ABSTRACT
Following the recent detection of 7Be ii in the outburst spectra of classical novae, we report the search for this isotope in the outbursts of four recent bright novae by means of ...high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations. The 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines are detected in the high-velocity components of Nova Mus 2018 and ASASSN-18fv during outbursts. However, 7Be ii is not detected in ASASSN-17hx and possibly not in Nova Cir 2018, which shows that 7Be is not always ejected in the thermonuclear runaway. Taking into account the 7Be decay, we find X(7Be)/X(H) ≈ 1.5 × 10−5 and 2.2 × 10−5 in Nova Mus 2018 and ASASSN-18fv, respectively. A value of 7Be/H ≈ 2 × 10−5 is found in five out of the seven extant measurements, and it can be considered as a typical 7Be yield for novae. However, this value is almost one order of magnitude larger than predicted by current theoretical models. We argue that the variety of high 7Be/H abundances could be the result of a higher than solar content of 3He in the donor star. The cases with 7Be not detected might be related to the small mass of the white dwarf (WD) or to relatively little mixing with the core material of the WD. The 7Be/H, or 7Li/H, abundance is ≈ 4 dex above meteoritic abundance, thus confirming the novae as the main sources of 7Li in the Milky Way.
7Be detection in the 2021 outburst of RS Oph Molaro, P; Izzo, L; Selvelli, P ...
Monthly notices of the Royal Astronomical Society,
2023, Letnik:
518, Številka:
2
Journal Article
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ABSTRACT
The recurrent nova RS Oph underwent a new outburst on 2021 August 8, reaching a visible brightness of V = 4.8 mag. Observations of the 2021 outburst made with the high-resolution UVES ...spectrograph at the Kueyen-UT2 telescope at ESO-VLT in Paranal enabled detection of the possible presence of 7Be newly made in the thermonuclear runaway reactions. The 7Be yields can be estimated at N(7Be)/N(H) = 5.7 × 10−6, which are close to the lowest yields measured in classical novae so far. 7Be is short-lived and decays only into 7Li. By means of a spectrum taken during the nebular phase we estimated an ejected mass of ≈ 1.1 × 10−5 M⊙, providing an amount of ≈ 4.4 × 10−10 M⊙ of 7Li created in the 2021 event. Recurrent novae of the RS Oph type may synthesize slightly lower amounts of 7Li per event than classical novae, but occur 103 times more frequently. The recurrent novae fraction is in the range of 10–30 per cent and they could have contributed to the making of the 7Li that we observe today. The detection of 7Be in RS Oph provides further support to the recent suggestion that novae are the most effective source of 7Li in the Galaxy.
Crucial information on nova nucleosynthesis can be potentially inferred from γ-ray signals powered by 18F decay. Therefore, the reaction network producing and destroying this radioactive isotope has ...been extensively studied in the last years. Among those reactions, the 18F(p, )15O cross-section has been measured by means of several dedicated experiments, both using direct and indirect methods. The presence of interfering resonances in the energy region of astrophysical interest has been reported by many authors including the recent applications of the Trojan Horse Method. In this work, we evaluate what changes are introduced by the Trojan Horse data in the 18F(p, )15O astrophysical factor recommended in a recent R-matrix analysis, accounting for existing direct and indirect measurements. Then the updated reaction rate is calculated and parameterized and implications of the new results on nova nucleosynthesis are thoroughly discussed.
The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 yr, making it the most rapidly recurring system known, and ...a strong single-degenerate Type Ia supernova progenitor candidate. Following the 2013 eruption, a campaign was initiated to detect the predicted 2014 eruption and to then perform high cadence optical photometric and spectroscopic monitoring using ground-based telescopes, along with rapid UV and X-ray follow-up with the Swift satellite. Here we report the results of a high cadence multi-colour optical monitoring campaign, the spectroscopic evolution, and the UV photometry. We also discuss tantalising evidence of a potentially related, vastly-extended, nebulosity. The 2014 eruption was discovered, before optical maximum, on October 2, 2014. We find that the optical properties of M31N 2008-12a evolve faster than all Galactic recurrent novae known, and all its eruptions show remarkable similarity both photometrically and spectroscopically. Optical spectra were obtained as early as 0.26 days post maximum, and again confirm the nova nature of the eruption. A significant deceleration of the inferred ejecta expansion velocity is observed which may be caused by interaction of the ejecta with surrounding material,possibly a red giant wind. We find a low ejected mass and low ejection velocity, which are consistent with high mass-accretion rate, high mass white dwarf, and short recurrence time models of novae. We encourage additional observations, especially around the predicted time of the next eruption, towards the end of 2015.
► Spanish and Catalan emphatic polarity particles split into a high and a low pattern. ► Emphatic polarity particles (EPPA) are polar elements with an added emphatic value. ► High EPPA merge with ...PolP and move to FocusP. They display WH-operator properties. ► High EPPA are constrained to root and embedded clauses with a full-fledged left periphery. ► ForceP is also involved in the distribution of EPPA.
This paper explores the syntactic analysis of emphatic polarity particles (EPPA) in Spanish and Catalan and shows that these elements fall under a more complex paradigm than previously assumed. It is proposed that EPPA split into a high and a low pattern. We provide evidence in favour of the claim that EPPA are polar elements with an added emphatic value, and present a syntactic analysis where (i) High EPPA are merged with PolP and move to FocusP; (ii) High EPPA display WH-operator properties; (iii) The occurrence of high EPPA is constrained to root and embedded clauses that have a full-fledged left periphery, as predicted by the proposed analysis. Further understanding of EPPA syntactic hierarchy can be attained by assuming that the topmost projection of the CP domain, ForceP, is also involved in the distribution of EPPA.
