The main advances in the field of multinucleon transfer reactions at energies close to the Coulomb barrier are reviewed. After a short presentation of the experimental techniques and some gleams from ...the theory the new data are presented. The possibilities offered by the coupling of large gamma-array detectors with tracking spectrometers are discussed.
Stars are generally spherical, yet their gaseous envelopes often appear nonspherical when ejected near the end of their lives. This quirk is most notable during the planetary nebula phase, when these ...envelopes become ionized. Interactions among stars in a binary system are suspected to cause the asymmetry. In particular, a precessing accretion disk around a companion is believed to launch point-symmetric jets, as seen in the prototype Fleming 1. Our finding of a post-common-envelope binary nucleus in Fleming 1 confirms that this scenario is highly favorable. Similar binary interactions are therefore likely to explain these kinds of outflows in a large variety of systems.
ABSTRACT We present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula M 3-1 – the shortest period photometrically variable central star known and second only to ...V458 Vul, in general. Combined modelling of light and radial velocity curves reveals both components to be close to Roche lobe filling, strongly indicating that the central star will rapidly evolve to become a cataclysmic variable, perhaps experiencing a similar evolution to V458 Vul resulting in a nova eruption before the planetary nebula has fully dissipated. While the short orbital period and near Roche lobe filling natures of both components make the central binary of M 3-1 an important test case with which to constrain the formation processes of cataclysmic variables, novae, and perhaps even supernovae type Ia.
We present a study of Hen 2-155 and Hen 2-161, two planetary nebulae which bear striking morphological similarities to other planetary nebulae known to host close-binary central stars. Both central ...stars are revealed to be photometric variables while spectroscopic observations confirm that Hen 2-155 is host to a double-eclipsing, post-common-envelope system with an orbital period of 3h33m making it one of the shortest period binary central stars known. The observations of Hen 2-161 are found to be consistent with a post-common-envelope binary of period ~1 day. A detailed model of the central star of Hen 2-155 is produced, showing the nebular progenitor to be a hot, post-AGB remnant of approximately 0.62 M⊙, consistent with the age of the nebula, and the secondary star to be an M dwarf whose radius is almost twice the expected zero age main sequence radius for its mass. In spite of the small numbers, all main-sequence companions, of planetary nebulae central stars, to have had their masses and radii constrained by both photometric and spectroscopic observations have also been found to display this “inflation”. The cause of the “inflation” is uncertain but is probably related to rapid accretion, immediately before the recent common-envelope phase, to which the star has not yet thermally adjusted. The chemical composition of both nebulae is also analysed, showing both to display elevated abundance discrepancy factors. This strengthens the link between elevated abundance discrepancy factors and close binarity in the nebular progenitor.
Abstract Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the ...colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions $$E\sigma $$ E σ in relation to their first energy derivatives $$d(E\sigma )/dE$$ d ( E σ ) / d E . The relation between $$d(E\sigma )/dE$$ d ( E σ ) / d E and $$E\sigma $$ E σ removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.
We address the general problem of the luminosity-specific planetary nebula (PN) number, better known as the ‘α’ ratio, given by α=NPN/Lgal, and its relationship with the age and metallicity of the ...parent stellar population. Our analysis relies on population synthesis models that account for simple stellar populations (SSPs), and more elaborate galaxy models covering the full star formation range of the different Hubble morphological types. This theoretical framework is compared with the updated census of the PN population in Local Group (LG) galaxies and external ellipticals in the Leo group, and the Virgo and Fornax clusters. The main conclusions of our study can be summarized as follows. According to the post-asymptotic giant branch (AGB) stellar core mass, PN lifetime in a SSP is constrained by three relevant regimes, driven by the nuclear (Mcore≳ 0.57 M⊙), dynamical (0.57 M⊙≳Mcore≳ 0.55 M⊙) and transition (0.55 M⊙≳Mcore≳ 0.52 M⊙) time-scales. The lower limit for Mcore also sets the minimum mass for stars to reach the AGB thermal-pulsing phase and experience the PN event. Mass loss is the crucial mechanism to constrain the value of α, through the definition of the initial-to-final mass relation (IFMR). The Reimers mass-loss parametrization, calibrated on Pop II stars of Galactic globular clusters, poorly reproduces the observed value of α in late-type galaxies, while a better fit is obtained using the empirical IFMR derived from white dwarf observations in the Galaxy open clusters. The inferred PN lifetime for LG spirals and irregulars exceeds 10 000 yr, which suggests that Mcore≲ 0.65 M⊙ cores dominate, throughout. The relative PN deficiency in elliptical galaxies, and the observed trend of α with galaxy optical colours, support the presence of a prevailing fraction of low-mass cores (Mcore≲ 0.55 M⊙) in the PN distribution and a reduced visibility time-scale for the nebulae as a consequence of the increased AGB transition time. The stellar component with Mcore≲ 0.52 M⊙, which overrides the PN phase, could provide an enhanced contribution to hotter HB and post-HB evolution, as directly observed in M 32 and the bulge of M 31. This implies that the most UV-enhanced ellipticals should also display the lowest values of α, as confirmed by the Virgo cluster early-type galaxy population. Any blue-straggler population, invoked as progenitor of the Mcore≳ 0.7 M⊙ PNe in order to preserve the constancy of the bright luminosity-function cut-off magnitude in ellipticals, must be confined to a small fraction (a few per cent at most) of the whole galaxy PN population.
