Index: /trunk/psastro/src/psastroChipAstrom.c
===================================================================
--- /trunk/psastro/src/psastroChipAstrom.c	(revision 10784)
+++ /trunk/psastro/src/psastroChipAstrom.c	(revision 10785)
@@ -1,3 +1,4 @@
 # include "psastro.h"
+# define NONLIN_TOL 0.001 /* tolerance in pixels */
 
 bool psastroChipAstrom (pmConfig *config, psArray *refs) {
@@ -55,5 +56,5 @@
 		    return false;
 		}
-		pmAstromWriteWCS (updates, fpa, chip);
+		pmAstromWriteWCS (updates, fpa, chip, NONLIN_TOL);
 		psMetadataAdd (readout->analysis, PS_LIST_TAIL, "PSASTRO.HEADER",  PS_DATA_METADATA, "psastro header stats", updates);
 		psFree (updates);
Index: /trunk/psastro/src/psastroChooseRefstars.c
===================================================================
--- /trunk/psastro/src/psastroChooseRefstars.c	(revision 10784)
+++ /trunk/psastro/src/psastroChooseRefstars.c	(revision 10785)
@@ -80,5 +80,10 @@
                 psFree (refstars);
 
-                psastroRefstarSubset (readout);
+		// XXX this error means the readout fails, but should probably not kill the entire program
+		// in this case, no PSASTRO.REFSTARS is added to readout->analysis
+                if (!psastroRefstarSubset (readout)) {
+		    psError(PSASTRO_ERR_DATA, false, "Can't determine an appropriate refstar subset\n");
+		    return false;
+		}
             }
         }