Lying near the boundary with Ophiuchus are Zeta, Nu, and Omicron Serpentis. All three are 4th-magnitude main-sequence stars, with Nu and Omicron being of spectral type A[47][48] and Zeta being of spectral type F.[49] Nu is a single star[4] with a 9th-magnitude visual companion,[50] while Omicron is a Delta Scuti variable with amplitude variations of 0.01 magnitudes.[51] In 1909, the symbiotic nova[52] RT Serpentis appeared near Omicron, although it only reached a maximum magnitude of 10.[53]