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Context. The progenitors of many core-collapse supernovae (CCSNe) are expected to be in binary systems. After the SN explosion in a binary, the companion star may suffer from mass stripping and be shock heated as a result of the impact of the SN ejecta. If the binary system is disrupted by the SN explosion, the companion star is ejected as a runaway star, and in some cases as a hypervelocity star. Aims. By performing a series of three-dimensional (3D) hydrodynamical simulations of the collision of SN ejecta with the companion star, we investigate how CCSN explosions affect their binary companion. Methods. We use the BEC stellar evolution code to construct the detailed companion structure at the moment of SN explosion. The impact of the SN blast wave on the companion star is followed by means of 3D smoothed particle hydrodynamics (SPH) simulations using the Stellar GADGET code. Results. Formain-sequence (MS) companion stars, we find that the amount of removed stellar mass, the resulting impact velocity, and the chemical contamination of the companion that results from the impact of the SN ejecta strongly increases with decreasing binary separation and increasing explosion energy. Their relationship can be approximately fitted by power laws, which is consistent with the results obtained from impact simulations of Type Ia SNe. However, we find that the impact velocity is sensitive to the momentum profile of the outer SN ejecta and, in fact, may decrease with increasing ejecta mass, depending on the modeling of the ejecta. Because most companion stars to Type Ib/c CCSNe are in their MS phase at the moment of the explosion, combined with the strongly decaying impact effects with increasing binary separation, we argue that the majority of these SNe lead to inefficient mass stripping and shock heating of the companion star following the impact of the ejecta. Conclusions. Our simulations show that the impact effects of Type Ib/c SN ejecta on the structure of MS companion stars, and thus their long-term post-explosion evolution, is in general not dramatic. We find that at most 10% of their mass is lost and their resulting impact velocities are less than 100 kms-1. [ABSTRACT FROM AUTHOR]

Context. Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Aims. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities. Methods. Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries. We investigated the mass transfer onto a massive WD (treated as a point mass) in 240 systems with three different types of non-degenerate donor stars: main-sequence stars, red giants, and helium stars. When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) we assumed it collapses to form a NS and we studied the dynamical effects of this implosion on the binary orbit. Subsequently, we followed the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculated the continued LMXB evolution until the end. Results. We show that recycled pulsars may form via AIC from all three types of progenitor systems investigated and find that the final properties of the resulting MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel. However, as a consequence of the fine-tuned mass-transfer rate necessary to make the WD grow in mass, the resultant MSPs created via the AIC channel preferentially form in certain orbital period intervals. In addition, their predicted small space velocities can also be used to identify them observationally. The production time of NSs formed via AIC can exceed 10 Gyr which can therefore explain the existence of relatively young NSs in globular clusters. Our calculations are also applicable to progenitor binaries of SNe Ia under certain conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT Millisecond pulsars are mainly characterized by their spin periods, B-fields and masses - quantities that are largely affected by previous interactions with a companion star in a binary system. In this paper, we investigate the formation mechanism of millisecond pulsars by considering the pulsar recycling process in both intermediate-mass X-ray binaries (IMXBs) and low-mass X-ray binaries (LMXBs). The IMXBs mainly lead to the formation of binary millisecond pulsars with a massive carbon-oxygen (CO) or an oxygen-neon-magnesium white dwarf (ONeMg WD) companion, whereas the LMXBs form recycled pulsars with a helium white dwarf (He WD) companion. We discuss the accretion physics leading to the spin-up line in the [ABSTRACT FROM AUTHOR]

