RXJ0019.8+2156 is a Supersoft X-ray Source (SSS) discovered by ROSAT and identified (Beuermann et al. 1995) as an object of magnitude V = 12.2, brighter than any other known SSS. The mass function and the optical spectrum are similar to CAL 83, but the X-ray luminosity seems to be lower. The main light variations are: a cyclic modulation with a 15.8 h period and a 0.3 mag amplitude, a quasi-periodic pulsation less than 0.1 mag in 2 h (Beuermann et al. 1995), variations of about 1 mag over a time-scale of 20 yr and small irregular fluctuations on a time-scale of weeks to months (Greiner & Wenzel 1995).

The most promising model, at present, involves a binary system in which a hot 1 M⊙ white dwarf with an accretion disk is accreting at a mean rate of Ṁ ≈ 10−7 M⊙yr−1; sporadic hydrogen burning caused by an unstable mass transfer (Greiner & Wenzel 1995) seems to be present.