On the Variability of the Central Star of the Planetary Nebula H_Z 1–5

Extract

During 1960–67 we have studied the variable star FG Sge=377·1943 Sge, which is located exactly in the centre of an image of the planetary nebula H_z 1–5, as shown on Figure 1. The most significant feature of the central star is the continuous increase of its brightness during the past 70 years, as one can see from Figure 2. During the same time, the temperature of the central star has apparently decreased, although direct information to this effect is available only since 1955. In 1955 the star had spectral type B4, while by 1967 it had become A5. The observational data can be explained by the continuous ejection of gas from the central star, which began at the end of the preceding century. The central star at that time must have had T_∗≈63 300°K and M_pg≈ + 1·3, on this model.