Degenerate Core Research Articles

The formation of ultra-massive carbon-oxygen core white dwarfs and their evolutionary and pulsational properties

Context.The existence of ultra-massive white dwarf stars,MWD ≳ 1.05 M⊙, has been reported in several studies. These white dwarfs are relevant for the role they play in type Ia supernova explosions, the occurrence of physical processes in the asymptotic giant-branch phase, the existence of high-field magnetic white dwarfs, and the occurrence of double-white-dwarf mergers.Aims.We aim to explore the formation of ultra-massive, carbon-oxygen core white dwarfs resulting from single stellar evolution. We also intend to study their evolutionary and pulsational properties and compare them with those of the ultra-massive white dwarfs with oxygen-neon cores resulting from carbon burning in single progenitor stars, and with binary merger predictions. The aim is to provide a theoretical basis that can eventually help to discern the core composition of ultra-massive white dwarfs and the circumstances of their formation.Methods.We considered two single-star evolution scenarios for the formation of ultra-massive carbon-oxygen core white dwarfs, which involve the rotation of the degenerate core after core helium burning and reduced mass-loss rates in massive asymptotic giant-branch stars. We find that reducing standard mass-loss rates by a factor larger than 5−20 yields the formation of carbon-oxygen cores more massive than 1.05 M⊙as a result of the slow growth of carbon-oxygen core mass during the thermal pulses. We also performed a series of evolutionary tests of solar-metallicity models with initial masses between 4 and 9.5M⊙and with different core rotation rates. We find that ultra-massive carbon-oxygen core white dwarfs are formed even for the lowest rotation rates we analyzed, and that the range of initial masses leading to these white dwarfs widens as the rotation rate of the core increases, whereas the initial mass range for the formation of oxygen-neon core white dwarfs decreases significantly. Finally, we compared our findings with the predictions from ultra-massive white dwarfs resulting from the merger of two equal-mass carbon-oxygen core white dwarfs, by assuming complete mixing between them and a carbon-oxygen core for the merged remnant.Results.These two single-evolution scenarios produce ultra-massive white dwarfs with different carbon-oxygen profiles and different helium contents, thus leading to distinctive signatures in the period spectrum and mode-trapping properties of pulsating hydrogen-rich white dwarfs. The resulting ultra-massive carbon-oxygen core white dwarfs evolve markedly slower than their oxygen-neon counterparts.Conclusions.Our study strongly suggests the formation of ultra-massive white dwarfs with carbon-oxygen cores from a single stellar evolution. We find that both the evolutionary and pulsation properties of these white dwarfs are markedly different from those of their oxygen-neon core counterparts and from those white dwarfs with carbon-oxygen cores that might result from double-degenerate mergers. This can eventually be used to discern the core composition of ultra-massive white dwarfs and their formation scenario.

On the formation and stability of fermionic dark matter haloes in a cosmological framework

ABSTRACT The formation and stability of collisionless self-gravitating systems are long-standing problems, which date back to the work of D. Lynden-Bell on violent relaxation and extends to the issue of virialization of dark matter (DM) haloes. An important prediction of such a relaxation process is that spherical equilibrium states can be described by a Fermi–Dirac phase-space distribution, when the extremization of a coarse-grained entropy is reached. In the case of DM fermions, the most general solution develops a degenerate compact core surrounded by a diluted halo. As shown recently, the latter is able to explain the galaxy rotation curves, while the DM core can mimic the central black hole. A yet open problem is whether these kinds of astrophysical core–halo configurations can form at all, and whether they remain stable within cosmological time-scales. We assess these issues by performing a thermodynamic stability analysis in the microcanonical ensemble for solutions with a given particle number at halo virialization in a cosmological framework. For the first time, we demonstrate that the above core–halo DM profiles are stable (i.e. maxima of entropy) and extremely long-lived. We find the existence of a critical point at the onset of instability of the core–halo solutions, where the fermion-core collapses towards a supermassive black hole. For particle masses in the keV range, the core-collapse can only occur for $M_{\rm vir} \gtrsim 10^{9}{\, \mathrm{M}_\odot}$ starting at zvir ≈ 10 in the given cosmological framework. Our results prove that DM haloes with a core–halo morphology are a very plausible outcome within non-linear stages of structure formation.

