He star evolutionary channel to intermediate-mass binary pulsar PSR J1802-2124

¹ School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, PR China
² Department of Physics, Shangqiu Normal University, Shangqiu 476000, PR China
³ Department of Astronomy, Nanjing University, Nanjing 210093, PR China
⁴ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, PR China
e-mail: chenwc@nju.edu.cn

Received: 18 January 2011
Accepted: 19 April 2011

Abstract

Context. The intermediate-mass binary pulsars (IMBPs) are characterized by relatively long spin periods (10 − 200 ms) and massive (≳ 0.4   M_⊙) white dwarf (WD) companions. Recently, precise mass measurements have been performed for the pulsar and the WD in the IMBP PSR J1802-2124. Some observed properties, such as the low mass of the pulsar, the high mass of the WD, the moderately long spin period, and the tight orbit, imply that this system has undergone a peculiar formation mechanism.

Aims. In this work, we attempt to simulate the detailed evolutionary history of PSR J1802-2124.

Methods. We propose that a binary system consisting of a neutron star (NS, of mass 1.3   M_⊙) and an He star (of mass 1.0   M_⊙), and with an initial orbital period of 0.5 d, may have been the progenitor of PSR J1802-2124. Once the He star overflows its Roche lobe, He-rich material is transferred onto the NS at a relatively high rate of  ~10^-7−10^-6   M_⊙   yr^-1, which is significantly higher than the Eddington accretion rate. A large amount of the transferred material is ejected from the vicinity of the NS by radiation pressure and results in the birth of a mildly recycled pulsar.

Results. Our simulated results are consistent with the observed parameters of PSR J1802-2124. Therefore, we argue that the NS + He star evolutionary channel may be responsible for the formation of most IMBPs with orbital periods  ≲ 3   d.