Nova Research Articles

The aftermath of nova Centauri 2013 (V1369 Centauri)

Context.Classical nova progenitors are cataclysmic variables and very old novae are observed to match systems with high mass transfer rates and (relatively) long orbital periods. However, the aftermath of a classical nova has never been studied in detail.Aims.We intend to probe the aftermath of a classical nova explosion in cataclysmic variables and observe as the binary system relaxes to quiescence.Methods.We used multiwavelength time-resolved optical and near-infrared spectroscopy for a bright, well-studied classical nova five years after outburst. We were able to disentangle the contribution of the ejecta at this late epoch using its previous characterization, separating the ejecta emission from that of the binary system.Results.We determined the binary orbital period (P = 3.76 h), the system separation, and the mass ratio (q ≳ 0.17 for an assumed white dwarf mass of 1.2M⊙). We find evidence of an irradiated secondary star and no unambiguous signature of an accretion disk, although we identify a second emission line source tied to the white dwarf with an impact point. The data are consistent with a bloated white dwarf envelope and the presence of unsettled gas within the white dwarf Roche lobe.Conclusions.At more than 5 years after eruption, it appears that this classical nova has not yet relaxed.

Classical Novae Masquerading as Dwarf Novae? Outburst Properties of Cataclysmic Variables with ASAS-SN

Abstract The unprecedented sky coverage and observing cadence of the All-Sky Automated Survey for SuperNovae (ASAS-SN) has resulted in the discovery and continued monitoring of a large sample of Galactic transients. The vast majority of these are accretion-powered dwarf nova outbursts in cataclysmic variable systems, but a small subset are thermonuclear-powered classical novae. Despite improved monitoring of the Galaxy for novae from ASAS-SN and other surveys, the observed Galactic nova rate is still lower than predictions. One way classical novae could be missed is if they are confused with the much larger population of dwarf novae. Here, we examine the properties of 1617 dwarf nova outbursts detected by ASAS-SN and compare them to classical novae. We find that the mean classical nova brightens by ∼11 mag during outburst, while the mean dwarf nova brightens by only ∼5 mag, with the outburst amplitude distributions overlapping by roughly 15%. For the first time, we show that the amplitude of an outburst and the time it takes to decline by two magnitudes from maximum are positively correlated for dwarf nova outbursts. For classical novae, we find that these quantities are negatively correlated, but only weakly, compared to the strong anticorrelation of these quantities found in some previous work. We show that, even if located at large distances, only a small number of putative dwarf novae could be misclassified as classical novae, suggesting that there is minimal confusion between these populations. Future spectroscopic follow-up of these candidates can show whether any are indeed classical novae.

Practical Effects of Integrating Temperature with Strang Split Reactions

Abstract Many astrophysical environments involve convective or explosive flows driven by thermonuclear reactions (Type Ia supernovae, classical novae, X-ray bursts, stellar evolution). Simulation codes need to accurately capture the interactions between reactions and hydrodynamics to produce realistic models of these events. For astrophysical reacting flows, operator splitting is commonly used to couple hydrodynamics and reactions. Each process operates independent of one another, but by staggering the updates in a symmetric fashion (via Strang splitting) second order accuracy in time can be achieved. However, approximations are often made to the reacting system, including the choice of whether or not to integrate temperature with the species. Here we demonstrate through a simple convergence test that integrating an energy equation together with reactions achieves the best convergence when modeling reactive flows with Strang splitting. Additionally, second order convergence cannot be achieved without integrating an energy or temperature equation.

Optical spectroscopic monitoring of the symbiotic star MWC 560 before and after the 2018 unpredicted brightening

Abstract MWC 560 (V694 Mon) is classified as a symbiotic binary consisting of a white dwarf and an M5III red giant. In this object, a very- high-speed component, thought to be a jet, has been reported in the hydrogen Balmer line. We have been conducting long-term spectroscopic monitoring since the brightening in 2016 February. An irregular rebrightening was reported by Goranskij et al. (2018, Astronomer’s Telegram, 12227), who also showed that the high-velocity absorption component was not seen on 2018 November 16. Our low-resolution spectroscopic observations showed no high-velocity absorption component on 2018 November 14, and wide emission lines in Balmer line region (Hα, Hβ). However, high-resolution spectroscopy revealed the presence of slow, weak absorbing components and an emission wing on 2018 December 25. MWC 560 began to brighten in 2018 November, and it is gradually brightening as of 2020 April 14. For the absorption component, we propose a shell expansion of a classical symbiotic nova that occurred in 2016. During the 2018 brightening a new emission wing with vFWHM ≈ 700 km s−1 was confirmed, which could be triggered by disk instability like a dwarf nova. This paper summarizes the results of long-term monitoring observations and the recent changes in MWC 560.