The RGB tip of galactic globular clusters and the revision of the axion-electron coupling bound

Context. The production of neutrinos by plasma oscillations is the most important energy sink process operating in the degenerate core of low-mass red giant stars. This process counterbalances the release of energy induced by nuclear reactions and gravitational contraction, and determines the luminosity attained by a star at the moment of the He ignition. This occurrence coincides with the tip of the red giant branch (RGB), whose luminosity is extensively used as a calibrated standard candle in several cosmological studies. Aims. We aim to investigate the possible activation of additional energy sink mechanisms, as predicted by many extensions of the so-called Standard Model. In particular, our objective is to test the possible production of axions or axion-like particles, mainly through their coupling with electrons. Methods. By combining Hubble Space Telescope and ground-based optical and near-infrared photometric samples, we derived the RGB tip absolute magnitude of 22 galactic globular clusters (GGCs). The effects of varying the distance and the metallicity scales were also investigated. Then we compared the observed tip luminosities with those predicted by state-of-the-art stellar models that include the energy loss due to the axion production in the degenerate core of red giant stars. Results. We find that theoretical predictions including only the energy loss by plasma neutrinos are, in general, in good agreement with the observed tip bolometric magnitudes, even though the latter are ∼0.04 mag brighter on average. This small shift may be the result of systematic errors affecting the evaluation of the RGB tip bolometric magnitudes, or, alternatively, it could be ascribed to an axion-electron coupling causing a non-negligible thermal production of axions. In order to estimate the strength of this possible axion sink, we performed a cumulative likelihood analysis using the RGB tips of the whole set of 22 GGCs. All the possible sources of uncertainties affecting both the measured bolometric magnitudes and the corresponding theoretical predictions were carefully considered. As a result, we find that the value of the axion-electron coupling parameter that maximizes the likelihood probability is gae/10−13 ∼ 0.60−0.58+0.32. This hint is valid, however, if the dominant energy sinks operating in the core of red giant stars are standard neutrinos and axions coupled with electrons. Any additional energy-loss process, not included in the stellar models, would reduce such a hint. Nevertheless, we find that values gae/10−13 > 1.48 can be excluded with 95% confidence. Conclusions. The new bound we find represents the most stringent constraint for the axion-electron coupling available so far. The new scenario that emerges after this work represents a greater challenge for future experimental axion searches. In particular, we can exclude that the recent signal seen by the XENON1T experiment was due to solar axions.

Impact of forbidden electron capture in intermediate-mass stars

Intermediate-mass stars (7-11 M⊙) form degenerate ONe cores following carbon burning. In some cases the cores grow dense enough to trigger electron capture on various nuclei. The double electron capture 20Ne(e^-, v e)20F(e^-, νe )20O releases enough heat to trigger runaway oxygen burning. Depending on the conditions at ignition the outcome is either a collapse to a neutron star or a thermonuclear explosion with an ONeFe remnant. We have investigated the impact of two forbidden transitions on the ignition conditions using the MESA stellar evolution code. The 0+ → 2+ transition between the ground states of 20Ne and 20F has been measured experimentally and is found to decrease the ignition density while pushing the point of ignition off-centre. We have also studied the 2+ → 4+ transition between 24Na and 24Ne through a shell model calculation. Its impact is found to be marginal in our simulations, but it might play a role in the development of convectional instabilities.

Carbon star formation as seen through the non-monotonic initial–final mass relation

The initial–final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved. A new analysis of a few carbon–oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR, located over a range of initial masses, 1.65 ≲ Mi/M⊙ ≲ 2.10. The kink’s peak in white dwarf mass of about 0.70−0.75 M⊙ is produced by stars with Mi ≈ 1.8−1.9 M⊙, corresponding to ages of about 1.8−1.7 Gyr. Interestingly, this peak coincides with the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their impact on the spectrophotometric properties of galaxies. An analysis of the relation between a star’s initial mass and its final mass (as a white dwarf) reveals a kink in the initial mass range 1.65–2.10 M⊙. This kink appears to correspond to the minimum mass required for carbon star formation in the Milky Way at solar metallicity.

