Nova Research Articles

The Masses and Accretion Rates of White Dwarfs in Classical and Recurrent Novae

Abstract Models have long predicted that the frequency-averaged masses of white dwarfs (WDs) in Galactic classical novae are twice as large as those of field WDs. Only a handful of dynamically well-determined nova WDs masses have been published, leaving the theoretical predictions poorly tested. The recurrence time distributions and mass accretion rate distributions of novae are even more poorly known. To address these deficiencies, we have combined our extensive simulations of nova eruptions with the Strope et al. and Schaefer databases of outburst characteristics of Galactic classical and recurrent novae (RNe) to determine the masses of 92 WDs in novae. We find that the mean mass (frequency-averaged mean mass) of 82 Galactic classical novae is 1.06 (1.13) M ⊙, while the mean mass of 10 RNe is 1.31 M ⊙. These masses, and the observed nova outburst amplitude and decline time distributions allow us to determine the long-term mass accretion rate distribution of classical novae. Remarkably, that value is just 1.3 × 10−10 M ⊙ yr−1, which is an order of magnitude smaller than that of cataclysmic binaries in the decades before and after classical nova eruptions. This predicts that old novae become low-mass transfer rate systems, and hence dwarf novae, for most of the time between nova eruptions. We determine the mass accretion rates of each of the 10 known Galactic recurrent nova, finding them to be in the range of 10−7–10−8 M ⊙ yr−1. We are able to predict the recurrence time distribution of novae and compare it with the predictions of population synthesis models.

Susceptibility of Euschistus heros (Fabr 1794.) (Heteroptera: Pentatomidae) to insecticides in Mato Grosso

The stink bug Euschistus heros attacks several crops of grains and fiber the state of Mato Grosso, which may cause severe damage to the productivity and quality of the seeds/plume. The repeated use of molecules with the same mode of action to control this insect favors selecting individual resistant individuals to insecticides. Aiming to evaluate the susceptibility of E. heros to the insecticides molecules thiamethoxan, imidacloprid, betacyfluthrin and lambdacyhalothrin populations from Sinop, Nova Mutum and Rondonopolis were collected. Susceptibility curve in a laboratory susceptible population was determined in order to establish diagnostic doses (CL95) to monitor the susceptibility of populations of E. heros to the insecticides molecules. Regarding the toxicity of the assayed molecules, thiamethoxam was the most toxic to E. heros , while the betacyfluthrin had the lowest toxicity (68 fold lower than thiametoxam). As result of the bioassays, we concluded that all populations tested behaved as susceptible to the tested molecules.

Complex long-term activity of the post-nova X Serpentis

Aims. X Ser is a cataclysmic variable (CV) which erupted as a classical nova in 1903. In this work we use over 100 years of photometry to characterize the long-term light curve of X Ser, with the aim of interpreting the post-nova activity in X Ser in the context of behaviors in other old novae. Methods. This analysis of its long-term optical activity uses the data from the Digital Access to a Sky Century @ Harvard (DASCH), AAVSO, and Catalina Real-time Transient Survey databases, supplemented by the data of other authors. Results. We show that X Ser displays a strong complex activity with the characteristics of various CV types after the return to quiescence from its classical nova outburst. Both nova-like and dwarf nova (DN) features are present. The decaying branches of the individual post-nova outbursts display large mutual similarities and obey the Bailey law for outbursts of DNe. These outbursts of X Ser constitute a uniform group (inside-out outbursts), and their decaying branches can be explained by propagation of cooling front through the accretion disk. In the interpretation, X Ser rapidly transitioned to a thermal-viscous instability regime of the disk, initially only intermittently. The occurrence of the DN outbursts shortly after the end of the nova outburst suggests that the mass transfer rate into the disk was usually not sufficiently high to prevent a thermal-viscous instability of this post-nova. The very long orbital period, and hence large accretion disk of X Ser can contribute to this.