The UBV Color Evolution of Classical Novae. IV. Time-stretched (U − B)0–(M B − 2.5 log f s) and (V − I)0–(M I − 2.5 log f s) Color–Magnitude Diagrams of Novae in Outbursts

Abstract Light curves and color evolutions of two classical novae can be largely overlapped if we properly squeeze or stretch the timescale of a target nova against that of a template nova by . Then, the brightness of the target nova is related to the brightness of the template nova by , where M[t] is the absolute magnitude and a function of time t, and f s is the ratio of timescales between the target and template novae. In the previous papers of this series, we show that many novae broadly overlap in the time-stretched (B − V)0– color–magnitude diagram. In the present paper, we propose two other (U − B)0– and (V − I)0– diagrams and show that their tracks overlap for 16 and 52 novae, respectively. Here (U − B)0, (B − V)0, and (V − I)0 are the intrinsic U − B, B − V, and V − I colors and not changed by the time stretch, and M B , M V , and M I are the absolute B, V, and I magnitudes. Using these properties, we considerably refine the previous estimates of their distance and reddening. The obtained distances are in reasonable agreement with those of the Gaia Data Release 2 catalog.

The precessing jets of classical nova YZ Reticuli

ABSTRACT The classical nova YZ Reticuli was discovered in 2020 July. Shortly after this, we commenced a sustained, highly time-sampled coverage of its subsequent rapid evolution with time-resolved spectroscopy from the Global Jet Watch observatories. Its H-alpha complex exhibited qualitatively different spectral signatures in the following weeks and months. We find that these H-alpha complexes are well described by the same five Gaussian emission components throughout the six months following eruption. These five components appear to constitute two pairs of lines, from jet outflows and an accretion disc, together with an additional central component. The correlated, symmetric patterns that these jet/accretion disc pairs exhibit suggest precession, probably in response to the large perturbation caused by the nova eruption. The jet and accretion disc signatures persist from the first 10 d after brightening – evidence that the accretion disc survived the disruption. We also compare another classical nova (V6568 Sgr) that erupted in 2020 July whose H-alpha complex can be described analogously, but with faster line-of-sight jet speeds exceeding 4000 km s−1. We suggest that classical novae with higher mass white dwarfs bridge the gap between recurrent novae and classical novae such as YZ Reticuli.

Transient Formation of C2 and CN in the Near-maximum Phase of Nova Cas 2020(=V1391 Cas)

Abstract Nova Cas 2020 was a second example of a classical nova forming both C2 and CN molecules during its near-maximum phase. The formation C2 and CN is indicative of the carbon-rich (C/O > 1) gas envelope of the nova. Our low-resolution spectroscopic observations in the optical from UT 2020 July 31 to August 19 revealed the appearance and the disappearance of the molecular absorption bands of C2 and CN in Nova Cas 2020. These molecules were present during ∼3 days only. Based on analysis of the C2 Swan band profiles, C2 (and probably CN also) formed at ∼5000 K in the nova envelope (see ∼8000 K for typical novae at their visual brightness maxima). Spectral evolution and the formation conditions of the molecules are similar to those of V2676 Oph, which is the first example of a C2/CN-forming nova. We predict that a late-phase grain formation episode similar to that seen in V2676 Oph will occur in Nova Cas 2020.

Search for slow magnetic monopoles with the NOvA detector on the surface

We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiment's Far Detector, a 14 kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of $2\times 10^{-14} \mathrm{cm^{-2}s^{-1}sr^{-1}}$ at 90% C.L. for monopole speed $6\times 10^{-4} < \beta < 5\times 10^{-3}$ and mass greater than $5\times 10^{8}$ GeV. Because of NOvA's small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.