On the most luminous planetary nebulae of M 31 Galera-Rosillo, Rebeca; Mampaso, Antonio; Corradi, Romano L. M. ...
Astronomy and astrophysics (Berlin),
01/2022, Letnik:
657
Journal Article
Recenzirano
Odprti dostop
Context.
The planetary nebula luminosity function (PNLF) is a standard candle that comprises a key rung on the extragalactic distance ladder. The method is based on the empirical evidence that the ...luminosity function of planetary nebulae (PNe) in the O
III
λ
5007 nebular emission line reaches a maximum value that is approximately invariant with population age, metallicity, or host galaxy type. However, the presence of bright PNe in old stellar populations is not easily explained by single-star evolutionary models.
Aims.
To gain information about the progenitors of PNe at the tip of the PNLF, we obtained the deepest existing spectra of a sample of PNe in the galaxy M 31 to determine their physico-chemical properties and infer the post-asymptotic giant branch (AGB) masses of their central stars (CSs). Precise chemical abundances allow us to confront the theoretical yields for AGB stellar masses and metallicities expected at the bright end of the PNLF. Central star masses of the sampled PNe provide direct information on the controversial origin of the universal cutoff of the PNLF.
Methods.
Using the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias (GTC), optical spectra of nine bright M 31 PNe were obtained: four of them at the tip of the PNLF, and the other five some 0.5 mag fainter. A control sample of 21 PNe with previous GTC spectra from the literature is also included. We analyze their physical properties and chemical abundances (He, N, O, Ar, Ne, and S), searching for relevant differences between bright PNe and the control samples. The CS masses are estimated with Cloudy modeling using the most recent evolutionary tracks.
Results.
The studied PNe show a remarkable uniformity in all their nebular properties, and the brightest PNe show relatively large electron densities. Stellar characteristics also span a narrow range: ⟨
L
*
/
L
⊙
⟩ = 4300 ± 310, ⟨
T
eff
⟩ = 122 000 ± 10 600 K for the CSs of the four brightest PNe, and ⟨
L
*
/
L
⊙
⟩ = 3300 ± 370, ⟨
T
eff
⟩ = 135 000 ± 26 000 K for those in the control set. This groups all the brightest PNe at the location of maximum temperature in the post-AGB tracks for stars with initial masses
M
i
= 1.5
M
⊙
.
Conclusions.
These figures provide robust observational constraints for the stellar progenitors that produce the PNLF cutoff in a star-forming galaxy such as M 31, where a large range of initial masses is in principle available. Inconsistency is found, however, in the computed N/O abundance ratios of five nebulae, which are 1.5 to 3 times larger than predicted by the existing nucleosynthesis models for stars of these masses.
Absolute cross sections for isotopically identified products formed in multinucleon transfer in the (136)Xe+(198)Pt system at ∼8 MeV/nucleon are reported. The isotopic distributions obtained using a ...large acceptance spectrometer demonstrated the production of the "hard-to-reach" neutron-rich isotopes for Z<78 around the N=126 shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around N=126 which are crucial for understanding both astrophysically relevant processes and the evolution of "magic" numbers far from stability.
ABSTRACT
The long-standing difference in chemical abundances determined from optical recombination lines and collisionally excited lines raises questions about our understanding of atomic physics, as ...well as the assumptions made when determining physical conditions and chemical abundances in astrophysical nebulae. Here, we study the recombination contribution of O iii 4363 and the validity of the line ratio O iii 4363/4959 as a temperature diagnostic in planetary nebulae with a high abundance discrepancy. We derive a fit for the recombination coefficient of O iii 4363 that takes into account the radiative and dielectronic recombinations, for electron temperatures from 200 to 30 000 K. We estimate the recombination contribution of O iii 4363 for the planetary nebulae Abell 46 and NGC 6778 by subtracting the collisional contribution from the total observed flux. We find that the spatial distribution for the estimated recombination contribution in O iii 4363 follows that of the O ii 4649 recombination line, both peaking in the central regions of the nebula, especially in the case of Abell 46 that has a much higher abundance discrepancy. The estimated recombination contribution reaches up to 70 and 40 per cent of the total O iii 4363 observed flux, for Abell 46 and NGC 6778, respectively.
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