ABSTRACT The recent discovery of a 2 M⊙ binary millisecond pulsar not only has important consequences for the equation of state of nuclear matter at high densities but also raises the interesting question of whether the neutron star PSR J1614−2230 was born massive. The answer is vital for understanding neutron star formation in core collapse supernovae. Furthermore, this system raises interesting issues about the nature of the progenitor binary and how it evolved during its mass-exchanging X-ray phase. In this paper we discuss the progenitor evolution of PSR J1614−2230. We have performed detailed stellar evolution modelling of intermediate-mass X-ray binaries undergoing Case A Roche lobe overflow (RLO) and applied an analytic parametrization for calculating the outcome of either a common envelope evolution or the highly super-Eddington isotropic re-emission mode. We find two viable possibilities for the formation of the PSR J1614−2230 system: either it contained a 2.2-2.6 M⊙ giant donor star and evolved through a common envelope and spiral-in phase or, more likely, it descended from a close binary system with a 4.0-5.0 M⊙ main-sequence donor star via Case A RLO. We conclude that the neutron star must have been born with a mass of either ∼1.95 M⊙ or 1.7 ± 0.15 M⊙, which significantly exceeds neutron star birth masses in previously discovered radio pulsar systems. Based on the expected neutron star birth masses from considerations of stellar evolution and explosion models, we find it likely that the progenitor star of PSR J1614−2230 was more massive than 20 M⊙. [ABSTRACT FROM AUTHOR]

ABSTRACT We have performed a detailed population synthesis on a large number (2 × 10[sup 7]) of binary systems in order to investigate the properties of massive double degenerate binaries. We have included new important results in our input physics in order to obtain more reliable estimates of the merging time-scales and relative formation rates. These improvements include refined treatment of the binding energy in a common envelope, helium star evolution and reduced kicks imparted to new-born black holes. The discovery and observations of gamma-ray burst afterglows and the identification of host galaxies have allowed comparisons of theoretical distributions of merger sites with the observed distribution of afterglow positions relative to host galaxies. To help investigate the physical nature of short- and long-duration gamma-ray bursts, we compute the distances of merging neutron stars (NS) and/or black holes (BH) from the centres of their host galaxies, as predicted by their formation scenario combined with motion in galactic potentials. Furthermore, we estimate the formation rate and merging rate of these massive double degenerate binaries. The latter is very important for the prospects of detecting gravitational waves with LIGO/VIRGO. We find that the expected detection rate for LIGO II is ∼850 yr[sup -1] for galactic field sources and that this rate is completely dominated by merging double black hole (BHBH) binaries. Even LIGO I may detect such an event (∼0.25 yr[sup -1]) . Our preferred model estimates the Galactic field double neutron star (NSNS) merger rate to be ∼1.5 × 10[sup -6] yr[sup -1] . For BHBH systems this model predicts a merger rate of ∼9.7 × 10[sup -6] yr[sup -1] . Our studies also reveal an accumulating numerous population of very wide-orbit BHBH systems which never merge (τ≫τ[sub Hubble]) . [ABSTRACT FROM AUTHOR]

We have analysed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (<=2.0 M⊙) unevolved star and that the eccentricity of the orbit is 0.94±0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average, we find that a kick of ∼740 km s-1 is needed to account for the recently measured radial velocity of +430 km s-1 (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is ∼500 km s-1. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of ∼60 000 yr. Furthermore, we predict that the companion star has lost ∼10 per cent of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion. [ABSTRACT FROM AUTHOR]

Neutron star (NS) mergers where both stars have negligible spins are commonly considered as the most likely 'standard' case. In globular clusters, however, the majority of NSs have been spun up to millisecond (ms) periods and, based on observed systems, we estimate that a non-negligible fraction of all double NS mergers (⁠|$\sim 4\pm 2\, {{\ \rm per\ cent}}$|⁠) contains one component with a spin of a (few) ms. We use the Lagrangian numerical relativity code SPHINCS_BSSN  to simulate mergers where one star has no spin and the other has a dimensionless spin parameter of χ = 0.5. Such mergers exhibit several distinct signatures compared to irrotational cases. They form only one, very pronounced spiral arm and they dynamically eject an order of magnitude more mass of unshocked material at the original, very low electron fraction. One can therefore expect particularly bright, red kilonovae. Overall, the spinning case collisions are substantially less violent and they eject smaller amounts of shock-generated semirelativistic material. Therefore, the ejecta produce a weaker blue/ultraviolet kilonova precursor signal, but – since the total amount is larger – brighter kilonova afterglows months after the merger. The spinning cases also have significantly more fallback accretion and thus could power late-time X-ray flares. Since the post-merger remnant loses energy and angular momentum significantly less efficiently to gravitational waves, such systems can delay a potential collapse to a black hole and are therefore candidates for merger-triggered gamma-ray bursts with longer emission time-scales. [ABSTRACT FROM AUTHOR]