Study of Neutrino Oscillations in the NOvA Experiment

NOvA is a neutrino experiment deployed at Fermi National Accelerator Laboratory (FNAL, USA) and designed for studying oscillations—namely, the appearance of electron neutrinos and the survival of muon neutrinos. Two detectors, a near and a far one, are separated by a distance of 810 km and are positioned at an angle of 14 mrad with respect to the axis of a beam from the NuMI accelerator complex. This configuration provides an optimum relationship between the energy and distance for neutrino oscillations. The experiment is aimed at measuring the neutrino mass hierarchy, determining the phase of $$CP$$ violation in the lepton sector, and refining value of the parameters $$\theta_{23}$$ and $$\Delta m^{2}_{32}$$ , as well as at performing some other tasks. The results of the NOvA analysis performed jointly for a $$8.85\times 10^{20}$$ proton-on-target (POT) neutrino beam and a $$12.33\times 10^{20}$$ POT antineutrino beams are discussed. Also, further prospects of the experiment are outlined.

New constraints on the Al 25 (p,γ) reaction and its influence on the flux of cosmic γ rays from classical nova explosions

New constraints on the Al 25 (p,γ) reaction and its influence on the flux of cosmic γ rays from classical nova explosions

The objects in observations of Perseus cluster region

AbstractThe results of 20‐year observations of the Perseus cluster centering on the NGC 1275 including IC 310 radio galaxy and extragalactic supernova SN 2006gy at energies 800 GeV to 45 TeV by the SHALON telescope are presented. Also, the emission from the galactic source of non‐thermal radio and X‐ray emission GK Per (Nova 1901) of classical nova type was found as it accompanied to the observations. For NGC 1275, it was found that the TeV γ‐ray emission at energies &gt;800 GeV has an extended structure with a distinct core centered at the NGC 1275 nucleus and well correlates with the photon emission regions viewed in X‐rays by Chandra and anti‐correlates with radio‐structures. Also, the variations of TeV γ‐ray flux both at year‐ and day scales were found. The obtained data indicate that the part of TeV γ‐ray emission is generated by relativistic jets in the nucleus of NGC 1275. Whereas the presence of an extended structure around NGC 1275 and the slow rise of the γ‐ray flux is the evidence of the interaction of cosmic rays and magnetic fields generated in the jets at the galactic center with the gas of the Perseus cluster.

RIB studies for explosive scenarios and future opportunities at FRIB

An accreting compact star in a binary system can generate periodic thermonuclear runaways on its surface. In the case of a white dwarf star, the result is a classical nova, which enriches the interstellar medium with newly synthesized nuclides. In the case of a neutron star, a detectable burst of X-rays is emitted. Nucleosynthesis and energy generation in these events depends on resonant thermonuclear reaction rates, which are especially challenging to measure directly in the laboratory when they involve radioactive reactants. Fortunately, the resonances can be discovered and their relevant properties can be constructed using nuclear structure experiments. We will describe a program of beta decay experiments the National Superconducting Cyclotron Laboratory to this end. In particular, the Gaseous Detector with Germanium Tagging (GADGET) system, developed to measure very weak low-energy beta delayed proton emission branches and gamma rays, is now operational. Recent results and future opportunities at the Facility for Rare Isotope Beams will be discussed.

Recent three-flavor neutrino oscillation results from the NOvA experiment

NOvA is a long-baseline experiment studying primarily neutrino oscillations in the NuMI beam from Fermi National Laboratory (FNAL), USA. It consists of two functionally identical, finely granulated detectors which are separated by 810 km and situated 14.6 mrad off the NuMI beam axis from FNAL. By measuring the transition probabilities P(vμ → ve ) and P(vμ → vμ ), NOvA is able to probe the following parameters: , the mixing angle θ 23, the CP violating phase δCP and the neutrino mass hierarchy. This document is devoted to the latest NOvA measurements of the neutrino oscillation parameters using neutrino and antineutrino disappearance and appearance obtained in 2020.

