Iodine Cell

Geoffrey Marcy's Iodine Cell spectral lines have a resolution of 170,000 and a signal-to-noise of ~ 700 per pixel.

Info on the iodine cell from the Hires Manual (page 13):

Iodine Absorption Cell An iodine absorption cell can also be slid into position directly in front of the slit. This cell is basically a sealed glass bottle with a sma ll amount of iodine crystal within. When heated to a temperature above 35C, the iodine sublimes and the gas then produces an absorption spectrum on the beam from the telescope as it enters the spectrometer. The iodine absorption spectrum is a rich forest of deep, very narrow lines. This forest of lines starts at about 4800A and ends near 6000A. The absorption spectrum thus yields a very stable zero-velocity reference spectrum superimposed on the spectrum of the object being observed. It is intended to be used primarily for very accurate radial velocity studies involving asteroseismology and searches for planetary companions of stars. A detailed description of the iodine cell and its use for ultra-precise radial velocity work can be found in Marcy and Butler, 1992.

Here is what the raw data looks like:


The wavelength region for this data is: [4950:6400] angstroms.

To make this data useful for our purposes, we had to fit a continuum to this.

Our procedure was the following:

The continuum was fit by taking the largest 3 flux values in a region 300 data points wide. (a region about an angstrom wide)

The three largest flux values (and their corresponding wavelengths) were averaged together to get a single number per 300 data point region.

An IDL cubic spline was fit through these points — the spline was then used as the continuum.

To normalize this data, the flux values were divided by the continuum.


Notes to myself:

In Kingpin:


You'll see:

run idl:

> idl
% Compiled module: RDFTS.
% Compiled module: FIRST_EL.

Output Iodine Lines to Ascii

IDL> rdfts,w,s,5315.,5335.,dfn='ftskeck50.bin',dfd='/home/jonathan/Iodine/'
IDL> forprint, w,s, Format = '(D,D)', TEXTOUT='iodinelines.ascii', /nocomment
Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-Share Alike 2.5 License.