Hate to be the one to tell you this, John. If you would have done your homework before buying those stars you would have found them to be poor choices. Both stars are more than likely going to die in a short period of time. They should not be collected and
LFSs that buy them to sell to unsuspecting, or uninformed hobbyists should be taken off your list of
LFSs to be supported. They are not conservation minded.
To answer your question about feeding them, your guess is as good as any. That's why they should not be bought. If we buy them, that encourages the
LFS to keep buying them, which encourages the importer/wholesaler to keep buying them, which encourages the collector to keep collecting them. Do you see where we, as conservation minded hobbyists, fit into the equation??? We are the decision maker.
On an encouraging note, I know of one Feather Star that has been in captivity for over a year. The owner doesn't have a clew as to what it eats. It survives in a Seahorse tank with low flow. Here's a pic of it....
They are a beautiful critter. this one is being kept by a very experienced reefer. she says, "It never moves from this spot but occasionally opens and expands it's arms." She also says, "It beautiful but, boring."
One of the most important things we can do as reefing forum members is to keep us informed with progress you are having.....good and bad.
The only thing I can add is good luck, with your stars.
Dick