Early Spectral Evolution of Classical Novae: Consistent Evidence for Multiple Distinct Outflows

Abstract The physical mechanism driving mass ejection during a nova eruption is still poorly understood. Possibilities include ejection in a single ballistic event, a common-envelope interaction, a continuous wind, or some combination of these processes. Here, we present a study of 12 Galactic novae, for which we have premaximum high-resolution spectroscopy. All 12 novae show the same spectral evolution. Before optical peak, they show a slow P Cygni component. After peak, a fast component quickly arises, while the slow absorption remains superimposed on top of it, implying the presence of at least two physically distinct flows. For novae with high-cadence monitoring, a third, intermediate-velocity component is also observed. These observations are consistent with a scenario where the slow component is associated with the initial ejection of the accreted material and the fast component with a radiation-driven wind from the white dwarf. When these flows interact, the slow flow is swept up by the fast flow, producing the intermediate component. These colliding flows may produce the γ-ray emission observed in some novae. Our spectra also show that the transient heavy-element absorption lines seen in some novae have the same velocity structure and evolution as the other lines in the spectrum, implying an association with the nova ejecta rather than a preexisting circumbinary reservoir of gas or material ablated from the secondary. While this basic scenario appears to qualitatively reproduce multiwavelength observations of classical novae, substantial theoretical and observational work is still needed to untangle the rich diversity of nova properties.

Radio light curves and imaging of the helium nova V445 Puppis reveal seven years of synchrotron emission

ABSTRACT V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km s−1, and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multifrequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5–43.3 GHz, and between 2001 January and 2008 March (days ∼89–2700 after eruption). The radio light curve is dominated by synchrotron emission over these 7 yr, and shows four distinct radio flares. Resolved radio images obtained in the VLA’s A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta – not the fastest ejecta – that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, but V445 Pup is remarkable in that these shocks persist for almost a decade, much longer than the weeks or months for which shocks are typically observed in classical novae.

Near-infrared Spectroscopy of CK Vulpeculae: Revealing a Remarkably Powerful Blast from the Past

Abstract CK Vulpeculae (CK Vul), which erupted in AD 1670–71, was long considered to be a nova outburst; however, recent observations have required that alternative scenarios be considered. Long-slit infrared spectroscopy of a forbidden line of iron reported here has revealed high line-of-sight velocities (∼±900 km s−1) of the ansae at the tips of the bipolar lobes imaged in Hα in 2010. The deprojected velocities of the tips are approximately ±2130 km s−1 assuming the previously derived inclination angle of 65° for the axis of cylindrical symmetry of the bipolar nebula. Such high velocities are in stark contrast to previous reports of much lower expansion velocities in CK Vul. Based on the deprojected velocities of the tips and their angular expansion measured over a 10 yr baseline, we derive a revised estimate, with estimated uncertainties, of kpc for the distance to CK Vul. This implies that the absolute visual magnitude at the peak of the 1670 explosion was , indicating that the 1670 event was far more luminous than previous estimates and brighter than any classical nova or any Galactic stellar merger. We propose that CK Vul belongs to the class of intermediate-luminosity optical transients (ILOTs), objects which bridge the luminosity gap between novae and supernovae. While eruptions in lower luminosity ILOTs are attributed to merger events, the origin of the highly luminous ILOT outbursts is currently not known.

Indirect Measurements of n- and p-Induced Reactions of Astrophysical Interest on Oxygen Isotopes

