Get the column names from sys.columns -- if it is a table it will have a row in sys.objects and one row for each column in sys.columns. Here's a query that I use:

select Case when ROW_NUMBER() over (order by column_id) > 1 then ',' else '' end+C.name

from sys.sysobjects O

join sys.columns C on O.id = C.[object_id]

where O.type = 'U' and O.name = '##zzz'

order by column_id