Type Ia supernovae from non-accreting progenitors

Type Ia supernovae (SNe Ia) are manifestations of stars that are deficient in hydrogen and helium, and disrupt in a thermonuclear runaway. While explosions of carbon-oxygen white dwarfs are thought to account for the majority of events, part of the observed diversity may be due to varied progenitor channels. We demonstrate that helium stars with masses between ∼1.8 and 2.5 M⊙ may evolve into highly degenerate cores with near-Chandrasekhar mass and helium-free envelopes that subsequently ignite carbon and oxygen explosively at densities of ∼(1.8−5.9) × 109 g cm−3. This occurs either due to core growth from shell burning (when the core has a hybrid CO/NeO composition), or following ignition of residual carbon triggered by exothermic electron captures on 24Mg (for a NeOMg-dominated composition). We argue that the resulting thermonuclear runaway is likely to prevent core collapse, leading to the complete disruption of the star. The available nuclear energy at the onset of explosive oxygen burning suffices to create ejecta with a kinetic energy of ∼1051 erg, as in typical SNe Ia. Conversely, if these runaways result in partial disruptions, the corresponding transients would resemble SN Iax events similar to SN 2002cx. If helium stars in this mass range indeed explode as SNe Ia, then the frequency of events would be comparable to the observed SN Ib/c rates, thereby sufficing to account for the majority of SNe Ia in star-forming galaxies.

АНАЛИТИЧЕСКОЕ РЕШЕНИЕ ИНТЕГРАЛЬНОГО УРАВНЕНИЯ ШРЕДИНГЕРА

In this paper, the question about the use of wave dynamics for solving problems of membrane separation of helium isotopes in the gas state at cryogenic temperatures is considered. The dimensionless form of the stationary Schrödinger differential equation is obtained. Following that, the integral representation form of the wave function is written. This form, which is equivalent to the classical equation, is similar to the integral equation with a degenerate core; however, it contains a modulus of the argument with a shift along the real axis. Using the shift operator, the existing exponential function in the Schrödinger integral equation can be split into a differential operator and an exponential function of the argument module which does not contain a shift. The Fourier identity allows reducing the exponent of the modulus of the argument to a regular exponent. Next, based on the general property of a differential operator acting on an exponent, it is possible to calculate the spectral functions of the problem and write down the distribution for the wave function. This distribution is ultimately expressed through the spectra of the potential barrier. Thereafter, the structure and the spectrum of the composite barrier are considered. With the expression determining the reflection coefficient, it is found that the double-barrier system can have a resonant passage of one of the components in the sequence of distances between the layers of the membrane.

Boundary Values of Degenerate Configuration Core of White Dwarfs using Ramanujan’s Method

In this paper we have found out boundary values of degenerate configuration core of White Dwarf using Ramanujan’s method. By converting non-linear Lane Emden-type equation for degenerate core into a series using an iterative method. Considering the first five terms of the series numerical values has been calculated. The applied method is efficient and simplifies the calculation. The obtained result has been compared with exact values. Ramanujan’s method and the new iterative method are used for the first time to solve the Lane Emden equation for white dwarf core.

Discovery of an Exceptionally Strong β-Decay Transition of ^{20}F and Implications for the Fate of Intermediate-Mass Stars.

A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on ^{20}Ne in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of ^{20}Ne and ^{20}F, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. Importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood.

Measurement of the 2+→0+ ground-state transition in the β decay of F20

We report the first detection of the second-forbidden, non-unique, $2^+\rightarrow 0^+$, ground-state transition in the $\beta$ decay of $^{20}$F. A low-energy, mass-separated $^{20}\rm{F}^+$ beam produced at the IGISOL facility in Jyv\"askyl\"a, Finland, was implanted in a thin carbon foil and the $\beta$ spectrum measured using a magnetic transporter and a plastic-scintillator detector. The $\beta$-decay branching ratio inferred from the measurement is $b_{\beta} = [ 0.41\pm 0.08\textrm{(stat)}\pm 0.07\textrm{(sys)}] \times 10^{-5}$ corresponding to $\log ft = 10.89(11)$, making this one of the strongest second-forbidden, non-unique $\beta$ transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on $^{20}$Ne is now known to within better than 25% at the relevant temperatures and densities.

The Evolution of Unusually Small Amelogenin Genes in Cetaceans; Pseudogenization, X-Y Gene Conversion, and Feeding Strategy.