Observations of abundances and isotopic ratio determinations in stars yield powerful constraints on stellar models. In particular, the oxygen isotopic ratios are of particular interest because they are affected not only by nucleosynthesis but also by mixing processes. This review is focused on the measurements via the Trojan Horse Method (THM) that have been carried out to investigate the low-energy cross sections of proton and neutron-induced reactions on 17O as well as the proton-induced reaction on 18O, overcoming extrapolation procedures and enhancement effects due to electron screening. The (p,a) reactions induced on these oxygen isotopes are of paramount importance for the nucleosynthesis in many stellar sites, including red giants (RGs), asymptotic giant branch (AGB) stars, massive stars, and classical novae. The indirect measurement of the 17O(p,a)14N reaction was performed. The strength of the narrow resonance at 65 keV was evaluated and it was used to renormalize the corresponding resonance strength in the 17O+p radiative capture channel. The reaction rate was evaluated for both the 17O(p,a)14N and the 17O(p,g)18F, and a significant difference of 30% and 20% with respect to the literature was found in the temperature range relevant for RG, AGB and massive stars nucleosynthesis. Regarding the 18O(p,a)15N reaction, the strength of the 20 keV resonance was extracted, which is the main contribution to the reaction rate for astrophysics. This approach allowed us to improve the data accuracy of a factor 8.5, as it is based on the measured strength instead of extrapolations or spectroscopic measurements. Finally, the 17O(n,a)14C reaction was studied because of its role during the s-process nucleosynthesis as a possible neutron poison. This study represents the extension of THM to resonant neutron-induced reactions. In this measurement, the subthreshold level centered at -7 keV in the center-of-mass, corresponding to the 8.039 MeV 18O excited level, was observed. Moreover, the THM measurements showed a clear agreement with the available direct measurements because of the additional contribution of the 8.121 MeV 18O level, strongly suppressed in direct measurements because of its l=3 angular momentum. The contributions to the total reaction rate were than evaluated for future astrophysical applications.

High-energy Neutrinos and Gamma Rays from Nonrelativistic Shock-powered Transients

Abstract Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae, classical novae, stellar mergers, tidal disruption events, and fast blue optical transients. These same shocks can accelerate relativistic ions, generating high-energy neutrino and gamma-ray emission via hadronic pion production. The recent discovery of time-correlated optical and gamma-ray emission in classical novae has revealed the important role of radiative shocks in powering these events, enabling an unprecedented view of the properties of ion acceleration, including its efficiency and energy spectrum, under similar physical conditions to shocks in extragalactic transients. Here we introduce a model for connecting the radiated optical fluence of nonrelativistic transients to their maximal neutrino and gamma-ray fluence. We apply this technique to a wide range of extragalactic transient classes in order to place limits on their contributions to the cosmological high-energy gamma-ray and neutrino backgrounds. Based on a simple model for diffusive shock acceleration at radiative shocks, calibrated to novae, we demonstrate that several of the most luminous transients can accelerate protons up to 1016 eV, sufficient to contribute to the IceCube astrophysical background. Furthermore, several of the considered sources—particularly hydrogen-poor supernovae—may serve as “gamma-ray-hidden” neutrino sources owing to the high gamma-ray opacity of their ejecta, evading constraints imposed by the nonblazar Fermi Large Area Telescope background. However, adopting an ion acceleration efficiency of ∼0.3%–1% motivated by nova observations, we find that currently known classes of nonrelativistic, potentially shock-powered transients contribute at most a few percent of the total IceCube background.

Against Amnesia: African Nova Scotia Women’s Generational Leadership in Civil Rights Organizing, 1950–79

Le présent article met en lumière le rôle essentiel que les femmes africaines de Nouvelle-Écosse ont joué dans l’organisation des droits civils à Halifax et au Canada. L’article porte sur le développement du mouvement des droits civils au cœur de la lutte pour l’égalité raciale de 1950 à 1979. J’essaie de contrer l’effacement systémique de l’histoire des femmes noires en relatant les contributions communautaires de trois femmes de la célèbre famille Jones : Willena, Joan et Lynn. Cet article rétablit la connaissance de l’histoire des femmes noires et revisite les notions d’activisme, d’organisation et de développement d’un mouvement, bousculant leur conceptualisation dominante.

Towards the identification of carriers of the unidentified infrared (UIR) bands in novae

AbstractThe unidentified infrared (UIR) bands, whose carriers are thought to be organics, have been widely observed in various astrophysical environments. However, our knowledge of the detailed chemical composition and formation process of the carriers is still limited. We have synthesized laboratory organics named Quenched Nitrogen-included Carbonaceous Composite (QNCC) by quenching plasma produced from nitrogen gas and hydrocarbon solids. Infrared and X-ray analyses of QNCC showed that infrared properties of QNCC well reproduce the UIR bands observed in novae and amine structures contained in QNCC play an important role in the origin of the broad 8 m feature, which characterizes the UIR bands in novae. QNCC is at present the best laboratory analog of organic dust formed around dusty classical novae, which carries the UIR bands in novae via thermal emission process [Endo et al.(2021)].