Context. Ultra-luminous X-ray sources (ULXs) are those X-ray sources located away from the centre of their host galaxy with luminosities exceeding the Eddington limit of a stellar-mass black hole (LX >  1039 erg s−1). Observed X-ray variability suggests that ULXs are X-ray binary systems. The discovery of X-ray pulsations in some of these objects (e.g. M82 X-2) suggests that a certain fraction of the ULX population may have a neutron star as the accretor. Aims. We present systematic modelling of low- and intermediate-mass X-ray binaries (LMXBs and IMXBs; donor-star mass range 0.92–8.0 M⊙ and neutron-star accretors) to explain the formation of this sub-population of ULXs. Methods. Using MESA, we explored the allowed initial parameter space of binary systems consisting of a neutron star and a low- or intermediate-mass donor star that could explain the observed properties of ULXs. These donors are transferring mass at super-Eddington rates while the accretion is limited locally in the accretion disc by the Eddington limit. Thus, our simulations take into account beaming effects and also include stellar rotation, tides, general angular momentum losses, and a detailed and self-consistent calculation of the mass-transfer rate. Results. Exploring the initial parameters that lead to the formation of neutron-star ULXs, we study the conditions that lead to dynamical stability of these systems, which depends strongly on the response of the donor star to mass loss. Using two values for the initial neutron star mass (1.3 M⊙ and 2.0 M⊙), we present two sets of mass-transfer calculation grids for comparison with observations of NS ULXs. We find that LMXBs/IMXBs can produce NS-ULXs with typical time-averaged isotropic-equivalent X-ray luminosities of between 1039 and 1041 erg s−1 on a timescale of up to ∼1.0 Myr for the lower luminosities. Finally, we estimate their likelihood of detection, the types of white-dwarf remnants left behind by the donors, and the total amount of mass accreted by the neutron stars. Conclusions. We show that observed super-Eddington luminosities can be achieved in LMXBs/IMXBs undergoing non-conservative mass transfer while assuming geometrical beaming. We also compare our results to the observed pulsating ULXs and infer their initial parameters. Our results suggest that a large subset of the observed pulsating ULX population can be explained by LMXBs/IMXBs in a super-Eddington mass-transfer phase. [ABSTRACT FROM AUTHOR]

Radio pulsars found in binary systems with short orbital periods are usually fast spinning as a consequence of recycling via mass transfer from their companion stars; this process is also thought to decrease the magnetic field of the neutron star being recycled. Here, we report on timing observations of the recently discovered binary PSR J1755-2550 and find that this pulsar is an exception: with a characteristic age of 2.1Myr, it is relatively young; furthermore, with a spin period of 315 ms and a surface magnetic field strength at its poles of 0.88 x 1012 G, the pulsar shows no sign of having been recycled. Based on its timing and orbital characteristics, the pulsar either has a massive white dwarf (WD) or a neutron star (NS) companion. To distinguish between these two cases, we searched radio observations for a potential recycled pulsar companion and analysed archival optical data for a potential WD companion. Neither work returned conclusive detections. We apply population synthesis modelling and find that both solutions are roughly equally probable. Our population synthesis also predicts a minimum mass of 0.90Mʘ for the companion star to PSR J1755-2550 and we simulate the systemic runaway velocities for the resulting WDNS systems which may merge and possibly produce Ca-rich supernovae. Whether PSR J1755-2550 hosts a WD or a NS companion star, it is certainly a member of a rare subpopulation of binary radio pulsars. [ABSTRACT FROM AUTHOR]

Context. A large number of low-mass (≲0.20 M☉) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show pulsations or to have a main-sequence star companion. There appear to be discrepancies between the current theoretical modelling of such lowmass He WDs and a number of key observed cases, indicating that their formation scenario yet remains to be fully understood. Aims. Here we investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). Our prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Our calculations are then compared to the most recent observational data. Methods. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs with different initial values of donor star mass, neutron star mass, orbital period, and strength of magnetic braking. Subsequently, we followed the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. Results. We find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Δtproto = 0.5-2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The lowest WD mass for developing shell flashes is ∼0.21 M☉ for progenitor stars of mass M2 ⩽ 1.5 M☉ (and ∼0.18 M☉for M2 = 1.6 M☉). Conclusions. The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very low surface gravities and high effective temperatures. We find no evidence for Δtproto to depend on the occurrence of flashes and thus question the suggested dichotomy in thermal evolution of proto-WDs. [ABSTRACT FROM AUTHOR]