Among extant cetaceans, mysticetes are filter feeders that do not possess teeth and use their baleen for feeding, while most odontocetes are considered suction feeders, which capture prey by suction without biting or chewing with teeth. In the present study, we address the functionality of amelogenin (AMEL) genes in cetaceans. AMEL encodes a protein that is specifically involved in dental enamel formation and is located on the sex chromosomes in eutherians. The X-copy AMELX is functional in enamel-bearing eutherians, whereas the Y-copy AMELY appears to have undergone decay and was completely lost in some species. Consistent with these premises, we detected various deleterious mutations and/or non-canonical splice junctions in AMELX of mysticetes and four suction feeding odontocetes, Delphinapterus leucas, Monodon monoceros, Kogia breviceps, and Physeter macrocephalus, and in AMELY of mysticetes and odontocetes. Regardless of the functionality, both AMELX and AMELY are equally and unusually small in cetaceans, and even their functional AMELX genes presumably encode a degenerate core region, which is thought to be essential for enamel matrix assembly and enamel crystal growth. Furthermore, our results suggest that the most recent common ancestors of extant cetaceans had functional AMELX and AMELY, both of which are similar to AMELX of Platanista minor. Similar small AMELX and AMELY in archaic cetaceans can be explained by gene conversion between AMELX and AMELY. We speculate that common ancestors of modern cetaceans employed a degenerate AMELX, transferred from a decaying AMELY by gene conversion, at an early stage of their transition to suction feeders.

J0453+1559: A Neutron Star–White Dwarf Binary from a Thermonuclear Electron-capture Supernova?

Abstract The compact binary radio pulsar system J0453+1559 consists of a recycled pulsar as primary component of 1.559(5) M ⊙ and an unseen companion star of 1.174(4) M ⊙. Because of the relatively large orbital eccentricity of e = 0.1125, it was argued that the companion is a neutron star (NS), making it the NS with the lowest accurately determined mass to date. However, a direct observational determination of the nature of the companion is currently not feasible. Moreover, state-of-the-art stellar evolution and supernova modeling are contradictory concerning the possibility of producing such a low-mass NS remnant. Here we challenge the NS interpretation by reasoning that the lower-mass component could instead be a white dwarf born in a thermonuclear electron-capture supernova (tECSN) event, in which oxygen–neon deflagration in the degenerate stellar core of an ultra-stripped progenitor ejects several 0.1 M ⊙ of matter and leaves a bound ONeFe white dwarf as the second-formed compact remnant. We determine the ejecta mass and remnant kick needed in this scenario to explain the properties of PSR J0453+1559 by a NS–white dwarf system. More work on tECSNe is needed to assess the viability of this scenario.

Evolution of ONeMg Core in Super-AGB Stars toward Electron-capture Supernovae: Effects of Updated Electron-capture Rate

Stars with $\sim 8-10~{M}_{\odot}$ evolve to form a strongly degenerate ONeMg core. When the core mass becomes close to the Chandrasekhar mass, the core undergoes electron captures on $^{24}$Mg and $^{20}$Ne, which induce the electron-capture supernova (ECSN). In order to clarify whether the ECSN leads to a collapse or thermonuclear explosion, we calculate the evolution of an $8.4~M_\odot$ star from the main sequence until the oxygen ignition in the ONeMg core. We apply the latest electron-capture rate on $^{20}$Ne including the second forbidden transition, and investigate how the location of the oxygen ignition (center or off-center) and the $Y_e$ distribution depend on the input physics and the treatment of the semiconvection and convection. The central density when the oxygen deflagration is initiated, $\rho_{\rm c,def}$, can be significantly higher than that of the oxygen ignition thanks to the convection, and we estimate $\log_{10}(\rho_{\rm c,def}/\mathrm{g~cm^{-3}})>10.10$. We perform two-dimensional simulations of the flame propagation to examine how the final fate of the ONeMg core depends on the $Y_e$ distribution and $\rho_{\rm c,def}$. We find that the deflagration starting from $\log_{10}(\rho_{\rm c,def}/\mathrm{g~cm^{-3}})>10.01 (< 10.01)$ leads to a collapse (thermonuclear explosion). Since our estimate of $\rho_{\rm c,def}$ exceeds this critical value, the ONeMg core is likely to collapse, although further studies of the convection and semiconvection before the deflagration are important.

