No abstract

High resolution ALMA observations of the recent (2.52 yr old) shell of Nova V5668 Sgr (2015) show a highly structured ionized gas distribution with small (10 15 cm) clumps. These are the smallest structures ever observed in the remnant of a stellar thermonuclear explosion. No extended contiguous emission could be found above the 2.5σ level in our data, while the peak hydrogen densities in the clumps reach 10 6 cm −3 . The millimetre continuum image suggests that large scale structures previously distinguished in other recent nova shells may result from the distribution of bright unresolved condensations.

We present modeling and analysis of the ejecta of nova V723 Cas based on spatially resolved IR spectroscopic data from Keck-OSIRIS, with LGSAO (adaptive optics module). The 3D photoionization models include the shell geometry taken from the observations and an anisotropic radiation field, composed by a spherical central source and an accretion disk. Our simulations indicate revised abundances log(N Al /N H ) = −5.4, log(N Ca /N H ) = −6.4 and log(N Si /N H ) = −4.7 in the shell. The total ejected mass was found as M shell = 1.1 × 10 −5 M and the central source temperature and luminosity are T = 280, 000 K and L = 10 38 erg/s. The 3D models are compared to basic 1D simulations to demonstrate the importance of using more realistic treatments, stressing the differences in the shell mass, abundances and characterization of the central source. The possibility of V723 Cas being a neon nova and the puzzling central source features found are discussed.

We present HST optical images, Keck-OSIRIS NIR IFS data cubes and Keck-NIRC2 NIR images of nova V5668 Sgr from 2016 to 2019. The observations indicate enhanced emission at the polar caps and equatorial torus for low ionization lines, and enhanced high ionization emission lines only at the polar caps. The radial velocities are compatible with a homogeneous expansion velocity of v=590 km s−1 and a system inclination angle of 24○. These values were used to estimate an expansion parallax distance of 1200 ± 400 pc. The NIRC2 data indicate the presence of dust in 2016 and 2017, but no dust emission could be detected in 2019. The observational data were used for assembling 3D photoionization models of the ejecta. The model results indicate that the central source has a temperature of 1.88 × 105 K and a luminosity of 1.6 × 1035 erg s−1 in August of 2017 (2.4 years post eruption), and that the shell has a mass of 6.3 × 10−5 M⊙. The models also suggest an anisotropy of the ionizing flux, possibly by the contribution from a luminous accretion disc.