The emission/absorption FE 2 spectrum of HD 45677

The complex behavior of the emission/absorption spectrum of Fe II is analyzed. The far UV spectrum is characterized almost solely by absorption lines, while, in the near UV, strong emissions are predominant. Radiative excitation from the ground to the highest levels (chi is approximately 10 eV) with re-emission in the near UV, visible and I.R. seems to be the main mechanism capable of explaining the observed spectral features

Absorption and emission features of 7Be II in the outburst spectra of V838 Her (Nova Her 1991)

High- and low-resolution International Ultraviolet Explorer (IUE) spectra of V838 Her in the early outburst stages exhibit a strong absorption feature shortward of λ3130. We discuss the nature of this spectral feature and provide convincing evidence that it corresponds to the blueshifted resonance doublet of singly ionized 7Be recently discovered in other novae. During the evolution of the outburst the appearance of an emission feature close to λ3130 Å is also identified as 7Be II λ3132 because the usual identification as the O III λ3133.7 Bowen fluorescence line is hardly compatible with both the known oxygen underabundance in the nova ejecta and the low optical depths in the nebula due to the high outflow velocity. The average 7Be abundance relative to hydrogen, estimated by four different methods, i.e. the 7Be II/Mg II absorption ratio, and the 7Be II/Mg II, 7Be II/He II1640, and 7Be II/Hβ emission ratios, is N(Be)/N(H) ≈2.5 × 10-5 (by number), i.e. ≈1.7 × 10-4 by mass. This corresponds to an overproduction of 7Be by about 1 dex in comparison with the theoretical models of massive CO and ONe novae. Since 7Be all converts into 7Li, the 7Be/H abundance implies a 7Li/H overabundance of about 4 dex over the 7Li/H meteoritic value and indicates a total ejected mass of 7Li of ≈9.5 × 10-10 M⊙. These data are in line with previous observations and indicate that large amounts of 7Li can be synthesized in a variety of novae, including very fast ONe novae

7Be in the outburst of the ONe nova V6595 Sgr

We report on the search for the 7Be ii isotope in the outbursts of the classical nova V6595 Sgr by means of high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations taken at the European Southern Observatory's Very Large Telescope in 2021 April, about two weeks after its discovery and under difficult circumstances due to the pandemic. Narrow absorption components with velocities at -2620 and-2820 km s-1, superposed on broader and shallow absorption, are observed in the outburst spectra for the 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines, as well as in several other elements such as Ca ii, Fe i, Mg i, Na i, H i and Li i. Using the Ca ii K line as a reference element, we infer N(7Be)/N(H) ≈ 7.4 × 10-6, or ≈ 9.8 × 10-6 when the 7Be decay is taken into account. The 7Be abundance is about half of the value most frequently measured in novae. The possible presence of overionization in the layers where 7Be ii is detected is also discussed. Observations taken at the Telescopio Nazionale Galileo in La Palma 91 days after discovery showed prominent emission lines of oxygen and neon, which allow us to classify the nova as ONe type. Therefore, although 7Be is expected to be higher in CO novae, it is found at comparable levels in both nova types

Detection of 7Be II in the Small Magellanic Cloud

We analyse high-resolution spectra of two classical novae that exploded in the Small Magellanic Cloud (SMC). 7 Be II resonance transitions are detected in both ASASSN-19qv and ASASSN-20ni novae. This is the first detection outside the Galaxy and confirms that thermo-nuclear runaway reactions, leading to the 7 Be formation, are ef fecti ve also in the low-metallicity regime, characteristic of the SMC. Derived yields are of N( 7 Be = 7 Li)/N(H) = (5.3 ±0.2) ×10 −6 which are a factor 4 lower than the typical values of the Galaxy. Inspection of two historical novae in the Large Magellanic Cloud observed with IUE in 1991 and 1992 showed also the possible presence of 7 Be and similar yields. For an ejecta of M H , ej = 10 −5 M ⊙, the amount of 7 Li produced is of M 7 Li = (3 . 7 ±0 . 6) ×10 −10 M ⊙per nova event. Detailed chemical evolutionary model for the SMC shows that no vae could hav e made an amount of lithium in the SMC corresponding to a fractional abundance of A(Li) ≈2.6. Therefore, it is argued that a comparison with the abundance of Li in the SMC, as measured by its interstellar medium, could ef fecti vely constrain the amount of the initial abundance of primordial Li, which is currently contro v ersial

7Be detection in the 2021 outburst of RS Oph

The recurrent nova RS Oph underwent a new outburst on August 8, 2021, 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 of ESO-VLT in Paranal enabled detection of the possible presence of 7Be freshly made in the thermonuclear runaway reactions. The 7Be yields can be estimated in N(Be)/N(H) = 5.7 x 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 about 1.1 x 10^(-5) Msun, providing an amount of about 4.4x 10^(-10) Msun of 7Li created in the 2021 event. Recurrent novae of the kind of RS Oph may synthesize slightly lower amount of 7Li per event as classical novae, but occur 10^3 times more frequently. The recurrent novae fraction is in the range of 10-30% and they could have contributed to the making of 7Li 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.Comment: Accepted 2022 September 17. Received 2022 September 16; in original form 2022 April 20. 12 pages, 13 figure