Formation of Millisecond Pulsars From Intermediate- And Low-Mass X-Ray Binaries

Shao, Yong; Li, Xiangdong

doi:10.1088/0004-637x/756/1/85

Cited by 51 publications

(46 citation statements)

References 107 publications

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“…For the formation of binary MSPs, this relation proves to be very important because it provides a correlation between the mass of the newly formed WD and P orb following the mass transfer episode (Savonije 1987;Joss et al 1987;Rappaport et al 1995;Tauris & Savonije 1999;Nelson et al 2004;De Vito & Benvenuto 2010;Lin et al 2011;Shao & Li 2012;Jia & Li 2014;Istrate et al 2014a). Figure 19 shows the (M WD , P orb )-relation for all the models computed in this work.…”

Section: Relation Of Mass To Orbital Period In Wdsmentioning

confidence: 87%

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Istrate

Marchant

Tauris

et al. 2016

A&A

193

321

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A large number of extremely low-mass helium white dwarfs (ELM WDs) have been discovered in recent years. The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system. Here, we investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities. We study for the first time the combined effects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs. We present state-of-the-art binary stellar evolution models computed with MESA for metallicities of Z = 0.02, 0.01, 0.001 and 0.0002, producing WDs with masses between ∼0.16−0.45 M . Our results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience hydrogen shell flashes. The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars. In addition, we confirm that the threshold mass at which this dichotomy occurs depends on metallicity. Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances, i.e. the observed presence of metals in their atmospheres. We predict that these proto-WDs have helium-rich envelopes through a significant part of their lifetime. This is of great importance as helium is a crucial ingredient in the driving of the κ-mechanism suggested for the newly observed ELM proto-WD pulsators. However, we find that the number of hydrogen shell flashes and, as a result, the hydrogen envelope mass at the beginning of the cooling track, are not influenced significantly by rotational mixing. In addition to being dependent on proto-WD mass and metallicity, the hydrogen envelope mass of the newly formed proto-WDs depends on whether or not the donor star experiences a temporary contraction when the H-burning shell crosses the hydrogen discontinuity left behind by the convective envelope. The hydrogen envelope at detachment, although small compared to the total mass of the WD, contains enough angular momentum such that the spin frequency of the resulting WD on the cooling track is well above the orbital frequency.

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Section: Relation Of Mass To Orbital Period In Wdsmentioning

confidence: 87%

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Istrate

Marchant

Tauris

et al. 2016

A&A

193

321

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“…This relationship is very important for the formation of binary MSPs because it results in a unique relation between their orbital period (P orb ) and WD mass (M WD ) following the LMXB mass-transfer phase (Savonije 1987;Joss et al 1987;Rappaport et al 1995;Tauris & Savonije 1999;Nelson et al 2004;De Vito & Benvenuto 2010;Shao & Li 2012). The masses of the He WD companions are expected to be between 0.13 < M WD /M < 0.46.…”

Section: The (M Wd P Orb )-Relation For Tight Orbitsmentioning

confidence: 99%

The formation of low-mass helium white dwarfs orbiting pulsars

Istrate

Tauris

Langer

2014

A&A

117

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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 P orb 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 (M WD , P orb ) is valid for systems with P orb < 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 (M WD , P orb )-relation is in general also valid for systems with P orb < 2 days, although with a large scatter in He WD 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).

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“…3, we compare the P f −M WD relations with two different initial NS mass of 1.4 and 2.0 M ⊙ . Though the increase in the NS mass may influence the initial parameter space to form BMSPs (Shao & Li 2012), it barely affects the final P f − M WD relation (De Vito & Benvenuto 2010), so we cannot tell the initial NS mass simply from the current WD mass.…”

Section: The Initial Ns Massmentioning

confidence: 99%

Formation of Millisecond Pulsars With Low-Mass Helium White Dwarf Companions in Very Compact Binaries

Jia

2014

ApJ

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Binary millisecond pulsars (BMSPs) are thought to have evolved from lowmass X-ray binaries (LMXBs). If the mass transfer in LMXBs is driven by nuclear evolution of the donor star, the final orbital period is predicted to be well correlated with the mass of the white dwarf (WD), which is the degenerate He core of the donor. Here we show that this relation can be extended to very small WD mass (∼ 0.14 − 0.17 M ⊙ ) and narrow orbital period (about a few hours), mainly depending on the metallicities of the donor stars. There is also discontinuity in the relation, which is due to the temporary contraction of the donor when the H-burning shell crosses the hydrogen discontinuity. BMSPs with low-mass He WD companions in very compact binaries can be accounted for if the progenitor binary experienced very late Case A mass transfer. The WD companion of PSR J1738+0333 is likely to evolve from a Pop II star. For PSR J0348+0432, to explain its extreme compact orbit in the Roche lobe-decoupling phase, even lower metallicity (Z = 0.0001) is required.

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Formation of Millisecond Pulsars From Intermediate- And Low-Mass X-Ray Binaries

Cited by 51 publications

References 107 publications

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

The formation of low-mass helium white dwarfs orbiting pulsars

Formation of Millisecond Pulsars With Low-Mass Helium White Dwarf Companions in Very Compact Binaries

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