The fundamental definition of "radial velocity''
By L. Lindegren, D. Dravins. 2003
162 citations recorded by the source corpus.
Accuracy levels of metres per second require the fundamental concept of "radial velocity" for stars and other distant objects to be examined, both as a physical velocity, and as measured by spectroscopic and astrometric techniques. Already in a classical (non-relativistic) framework the line-of-sight velocity component is an ambiguous concept, depending on whether, e.g., the time of light emission (at the object) or that of light detection (by the observer) is used for recording the time coordi- nate. Relativistic velocity eects and spectroscopic measurements made inside gravitational fields add further complications, causing wavelength shifts to depend, e.g., on the transverse velocity of the object and the gravitational potential at the source. Aiming at definitions that are unambiguous at accuracy levels of 1 m s 1 , we analyse dierent concepts of radial velocity and their interrelations. At this accuracy level, a strict separation must be made between the purely geometric concepts on one hand, and the spectroscopic measurement on the other. Among the geometric concepts we define kinematic radial velocity ,w hich corresponds most closely to the "textbook definition" of radial velocity as the line-of-sight component of space velocity; and astrometric radial velocity, which can be derived from astrometric observations. Consistent with these definitions, we propose strict definitions also of the complementary kinematic and astrometric quantities, namely transverse velocity and proper mo- tion. The kinematic and astrometric radial velocities depend on the chosen spacetime metric, and are accurately related by simple coordinate transformations. On the other hand, the observational quantity that should result from accurate spectroscopic measurements is the barycentric radial-velocity measure . This is independent of the metric, and to first order equals the line-of- sight velocity. However, it is not a physical velocity, and cannot be accurately transformed to a kinematic or astrometric radial velocity without additional assumptions and data in modelling the process of light emission from the source, the transmission of the signal through space, and its recording by the observer. For historic and practical reasons, the spectroscopic radial-velocity measure is expressed in velocity units as czB ,w herec is the speed of light and zB is the observed relative wavelength shift reduced to the solar-system barycentre, at an epoch equal to the barycentric time of light arrival. The barycentric radial-velocity measure and the astrometric radial velocity are defined by recent resolutions adopted by the International Astronomical Union (IAU), the motives and consequences of which are explained in this paper.
Subfields: Astronomy and Astrophysics, Oceanography
View Paper: https://www.semanticscholar.org/paper/e0df8fbbed17375e9e7550d32755537476bfc4a7
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Citations in the corpus
- SOAP 2.0: A TOOL TO ESTIMATE THE PHOTOMETRIC AND RADIAL VELOCITY VARIATIONS INDUCED BY STELLAR SPOTS AND PLAGES (2014, background): “…oscillations (Arentoft et al. 2008; Kjeldsen et al. 2005; Bouchy et al. 2005; Mayor et al. 2003), granulation phenomena (Dumusque et al. 2011b; Lindegren & Dravins 2003; Dravins 1982), and activity signals (Robertson et al. 2014; Jeffers et al. 2013; Meunier & Lagrange 2013; Lovis et al.…”
- The IAU 2000 Resolutions for Astrometry, Celestial Mechanics, and Metrology in the Relativistic Framework: Explanatory Supplement (2003, unknown): “The BCRS is the basic astrometric reference system, in which concepts such as ‘‘ radial velocity ’’ and ‘‘ proper motion ’’ are defined (Lindegren & Dravins 2003).”
- A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty (2019, methodology): “The surface gravity of S2 contributes ∆vz0 = GMS2/rS2c = 1.6 km s−1 (Lindegren & Dravins 2003), where we used rS2, the radius of S2, and MS2, its mass, from Habibi et al. (2017).”