This paper summarises an investigation into the wide-ranging methods employed to determine the distance to the Galactic centre, Ro. Remote methods commonly use luminosity reference objects such as RR Lyraes and red clump stars. Ruler methods involve annual parallax or line-of-sight velocity. Examples of all the methods are described and their limitations discussed. The main uncertainties with remote methods arise from calibration, extinction and group eccentricity.
The main uncertainties with ruler methods arise from object location error and unknowns in relation to Galactic rotation. A total of 63 determinations were studied, from which six remote method and six ruler method determinations are identified for refining the value of Ro. Both categories are found to give the same mean value of Ro = 7.9 0.3 kpc. High-precision astrometry of objects within the
Galactic nucleus provides the most potential for improvement in accuracy of the determination of
Keywords: Galaxy, Galactic centre, distance determination, parallax, astrometry, Sgr A*
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