Context. Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs) that have been spun up to high rotation rates via accretion of matter from a companion star in a low-mass X-ray binary (LMXB). This scenario has been strongly supported by various pieces of observational evidence. However, many details of this recycling scenario remain to be understood. Aims. Here we investigate binary evolution in close LMXBs to study the formation of radio MSPs with low-mass helium white dwarf companions (He WDs) in tight binaries with orbital periods Porb ≃ 2-9 h. In particular, we examine i) if the observed systems can be reproduced by theoretical modelling using standard prescriptions of orbital angular momentum losses (i.e. with respect to the nature and the strength of magnetic braking), ii) if our computations of the Roche-lobe detachments can match the observed orbital periods, and iii) if the correlation between WD mass and orbital period (MWD, Porb) is valid for systems with Porb <2 days. Methods. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in ∼400 close LMXB systems with different initial values of donor star mass, NS mass, orbital period, and the so-called γ-index of magnetic braking. Subsequently, we followed the orbital and the interior evolution of the detached low-mass (proto) He WDs, including stages with residual shell hydrogen burning. Results. We find that severe fine-tuning is necessary to reproduce the observed MSPs in tight binaries with He WD companions of mass <0.20 M☉, which suggests that something needs to be modified or is missing in the standard input physics of LMXB modelling. Results from previous independent studies support this conclusion. We demonstrate that the theoretically calculated (MWD, Porb)- relation is in general also valid for systems with Porb < 2 days, although with a large scatter in HeWD masses between 0.15-0.20 M☉. The results of the thermal evolution of the (proto) He WDs are reported in a follow-up paper (Paper II). [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

We report on a high-precision timing analysis and an astrophysical study of the binary millisecond pulsar, PSR J1909−3744, motivated by the accumulation of data with well improved quality over the past decade. Using 15 yr of observations with the Nançay Radio Telescope, we achieve a timing precision of approximately 100 ns. We verify our timing results by using both broad-band and sub-band template matching methods to create the pulse time-of-arrivals. Compared with previous studies, we improve the measurement precision of secular changes in orbital period and projected semimajor axis. We show that these variations are both dominated by the relative motion between the pulsar system and the Solar system barycentre. Additionally, we identified four possible solutions to the ascending node of the pulsar orbit, and measured a precise kinetic distance of the system. Using our timing measurements and published optical observations, we investigate the binary history of this system using the stellar evolution code mesa , and discuss solutions based on detailed WD cooling at the edge of the WD age dichotomy paradigm. We determine the 3D velocity of the system and show that it has been undergoing a highly eccentric orbit around the centre of our Galaxy. Furthermore, we set up a constraint over dipolar gravitational radiation with the system, which is complementary to previous studies given the mass of the pulsar. We also obtain a new limit on the parametrized post-Newtonian parameter, |$\left| \hat\alpha_1 \right|$| < 2.1 × 10−5 at 95 per cent confidence level, which is fractionally better than previous best published value and achieved with a more concrete method. [ABSTRACT FROM AUTHOR]

Radio pulsars in short-period eccentric binary orbits can be used to study both gravitational dynamics and binary evolution. The binary system containing PSR J1141–6545 includes a massive white dwarf (WD) companion that formed before the gravitationally bound young radio pulsar. We observed a temporal evolution of the orbital inclination of this pulsar that we infer is caused by a combination of a Newtonian quadrupole moment and Lense–Thirring (LT) precession of the orbit resulting from rapid rotation of the WD. LT precession, an effect of relativistic frame dragging, is a prediction of general relativity. This detection is consistent with an evolutionary scenario in which the WD accreted matter from the pulsar progenitor, spinning up the WD to a period of <200 seconds. [ABSTRACT FROM AUTHOR]

