Elias Aydi

We present photometric and spectroscopic observations of the 2017 Galactic nova V612 Sct, whose optical evolution was marked by multiple unusually large maxima. The eruption included two prominent flares lasting around a month each and reaching amplitudes of about 2.5 mag, followed by a series of smaller flares. Extensive spectroscopic monitoring reveals a striking pattern: with each flare, new absorption systems emerge at progressively higher velocities. This behaviour, also seen in other flaring novae, provides evidence for repeated episodes of mass ejection or outflow at increasing velocities. V612 Sct also alternated between Fe ii and He/N spectral phases during different stages of the eruption, establishing a clear connection between the photometric flares and major spectral transitions. We present two-dimensional dynamic spectra that directly trace the appearance of new absorption features contemporaneous with the light-curve flares. We also introduce a sonification of the spectroscopic sequence, offering an alternative representation of the temporal evolution of the eruption. These results support a picture in which repeated ejection episodes and shock formation play a central role in powering the multiple maxima observed in flaring novae.

This paper presents the findings from our study of nova V1405 Cas over the first 1051 days after the outburst. The study includes an analysis of the photometric light-curve evolution, along with a detailed spectroscopic analysis. Photometric analysis shows that the nova is a very slow nova, with a decline timescale of t ₂ ≈ 165 days. The mass of the white dwarf (WD) is calculated as M _WD ∼ 0.7 M _⊙ . The secondary star is a low-mass main-sequence star, with a mass of M sec ≈ 0.43 M ⊙ . Spectral observations show initial dominance of Balmer emission lines accompanied by prominent P Cygni profiles during the first +339 days. These features disappeared in later epochs, being replaced by high-ionization coronal lines, indicating that the nova had transitioned to the coronal phase by day +371. To investigate the physical conditions of the ejecta and the central source, we conducted photoionization modeling using cloudy . Our model reveals a gradual increase in the temperature and luminosity of the system, and suggests that the ejecta were primarily composed of He, N, Fe, Ne, and Ca, with noticeable temporal variations in their relative abundances. The estimated mean ejected mass is approximately 1.10 × 10 ⁻⁴ M _⊙ , which is relatively high and suggests a low-mass WD. Our optical spectroscopic and photometric analyses, combined with detailed photoionization modeling, indicate that the WD in Nova V1405 Cas is unlikely to be of the ONeMg type.

Novae are thermonuclear eruptions on accreting white dwarfs in interacting binaries. Although most of the accreted envelope is expelled, the mechanism—impulsive ejection, multiple outflows or prolonged winds, or a common-envelope interaction—remains uncertain. Gigaelectronvolt γ-ray detections from >20 Galactic novae establish these eruptions as nearby laboratories for shock physics and particle acceleration, underscoring the need to determine how novae eject their envelopes. Here we report on near-infrared interferometry, supported by multiwavelength observations, of two γ-ray-detected novae. The images of the very fast 2021 nova V1674 Her, taken just 2–3 days after discovery, reveal the presence of two perpendicular outflows. The interaction between these outflows probably drives the observed γ-ray emission. Conversely, the images of the very slow 2021 nova V1405 Cas suggest that the bulk of the accreted envelope was ejected more than 50 days after the eruption began, as the nova slowly rose to its visible peak, during which the envelope engulfed the system in a common-envelope phase. These images offer direct observational evidence that the mechanisms driving mass ejection from the surfaces of accreting white dwarfs are not as simple as previously thought, revealing multiple outflows and delayed ejections.

We present the first high-resolution X-ray spectrum of NGC 7213 obtained with XRISM/Resolve, supported by simultaneous XMM-Newton, NuSTAR, and SOAR optical data. The XRISM spectrum resolves the neutral Fe K α into two components: a narrow core ( FWHM = 65 0 − 220 + 240 km s − 1 ), consistent with emission at the dust sublimation radius, and a broader asymmetric line, best described by disklike emission from ∼100 R _g . This disk component mirrors the profile of the double-peaked H α line observed in the optical. In addition, we detect broadened Fe xxv and Fe xxvi emission lines, whose inferred locations bridge the gap between the inner disk and the optical broad-line region. The weak narrow Fe K α equivalent width (EW = 32 ± 6 eV) and the absence of a Compton hump imply a low-covering-fraction, Compton-thin torus. Together, these results reveal a radially stratified structure in NGC 7213, spanning nearly 4 orders of magnitude in radius, and place the source in an intermediate-accretion state ( λ _Edd = 0.1%–1%), where the inner disk and broad-line region remain, while the torus shows signs of dissipation.