astrolibR (version 0.1)

lsf_rotate: Create a 1-d convolution kernel to broaden a spectrum from a rotating star

Description

Create a 1-d convolution kernel to broaden a spectrum from a rotating star

Usage

lsf_rotate(deltav, vsini, epsilon=0.6)

Arguments

deltav

step increment in the output rotation kernel, scalar, in km/s

vsini

rotational velocity projected along the line of sight, scalar, in km/s

epsilon

limb-darkening coefficient, scalar (default = 0.6)

Value

lsf

convolution kernel vector for the specified rotational velocity

Details

This function can be used to derive the broadening effect, or line spread function (LSF), due to stellar rotation on a synthetic stellar spectrum. It assumes constant limb darkening across the disk. To actually compute the broadening. the spectrum should be convolved with the rotational LSF using a function like kernapply or filter.

The number of points in the output lsf will be always be odd (the kernel is symmetric) and equal to either ceil(2*Vsini/deltav) or ceil(2*Vsini/deltav) +1 (whichever number is odd).

The limb darkening coefficient epsilon = 0.6 is typical for photospheric lines. The specific intensity I at any angle theta from the specific intensity Icen at the center of the disk is given by

I = Icen*(1-epsilon*(1-cos(theta))

.

The algorithm is adapted from rotin3.f in the SYNSPEC software of Hubeny & Lanz http://nova.astro.umd.edu/. Also see Eq. 17.12 in Gray (1992).

References

Gray, D., 1992, "The Observation and Analysis of Stellar Photospheres"

Examples

# Plot the LSF for a star rotating at 90 km/s in both velocity space and
# for a central wavelength of 4300 A.    Compute the LSF every 3 km/s

lsf = lsf_rotate(3,90)      # LSF will contain 61 pts