astrolibR (version 0.1)

gal_uvw: Calculate the Galactic space velocity (U,V,W) of a star

Description

Calculate the Galactic space velocity (U,V,W) of a star

Usage

gal_uvw(distance, lsr=F, ra, dec, pmra, pmdec, vrad, plx)

Arguments

distance

distance, scalar or vector, in parsecs

lsr

if =TRUE, then output velocities are corrected for solar motion

ra

Right Ascension, scalar or vector, in decimal degrees

dec

declination, scalar or vector, in decimal degrees

pmra

proper motion in R.A., scalar or vector, in milliarcseconds/yr

pmdec

proper motion in declination, scalar or vector, in milliarcseconds/yr

vrad

radial velocity, scalar or vector, in km/s

plx

parallax, scalar or vector, in milliarcseconds

Value

U

velocity positive toward the Galactic anticenter, in km/s

V

velocity positive in the direction of Galactic rotation, in km/s

W

velocity positive toward the North Galactic Pole, in km/s

Details

Calculates the Galactic space velocity U, V, W of star given its coordinates, proper motion, distance (or parallax), and radial velocity. ; The calculation follows the general outline of Johnson & Soderblom (1987) except that U is positive outward toward the Galactic anticenter, and the J2000 transformation matrix to Galactic coordinates is taken from the introduction to the Hipparcos catalog.

The distance parameter should be zero if parallax plx is provided. If the user has proper motion in R.A. given in seconds of time/yr, mu_alpha, then it should first be converted to seconds of time/yr using

pmra = 15*mu_alpha*cos(dec)

.

If lsr=TRUE, then output velocities are corrected to the local standard of rest (LSR) assuming a solar motion (U,V,W)_Sun = (-8.5, 13.38, 6.49) km/s, as given by Coskunoglu et al. 2011). Note that the value of the solar motion through the LSR remains poorly determined.

References

Coskunoglu, B., Ak, S., Bilir, S., et al. 2011, Local stellar kinematics from the RAVE data. I. Local standard of rest, Mon. Not. Royal Astron. Soc., 412, 1237-1245. http://adsabs.harvard.edu/abs/2011MNRAS.412.1237C Johnson, D. R. H. and Soderblom, D. R., 1987, Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group, Astron. J., 93, 864-867. http://adsabs.harvard.edu/abs/1987AJ.....93..864J

Examples

#  Compute (U,V,W) for the halo star HD 6755 using measurments by the Hipparcos satellite
#  Result: u=141.2  v = -491.7  w = 93.9        ;km/s

gal_uvw(139, lsr=TRUE, ten(1,9,42.3)*15., ten(61,32,49.5), 628.42, 76.65, -321.4)