Relativistic gravitational phase transitions and instabilities of the Fermi gas

We describe microcanonical phase transitions and instabilities of the ideal Fermi gas in general relativity at nonzero temperature confined in the interior of a spherical shell. The thermodynamic behaviour is governed by the compactness of rest mass, namely of the total rest mass over radius of the system. For a fixed value of rest mass compactness, we study the caloric curves as a function of the size of the spherical box. At low compactness values, low energies and for sufficiently big systems the system is subject to a gravothermal catastrophe, which cannot be halted by quantum degeneracy pressure, and the system collapses. For small systems, there appears no instability at low energies. For intermediate sizes, between two marginal values, gravothermal catastrophe is halted and a microcanonical phase transition occurs from a gaseous phase to a condensed phase with a nearly degenerate core. The system is subject to a relativistic instability at low energy, when the core gets sufficiently condensed above the Oppenheimer–Volkoff limit. For sufficiently high values of rest mass compactness the microcanonical phase transitions are suppressed. They are replaced either by an Antonov type gravothermal catastrophe for sufficiently big systems or by stable equilibria for small systems. At high energies the system is subject to the ‘relativistic gravothermal instability’, identified by Roupas (2015 Class. Quantum Grav. 32 135023), for all values of compactness and any size.

Seismic characterization of red giants going through the helium-core flash

Context. First-ascent red giants in the approximate mass range 0.7 ≲ M/M⊙ ≲ 2 ignite helium in their degenerate core as a flash. Stellar evolution codes predict that the He flash consists of a series of consecutive subflashes. Observational evidence of the existence of the He flash and subflashes is lacking. The detection of mixed modes in red giants from space missions CoRoT and Kepler has opened new opportunities to search for such evidence. Aims. During a subflash, the He-burning shell is convective, which splits the cavity of gravity modes in two. We here investigate how this additional cavity modifies the oscillation spectrum of the star. We also address the question of the detectability of the modes, to determine whether they could be used to seismically identify red giants passing through the He flash. Methods. We calculate the asymptotic mode frequencies of stellar models going through a He subflash using the Jeffreys-Wentzel-Kramers-Brillouin (JWKB) approximation. To predict the detectability of the modes, we estimate their expected heights, taking into account the effects of radiative damping in the core. Our results are then compared to the oscillation spectra obtained by numerically calculating the mode frequencies during a He subflash. Results. We show that during a He subflash, the detectable oscillation spectrum mainly consists of modes trapped in the acoustic cavity and in the outer g-mode cavity. The spectrum should thus at first sight resemble that of a core-helium-burning giant. However, we find a list of clear, detectable features that could enable us to identify red giants passing through a He subflash. In particular, during a He subflash, several modes that are trapped in the innermost g-mode cavity are expected to be detectable. We show that these modes could be identified by their frequencies or by their rotational splittings. Other features, such as the measured period spacing of gravity modes or the location of the H-burning shell within the g-mode cavity could also be used to identify stars going through a He subflash. Conclusions. The features derived in this study can now be searched for in the large datasets provided by the CoRoT and Kepler missions.

Origin of magnetic fields in cataclysmic variables

In a series of recent papers, it has been proposed that high field magnetic white dwarfs are the result of close binary interaction and merging. Population synthesis calculations have shown that the origin of isolated highly magnetic white dwarfs is consistent with the stellar merging hypothesis. In this picture, the observed fields are caused by an alpha-Omega dynamo driven by differential rotation. The strongest fields arise when the differential rotation equals the critical break-up velocity and result from the merging of two stars (one of which has a degenerate core) during common envelope evolution or from the merging of two white dwarfs. We now synthesise a population of binary systems to investigate the hypothesis that the magnetic fields in the magnetic cataclysmic variables also originate during stellar interaction in the common envelope phase. Those systems that emerge from common envelope more tightly bound form the cataclysmic variables with the strongest magnetic fields. We vary the common envelope efficiency parameter and compare the results of our population syntheses with observations of magnetic cataclysmic variables. We find that common envelope interaction can explain the observed characteristics of these magnetic systems if the envelope ejection efficiency is low.

X-ray binary Beta Lyrae and its donor component structure

AbstractWe show that the structure of magnetized accretion gas flows between the components of the Beta Lyrae system can cause a scattering gas shell that masks completely these components in soft X-ray region. Also we have calculated the inner structure of the donor that is filling a Roche lobe and is preceding a forming of the degenerate dwarf. We show that mass of the degenerate core of the donor is in region 0.3−0.5M⊙.

