Select all table column names for a specified tablename (per the system catalogs)

Hi List;

I want to pull the list of column names from the system catalogs for a
specified table. I only want column names, I want to exclude any index
names, or other non-column name rows.  I got this far (see below)
however this query produces additional rows with attname's like
tableoid, cmax, xmax ctid, etc.

select attname from pg_attribute where attrelid = (select oid from
pg_class where relname = 'my_tablename');

Any thoughts ?

Thanks in advance...