idlastro / Astronomical Utilities: LSF_ROTATE

[Source code]

NAME
LSF_ROTATE:
PURPOSE
Create a 1-d convolution kernel to broaden a spectrum from a rotating star
EXPLANATION
Can be used to derive the broadening effect (line spread function; LSF) 
due to  rotation on a synthetic stellar spectrum.     Assumes constant 
limb darkening across the disk.
CALLING SEQUENCE
lsf = LSF_ROTATE(deltav, vsini, EPSILON=, VELGRID=)
INPUT PARAMETERS
deltaV - numeric scalar giving the step increment (in km/s) in the output 
         rotation kernel.  
Vsini - the rotational velocity projected  along the line of sight (km/s)
OUTPUT PARAMETERS
LSF - The convolution kernel vector for the specified rotational velocity.
      The  number of points in 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).    LSF will 
      always be of type FLOAT.
      To actually compute the broadening. the spectrum should be convolved
      with the rotational LSF. 
OPTIONAL INPUT PARAMETERS
Epsilon - numeric scalar giving the limb-darkening coefficient, 
      default = 0.6 which 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))
OPTIONAL OUTPUT PARAMETER
Velgrid - Vector with the same number of elements as LSF 
EXAMPLE
(1) 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
   IDL> lsf = lsf_rotate(3,90,velgrid=vel)      ;LSF will contain 61 pts
   IDL> plot,vel,lsf                    ;Plot the LSF in velocity space
   IDL> wgrid = 4300*(1+vel/3e5)       ;Speed of light = 3e5 km/s
   IDL> oplot,wgrid,lsf                ;Plot in wavelength space
NOTES
Adapted from rotin3.f in the SYNSPEC software of Hubeny & Lanz 
    .http://nova.astro.umd.edu/index.html    Also see Eq. 17.12 in 
"The Observation and Analysis of Stellar Photospheres" by D. Gray (1992)
REVISION HISTORY
Written,   W. Landsman                November 2001