Galactocentric acceleration in VLBI analysis

Findings of IVS WG8

¹ NVI Inc. at NASA Goddard Space Flight Center, Greenbelt, MD, USA
e-mail: daniel.s.macmillan@nasa.gov
² United States Naval Observatory, Washington, DC, USA
³ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
⁴ Technische Universität Wien, Vienna, Austria
⁵ Astronomical Institute, Czech Academy of Sciences, Prague, Czech Republic
⁶ SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, LNE, Paris, France
⁷ Pulkovo Observatory, Pulkovskoe Sh. 65, St. Petersburg 196140, Russia
⁸ Kazan Federal University, Kazan 420000, Russia
⁹ Geoscience Australia, PO Box 378, Canberra 2601 Australia
¹⁰ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, PR China
¹¹ PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, PR China
¹² Institute of Geodesy and Geoinformation Science, Technische Universität at Berlin, Berlin, Germany

Received: 27 February 2019
Accepted: 21 June 2019

Abstract

Aims. The IVS Working Group on Galactic Aberration (WG8) was established to investigate issues related to incorporating the effect of Galactic aberration in IVS analysis. The circular motion of the solar system barycenter around the Galactic center causes a change in aberration, which in the case of geodetic VLBI observing is over time scales of several decades. One of the specific goals was to recommend a Galactic aberration model to be applied by the IAU ICRF3 working group in the generation of ICRF3 as well as in other IVS analysis. Studies made by working group members have shown that the three-dimensional acceleration vector of the solar system barycenter can be estimated from VLBI delay observations.

Methods. Among the working group members, three methods were used to estimate the acceleration vector. One is to directly estimate the acceleration vector as a global parameter. The second is to estimate the acceleration vector from source proper motions determined from estimated source position time series. A third method estimated a global reference frame scale parameter for each source and derived the acceleration vector from these estimates. The acceleration vector estimate consists of a galactocentric component along with the non-galactocentric components.

Results. The geodetic reference frame VLBI estimates of the galactocentric aberration constant from the different working group members are in the range 5.1–6.4 μas yr⁻¹. These estimates are relatively close to independent estimates of 4.8–5.4 μas yr⁻¹ that can be derived from astrometric measurements of proper motions and parallaxes of masers in the Milky Way galaxy. Based on the most recent geodetic VLBI solutions, we find an upper bound of 0.8 μas yr⁻¹ for the non-galactocentric component of the secular aberration.

Conclusions. The working group made a recommendation only for the galactocentric component of the observed acceleration vector. For the recommended galactocentric aberration constant, the working group chose a geodetic value to be consistent with geodetic VLBI applications. The recommended value 5.8 μas yr⁻¹ was estimated directly in a global solution that used the ICRF3 solution data set: 1979–May 2018.