CCD astrometric measurements for the dwarf planet Haumea by ground-based telescopes

Abstract

Aims. The purpose of this work is to investigate an astrometric method to accurately measure the precise position of the center of mass of the dwarf planet Haumea and its satellites, based on the unresolved images taken by ground-based telescopes. Methods. A total of 29 nights of CCD observations are reported of the dwarf planet Haumea, taken during the period from February 7 to May 25, 2022 by three telescopes located in Yunnan Province, China. The pixel centroid of the unresolved image of Haumea and its satellites is measured with respect to its reference stars in the Gaia EDR3 star catalog. The new theoretical position of Haumea (the center of mass of Haumea and its satellites is assumed) is computed by the Jet Propulsion Laboratory (JPL) Horizon System. The observed minus computed (O–C) positional residuals of Haumea in right ascension and in declination show a significant and periodic variation. Furthermore, when the ephemeris position of Hi’iaka, the larger and brighter satellite of Haumea, with respect to Haumea itself is taken from the Miriade ephemeris service of the Institut de mécanique céleste et de calcul des éphémérides (IMCCE) website, the observed positional measurements of the center of mass of Haumea and Hi’iaka are derived precisely after using a new method. Results. The (O–C) positional residuals are confirmed to be caused mainly by the motion of Hi’iaka around its primary. The final mean (O–C) residuals of Haumea and its satellites are found with respect to the most recent version of the JPL ephemeris. As a by-product, a parameter that connects the mass ratio to the light ratio of Haumea and Hi’iaka (by Eq. (2) in the text), is introduced to derive the final mean (O–C) residuals.