Discovery of a New Classical Nova Shell Around a Nova-like Cataclysmic Variable

Abstract The morphology and optical spectrum of IPHASX J210204.7+471015, a nebula classified as a possible planetary nebula are, however, strikingly similar to those of AT Cnc, a classical nova shell around a dwarf nova. To investigate its true nature, we have obtained high-resolution narrowband [O iii] and [N ii] images and deep optical spectra. The nebula shows an arc of [N ii]-bright knots notably enriched in nitrogen, while an [O iii]-bright bow shock is progressing throughout the ISM. Diagnostic line ratios indicate that shocks are associated with the arc and bow shock. The central star of this nebula has been identified by its photometric variability. Time-resolved photometric and spectroscopic data of this source reveal a period of 4.26 hr, which is attributed to a binary system. The optical spectrum is notably similar to that of RW Sex, a cataclysmic variable star (CV) of the UX UMa nova-like (NL) type. Based on these results, we propose that IPHASX J210204.7 + 471015 is a classical nova shell observed around a CV-NL system in quiescence.

Gamma-ray emission from internal shocks in novae

Context. Gamma-ray emission at energies ≥100 MeV has been detected from nine novae using the Fermi Large Area Telescope (LAT), and can be explained by particle acceleration at shocks in these systems. Eight out of these nine objects are classical novae in which interaction of the ejecta with a tenuous circumbinary material is not expected to generate detectable gamma-ray emission. Aim. We examine whether particle acceleration at internal shocks can account for the gamma-ray emission from these novae. The shocks result from the interaction of a fast wind radiatively-driven by nuclear burning on the white dwarf with material ejected in the initial runaway stage of the nova outburst. Methods. We present a one-dimensional model for the dynamics of a forward and reverse shock system in a nova ejecta, and for the associated time-dependent particle acceleration and high-energy gamma-ray emission. Non-thermal proton and electron spectra are calculated by solving a time-dependent transport equation for particle injection, acceleration, losses, and escape from the shock region. The predicted emission is compared to LAT observations of V407 Cyg, V1324 Sco, V959 Mon, V339 Del, V1369 Cen, and V5668 Sgr. Results. The ≥100 MeV gamma-ray emission arises predominantly from particles accelerated up to ~100 GeV at the reverse shock and undergoing hadronic interactions in the dense cooling layer downstream of the shock. The emission rises within days after the onset of the wind, quickly reaches a maximum, and its subsequent decrease reflects mostly the time evolution of the wind properties. Comparison to gamma-ray data points to a typical scenario where an ejecta of mass 10−5–10−4 M⊙ expands in a homologous way with a maximum velocity of 1000–2000 km s−1, followed within a day by a wind with a velocity <2000 km s−1 and a mass-loss rate of 10−4–10−3 M⊙ yr−1 declining over a time scale of a few days. Because of the large uncertainties in the measurements, many parameters of the problem are degenerate and/or poorly constrained except for the wind velocity, the relatively low values of which result in the majority of best-fit models having gamma-ray spectra with a high-energy turnover below ~10 GeV. Our typical model is able to account for the main features in the observations of the recent gamma-ray nova ASASSN-16ma. Conclusions. The internal shock model can account for the gamma-ray emission of the novae detected by Fermi LAT. Gamma-ray observations hold potential for probing the mechanism of mass ejection in novae, but should be combined to diagnostics of the thermal emission at lower energies to be more constraining.

Two peculiar fast transients in a strongly lensed host galaxy

A massive galaxy cluster can serve as a magnifying glass for distant stellar populations, with strong gravitational lensing exposing details in the lensed background galaxies that would otherwise be undetectable. The MACS J0416.1-2403 cluster (hereafter MACS0416) is one of the most efficient lenses in the sky, and in 2014 it was observed with high-cadence imaging from the Hubble Space Telescope (HST). Here we describe two unusual transient events that appeared behind MACS0416 in a strongly lensed galaxy at redshift $z = 1.0054 \pm 0.0002$. These transients---designated HFF14Spo-NW and HFF14Spo-SE and collectively nicknamed "Spock"---were faster and fainter than any supernova (SN), but significantly more luminous than a classical nova. They reached peak luminosities of $\sim10^{41}$ erg s$^{-1}$ ($M_{\rm AB} < -14$ mag) in 5 rest-frame days, then faded below detectability in roughly the same time span. Models of the cluster lens suggest that these events may be spatially coincident at the source plane, but are most likely not temporally coincident. We find that HFF14Spo can be explained as a luminous blue variable (LBV), a recurrent nova (RN), or a pair of stellar microlensing events. To distinguish between these hypotheses will require a clarification of the positions of nearby critical curves, along with high-cadence monitoring of the field that could detect new transient episodes in the host galaxy.

