Neutron star retention and millisecond pulsar production in globular clusters

We investigate the conditions by which neutron star retention in globular clusters is favoured. We find that neutron stars formed in massive binaries are far more likely to be retained. Such binaries are likely to then evolve into contact before encountering other stars, possibly producing a single neutron star after a common envelope phase. A large fraction of the single neutron stars in globular clusters are then likely to exchange into binaries containing moderate-mass main-sequence stars, replacing the lower-mass components of the original systems. These binaries will become intermediate-mass X-ray binaries (IMXBs), once the moderate-mass star evolves off the main sequence, as mass is transferred on to the neutron star, possibly spinning it up in the process. Such systems may be responsible for the population of millisecond pulsars (MSPs) that has been observed in globular clusters. Additionally, the period of mass-transfer (and thus X-ray visibility) in the vast majority of such systems will have occurred 5–10 Gyr ago, thus explaining the observed relative paucity of X-ray binaries today, given the MSP population.     

High-velocity stars from decay of small stellar systems

In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3 ≤  N  ≤ 10, and various mass spectra, initial velocities and initial configurations). The numerical treatment uses the CHAIN1 code (Mikkola &38; Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s⁻¹. These numerical experiments confirm that small N -body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s⁻¹ is ∼1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc.     

The polarimetric nature of HD 108

V -band polarimetric observations of HD 108 were obtained during 1994 August and September. This is the first time that the temporal polarimetric variability of this star has been investigated. Its percentage polarization and position angle vary randomly, and no evidence of its proposed binary nature is detected. The random variability is consistent with that seen for previously observed Wolf–Rayet stars and OB supergiants. Nightly variations do show some systematic behaviour consistent with the blob ejection model of Underhill & Fehey (1984). From the data it is estimated that the mass-loss rate resulting from blobs is ∼1-10⁻⁷ M⊙ yr⁻¹. The total mass-loss rate of the star is estimated to be ∼1-10⁻⁵ M⊙ yr⁻¹. The stellar rotation rate is estimated to be V _rot∼400 km s⁻¹ with an inclination of i <20c. The data are also interpreted in terms of perturbations occurring in an equatorial disc plus bipolar jets viewed equatorially (Underhill 1994). It is found that the perturbation mass-loss rate is about ∼3-10⁻⁷ M⊙ yr⁻¹, giving a total mass-loss rate for the star of 13-10⁻⁵ M⊙ yr⁻¹. Both models are consistent with HD 108 being an OB supergiant or of the class Ofpe/WR9.     

恒星的非径向脉动和模式证认

介绍了恒星非径向脉动的一般特性和可观测特征．着重评述早型恒星非径向脉动研究的最新进展以及非径向脉动模式证认的各种方法．     

Is IRAS 03134 + 5958 a Herbig-Haro object?

The source IRAS 03134 + 5958 identified by Iyengar & Verma (1984) on the Palomar Observatory Sky Survey (POSS) prints with a nonstellar optical object with [P – R]≃ 5.3 ± 1.5 is near the edge of Lynds dark cloud No. 1384 and is either embedded in or behind the cloud. The galactic latitude of this source (b ^II = 2‡.3), its positionvis-a-vis the Lynds dark cloud, its nonstellar appearance, high [P – R] colour and its far-infrared spectrum, all suggest the possibility of its being a Herbig-Haro (HH) object. To test this possibility we undertook measurements of its proper motion and variability (two of the characteristic properties of HH objects). These yield μ_a = (3.6 ± 2.3) arcsec/century and μ_δ= (−1.2 ± 2.0) arcsec/century for its proper motion. The source reveals large variation in brightness between 1950 and 1954. Optical line studies of the source are required to confirm its classification as an HH object.     

Relation of Velocity Distribution and Mass for DA White Dwarfstwo

White dwarfs are the evolutionary endpoint of the low-and-medium mass stars. In the studies of white dwarfs, the mass of white dwarf is an important physical parameter. In this paper, we give an analysis about the velocity distribution of DA white dwarfs in the Sloan Digital Sky Survey (SDSS), and hope to find the relation between mass and velocity distribution of white dwarfs. We get the radial velocity and tangential velocity of every DA white dwarf according to their proper motion and spectral shift. Through analyzing the velocity distribution of DA white dwarfs, we find that the small-mass white dwarfs, which are produced from the single-star evolution channel, have a relatively large velocity dispersion.     

Spectral properties of the X-ray binary pulsar LMC X-4 during different Intensity states

We present spectral variations of the binary X-ray pulsar LMC X-4 observed with the RXTE/PCA during different phases of its 30.5 day long third period. Only out-of-eclipse data were used for this study. The 3–25 keV spectrum, modeled with high energy cut-off power-law and iron line emission is found to show strong dependence on the intensity state. Correlations between the Fe line emission flux and different parameters of the continuum are presented here.     

CCD photometry of asteroids (58) Concordia, (360) Carlova and (405) Thia

Three selected asteroids, numbered 58, 360 and405, were observed during 2000at Yunnan Observatory, China. Thenew lightcurves are presented inthis paper. The synodic period of (58)Concordia is estimated as 9.90 ± 0.01hfor the first time. The synodic period of (405) Thia derived from ourobservation is 9.96 ± 0.01h, which is slightly different from the previousresult. For 360, we obtained the synodic period of 6.18 ± 0.02h which isconsistent with previous values. Additionally, the BV and UB-colourindexes for the three asteriods were also determined.