'NN' stands for the sources found by Imai+ in 2007, IAU Symp. 242, Astrophysical Masers and their Environments.
in source:IRAS 19134+2131Ref:=2007ApJ...669..424I
, SAHAI R., MORRIS M.
Astrophys. J., 669, 424-434 (2007)
The spatio-kinematical structure and distance of the preplanetary nebula IRAS 19134+2131.
oTable 3: <I2007 IRAS 19134+2131 NN> (Nos 1-20).
=E=Catalogue in electronic form as J/ApJ/669/424 ====Sorry, no entry could be found====