Nonradial Pulsations in Post-outburst Novae

Abstract After an optical peak, a classical or recurrent nova settles into a brief (days to years) period of quasi-stable thermonuclear burning in a compact configuration nearly at the white dwarf (WD) radius. During this time, the underlying WD becomes visible as a strong emitter of supersoft X-rays. Observations during this phase have revealed oscillations in the X-ray emission with periods on the order of tens of seconds. A proposed explanation for the source of these oscillations is internal gravity waves excited by nuclear reactions at the base of the hydrogen-burning layer. In this work, we present the first models exhibiting unstable surface g-modes with periods similar to oscillation periods found in galactic novae. However, when comparing mode periods of our models to the observed oscillations of several novae, we find that the modes that are excited have periods shorter than that observed.

On Presolar Stardust Grains from CO Classical Novae

Abstract About 30%–40% of classical novae produce dust 20–100 days after the outburst, but no presolar stardust grains from classical novae have been unambiguously identified yet. Although several studies claimed a nova paternity for certain grains, the measured and simulated isotopic ratios could only be reconciled, assuming that the grains condensed after the nova ejecta mixed with a much larger amount of close-to-solar matter. However, the source and mechanism of this potential post-explosion dilution of the ejecta remains a mystery. A major problem with previous studies is the small number of simulations performed and the implied poor exploration of the large nova parameter space. We report the results of a different strategy, based on a Monte Carlo technique, that involves the random sampling over the most important nova model parameters: the white dwarf composition; the mixing of the outer white dwarf layers with the accreted material before the explosion; the peak temperature and density; the explosion timescales; and the possible dilution of the ejecta after the outburst. We discuss and take into account the systematic uncertainties for both the presolar grain measurements and the simulation results. Only those simulations that are consistent with all measured isotopic ratios of a given grain are accepted for further analysis. We also present the numerical results of the model parameters. We identify 18 presolar grains with measured isotopic signatures consistent with a CO nova origin, without assuming any dilution of the ejecta. Among these, the grains G270_2, M11-334-2, G278, M11-347-4, M11-151-4, and Ag2_6 have the highest probability of a CO nova paternity.

Polarimetry and spectroscopy of the “oxygen flaring” DQ Herculis-like nova: V5668 Sagittarii (2015)

Context. Classical novae are eruptions on the surface of a white dwarf in a binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell of gas and dust around the system. The three-dimensional structure of these shells is difficult to untangle when viewed on the plane of the sky. In this work a geometrical model is developed to explain new observations of the 2015 nova V5668 Sagittarii. Aim. We aim to better understand the early evolution of classical nova shells in the context of the relationship between polarisation, photometry, and spectroscopy in the optical regime. To understand the ionisation structure in terms of the nova shell morphology and estimate the emission distribution directly following the light curve’s dust-dip. Methods. High-cadence optical polarimetry and spectroscopy observations of a nova are presented. The ejecta is modelled in terms of morpho-kinematics and photoionisation structure. Results. Initially observational results are presented, including broadband polarimetry and spectroscopy of V5668 Sgr nova during eruption. Variability over these observations provides clues towards the evolving structure of the nova shell. The position angle of the shell is derived from polarimetry, which is attributed to scattering from small dust grains. Shocks in the nova outflow are suggested in the photometry and the effect of these on the nova shell are illustrated with various physical diagnostics. Changes in density and temperature as the super soft source phase of the nova began are discussed. Gas densities are found to be of the order of 109 cm−3 for the nova in its auroral phase. The blackbody temperature of the central stellar system is estimated to be around 2.2 × 105 K at times coincident with the super soft source turn-on. It was found that the blend around 4640 Å commonly called “nitrogen flaring” is more naturally explained as flaring of the O II multiplet (V1) from 4638–4696 Å, i.e. “oxygen flaring”. Conclusions. V5668 Sgr (2015) was a remarkable nova of the DQ Her class. Changes in absolute polarimetric and spectroscopic multi-epoch observations lead to interpretations of physical characteristics of the nova’s evolving outflow. The high densities that were found early-on combined with knowledge of the system’s behaviour at other wavelengths and polarimetric measurements strongly suggest that the visual “cusps” are due to radiative shocks between fast and slow ejecta that destroy and create dust seed nuclei cyclically.

