SharePoint2010 keywordQuery

I am using the keyworkQuery class to fetch some items from a Sharepoint2010 list.

I need to fetch also the Attachments for each item how can I do?.

I tried:

KeywordQuery kw = new KeywordQuery(proxy);
kw.SelectProperties.Add("Attachments");

But I get this error:

Property doesnt exist or is used in a manner inconsistent with schema settings