We study the evolution of close binary systems formed by a normal (solar composition), intermediate-mass-donor star together with a neutron star. We consider models including irradiation feedback and ...evaporation. These nonstandard ingredients deeply modify the mass-transfer stages of these binaries. While models that neglect irradiation feedback undergo continuous, long-standing mass-transfer episodes, models including these effects suffer a number of cycles of mass transfer and detachment. During mass transfer, the systems should reveal themselves as low-mass X-ray binaries (LMXBs), whereas when they are detached they behave as binary radio pulsars. We show that at these stages irradiated models are in a Roche lobe overflow (RLOF) state or in a quasi-RLOF state. Quasi-RLOF stars have radii slightly smaller than their Roche lobes. Remarkably, these conditions are attained for an orbital period as well as donor mass values in the range corresponding to a family of binary radio pulsars known as "redbacks." Thus, redback companions should be quasi-RLOF stars. We show that the characteristics of the redback system PSR J1723-2837 are accounted for by these models. In each mass-transfer cycle these systems should switch from LMXB to binary radio pulsar states with a timescale of approximately one million years. However, there is recent and fast growing evidence of systems switching on far shorter, human timescales. This should be related to instabilities in the accretion disk surrounding the neutron star and/or radio ejection, still to be included in the model having the quasi-RLOF state as a general condition.
ABSTRACT
The standard model of stellar evolution in close binary systems assumes that during mass transfer episodes, the system is in a synchronized and circularized state. Remarkably, the redback ...system PSR J1723–2837 has an orbital period derivative $\dot{P}_{\rm orb}$ too large to be explained by this model. Motivated by this fact, we investigate the action of tidal forces in between two consecutive mass transfer episodes for a system under irradiation feedback, which is a plausible progenitor for PSR J1723–2837. We base our analysis on Hut’s treatment of equilibrium tidal evolution, generalized by considering the donor as a two layers object that may not rotate as a rigid body. We also analyse three different relations for the viscosity with the tidal forcing frequency. We found that the large value measured for $\dot{P}_{\rm orb}$ can be reached by systems where the donor star rotates slower (by few per cent) than the orbit just after mass transfer episodes. Van Staden & Antoniadis have observed this object and reported a lack of synchronism, opposite to that required by the Hut’s theory to account for the observed $\dot{P}_{\rm orb}$. Motivated by this discrepancy, we analyse photometric data obtained by the spacecraft Kepler second mission K2, with the purpose of identifying the periods present in PSR J1723–2837. We notice several periods close to those of the orbit and the rotation. The obtained periods pattern reveals the presence of a more complex phenomenology, which would not be well described in the frame of the weak friction model of equilibrium tides.
ABSTRACT
We study the evolution of close binary systems in order to account for the existence of the recently observed binary system containing the most massive millisecond pulsar ever detected, PSR ...J0740+6620, and its ultra-cool helium white dwarf companion. In order to find a progenitor for this object we compute the evolution of several binary systems composed by a neutron star and a normal donor star employing our stellar code. We assume conservative mass transfer. We also explore the effects of irradiation feedback on the system. We find that irradiated models also provide adequate models for the millisecond pulsar and its companion, so both irradiated and non irradiated systems are good progenitors for PSR J0740+6620. Finally, we obtain a binary system that evolves and accounts for the observational data of the system composed by PSR J0740+6620 (i.e. orbital period, mass, effective temperature and inferred metallicity of the companion, and mass of the neutron star) in a time scale smaller than the age of the Universe. In order to reach an effective temperature as low as observed, the donor star should have an helium envelope as demanded by observations.
ABSTRACT
We present the first spectroscopic orbit of the O-type double-lined star HD 168112 A,B. We analyse 101 high-resolution optical spectra identifying the absorption lines of both components. ...The orbital solution presents a relatively long period, P = 513.52 ± 0.01 d, and a high eccentricity, e = 0.743 ± 0.005. The binary system consists of two very similar stars of minimum masses of ∼25 M⊙, effective temperatures of ∼40 000 K, and surface gravities of ∼3.7 dex. The system has a minimum semimajor axis a sin i ∼ 1000 R⊙. We confirm that the A and B visual components identified via interferometry do correspond to the spectroscopic ones. We also analyse the underlying stellar groups using Gaia DR3 data and ground-based spectroscopy as part of the Villafranca project, determining that NGC 6604 is at a distance of $1942^{+38}_{-36}$ pc and giving spectral classifications for 23 massive stellar systems in Villafranca O-035 and the surrounding Ser OB2 association, for which we provide the most complete census of massive stars to date.
