Formation of the binary pulsars PSR B2303+46 and PSR J1141-6545 - young neutron stars with old white dwarf companions

We have investigated the formation of the binary radio pulsars PSR B2303+46 and PSR J1141-6545 via Monte Carlo simulations of a large number of interacting stars in binary systems. PSR B2303+46 has recently been shown (van Kerkwijk & Kulkarni 1999) to be the first neutron star - white dwarf binary system observed, in which the neutron star was born after the formation of the white dwarf. We discuss the formation process for such a system and are able to put constraints on the parameters of the initial ZAMS binary. We present statistical evidence in favor of a white dwarf companion to the binary pulsar PSR J1141-6545, just recently discovered in the Parkes Multibeam Survey. If this is confirmed by observations this system will be the second one known in which the neutron star was born after its white dwarf companion. We also predict a minimum space velocity of 150 km/s for PSR J1141-6545, and show it must have experienced an asymmetric SN in order to explain its low eccentricity. Finally, we estimate the birthrate of these systems relative to other binary pulsar systems and present the expected distribution of their orbital periods, eccentricities and velocities.Comment: 9 pages, 4 figures, 2 tables, some revisions, accepted for publication in A&A Main Journa

The case of PSR J1911-5958A in the outskirts of NGC 6752: signature of a black hole binary in the cluster core?

We have investigated different scenarios for the origin of the binary millisecond pulsar PSR J1911-5958A in NGC 6752, the most distant pulsar discovered from the core of a globular cluster to date. The hypothesis that it results from a truly primordial binary born in the halo calls for accretion-induced collapse and negligible recoil speed at the moment of neutron star formation. Scattering or exchange interactions off cluster stars are not consistent with both the observed orbital period and its offset position. We show that a binary system of two black holes with (unequal) masses in the range of 3-100 solar masses can live in NGC 6752 until present time and can have propelled PSR J1911-5958A into an eccentric peripheral orbit during the last ~1 Gyr.Comment: Accepted by ApJ Letter. 5 pages, 1 figure, 1 tabl

Formation of undermassive single white dwarfs and the influence of planets on late stellar evolution

We propose a scenario to form low-mass, single, slow rotating white dwarfs from a solar-like star accompanied by a massive planet, or a brown dwarf, in a relatively close orbit (e.g. HD 89707). Such white dwarfs were recently found by Maxted & Marsh (1998). When the solar-like star ascends the giant branch it captures the planet and the subsequent spiral-in phase expels the envelope of the giant leaving a low-mass helium white dwarf remnant. In case the planet evaporizes, or fills its own Roche-lobe, the outcome is a single undermassive white dwarf. The observed distribution of planetary systems supports the applicability of this scenario.Comment: 4 pages, accepted for publication in A&A letter

Recycling Pulsars: spins, masses and ages

Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the (P,Pdot)-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the (P,Pdot)-diagram.Comment: Contributed talk, Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and Opportunities after 80 years", J. van Leeuwen (ed.); 4 pages, 2 figure

Formation of millisecond pulsars. I. Evolution of low-mass X-ray binaries with P > 2 days

We have performed detailed numerical calculations of the non-conservative evolution of close binary systems with low-mass (1.0-2.0 M_sun) donor stars and a 1.3 M_sun accreting neutron star. Rather than using analytical expressions for simple polytropes, we calculated the thermal response of the donor star to mass loss, in order to determine the stability and follow the evolution of the mass transfer. Tidal spin-orbit interactions and Reimers wind mass-loss were also taken into account. We have re-calculated the correlation between orbital period and white dwarf mass in wide binary radio pulsar systems. Furthermore, we find an anti-correlation between orbital period and neutron star mass under the assumption of the "isotropic re-emission" model and compare this result with observations. We conclude that the accretion efficiency of neutron stars is rather low and that they eject a substantial fraction of the transferred material even when accreting at a sub-Eddington level. The mass-transfer rate is a strongly increasing function of initial orbital period and donor star mass. For relatively close systems with light donors (P < 10 days and M_2 < 1.3 M_sun) the mass-transfer rate is sub-Eddington, whereas it can be highly super-Eddington by a factor of 10^4 for wide systems with relatively heavy donor stars (1.6 - 2.0 M_sun) as a result of their deep convective envelopes. We briefly discuss the evolution of X-ray binaries with donor stars in excess of 2 M_sun. Based on our calculations we present evidence that PSR J1603-7202 evolved through a phase with unstable mass transfer from a relatively heavy donor star and therefore is likely to host a CO white dwarf companion.Comment: Accepted for publication in A&A. 18 pages, 6 figures, 2 table

PSR J2019+2425: A Unique Testing Ground for Binary Evolution

If the theoretical relationship between white dwarf mass and orbital period for wide-orbit binary radio pulsars is assumed to be correct, then the neutron star mass of PSR J2019+2425 is shown to be ~1.20 M_sun. Hence the mass of the neutron star in this system prior to the mass transfer phase is expected to have been < 1.1 M_sun. Alternatively this system descends from the accretion induced collapse (AIC) of a massive white dwarf. We estimate the magnetic inclination angles of all the observed wide-orbit low-mass binary pulsars in the Galactic disk using the core-mass period relation and assuming that the spin axis of an accreting neutron star aligns with the orbital angular momentum vector in the recycling process of the pulsar. The large estimated magnetic inclination angle of PSR J2019+2425, in combination with its old age, gives for this system evidence against alignment of the magnetic field axis with the rotational spin axis. However, in the majority of the similar systems the distribution of magnetic inclination angles is concentrated toward low values (if the core-mass period relation is correct) and suggests that alignment has taken place.Comment: 4 pages, 2 figures, accepted for publication in A&A Letter

On the pre-RLO spin-orbit couplings in LMXBs

We investigate the effect of orbital decay caused by nuclear expansion of a (sub)giant star in synchronous binary system. We compare this effect with the presence of a magnetic stellar wind and show that the additional transfer of orbital angular momentum into spin angular momentum is relatively important -- especially since it has been shown that the effect of magnetic braking saturates at short orbital periods

New Direct Observational Evidence for Kicks in SNe

We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141-6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).Comment: 2 pages, to appear in the proceedings of the IAU Colloq. 177 "Pulsar Astronomy - 2000 and beyond

On the non-detection of gamma-rays from energetic millisecond pulsars -- dependence on viewing geometry

Millisecond pulsars (MSPs) and normal non-recycled pulsars are both detected in $\gamma$-rays. However, it appears that a much larger fraction of known energetic and nearby MSPs are detected in $\gamma$-rays, in comparison with normal pulsars, thereby making undetected $\gamma$-ray MSPs exceptions. In this paper, we demonstrate that the viewing angles (i.e. between the pulsar spin axis and the line of sight) are well described by the orbital inclination angles which, for binary MSPs with helium white dwarf companions, can be determined using the relationship between the orbital period and the white dwarf mass. We use the predicted viewing angles, in complement with values obtained from other constraints when available, to identify the causes of non-detection of energetic and nearby MSPs from the point of view of beaming geometry and orientation. We find evidence for slightly different viewing angle distributions, and postulate that energetic and nearby MSPs are mainly undetected in $\gamma$-rays simply because they are seen under unfavourable (i.e. small) viewing angles. We finally discuss the magnetic fields of $\gamma$-ray detected pulsars and show that pulsars which are efficient at converting their rotational energy into $\gamma$-ray emission may have overestimated dipolar magnetic field strengths.Comment: 11 pages, 6 figures. MNRAS, in press. Updated to reflect changes made at the proof stag