We determine the properties of the binary star V106 in the old open cluster NGC 6791 . We identify the system to be a blue straggler cluster member by using a combination of ground-based and Kepler photometry and multi-epoch spectroscopy. The properties of the primary component are found to be |$M_{\rm p}\sim 1.67\, \rm M_{\odot }$|⁠, more massive than the cluster turn-off, with |$R_{\rm p}\sim 1.91\, \rm R_{\odot }$| and T eff= 7110 ± 100 K. The secondary component is highly oversized and overluminous for its low mass with |$M_{\rm s}\sim 0.182\, \rm M_{\odot }$|⁠, |$R_{\rm s}\sim 0.864\, \rm R_{\odot }$|⁠, and T eff= 6875 ± 200 K. We identify this secondary star as a bloated (proto) extremely low-mass helium white dwarf. These properties of V106 suggest that it represents a typical Algol-paradox system and that it evolved through a mass-transfer phase, which provides insight into its past evolution. We present a detailed binary stellar evolution model for the formation of V106 using the mesa code and find that the mass-transfer phase only ceased about |$40\, {\rm Myr}$| ago. Due to the short orbital period (P = 1.4463 d), another mass-transfer phase is unavoidable once the current primary star evolves towards the red giant phase. We argue that V106 will evolve through a common-envelope phase within the next |$100\, {\rm Myr}$| and merge to become a single overmassive giant. The high mass will make it appear young for its true age, which is revealed by the cluster properties. Therefore, V106 is potentially a prototype progenitor of old field giants masquerading as young. [ABSTRACT FROM AUTHOR]

To confirm the nature of the donor star in the ultracompact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3000-10 000 Å) with the Hubble Space Telescope / Space Telescope Imaging Spectrograph. We find no strong emission or absorption features in the spectrum of X9. In particular, we place 3σ upper limits on the Hα and He II λ4686 emission line equivalent widths -EWHα ≲ 14Å and -EWHe II ≲ 9Å, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for L2-10keV ≈ 1033-1034 erg s-1 is typically -EWHα ~ 50 Å). This supports our previous suggestion, by Bahramian et al., of an H-poor donor in X9. We perform timing analysis on archival far-ultraviolet, V- and I-band data to search for periodicities. In the optical bands, we recover the 7-d superorbital period initially discovered in X-rays, but we do not recover the orbital period. In the far-ultraviolet, we find evidence for a 27.2 min period (shorter than the 28.2 min period seen in X-rays). We find that either a neutron star or black hole could explain the observed properties of X9. We also perform binary evolution calculations, showing that the formation of an initial black hole/ He-star binary early in the life of a globular cluster could evolve into a present-day system such as X9 (should the compact object in this system indeed be a black hole) via mass-transfer driven by gravitational wave radiation. [ABSTRACT FROM AUTHOR]

We present a high-precision timing analysis of PSR J1933-6211, a millisecond pulsar with a 3.5 ms spin period and a white dwarf (WD) companion, using data from the Parkes radio telescope. Since we have accurately measured the polarization properties of this pulsar, we have applied the matrix template matching approach in which the times of arrival are measured using full polarimetric information. We achieved aweighted root-mean-square timing residuals of the timing residuals of 1.23 µs, 15.5 per cent improvement compared to the total intensity timing analysis. After studying the scintillation properties of this pulsar, we put constraints on the inclination angle of the system. Based on these measurements and on χ² mapping we put a 2σ upper limit on the companion mass (0.44 M⊙). Since this mass limit cannot reveal the nature of the companion, we further investigate the possibility of the companion to be a He WD. Applying the orbital period-mass relation for such WDs, we conclude that the mass of a He WD companion would be about 0.26±0.01 M⊙, which combined with the measured mass function and orbital inclination limits, would lead to a light pulsar mass ≤ 1.0M⊙. This result seems unlikely based on current neutron star formation models and we therefore conclude that PSR J1933-6211 most likely has a CO WD companion, which allows for a solution with a more massive pulsar. [ABSTRACT FROM AUTHOR]

In a search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multiwavelength campaign: in the X-ray band with Swift and XMM–Newton; in the infrared and optical with OAGH, ESO-NTT and IAC80; and in the radio with ATCA observations. We also used archival hard X-ray data obtained by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source. We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as being caused by the binary system orbital period of ∼1.64 h and the white dwarf spin period of ∼1.47 h. A strong flux modulation at ∼15 h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hβ, He I and He II emission lines that are Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827 accretes through a disc-less configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system on its way to reaching synchronism. Regarding the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting for ∼600 s, similar to what is observed in transitional millisecond pulsars during the subluminous disc state: this observation possibly means that this source can be associated with the Fermi-LAT source. [ABSTRACT FROM AUTHOR]

