helio_rv: Calculate the heliocentric radial velocity of a spectroscopic...

In astrolibR: Astronomy Users Library

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

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.

Value

status	Iterations needed for convergence
rv	predicted heliocentric radial velocity for the date(s) specified by hjd, same units as v0

Author(s)

Written by Pierre Maxted ()CUOBS) 1994

R adaptation by Arnab Chakraborty June 2013

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)

Example output

$status
[1] "convergence after 1 iterations"

$rv
[1] -62.96033

astrolibR documentation built on May 2, 2019, 3:26 a.m.