arXiv subjects

Larissa Takeda

Publications and source records attributed to Larissa Takeda.

5 recordsLinked to original sources

arXiv2026

The Nova Synthetic Data Base: A Principal Component/AI Analysis of Novae Synoptic Spectra

The Nova Synthetic Data Base (NSDB) is presented as the first publicly available database of synthetic spectra for classical nova shells, spanning an unprecedented range of physical parameters (e.g., ejecta mass, chemical composition, temperature, and luminosity of the white dwarf) at several post-eruption ages. Generated using detailed 3D photoionization models, this homogeneous database enables a systematic exploration of spectral features in novae. In this work, we introduce a principal component analysis/AI-based framework to derive time-dependent proxies for retrieving the physical properties of novae from limited spectral data. By analyzing the correlations between the eigenspectra and the grid's variables, a reduced set of diagnostic spectral lines is derived, paving the way for robust multiregressor machine-learning algorithms with a minimal effort observational set. The prediction capability of the method is high and robust to data noise. The results establish a proof of concept for the use of model grids combined with physically controlled AI as a tool to interpret novae observations in the context of the large number of events expected from future wide-area surveys.

astro-ph.SR↗

arXiv2023

A two-component clumpy model for the shell evolution of classical novae: the case of V5668 Sgr

The shell of the classical nova V5668 Sgr was resolved by ALMA at the frequency of 230 GHz 927 days after eruption, showing that most of the continuum bremsstrahlung emission originates in clumps with diameter smaller than $10^{15}$ cm. Using VLA radio observations, obtained between days 2 and 1744 after eruption, at frequencies between 1 and 35 GHz, we modeled 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$_{\odot}$ for the mass of the white dwarf, a central temperature of $10^7$ K and an accretion rate from the secondary star of $10^{-9}-10^{-8}$ M$_{\odot}$ y$^{-1}$.

astro-ph.GA↗

arXiv2019

Imaging and analysis of neon nova V382 Vel shell

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$α$ and [O III] 5007Å, revealing different structures in each filter. The shell's angular diameter obtained was $9.9$ arcsec, equivalent to $2.8 \times 10^{17}$ cm, using the distance of $1.79$ kpc obtained by Gaia mission. The upper limit for total shell mass derived from recombination lines is $M_{s} = 1.4 \times 10^{-4}$ M$_{\odot}$. Our photoionization models indicate an accretion disk with $T_d=60,000$ K and L=$10^{36}$ erg/s as main ionizing source.

astro-ph.SR↗

arXiv2018

The structure of a recent nova shell as observed by ALMA

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 $σ$ 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.

astro-ph.SR↗

arXiv2014

A search and modeling of peculiar narrow transient line components in novae spectra

In this paper we discuss the formation of peculiar narrow emission line components observed in the spectra of a few novae. We aim to identify the physical source responsible for transient narrow components that present orbital radial velocity modulations, first observed in the post-outburst recombination lines of Nova U Sco 2010. A search for candidate novae showing similar narrow components is presented. Photoionization simulations indicate that the forming region cannot be restricted to the primary Roche Lobe, but could be located around the outer Lagrangian point L3. Further analysis disfavors an origin at the accretion disk and 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 phase.

astro-ph.SR↗