astrolibR (version 0.1)

helio_rv: Calculate the heliocentric radial velocity of a spectroscopic binary

Description

Calculate the heliocentric radial velocity of a spectroscopic binary

Usage

helio_rv(hjd, t, p, v0, k, e, omega, maxiter=100)

Arguments

hjd

time of observation

t

time of periastron passage (maximum positive velocity for circular orbits), same time system as hjd

p

orbital period, same time system as hjd

v0

systemic velocity

k

velocity semi-amplitude, same units as v0

e

orbital eccentricity (default=0.0)

omega

longitude of periastron, in degrees (default=0.0, but must be specified for eccentric orbits

maxiter

maximum number of iterations to achieve 1e-8 convergence

Value

status

Iterations needed for convergence

rv

predicted heliocentric radial velocity for the date(s) specified by hjd, same units as v0

Details

The user should ensure consistency with time and velocity systems being used (e.g. days and km/s). Generally, users should reduce large time values by subtracting a large constant offset, which may improve numerical accuracy.

Examples

# What was the heliocentric radial velocity of the primary component of HU Tau
# at 1730 UT 25 Oct 1994?
# Result: -63.66 km/s

jd <- juldate(c(94,10,25,17,30))   #  obtain Geocentric julian date
hjd <- helio_jd(jd, ten(04,38,16)*15., ten(20,41,05)) #  convert to HJD
helio_rv(hjd, 46487.5303, 2.0563056, -6.0, 59.3)

# Plot two cycles of an eccentric orbit, e=0.6, omega=45 for both
# components of a binary star

phase <- seq(0.0,2.0,length=100)   #  generate 100 phase points
plot(phase, helio_rv(phase, 0, 1, 0, 100, 0.6, 45)$rv, ylim=c(-100,150), pch=20)
lines(phase, helio_rv(phase, 0, 1, 0, 50, 0.6, 45+180)$rv)