Optical polarization of the Crab pulsar: precision measurements and comparison to the radio emission     

A. S&#;owikowska  G. Kanbach  M. Kramer  A. Stefanescu 《Monthly notices of the Royal Astronomical Society》2009,397(1):103-123

The linear polarization of the Crab pulsar and its close environment was derived from observations with the high-speed photopolarimeter Optical Pulsar TIMing Analyser at the 2.56-m Nordic Optical Telescope in the optical spectral range (400–750 nm). Time resolution as short as 11 μs, which corresponds to a phase interval of 1/3000 of the pulsar rotation, and high statistics allow the derivation of polarization details never achieved before. The degree of optical polarization and the position angle correlate in surprising details with the light curves at optical wavelengths and at radio frequencies of 610 and 1400 MHz. Our observations show that there exists a subtle connection between presumed non-coherent (optical) and coherent (radio) emissions. This finding supports previously detected correlations between the optical intensity of the Crab and the occurrence of giant radio pulses. Interpretation of our observations requires more elaborate theoretical models than those currently available in the literature.  相似文献   

LoCuSS: luminous infrared galaxies in the merging cluster Abell 1758 at z= 0.28     

C. P. Haines  G. P. Smith  E. Egami  N. Okabe  M. Takada  R. S. Ellis  S. M. Moran  K. Umetsu 《Monthly notices of the Royal Astronomical Society》2009,396(3):1297-1307

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Dry mergers: a crucial test for galaxy formation     

S. Khochfar  J. Silk 《Monthly notices of the Royal Astronomical Society》2009,397(1):506-510

We investigate the role that dry mergers play in the build-up of massive galaxies within the cold dark matter paradigm. Implementing an empirical shut-off mass scale for star formation, we find a nearly constant dry merger rate of  ∼6 × 10⁻⁵ Mpc⁻³ Gyr⁻¹  at   z ≤ 1  and a steep decline at larger z . Less than half of these mergers are between two galaxies that are morphologically classified as early-types, and the other half is mostly between an early- and late-type galaxy. Latter are prime candidates for the origin of tidal features around red elliptical galaxies. The introduction of a transition mass scale for star formation has a strong impact on the evolution of galaxies, allowing them to grow above a characteristic mass scale of   M _{*, c} ∼ 6.3 × 10¹⁰ M_⊙  by mergers only. As a consequence of this transition, we find that around   M _{*, c}   , the fraction of 1:1 mergers is enhanced with respect to unequal mass major mergers. This suggests that it is possible to detect the existence of a transition mass scale by measuring the relative contribution of equal mass mergers to unequal mass mergers as a function of galaxy mass. The evolution of the high-mass end of the luminosity function is mainly driven by dry mergers at low z . We however find that only 10–20 per cent of galaxies more massive than   M _{*, c}   experience dry major mergers within their last Gyr at any given redshift   z ≤ 1  .  相似文献   

Modelling the binary progenitor of Supernova 1993J     

Richard J. Stancliffe  John J. Eldridge 《Monthly notices of the Royal Astronomical Society》2009,396(3):1699-1708

We have developed a detailed stellar evolution code capable of following the simultaneous evolution of both stars in a binary system, together with their orbital properties. To demonstrate the capabilities of the code, we investigate potential progenitors for the Type IIb Supernova 1993J, which is believed to have been an interacting binary system prior to its primary exploding. We use our detailed binary stellar evolution code to model this system to determine the possible range of primary and secondary masses that could have produced the observed characteristics of this system, with particular reference to the secondary. Using the luminosities and temperatures for both stars (as determined by Maund et al.) and the remaining mass of the hydrogen envelope of the primary at the time of explosion, we find that if mass transfer is 100 per cent efficient, the observations can be reproduced by a system consisting of a  15 M_⊙  primary and a  14 M_⊙  secondary in an orbit with an initial period of 2100 days. With a mass transfer efficiency of 50 per cent, a more massive system consisting of a  17 M_⊙  primary and a  16 M_⊙  secondary in an initial orbit of 2360 days is needed. We also investigate some of the uncertainties in the evolution, including the effects of tidal interaction, convective overshooting and thermohaline mixing.  相似文献   

The shapes of asymptotic giant branch envelopes as probes of binary companions     

P. J. Huggins  N. Mauron  E. A. Wirth † 《Monthly notices of the Royal Astronomical Society》2009,396(3):1805-1814

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A new technique for timing the double pulsar system     

P. C. C. Freire  N. Wex  M. Kramer  D. R. Lorimer  M. A. McLaughlin  I. H. Stairs  R. Rosen  A. G. Lyne 《Monthly notices of the Royal Astronomical Society》2009,396(3):1764-1770