The existence of millisecond pulsars with planet-mass companions in close orbits is challenging from the stellar evolution point of view. We calculate in detail the evolution of binary systems ...self-consistently, including mass transfer, evaporation, and irradiation of the donor by X-ray feedback, demonstrating the existence of a new evolutionary path leading to short periods and compact donors as required by the observations of PSR J1719-1438. We also point out the alternative of an exotic nature of the companion planet-mass star.
ABSTRACT
We present a new spectroscopic orbit of the O-type binary system HD 152147. We identify absorption lines in both components and use their radial velocities to determine the orbit, which ...results in a period of P = 50.2199 ± 0.0007 d, an eccentricity e = 0.738 ± 0.007, and a mean separation between the components of asin i = 151 ± 1 R⊙. Considering that the distance to the system is 1600 pc, this implies an angular separation of ∼0.44 mas, making it suitable for modern interferometric observations. In addition, we determine the fundamental stellar parameters of each component by means of a quantitative spectral analysis. We obtain Ma = 31.9−34.6 M⊙ and Ra = 17−24 R⊙ for the primary, and Mb = 14−15 M⊙ and Rb = 5−10 R⊙ for the secondary. We apply models with rotation to try to characterize the evolutionary status of the HD 152147 system. We find that the two components are compatible with a common age of 4.5 Myr. We also detect variations in the profile of Hα that are not modulated by the orbital cycle. Moreover, TESS photometry also presents intrinsic variability and was analysed for periodicities. We find a most relevant frequency of 20 times the orbital one, in a TESS data set that includes the periastron passage, and we interpret it as a tidally induced pulsation that seems to dissipate on a time-scale shorter than the orbital cycle because it is not present in another TESS data set that nearly covers the apoastron.
Aims. The equation of state calculated by Saumon and collaborators has been adopted in most core-accretion simulations of giant-planet formation performed to date. Since some minor errors have been ...found in their original paper, we present revised simulations of giant-planet formation that considers a corrected equation of state. Methods. We employ the same code as Fortier and collaborators in repeating our previous simulations of the formation of Jupiter. Results. Although the general conclusions of Fortier and collaborators remain valid, we obtain significantly lower core masses and shorter formation times in all cases considered. Conclusions. The minor errors in the previously published equation of state have been shown to affect directly the adiabatic gradient and the specific heat, causing an overestimation of both the core masses and formation times.
We present a set of calculations of the evolution of low-mass, solar composition stars in close binary systems together with a canonical 1.4-M⊙, neutron star (NS). We restrict the initial mass and ...period values to those that give rise to the formation of ultracompact systems or low-mass helium white dwarf (He WD) stars. Specifically, we computed the evolution of 40 systems for which the initial masses of the normal (donor) stars were of 1.00, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00 and 3.50 M⊙, while the range of initial periods covered in this work was from 0.5 to 12 d. Calculations were performed employing the binary hydro code developed by the present authors, which handles the mass transfer rate in a fully implicit way together with state-of-the-art physical ingredients and diffusion processes. In this work we have assumed the standard scheme for the orbital evolution of the binary, considering the usual processes that produce angular momentum losses: mass loss from the system, magnetic braking and gravitational radiation. In the main part of this work we assume that the NS is able to retain only half of the matter coming from the donor star. The range of final masses has been from 0.01961 to 0.34351 M⊙ and periods from 39 min to 187 d. 26 out of the 40 considered systems give rise to the formation of a He WD as a compact remnant. In performing a comparison of our results with observations, we have employed three WD-NS systems, which are among the best known ones. These are PSR J0437−4715, PSR J1012+5307 and PSR B1855+09. In order to obtain good agreement between models and observations we have had to assume that the NS is able to retain only ≈10 per cent of the material released by the donor star. Otherwise, for the cases of PSR J0437−4715 and PSR B1855+09 we would be in conflict with the observed NS masses. For these two objects we have been able to fit WD and NS masses, the orbital period and also the time-scale for cooling of the WD with the evolution of one binary system. For the case of PSR J1012+5307, the problem is more delicate because the object has a mass near the threshold for the occurrence of thermonuclear flashes and the initial period is close to bifurcation point.
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