimate provided in the TESS light curve files. The dispersion of coordinate differences appears to be affected by long term variation and noisy periods, at the level of 0.01 pixel. The residuals with respect to low-pass filtered data (tracing the secular evolution), which are interpreted as the experimental astrometric noise, reach the level of a few milli-pixel or below, down to 1/5900 pixel. Saturated images are present, evidencing that the astrometric precision is mostly preserved across the CCD columns, whereas it features a graceful degradation in the along column direction. The cumulative performance of the image set is a few micropixel across columns, or a few 10 μpx along columns. The idea of astrometric precision down to a small fraction of a CCD pixel, given sufficient signal to noise ratio, is confirmed by real data from an in-flight science instrument to the 10−6 pixel level. Implications for future high precision astrometry missions are briefly discussed.

Theia : science cases and mission profiles for high precision astrometry in the future

“…Crouzier et al 22 and Nemati et al 23 have achieved 6×10 −5 pixel precision in the laboratory on a e2V CCD. Centroiding algorithms for differential astrometry on TESS science data have demonstrated in-flight uncertainties of ≤ 1×10 −5 pixels on single frames and ∼ 2×10 −6 as collective performance for an observing sequence 24 .…”

Consolidation of the Gaia catalogue with Chinese Space Station Telescope astrometry

“…It may be noted that the bright limiting magnitude is significantly affected not only by the different exposure time of Wide and Deep Surveys but also by the actual source spectrum; precision is affected also by the number of observations in different filters. Also, saturation may not impose a severe limitation to astrometric performance, depending on detector response and operation, for example, CCD images affected by moderate blooming (Gai et al, 2022b) still provide highastrometric precision in the horizontal (row) direction. Further investigations are in progress and will be presented in a forthcoming study.…”

“…In the most conservative case (G ≥ 18 mag), the reference frame materialization is affected by a typical error in the 3-5 μas range, which is reduced to 1.5-2 μas in the intermediate case (G ≥ 16 mag), and drops below 1 μas for most fields in the most optimistic case in which all Gaia sources are included. This may be achieved, for example, by extending CSST-OS observations with shorter exposures or by exploitation of moderately saturated images (Gai et al, 2022b). The feasibility and benefits of extended dynamic range observations shall be addressed in future with more detailed investigations.…”