We report the discovery and the results of follow-up timing observations of PSR J2045+3633 and PSR J2053+4650, two binary pulsars found in the Northern High Time Resolution Universe pulsar survey being carried out with the Effelsberg radio telescope. Having spin periods of 31.7 and 12.6 ms, respectively, and both with massive white dwarf companions,Mc >0.8M☉, the pulsars can be classified as mildly recycled. PSR J2045+3633 is remarkable due to its orbital period (32.3 d) and eccentricity e=0.017 212 44(5), which is amongst the largest ever measured for this class. After almost two years of timing, the large eccentricity has allowed the measurement of the rate of advance of periastron at the 5σ level, 0.0010(2)°yr-1. Combining this with a detection of the orthometric amplitude of the Shapiro delay, we obtained the following constraints on the component masses (within general relativity):Mp = 1.33-0.28+0.30M☉; andMc = 0.94-0.13+0.14M☉. PSR J2053+4650 has a 2.45 d circular orbit inclined to the plane of the sky at an angle i = 85.0-0.9+0.8 deg. In this nearly edge-on case the masses can be obtained from the Shapiro delay alone. Our timing observations resulted in a significant detection of this effect giving: Mp = 1.40-0.18+0.21M☉; and Mc = 0.86-0.6+0.07M☉. [ABSTRACT FROM AUTHOR]

Timing results for the black-widow pulsar J2051-0827 are presented, using a 21 year data set from four European Pulsar Timing Array telescopes and the Parkes radio telescope. This data set, which is the longest published to date for a black-widow system, allows for an improved analysis that addresses previously unknown biases. While secular variations, as identified in previous analyses, are recovered, short-term variations are detected for the first time. Concurrently, a significant decrease of ~2.5 × 10-3 cm-3 pc in the dispersion measure associated with PSR J2051-0827 is measured for the first time and improvements are also made to estimates of the proper motion. Finally, PSR J2051-0827 is shown to have entered a relatively stable state suggesting the possibility of its eventual inclusion in pulsar timing arrays. [ABSTRACT FROM AUTHOR]

We report on 22 yr of radio timing observations of the millisecond pulsar J1024-0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869-0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = -1.0, Teff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024-0719. We conclude that PSR J1024-0719 and 2MASS J10243869-0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (Pb >200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s-1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024-0719 in light of its inclusion in pulsar timing arrays. [ABSTRACT FROM AUTHOR]

We present Hubble Space Telescope UV spectra of the 4.6-h-period double white dwarf SDSS J125733.63+542850.5. Combined with Sloan Digital Sky Survey optical data, these reveal that the massive white dwarf (secondary) has an effective temperature T2 = 13 030 ± 70 ± 150 K and a surface gravity log g2 = 8.73 ± 0.05 ± 0.05 (statistical and systematic uncertainties, respectively), leading to a mass of M2 = 1.06 M⊙. The temperature of the extremely low-mass white dwarf (primary) is substantially lower at T1 = 6400 ± 37 ± 50 K, while its surface gravity is poorly constrained by the data. The relative flux contribution of the two white dwarfs across the spectrum provides a radius ratio of R1/R2 ≃ 4.2, which, together with evolutionary models, allows us to calculate the cooling ages. The secondary massive white dwarf has a cooling age of ~1 Gyr, while that of the primary low-mass white dwarf is likely to be much longer, possibly ≳5 Gyr, depending on its mass and the strength of chemical diffusion. These results unexpectedly suggest that the low-mass white dwarf formed long before the massive white dwarf, a puzzling discovery which poses a paradox for binary evolution. [ABSTRACT FROM AUTHOR]

