lsf_rotate: Create a 1-d convolution kernel to broaden a spectrum from a...
In astrolibR: Astronomy Users Library

Description Usage Arguments Details Value Author(s) References Examples

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

1	lsf_rotate(deltav, vsini, epsilon=0.6)

`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)

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

1	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).

lsf

convolution kernel vector for the specified rotational velocity

Written by W. Landsman 2001

R adaptation by Arnab Chakraborty June 2013

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

# 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