add ref

teuben · teuben · commit 60919672f080 · 2025-12-22T22:13:07.000-05:00
diff --git a/man/man1/mkpolytrope.1 b/man/man1/mkpolytrope.1
@@ -45,6 +45,9 @@ mkommod(1NEMO), mkplummer(1NEMO)
 (Kluwer, Dordrecht, 1994) - Appendix A.
 .PP
 BGH A14
+.PP
+Gravitational Energy Formula of Polytropic Spheres -
+https://iopscience.iop.org/article/10.3847/2515-5172/ae12a4
 
 .SH "AUTHOR"
 Joshua E. Barnes
