ABSTRACT The shell of the classical nova V5668 Sgr was resolved by ALMA at the frequency of 230 GHz 927 d after eruption, showing that most of the continuum bremsstrahlung emission originates in clumps with diameter smaller than 1015 cm. Using Very Large Array radio observations, obtained between days 2 and 1744 after eruption, at frequencies between 1 and 35 GHz, we modelled the nova spectra, assuming first that the shell is formed by a fixed number of identical clumps, and afterwards with the clumps having a power-law distribution of sizes, and were able to obtain the clump’s physical parameters (radius, density, and temperature). We found that the density of the clumps decreases linearly with the increase of the shell’s volume, which is compatible with the existence of a second media, hotter and thinner, in pressure equilibrium with the clumps. We show that this thinner media could be responsible for the emission of the hard X-rays observed at the early times of the nova eruption, and that the clump’s temperature evolution follows that of the super-soft X-ray luminosity. We propose that the clumps were formed in the radiative shock produced by the collision of the fast wind of the white dwarf after eruption, with the slower velocity of the thermonuclear ejecta. From the total mass of the clumps, the observed expansion velocity and thermonuclear explosion models, we obtained an approximate value of 1.25 M⊙ for the mass of the white dwarf, a central temperature of 107 K and an accretion rate from the secondary star of 10−9–10−8 M⊙ yr−1.

ABSTRACT We present Hubble Space Telescope optical images, Keck-OSIRIS near-infrared (NIR) integral field spectroscopy data cubes and Keck-Near InfraRed Camera-2 (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 yr post eruption), and that the shell has a mass of 6.3 × 10−5 M⊙. The models also suggest anisotropy of the ionizing flux, possibly by the contribution from a luminous accretion disc.

We present the detection and imaging of the spatially resolved shell of nova V382 Vel with SOAR adaptive optics module (SAM). The shell was observed in narrow-band filters H alpha and [O III] 5007 angstrom revealing different structures in each filter. The shell's angular diameter obtained was 9.9 arcsec, equivalent to 2.8 x 10(17) cm, using the distance of 1.79 kpc obtained by the Gaia mission. The upper limit for total shell mass derived from recombination lines is M-s = 1.4 x 10(-4) M-circle dot. Our photoionization models indicate an accretion disk with T-d = 60,000 K and L = 10(36) ergs as main ionizing source.

We present modelling and analysis of the ejecta of nova V723 Cas based on spatially resolved infrared 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 disc. 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 x 10(-5) M-circle dot and the central source temperature and luminosity are T = 280 000 K and L = 10(38) erg s(-1). 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.

High resolution ALMA observations of the recent (2.52 yrs old) shell of Nova V5668 Sgr (2015) show a highly structured ionised 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 2.5 $\sigma$ 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.

The formation of peculiar transient narrow emission line components observed in the spectra of a few novae is discussed. We aim to constrain the possible physical sources responsible for those unexpected components that present orbital radial velocity modulations, which were first observed in the post-outburst recombination lines of Nova U Sco 2010. A search for candidates showing similar narrow components is presented. Exploratory photoionization simulations indicate that the forming region cannot be restricted to the Roche Lobe of the primary, but could be located around the outer Lagrangian point L-3. Further analysis disfavors an origin at the companion star. In addition, we analyze possible correlations between the presence of the narrow components, the basic nova parameters and the spectral classification in the initial permitted line phase. (C) 2015 Elsevier B.V. All rights reserved.

The spectral evolution of the recurrent nova U Sco presented conspicuous formation of narrow emission line components in the recombination lines a few days after maximum. The physical origin of these lines and their frequency among classical and recurrent novae have not been well established yet. In this work we identify additional novae showing this phenomenon. On the basis of photoionization modeling we propose that the forming region is not restricted to the primary Roche Lobe.

Synoptic spectroscopic observations of the U Sco 2010 outburst from maximum light to quiescence as well as a contemporaneous X-ray observation are presented and analyzed. The X-ray spectrum 52 days after outburst indicates a hot source (kTbb ∼ 70 eV). Narrow-line components from the irradiated companion atmosphere were observed in hydrogen and helium optical recombination lines. The formation of a nebular spectrum is seen for the first time in this class of recurrent novae, allowing a detailed study of the ejecta using photoionization models. Unusual [O iii] auroral-to-nebular line ratios were found and possible scenarios of their origin are discussed. The modeling of the emission line spectrum suggests highly heterogeneous ejecta with masses around or above 3 × 10−6 Msun.