V745 Sco is a recurrent nova, with the most recent eruption occurring in February 2014. V745 Sco was first observed by Swift a mere 3.7 h after the announcement of the optical discovery, with the ...super-soft X-ray emission being detected around 4 d later and lasting for only ∼2 d, making it both the fastest follow-up of a nova by Swift and the earliest switch-on of super-soft emission yet detected. Such an early switch-on time suggests a combination of a very high velocity outflow and low ejected mass and, together with the high effective temperature reached by the super-soft emission, a high mass white dwarf (>1.3 M⊙). The X-ray spectral evolution was followed from an early epoch where shocked emission was evident, through the entirety of the super-soft phase, showing evolving column density, emission lines, absorption edges, and thermal continuum temperature. UV grism data were also obtained throughout the super-soft interval, with the spectra showing mainly emission lines from lower ionization transitions and the Balmer continuum in emission. V745 Sco is compared with both V2491 Cyg (another nova with a very short super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet discovered). The longer recurrence time compared to M31N 2008-12a could be due to a lower mass accretion rate, although inclination of the system may also play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft source phase yet discovered, providing a detailed and informative data set for study.
We developed a hydrostatic and stationary white dwarf envelope model for the study of the post-outburst phases of classical novae and their soft X-ray emission. We considered several white dwarf ...masses and chemical compositions typical of classical novae. Our results show that the luminosity, maximum effective temperature, and envelope masses depend on the white dwarf mass and on the chemical composition. Envelope masses for which equilibrium solutions exist are pretty small (~$ 10^{-7}{-}10^{-6}~ M_{\odot}$), thus leading to a short duration of the soft X-ray emitting phase of classical novae, in agreement with most observations. The models we present provide a useful tool for the determination of the white dwarf properties from observable parameters in the X-ray range.
Spectroscoplc observations of the 2006 outburst of the recurrent nova RS Ophiuchi at both infrared (IR) and X-ray wavelengths have shown that the blast wave has decelerated at a higher rate than ...predicted by the standard test-particle adiabatic shock wave model. Here we show that the observed evolution of the nova remnant can be explained by the diffusive shock acceleration of particles at the blast wave and the subsequent escape of the highest energy ions from the shock region. Nonlinear particle acceleration can also account for the difference of shock velocities deduced from the IR and X-ray data. The maximum energy that accelerated electrons and protons can have achieved in few days after outburst is found to be as high as a few TeV. Using the semianalytic model of nonlinear diffusive shock acceleration developed by Berezhko & Ellison, we show that the postshock temperature of the shocked gas measured with RXTE PCA and Swift XRT imply a relatively moderate acceleration efficiency characterized by a proton injection rate unk unk 10 super(-4).
Context. The optical light curve of Type Ia supernovae (SNIa) is powered by thermalized gamma-rays produced by the decay of 56Ni and 56Co, the main radioactive isotopes synthesized by the ...thermonuclear explosion of a C/O white dwarf. Aims. Gamma-rays escaping the ejecta can be used as a diagnostic tool for studying the characteristics of the explosion. In particular, it is expected that the analysis of the early gamma emission, near the maximum of the optical light curve, could provide information about the distribution of the radioactive elements in the debris. Methods. The gamma data obtained from SN2014J in M 82 by the instruments on board INTEGRAL were analysed paying special attention to the effect that the detailed spectral response has on the measurements of the intensity of the lines. Results. The 158 keV emission of 56Ni has been detected in SN2014J at ~5σ at low energy with both ISGRI and SPI around the maximum of the optical light curve. After correcting the spectral response of the detector, the fluxes in the lines suggest that, in addition to the bulk of radioactive elements buried in the central layers of the debris, there is a plume of 56Ni, with a significance of ~3σ, moving at high velocity and receding from the observer. The mass of the plume is in the range of ~0.03−0.08 M⊙. Conclusions. No SNIa explosion model has ever predicted the mass and geometrical distribution of 56Ni suggested here. According to its optical properties, SN2014J looks like a normal SNIa, so it is extremely important to discern whether it is also representative in the gamma-ray band.
Nova SMC 2016 has been the most luminous nova known in the direction of the Magellanic Clouds. It turned into a very luminous supersoft X-ray source between days 16 and 28 after the optical maximum. ...We observed it with Chandra, the HRC-S camera, and the Low Energy Transmission Grating on 2016 November and 2017 January (days 39 and 88 after optical maximum), and with XMM-Newton on 2016 December (day 75). We detected the compact white dwarf (WD) spectrum as a luminous supersoft X-ray continuum with deep absorption features of carbon, nitrogen, magnesium, calcium, probably argon, and sulfur on day 39, and oxygen, nitrogen, and carbon on days 75 and 88. The spectral features attributed to the WD atmosphere are all blueshifted, by about 1800 km s−1 on day 39 and up to 2100 km s−1 in the following observations. Spectral lines attributed to low-ionization potential transitions in the interstellar medium are also observed. Assuming the distance to the Small Magellanic Cloud, the bolometric luminosity exceeded the Eddington level for at least three months. A preliminary analysis with atmospheric models indicates an effective temperature of around 700,000 K on day 39, peaking at the later dates in the 850,000-900,000 K range, as expected for a 1.25 M WD. We suggest a possible classification as an oxygen-neon WD, but more precise modeling is needed to accurately determine the abundances. The X-ray light curves show a large, aperiodic flux variability, which is not associated with spectral variability. We detected red noise, but did not find periodic or quasiperiodic modulations.
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