= Galactic-centre stellar-orbit experiments
{c}
{title2=2002–2008}
<Rainer Schödel>, <Reinhard Genzel> and collaborators combined NTT imaging with VLT adaptive-optics <infrared> observations. Silicon-monoxide <masers> registered stellar images to the radio position of <Sagittarius A*>. Their 2002 observations included <S2>'s closest approach; a fitted <Kepler orbit> constrained a concentrated central mass. Rejecting a particular extended cluster also required its density and survival assumptions.<Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the Milky Way by Rainer Schödel and others>[PDF pp.2–5, image registration, fitted orbit and extended-mass tests]{ref}
<Andrea Ghez> and collaborators combined Keck speckle imaging and laser-guide-star <adaptive optics> with <infrared> spectra. Image fitting supplied angular positions; spectral lines supplied <velocities>. The 2008 analysis treated optical distortion, coordinate alignment and blended sources: a shifting photocentre can imitate motion. Joint angular and spectral fitting constrained both distance and mass, with assumptions about central radial motion affecting the result. Apparatus calibration and confusion tests are therefore part of the dynamical inference.<Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits by Andrea M. Ghez and others>[PDF §§2–4 and Appendices A–C: imaging, spectroscopy, source confusion and orbital fit]{ref}
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