Synoptic Optical/UV Studies of Recent Recurrent Novae in Outburst

Novae are semi-detached binary systems in which a cool star fills its Roche lobe. Material from the cool star (the secondary) flows through the inner Lagrangian point and is deposited onto the surface of a white dwarf (WD) via an accretion disc. In time, the base of the accreted layer becomes degenerate, and a thermonuclear runaway (TNR) occurs on the WD surface. This results in the explosive ejection of up to ∼ 10⁻⁴ M_⊙ of material at several 100s to several 1000s of km s⁻¹: a classical nova eruption has occurred. After the eruption, and the white dwarf has returned to quiescence, mass transfer resumes and in time (of order a million years) conditions again become suitable for another nova eruption. Therefore, all novae are recurrent, but there are those that repeat on a human timescale (of order < 100 yrs) and are known as Recurrent Novae (RNe). The latter are of particular interest because the WD in these systems is thought to be close to the Chandrasekhar limit. If the white dwarf has a CO composition, then it is potentially a progenitor of a Type Ia SN – a crucial tool in the determination of large-scale cosmic structure. If, on the other hand, the white dwarf has an ONe composition, then growth toward the Chandrasekhar Limit would drive accretion induced collapse to a neutron star and such an event should result in a low mass X-ray binary. Hence, understanding RNe events has wide application. Here, we discuss recent optical/UV synoptic studies of the RNe V3890 Sgr, RS Oph, and U Sco and highlight derived insights into the RNe phenomena.