Rotation-powered millisecond radio pulsars have been spun up to their present spin period by a 108-109 yr long X-ray-bright phase of accretion of matter and angular momentum in a low-to-intermediate mass binary system. Recently, the discovery of transitional pulsars that alternate cyclically between accretion and rotation-powered states on time scales of a few years or shorter, has demonstrated this evolutionary scenario. Here, we present a thorough statistical analysis of the spin distributions of the various classes of millisecond pulsars to assess the evolution of their spin period between the different stages. Accreting sources that showed oscillations exclusively during thermonuclear type I X-ray bursts (nuclear-powered millisecond pulsars) are found to be significantly faster than rotation-powered sources, while accreting sources that possess a magnetosphere and show coherent pulsations (accreting millisecond pulsars) are not. On the other hand, if accreting millisecond pulsars and eclipsing rotation-powered millisecond pulsars form a common class of transitional pulsars, these are shown to have a spin distribution intermediate between the faster nuclear-powered millisecond pulsars and the slower non-eclipsing rotation-powered millisecond pulsars. We interpret these findings in terms of a spin-down due to the decreasing mass-accretion rate during the latest stages of the accretion phase, and in terms of the different orbital evolutionary channels mapped by the various classes of pulsars. We summarize possible instrumental selection effects, showing that even if an unbiased sample of pulsars is still lacking, their influence on the results of the presented analysis is reduced by recent improvements in instrumentation and searching techniques. [ABSTRACT FROM AUTHOR]

This work aims to present our current best physical understanding of common-envelope evolution (CEE). We highlight areas of consensus and disagreement, and stress ideas which should point the way forward for progress in this important but long-standing and largely unconquered problem. Unusually for CEE-related work, we mostly try to avoid relying on results from population synthesis or observations, in order to avoid potentially being misled by previous misunderstandings. As far as possible we debate all the relevant issues starting from physics alone, all the way from the evolution of the binary system immediately before CEE begins to the processes which might occur just after the ejection of the envelope. In particular, we include extensive discussion about the energy sources and sinks operating in CEE, and hence examine the foundations of the standard energy formalism. Special attention is also given to comparing the results of hydrodynamic simulations from different groups and to discussing the potential effect of initial conditions on the differences in the outcomes. We compare current numerical techniques for the problem of CEE and also whether more appropriate tools could and should be produced (including new formulations of computational hydrodynamics, and attempts to include 3D processes within 1D codes). Finally we explore new ways to link CEE with observations. We compare previous simulations of CEE to the recent outburst from V1309 Sco, and discuss to what extent post-common-envelope binaries and nebulae can provide information, e.g. from binary eccentricities, which is not currently being fully exploited. [ABSTRACT FROM AUTHOR]

ABSTRACT PSR J1738+0333 is one of the four millisecond pulsars known to be orbited by a white dwarf companion bright enough for optical spectroscopy. Of these, it has the shortest orbital period, making it especially interesting for a range of astrophysical and gravity related questions. We present a spectroscopic and photometric study of the white dwarf companion and infer its radial-velocity curve, effective temperature, surface gravity and luminosity. We find that the white dwarf has properties consistent with those of low-mass white dwarfs with thick hydrogen envelopes, and use the corresponding mass-radius relation to infer its mass; M⊙. Combined with the mass ratio q= 8.1 ± 0.2 inferred from the radial velocities and the precise pulsar timing ephemeris, the neutron star mass is constrained to M⊙. Contrary to expectations, the latter is only slightly above the Chandrasekhar limit. We find that, even if the birth mass of the neutron star was only 1.20 M⊙, more than 60 per cent of the matter that left the surface of the white dwarf progenitor escaped the system. The accurate determination of the component masses transforms this system in a laboratory for fundamental physics by constraining the orbital decay predicted by general relativity. Currently, the agreement is within 1σ of the observed decay. Further radio timing observations will allow precise tests of white dwarf models, assuming the validity of general relativity. [ABSTRACT FROM AUTHOR]

ABSTRACT We report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657−415 obtained in the H band using ISAAC on the Very Large Telescope. Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s−1. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M⊙ and a mass of 14.3 ± 0.8 M⊙ for the Ofpe/WN9 highly evolved donor star. OAO 1657−415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657−415 becomes the ninth with a dynamically determined NS mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657−415 is much more highly evolved than the majority of the supergiant donors in other HMXBs, joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres. Considering the evolutionary development of OAO 1657−415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor's envelope via spiral-in, ruling out a common envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO 1657−415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657−415 current orbital configuration. [ABSTRACT FROM AUTHOR]