Finding foreign key relationships via AMO

Hi,

I am trying to find the relational columns used for the join between a fact table and a dimension table from a cube definition via AMO, just for a regular measure group-cube dimension relationship.

What I have found so far:

I can find the key attribute of each cube dimension via

var keyAttrib =
 myMeasureGroup.Dimensions[“MyCubeDimName”].Attributes
   .Where(a => a.Type = Type.Granularity)
   .Single()

from this, I can find the columns via

keyAttrib.Attribute.KeyColumns

which have TableID and ColumnID properties.
But I have now searched up and down, and not found any way to find out which columnsin the fact table to use for the join. In BIDS, this would be the columns I configure in:

Cube Editor/Dimension usage tab/double clicking the cell for the measure group and cube dimension, and then configuring the relationship properties.

TIA

Frank