A High-resolution investigation of the shell source G55.7+3.4
at 610 and 1415 MHz.
W.M. Goss, U.J. Schwarz, S.G. Siddesh and K.W. Weiler

The  610 MHz (49 cm) observations were made in 1973 in 12-h periods.
(beam 1.5'x1.4')
The 1415 MHz (21 cm) observations were made in 1971-72 in 12-h periods.
(beam 27" x 72").
The majority of the sources from table 1 were only observed  at 49 cm,
becauce of the larger field of view (1.4^o) at this frequency, compared to
only 0.6^o at 21 cm.
Source 12W21 is most likely the pulsar PRS 1920+21.