Spatio-kinematic models of five nova remnants: correlations between nova shell axial ratio, expansion velocity, and speed class

Abstract

We present long-slit intermediate-dispersion spectroscopic observations and narrow-band direct imaging of four classical nova shells, namely T Aur, HR Del, DQ Her and QU Vul, and the nova-like source CK Vul. These are used to construct models of their nebular remnants using the morpho-kinematic modelling tool to reveal their 3D shape. All these nova remnants but CK Vul can be described by prolate ellipsoidal shells with different eccentricity degree, from the spherical QU Vul to the highly elongated shell with an equatorial component HR Del. On the other hand, CK Vul shows a more complex structure, with two pairs of nested bipolar lobes. The spatio-kinematic properties of the ellipsoidal nova shells derived from our models include their true axial ratios. This parameter is expected to correlate with the expansion velocity and decline time 𝑡 3 (i.e., their speed class) of a nova as the result the interaction of the ejecta with the circumstellar material and rotation speed and magnetic field of the white dwarf. We have compared these three parameters including data available in the literature for another two nova shells, V533 Her and FH Ser. There is an anti-correlation between the expansion velocity and the axial ratio and decline time 𝑡 3 for nova remnants with ellipsoidal morphology, and a correlation between their axial ratios and decline times 𝑡 3 , confirming theoretical expectations that the fastest expanding novae have the smallest axial ratios. We note that the high expansion velocity of the nova shell HR Del of 615 km s −1 is inconsistent with its long decline time 𝑡 3 of 250 days.

On the Observability of Recurrent Nova Super-Remnants

“…The interaction of ejecta with different velocities (Aydi et al 2020b) will shock heat the gas leading to X-ray and radio emission such as that seen in RS Ophiuchi (Bode & Kahn 1985;O'Brien et al 1992) and V838 Her (O'Brien et al 1994). This ejected material then goes on to form a nova shell (see, e.g., Woudt & Ribeiro 2014;Harvey et al 2020;Santamaría et al 2020Santamaría et al , 2022. For the ∼10% of Galactic novae with observed shells (see, e.g., Wade 1990;Slavin et al 1995;Gill & O'Brien 1998;Santamaría et al 2019Santamaría et al , 2022, their morphologies can inform us of the underlying configuration of the binary.…”

“…This ejected material then goes on to form a nova shell (see, e.g., Woudt & Ribeiro 2014;Harvey et al 2020;Santamaría et al 2020Santamaría et al , 2022. For the ∼10% of Galactic novae with observed shells (see, e.g., Wade 1990;Slavin et al 1995;Gill & O'Brien 1998;Santamaría et al 2019Santamaría et al , 2022, their morphologies can inform us of the underlying configuration of the binary. In particular, nova shells are structured with an equatorial waist and polar cones of emission (Hutchings 1972).…”