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

Description

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

Usage

 `1` ```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)

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

 `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).

Value

 `lsf` convolution kernel vector for the specified rotational velocity

Author(s)

Written by W. Landsman 2001

R adaptation by Arnab Chakraborty June 2013

References

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

Examples

 ```1 2 3 4``` ```# 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 ```

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