Ultraviolet Spectral Evolution of V1974 Cyg Using IUE Low Resolution Spectra

We investigated the spectral evolution of some normalized UV emission lines through different stages of the outburst of the classical nova V1974 Cyg using International Ultraviolet Explorer (IUE) low resolution short wavelength spectra. The emission line fluxes were calculated and used to estimate the ultraviolet luminosity of the emitting region, and the latter is used to determine the average mass accretion rate during the post-nova phase. We found an average value of the ultraviolet continuum luminosity L cont ∼ 4.6 ± 0.4 × 1035 erg s-1 and the average mass accretion rate $$ {\overset{\cdot }{M}}_{acc}\sim 6.6\pm 0.6\times {10}^{-10}{M}_{\astrosun}\kern0.5em {yr}^{\hbox{-} 1} $$ . We used the fitted continuum luminosity to estimate the temperature of the central white dwarf, and we found an average value of ~ 3×105 K. The spectral behavior is attributed to the variation in the opacity, temperature, and density of the ejecta during the different phases of the outburst. Our results are consistent with the theoretical ONe classical nova models.

Beryllium detection in the very fast nova ASASSN-16kt (V407 Lupi)

We present high-resolution spectroscopic observations of the fast nova ASASSN-16kt (V407 Lup). A close inspection of spectra obtained at early stages has revealed the presence of low-ionization lines, and among the others we have identified the presence of the ionised $^7$Be doublet in a region relatively free from possible contaminants. After studying their intensities, we have inferred that ASASSN-16kt has produced (5.9 - 7.7)$ \times 10^{-9}$ M$_{\odot}$ of $^7$Be. The identification of bright Ne lines may suggest that the nova progenitor is a massive (1.2 M$_{\odot}$) oxygen-neon white dwarf. The high outburst frequency of oxygen-neon novae implies that they likely produce an amount of Be similar, if not larger, to that produced by carbon-oxygen novae, then confirming that classical novae are among the main factories of lithium in the Galaxy.

Direct measurement of astrophysically important resonances in K38(p,γ)Ca39

According to sensitivity studies, the $^{38}\mathrm{K}\left( p, \gamma \right){}^{39}\mathrm{Ca}$ reaction has a significant influence on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ production in classical novae. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate $\ell = 0$ resonances within the Gamow window, at $386 \pm 10~\mathrm{keV}$, $515 \pm 10~\mathrm{keV}$, and $689 \pm 10~\mathrm{keV}$. The experiment was performed in inverse kinematics using a beam of unstable $^{38}\mathrm{K}$ impinged on a windowless $\mathrm{H}_2$ target. The $^{39}\mathrm{Ca}$ recoils and prompt $\gamma$ rays from $^{38}\mathrm{K}\left( p, \gamma \right){}^{39}\mathrm{Ca}$ reactions were detected in coincidence using a recoil mass separator and a BGO array, respectively. For the $689$ keV resonance, we observed a clear recoil-$\gamma$ coincidence signal and extracted resonance strength and energy values of $120^{+50}_{-30}~\mathrm{(stat.)}^{+20}_{-60}~\mathrm{(sys.)}~\mathrm{meV}$ and $679^{+2}_{-1}~\mathrm{(stat.)} \pm 1~\mathrm{(sys.)}~\mathrm{keV}$, respectively. We also performed a singles analysis, extracting a resonance strength of $120 \pm 20~\mathrm{(stat.)} \pm 15~\mathrm{(sys.)}~\mathrm{meV}$, consistent with the coincidence result. For the $386$ keV and $515$ keV resonances, we extract $90\%$ confidence level upper limits of $2.54$ meV and $18.4$ meV, respectively. We have established a new recommended $^{38}\mathrm{K}(p, \gamma){}^{39}\mathrm{Ca}$ rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of ${\sim} 250$. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ synthesis to factors of $15$ or less in all cases.

