Tutorial & Examples
by Ian Boyle and Chuck Keeton
30 Aug 2005
INTRODUCTION
This tutorial provides step by step instructions for four
basic lensing calculations as an introduction to the
gravlens
software as well as one section that covers additional commands.
Each example is presented in two parts: the analytical solution and the
solution as found using
gravlens.
This tutorial assumes familiarity with basic lens theory.
For quantitative examples, the following values are assumed:
G = 6.67 x 10-8 dyne cm g-2
c = 3 x 1010 cm/s
M = 1012Msolar = 1.99 x 1045
g
Ds = 2000 Mpc = 2 x 109 pc = 6.67 x 1027
cm
Dl = 1000 Mpc = 109 pc = 3.09 x 1027
cm
Dls = 1000 Mpc = 109 pc = 3.09 x 1027
cm
Dls = Ds - Dl *
* Not the case for
cosmological distances in general
This tutorial progressively builds on the material presented so each
section assumes an understanding of the material explained in the
previous sections. The following index lists the gravlens
material reviewed in each part of the tutorial:
SECTION
I. Point Mass Lens
- gridlo1
variable
- gridhi1 variable
- Interactive runs
- Input files
- Model and parameter definition
- ptmass
model
- Lens position parameters
- findimg
command
- Relation between angular and Cartesian coordinate positions
- findimg
results
- alpha
model
- Power law index parameter
- Cental "ghost" image
SECTION III. Singular
Isothermal Sphere Lens With
Shear (At Origin)
- Shear parameter
- Source position on origin
SECTION IV. Singular
Isothermal Sphere Lens Without Shear
- Source position off origin
SECTION V. Additional Commands
- findimg3
command
- findsrc
command