The stars in a CCD image include stars in a cluster and stars in front of the cluster (i.e. starts that don't belong to it). One group has parallaxes clustered around of 3 milli-seconds of arc (or "3 mas"). The parallaxes of the other group range from 10 mas to 15 mas. Which group contains the stars in the cluster? Explain your answer.

The stars in a CCD image include stars in a cluster and stars in front of the cluster (i.e. starts that don't belong to it). One group has parallaxes clustered around of 3 milli-seconds of arc (or "3 mas"). The parallaxes of the other group range from 10 mas to 15 mas. Which group contains the stars in the cluster? Explain your answer.