Jubal, Pythagoras and the Myth of the Origin of Music - With some remarks concerning the illumination of Pit (It. 568)

At the end of the fourteenth century the iconography of Music shows a complex morphology based on the myth of the first founding father of the musical art. Its most sophisticated image appears in the opening illumination of Pit (Paris, Bibl. Nationale, It. 568), one of the most important manuscripts of the Italian Ars Nova. After reviewing the existing bibliography, the first part of the article traces the cultural context that produced this illumination. The second part reconstructs the whole history of the myth of the origin of music, its biblical tradition (Jubal), its pagan equivalent (Pythagoras), their association with the myth of translatio studii (the pillars of knowledge), and its syncretic form adopted from the twelfth century onward. The iconographic model was conceived in fourteenth-century Italy, and the illumination of Pit is its most complete form; it was later assimilated into the iconography of Saint Cecilia. The reconstruction of this stratification of myths aims to clarify how different musical traditions crossed each other, and at the same time proposes an earlier dating for the illumination of Pit (late fourteenth century) in connection with Silvestro dei Gherarducci’s Florentine workshop.

Spectral evolution of the two classical novae PW Vul and V1668 Cyg using International Ultraviolet Explorer low‐resolution spectra

We studied the evolution of the normalized flux of selected ultraviolet (UV) emission lines of two classical novae (PW Vul and V1668 Cyg) using International Ultraviolet Explorer (IUE) short wavelength observations. Different phases of the outburst are studied. Emission lines covering a wide range of ionization states are investigated. We use the calculated fluxes to estimate the mass accretion rates during quiescence of both novae. We found average values of the UV luminosity for PW Vul to be of 1.0 ± 0.1 × 1035 erg s−1, and the corresponding value for V1668 Cyg is 4.0 ± 0.2 × 1035 erg s−1. In quiescence, we obtained average values for the mass accretion rates of 8.7 ± 0.4 × 10−10 M⊙ year−1 and 1.8 ± 0.1 × 10−10 M⊙ year−1, respectively. We attribute the spectral behavior of the two systems to the variation of the optical thickness and temperature of the envelope during the different phases of the outburst. Our results demonstrate the effect of the white dwarf mass on the evolution of the nova. The results of IUE observations are consistent with the theoretical CO models of classical nova of.

Investigation of the cylindrical vacuum hohlraum energy in the first implosion experiment at the SGIII laser facility

The cylindrical vacuum hohlraum energy at the SGIII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007) and W. Zheng et al., High Power Laser Sci. Eng. 4, e21 (2016)] is investigated for the first time. The hohlraum size and the laser energy are intermediate between the Nova and NIF typical hohlraum experiments. It is found that the SGIII hohlraum exhibits an x-ray conversion efficiency of about 85%, which is more close to that of the NIF hohlraum. The LARED simulations of the SGIII hohlraum underestimate about 15% of the radiation flux measured from the laser entrance hole, while the capsule radiation drive inferred from the x-ray bangtime is roughly consistent with the experiments. The underestimation of the SGIII hohlraum radiation flux is mainly caused by the more enclosed laser entrance hole in the LARED simulation. The comparison between the SGIII and NIF hohlraum simulations by LARED indicates that the LARED generally underestimates the measured radiation flux by 15% for the high x-ray conversion efficiency hohlraums, while it can roughly predict the capsule radiation drive inside the hohlraum.

