Torsional oscillations of magnetized relativistic stars     

Neophytos Messios  Demetrios B. Papadopoulos  Nikolaos Stergioulas 《Monthly notices of the Royal Astronomical Society》2001,328(4):1161-1168

Strong magnetic fields in relativistic stars can be a cause of crust fracturing, resulting in the excitation of global torsional oscillations. Such oscillations could become observable in gravitational waves or in high-energy radiation, thus becoming a tool for probing the equation of state of relativistic stars. As the eigenfrequency of torsional oscillation modes is affected by the presence of a strong magnetic field, we study torsional modes in magnetized relativistic stars. We derive the linearized perturbation equations that govern torsional oscillations coupled to the oscillations of a magnetic field, when variations in the metric are neglected (Cowling approximation). The oscillations are described by a single two-dimensional wave equation, which can be solved as a boundary-value problem to obtain eigenfrequencies. We find that, in the non-magnetized case, typical oscillation periods of the fundamental     torsional modes can be nearly a factor of 2 larger for relativistic stars than previously computed in the Newtonian limit. For magnetized stars, we show that the influence of the magnetic field is highly dependent on the assumed magnetic field configuration, and simple estimates obtained previously in the literature cannot be used for identifying normal modes observationally.  相似文献   

Globular clusters and the Mira period–luminosity relation     

Michael Feast  Patricia Whitelock  John Menzies 《Monthly notices of the Royal Astronomical Society》2002,329(1):L7-L12

A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of M _K for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period–luminosity (PL) relation, PL( K ), in good agreement with that derived from Hipparcos parallaxes of nearby field Miras. The mean of these two estimates together with data on LMC Miras yields a Large Magellanic Cloud (LMC) distance modulus of     in evident agreement with a metallicity-corrected Cepheid modulus     .
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed.  相似文献   

The Galactic disc distribution of planetary nebulae with warm dust emission features – II     

S. Casassus  P. F. Roche 《Monthly notices of the Royal Astronomical Society》2001,320(4):435-444

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The ultraviolet line spectrum of the soft X-ray transient XTE J1118+480: a CNO-processed core exposed     

C. A. Haswell  R. I. Hynes  A. R. King  K. Schenker 《Monthly notices of the Royal Astronomical Society》2002,332(4):928-932

We compare ultraviolet (UV) spectra of the recent soft X-ray transients XTE J1118+480 and XTE J1859+226. The emission line strengths in XTE J1118+480 strongly suggest that the accreting material has been CNO processed. We show that this system must have come into contact with a secondary star of about 1.5 M_⊙, and an orbital period ∼15 h, very close to the bifurcation value at which the nuclear and angular momentum loss time-scales are similar. Subsequent evolution to the current period of 4.1 h was driven by angular momentum loss. In passing through a period of 7.75 h the secondary star would have shown essentially normal surface abundances. XTE J1118+480 could thus represent a slightly later evolutionary stage of A0620-00. We briefly discuss the broad Ly α absorption wings in XTE J1118+480.  相似文献   

Improved synthetic spectra of helium-core white dwarf stars     

R. D. Rohrmann  †‡  A. M. Serenelli  §  L. G. Althaus ¶  O. G. Benvenuto &#; 《Monthly notices of the Royal Astronomical Society》2002,335(2):499-511

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A submillimetre survey of the star formation history of radio galaxies   总被引：1，自引：0，他引：1  

E. N. Archibald  J. S. Dunlop  D. H. Hughes  S. Rawlings  S. A. Eales  R. J. Ivison 《Monthly notices of the Royal Astronomical Society》2001,323(2):417-444

We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range 1< z <5. The primary aim of this work is to elucidate the star formation history of this sub class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCMT, we have obtained 850-μm photometry of 47 radio galaxies to a consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The radio galaxy targets have been selected from a series of low-frequency radio surveys of increasing depth (3CRR, 6CE, etc.), in order to allow us to separate the effects of increasing redshift and increasing radio power on submillimetre luminosity. Although the dynamic range of our study is inevitably small, we find clear evidence that the typical submillimetre luminosity (and hence dust mass) of a powerful radio galaxy is a strongly increasing function of redshift; the detection rate rises from ≃15 per cent at z <2.5 to ≳75 per cent at z >2.5, and the average submillimetre luminosity rises at a rate ∝(1+ z )³ out to z ≃4. Moreover, our extensive sample allows us to argue that this behaviour is not driven by underlying correlations with other radio galaxy properties such as radio power, radio spectral index, or radio source size/age. Although radio selection may introduce other more subtle biases, the redshift distribution of our detected objects is in fact consistent with the most recent estimates of the redshift distribution of comparably bright submillimetre sources discovered in blank field surveys. The evolution of submillimetre luminosity found here for radio galaxies may thus be representative of massive ellipticals in general.  相似文献   

凸度量空间中渐近拟非扩张映象新的带误差的Ishikawa迭代逼近     

曾永琴  彭勇 《成都信息工程学院学报》2006,21(5):739-741

在凸度量空间中，利用新的解析法，征明了由集合序列{On}产生的在多值渐近拟非扩张映象下的新的带误差的lshikawa迭代序列的收敛性。  相似文献   

Circumstellar discs in the young σ Orionis cluster     

J. M. Oliveira  R. D. Jeffries  J. Th. van Loon  M. T. Rushton 《Monthly notices of the Royal Astronomical Society》2006,369(1):272-280

We present new K - and L '-band imaging observations for members of the young (3–5 Myr) σ Orionis cluster, obtained at the United Kingdom Infrared Telescope (UKIRT) with the UKIRT 1–5 micron Imager Spectrometer (UIST). We determine ( K − L ') colour excesses with respect to the photospheres, finding evidence for warm circumstellar dust around 27 out of 83 cluster members that have masses between 0.04 and  1.0 M_⊙  . This indicates a circumstellar disc frequency of at least (33 ± 6) per cent for this cluster, consistent with previous determinations from smaller samples and also consistent with the 3-Myr disc half-life suggested by Haisch et al. There is marginal evidence that the disc frequency declines towards lower masses, but the data are also consistent with no mass dependence at all. There is no evidence for spatial segregation of objects with and without circumstellar discs.  相似文献   

X1908+075: A Late O-Type Supergiant with a Neutron Star Companion     

Thierry Morel  Yves Grosdidier 《Astrophysics and Space Science》2006,304(1-4):295-297

X1908 + 075 is a highly-absorbed Galactic X-ray source likely made up of a pulsar accreting wind material from a massive companion. We have used near-IR photometric data complemented by follow-up spectroscopy to identify the likely counterpart to this X-ray source and to assign a spectral type O7.5–9.5 If to the primary. Further details can be found in Morel and Grosdidier (2005).  相似文献   

How many cosmological parameters?     

Andrew R. Liddle 《Monthly notices of the Royal Astronomical Society》2004,351(3):L49-L53

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