helio_rv {astrolibR} R Documentation

## 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

### 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)
```

[Package astrolibR version 0.1 Index]