V1369 Cen High-resolution Panchromatic Late Nebular Spectra in the Context of a Unified Picture for Nova Ejecta

Abstract Nova Cen 2013 (V1369 Cen) is the fourth bright nova observed panchromatically through high-resolution UV+optical multiepoch spectroscopy. It is also the nova with the richest set of spectra (in terms of both data quality and number of epochs) thanks to its exceptional brightness. Here, we use the late nebular spectra taken between day ∼250 and day ∼837 after outburst to derive the physical, geometrical, and kinematical properties of the nova. We compare the results with those determined for the other panchromatic studies in this series: T Pyx, V339 Del (nova Del 2013), and V959 Mon (nova Mon 2012). From this we conclude that in all these novae the ejecta geometry and phenomenology can be consistently explained by clumpy gas expelled during a single, brief ejection episode and in ballistic expansion, and not by a wind. For V1369 Cen the ejecta mass (∼1 × 10−4 M⊙) and filling factor (0.1 ≤ f ≤ 0.2) are consistent with those of classical novae but larger (by at least an order of magnitude) than those of T Pyx and the recurrent novae. V1369 Cen has an anomalously high (relative to solar) N/C ratio that is beyond the range currently predicted for a CO nova, and the Ne emission line strengths are dissimilar to those of typical ONe or CO white dwarfs.

The Photometric Evolution of the Classical Nova V723 Cassiopeia from 2006 through 2016

Abstract We present photometric data of the classical nova, V723 Cas (Nova Cas 1995), over a span of 10 years (2006 through 2016) taken with the 0.9 m telescope at Lowell Observatory, operated as the National Undergraduate Research Observatory (NURO) on Anderson Mesa near Flagstaff, Arizona. A photometric analysis of the data produced light curves in the optical bands (Bessel B, V, and R filters). The data analyzed here reveal an asymmetric light curve (steep rise to maximum, followed by a slow decline to minimum), the overall structure of which exhibits pronounced evolution including a decrease in magnitude from year to year, at the rate of ∼0.15 mag yr−1. We model these data with an irradiated secondary and an accretion disk with a hot spot using the eclipsing binary modeling program Nightfall. We find that we can model reasonably well each season of observation by changing very few parameters. The longitude of the hot spot on the disk and the brightness of the irradiated spot on the companion are largely responsible for the majority of the observed changes in the light curve shape and amplitude until 2009. After that, a decrease in the temperature of the white dwarf is required to model the observed light curves. This is supported by Swift/X-Ray Telescope observations, which indicate that nuclear fusion has ceased, and that V723 Cas is no longer detectable in the X-ray.

A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray-luminous Classical Nova to Date

Abstract It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during outburst, but the mechanisms involved in the production ofgamma-rays are still not well understood. We present here a comprehensive multiwavelength data set—from radio to X-rays—for the most gamma-ray-luminous classical nova to date, V1324 Sco. Using this data set, we show that V1324 Sco is a canonical dusty Fe ii-type nova, with a maximum ejecta velocity of 2600 km s−1 and an ejecta mass of a few . There is also evidence for complex shock interactions, including a double-peaked radio light curve which shows high brightness temperatures at early times. To explore why V1324 Sco was so gamma-ray luminous, we present a model of the nova ejecta featuring strong internal shocks and find that higher gamma-ray luminosities result from higher ejecta velocities and/or mass-loss rates. Comparison of V1324 Sco with other gamma-ray-detected novae does not show clear signatures of either, and we conclude that a larger sample of similarly well-observed novae is needed to understand the origin and variation of gamma-rays in novae.

Results from the NOvA Experiment

The NOvA experiment is a long-baseline accelerator-based neutrino oscillation experiment. It uses the upgraded NuMI beam from Fermilab to measure electron-neutrino appearance and muon-neutrino disappearance between the Near Detector, located at Fermilab, and the Far Detector, located at Ash River, Minnesota. The NuMI beam has recently reached and surpassed the 700 kW power benchmark. NOvA’s primary physics goals include precision measurements of oscillation parameters, such as [Formula: see text] and the atmospheric mass-squared splitting, along with probes of the mass hierarchy and of the CP violating phase. This talk will present the latest NOvA results, based on a neutrino beam exposure equivalent to [Formula: see text] protons-on-target.

Viola cassinensis subsp. lucana (Violaceae), a new subspecies from the Lucanian Apennine, southern Italy

Viola cassinensis subsp. lucana subsp. nova (Violaceae) is described and illustrated from Basilicata (southern Italy). Morphology, habitat and ecology are reported. This new taxon belonging to the Viola calcarata group is endemic to the Lucanian Apennine (southern Italy). It is compared with the similar taxa V. cassinensis subsp. cassinensis and V. cassinensis subsp. pseudogracilis.