1,3,1,3,4- 1Laboratoire Temps Espace, Observatoire de Paris-PSL,CNRS, Paris, France
- 2Nanjing University, Nanjing, China
- 3Shanghai Astronomical Observatory, Shanghai, China
- 4Macau University of Science and Technology (MUST), Taipa, Macao
Photocentre displacement is a well-known effect in optical observations of extended celestial bodies such as asteroids. It shows a shift in the observed position with respect to the actual centre of mass. This shift is linked to the physical properties of asteroids, such as surface composition, shape and size [1][2].
Similarly, in millimeter/sub-millimeter observations, the derived position of the target is usually the thermal centre, i.e.position of the peak flux density which may differ from the barycentre (the center of mass) due to the high resolution of the instrument. These differences can be of the order of a few milli-arcseconds. In a recent study on Kalliope-Linus, a main-belt binary asteroid system, a discrepancy was found between the separation of Kalliope and Linus obtained from ALMA data and that predicted by the ephemeris [3]. In this study, we aim to investigate this difference by considering the offset between the thermal centre and the centre of mass.
For each ALMA observation, we simulate the temperature distribution of Kalliope at different depths with a one-dimensional numerical thermophysical model [4]. By translating subsurface temperatures to thermal flux density, we could estimate the thermal center of Kalliope in each observation as well as its offset to barycenter. The estimates are then used to calibrate the observations for comparison with the ephemeris. In addition, it is possible to update the mutual orbit of the Kalliope system using this revised data.
[1] L. Lindegren, “Meridian observations of planets with a photoelectric multislit micrometer.,”, vol. 57, no. 1-2, pp. 55–72, May 1977
[2] D. Hestroffer, “Photocentre displacement of minor planets: analysis of HIPPARCOS astrometry,”, vol. 336, pp. 776–781, Aug. 1998.
[3] Katherine de Kleer et al 2024, Surface properties of the Kalliope-Linus system from ALMA and VLA data
[4] Shunjing Zhao et al 2024, Deep operator neural network applied to efficient computation of asteroid surface temperature and the Yarkovsky effect
How to cite: Liu, Z., Zhao, S., Shi, X., Hestroffer, D., and Hui, M.-T.: Analysis of thermalcentre-barycentre offsets and application to ALMA observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-750, https://doi.org/10.5194/epsc-dps2025-750, 2025.
