The very slow nova X Ser (t3 = 555d), situated at a large distance from the galactic plane (z ≈ 4kpc), reached maximum light at 9m in May 1903. It was discovered 5 years later on a Harvard plate (Leavitt 1908). No outburst spectrum is known. A photographic outburst light curve is given by Walker (1923); additional photometric data were published by Sakharov (1954) and Kinman et al. (1965). The light curve, shown in Fig. 1, presents 10-day means, based on all published data, and unpublished data taken from Emily Hughes Boyce’s notebook, Harvard College Observatory Plate Collection.

Hughes Boyce (1942) discovered a 275d periodicity during minimum light. From the fragmentary light curve in Fig. 1, including three more recent ‘oscillation’ maxima, a period of 277 days is found. If one assumes that the nova reached Mpg = −6 at maximum, the typical value for a slow nova, the mean absolute magnitude at minimum, Mpg = +2, together with the observed amplitude of about 2m and a relatively long mean period, suggests a very late-type (typically M6e) semi-regular variable.