1 Introduction

The RV program produces a report listing the components, in a given direction, of the observer’s velocity on a given date. This allows an observed radial velocity to be referred to an appropriate standard of rest – typically either the Sun or an LSR.

As a secondary function, RV computes light time components to the Sun, thus allowing the times of phenomena observed from a terrestrial observatory to be referred to a heliocentric frame of reference. (n.b. It will of course, in addition, be necessary to express the observations in the appropriate timescale as well as applying light time corrections. In particular, it is likely that an observed UTC will need to be converted to TDB as well as being corrected to the Sun.)

Section 4 contains an example of the report produced by RV. For every half hour throughout the given day, provided the source is above the horizon, the velocity components relative to the Earth’s centre, the Sun, the kinematical and dynamical LSRs,1 the Galactic centre, and the mean motion of the Local Group, are tabulated, in km s1. Light time components to the Sun, in seconds, are tabulated also.

The accuracies, of better than 0.01 km s1 and 0.1 s, are adequate for most classes of work, the notable exception being some pulsar observations.

The input/output arrangements of RV are flexible, to allow a variety of operating styles – interactive, input from a file, batch, etc. All input is free-format. The normal operating style is interactive; prompts either appear on a terminal or as part of a Graphical User Interface, data are entered specifying the report required, and a listing is sent to disc for later printing.

1The kinematical LSR is the one which is most often required. It is the mean standard of rest of specified star catalogues or stellar populations. The Sun’s motion with respect to a kinematical LSR is called the standard solar motion. The standard solar motion used by RV is 20 km s1 towards α = 18hδ = +30 (1900). (The other sort of LSR, the dynamical LSR, is a point in the vicinity of the Sun which is in circular orbit around the Galactic centre.)