In 2004, McLaughlin et al. discovered a phenomenon in the radio emission of PSR J0737−3039B (B) that resembles drifting subpulses. The repeat rate of the subpulses is equal to the spin frequency of PSR J0737−3039A (A); this led to the suggestion that they are caused by incidence upon B's magnetosphere of electromagnetic radiation from A. Here, we describe a geometrical model which predicts the delay of B's subpulses relative to A's radio pulses. We show that measuring these delays is equivalent to tracking A's rotation from the point of view of a hypothetical observer located near B. This has three main astrophysical applications: (i) to determine the sense of rotation of A relative to its orbital plane, (ii) to estimate where in B's magnetosphere the radio subpulses are modulated and (iii) to provide an independent estimate of the mass ratio of A and B. The latter might improve existing tests of gravitational theories using this system.  相似文献   

Stochastic wobble of accretion discs and jets from turbulent rocket torques     

Ryan Pettibone  Eric G. Blackman † 《Monthly notices of the Royal Astronomical Society》2009,396(3):1783-1788

Models of accretion discs and their associated outflows often incorporate assumptions of axisymmetry and symmetry across the disc plane. However, for turbulent discs these symmetries only apply to averaged quantities and do not apply locally. The local asymmetries can induce local imbalances in outflow power across the disc mid-plane, which can in turn induce local tilting torques. Here we calculate the effect of the resulting stochastic torques on disc annuli that are a consequence of standard mean field accretion disc models. The torques induce a random walk of the vector perpendicular to the plane of each averaged annulus. This random walk is characterized by a radially dependent diffusion coefficient which we calculate for small angle tilt. We use the coefficient to calculate a radially dependent time-scale for annular tilt and associated jet wobble. The wobble time depends on the square of the wander angle so the age of a given system determines the maximum wobble angle. We apply this to examples of blazars, young stellar objects and binary engines of pre-planetary nebulae and microquasars. It is noteworthy that for an averaging time   t _w∼ 3 d  , we estimate a wobble angle for jets in SS 433 of  θ∼ 0.8°  , not inconsistent with observational data. In general the non-periodic nature of the stochastic wobble could distinguish it from faster periodic jet precession.  相似文献   

The diverse nature of optical emission lines in brightest cluster galaxies: IFU observations of the central kiloparsec     

Louise O. V. Edwards †  Carmelle Robert  Mercedes Mollá  Sean L. McGee 《Monthly notices of the Royal Astronomical Society》2009,396(4):1953-1971

We present integral field spectroscopy of the nebular line emission in a sample of nine brightest cluster galaxies (BCGs). The sample was chosen to probe both cooling flow and non-cooling flow clusters, as well as a range of cluster X-ray luminosities. The line emission morphology and velocity gradients suggest a great diversity in the properties of the line emitting gas. While some BCGs show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and MKW 3s), others have extended emission (Abell 1204, Abell 2199), while still others have centrally concentrated emission (Abell 2052). We examine diagnostic line ratios to determine the dominant ionization mechanisms in each galaxy. Most of the galaxies show regions with active galactic nucleus like spectra, however, for two BCGs, Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which can be described by the emission from young stellar populations. The diversity of emission-line properties in our sample of BCGs suggests that the emission mechanism is not universal, with different ionization processes dominating different systems. Given this diversity, there is no evidence for a clear distinction of the emission-line properties between cooling flow and non-cooling flow BCGs. It is not always cooling flow BCGs which show emission (or young stellar populations), and non-cooling flow BCGs which do not.  相似文献   

A new gravitational lens from the MUSCLES survey: ULAS J082016.1+081216     

Neal Jackson  Eran O. Ofek  Masamune Oguri 《Monthly notices of the Royal Astronomical Society》2009,398(3):1423-1427

We present observations of a new double-image gravitational lens system, ULAS J082016.1+081216, of image separation 2.3 arcsec and high (∼6) flux ratio. The system is selected from the Sloan Digital Sky Survey (SDSS) spectroscopic quasar list using new high-quality images from the UKIRT (United Kingdom Infrared Telescope) Deep Sky Survey (UKIDSS). The lensed quasar has a source redshift of 2.024, and we identify the lens galaxy as a faint red object of redshift  0.803 ± 0.001  . Three other objects from the UKIDSS survey, selected in the same way, were found not to be lens systems. Together with the earlier lens found using this method, the SDSS–UKIDSS lenses have the potential to significantly increase the number of quasar lenses found in SDSS, to extend the survey to higher flux ratios and lower separations, and to give greater completeness which is important for statistical purposes.  相似文献   

The impact of binary-star yields on the spectra of galaxies     

A. E. Sansom  R. G. Izzard  P. Ocvirk 《Monthly notices of the Royal Astronomical Society》2009,399(2):1012-1025

One of the complexities in modelling integrated spectra of stellar populations is the effect of interacting binary stars besides Type Ia supernovae (SNeIa). These include common envelope systems, cataclysmic variables, novae, and are usually ignored in models predicting the chemistry and spectral absorption line strengths in galaxies. In this paper, predictions of chemical yields from populations of single and binary stars are incorporated into a galactic chemical evolution model to explore the significance of the effects of these other binary yields. Effects on spectral line strengths from different progenitor channels of SNeIa are also explored. Small systematic effects are found when the yields from binaries, other than SNeIa, are included, for a given star formation history. These effects are, at present, within the observational uncertainties on the line strengths. More serious differences can arise in considering different types of SNIa models, their rates and contributions.  相似文献