A critical re-evaluation of the Thorne–Żytkow object candidate HV 2112

It has been argued in the literature that the star HV~2112 in the Small Magellanic Cloud is the first known example of a T\.ZO, a Red Supergiant with a degenerate neutron core. This claim is based on the star having a high luminosity ($\log (L/L_\odot)$~> 5), an extremely cool effective temperature, and a surface enriched in in lithium, calcium and various $irp$-process elements. In this paper we re-examine this evidence, and present new measurements of the stellar properties. By compiling archival photometry from blue to mid-IR for HV~2112 and integrating under it's spectral energy distribution we find a bolometric luminosity in the range of $\log (L/L_\odot)$=4.70-4.91, lower than that found in previous work and comparable to bright asymptotic giant branch (AGB) stars. We compare a VLT+XSHOOTER spectrum of HV~2112 to other late type, luminous SMC stars, finding no evidence for enhancements in Rb, Ca or K, though there does seem to be an enrichment in Li. We therefore conclude that a much more likely explanation for HV~2112 is that it is an intermediate mass($\sim$5M$_\odot$) AGB star. However, from our sample of comparison stars we identify a new T\.ZO candidate, HV~11417, which seems to be enriched in Rb but for which we cannot determine a Li abundance.

Bose-Einstein condensate & degenerate Fermi cored dark matter halos

There has been considerable interest in the last several years in support of the idea that galaxies and clusters could have highly condensed cores of dark matter (DM) within their central regions. In particular, it has been suggested that dark matter could form Bose-Einstein condensates (BECs) or degenerate Fermi cores. We examine these possibilities under the assumption that the core consists of highly condensed DM (either bosons or fermions) that is embedded in a diffuse envelope (e.g., isothermal sphere). The novelty of our approach is that we invoke composite polytropes to model spherical collisionless structures in a way that is physically intuitive and can be generalized to include other equations of state (EOSs). Our model is very amenable to the analysis of BEC cores (composed of ultra-light bosons) that have been proposed to resolve small-scale CDM anomalies. We show that the analysis can readily be applied to bosons with or without small repulsive self-interactions. With respect to degenerate Fermi cores, we confirm that fermionic particle masses between 1—1000 keV are not excluded by the observations. Finally, we note that this approach can be extended to include a wide range of EOSs in addition to multi-component collisionless systems.

Case A and B evolution towards electron capture supernova

Context. Most super-asymptotic giant branch (SAGB) stars are expected to end their life as oxygen–neon white dwarfs rather than electron capture supernovae (ECSN). The reason is ascribed to the ability of the second dredge-up to significantly reduce the mass of the He core and of the efficient AGB winds to remove the stellar envelope before the degenerate core reaches the critical mass for the activation of electron capture reactions. Aims. In this study, we investigate the formation of ECSN through case A and case B mass transfer. In these scenarios, when Roche lobe overflow stops, the primary has become a helium star. With a small envelope left, the second dredge-up is prevented, potentially opening new paths to ECSN. Methods. We compute binary models using our stellar evolution code BINSTAR. We consider three different secondary masses of 8, 9, and 10 M⊙ and explore the parameter space, varying the companion mass, orbital period, and input physics. Results. Assuming conservative mass transfer, with our choice of secondary masses all case A systems enter contact either during the main sequence or as a consequence of reversed mass transfer when the secondary overtakes its companion during core helium burning. Case B systems are able to produce ECSN progenitors in a relatively small range of periods (3 ≲ P(d) ≤ 30) and primary masses (10.9 ≤ M∕M⊙≤ 11.5). Changing the companion mass has little impact on the primary’s fate as long as the mass ratio M1∕M2 remains less than 1.4–1.5, above which evolution to contact becomes unavoidable. We also find that allowing for systemic mass loss substantially increases the period interval over which ECSN can occur. This change in the binary physics does not however affect the primary mass range. We finally stress that the formation of ECSN progenitors through case A and B mass transfer is very sensitive to adopted binary and stellar physics. Conclusions. Close binaries provide additional channels for ECSN but the parameter space is rather constrained likely making ECSN a rare event.