Index: trunk/ppSim/src/ppSimStars.c
===================================================================
--- trunk/ppSim/src/ppSimStars.c	(revision 14667)
+++ trunk/ppSim/src/ppSimStars.c	(revision 17557)
@@ -26,2 +26,34 @@
     return galaxy;
 }
+
+float ppSimStarSkyNoise (float skySigma, float seeingSigma) {
+
+    float skyNoise = skySigma * sqrt(4*M_PI*PS_SQR(seeingSigma));
+    return skyNoise;
+}
+
+float ppSimStarPeakToFlux (float peak, float seeingSigma) {
+
+    float psfArea = 2.0*M_PI*PS_SQR(seeingSigma);
+    float flux = peak * psfArea;
+    return flux;
+}
+
+float ppSimStarFluxToPeak (float flux, float seeingSigma) {
+
+    float psfArea = 2.0*M_PI*PS_SQR(seeingSigma);
+    float peak = flux / psfArea;
+    return peak;
+}
+
+float ppSimFluxToMag (float flux, float zp) {
+
+    float mag = -2.5*log10(flux) + zp;
+    return mag;
+}
+
+float ppSimMagToFlux (float mag, float zp) {
+
+    float flux = powf (10.0, -0.4*(mag - zp));
+    return flux;
+}