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Isolated Neutron Stars (isolated + neutron_star)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Mountains on neutron stars: accreted versus non-accreted crusts

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
B. Haskell
ABSTRACT The aim of this paper is to compare the two cases of an isolated neutron star, with a non-accreted crust, and that of an accreting neutron star, with an accreted crust, and try to estimate which one of the two would make a better source of gravitational waves. In order to do this, we must evaluate the maximum ,mountain' that the crust can sustain in these two cases. We first do this using the formalism of Ushomirsky, Cutler & Bildsten and find that the maximum quadrupole is very similar in the two cases, with the non-accreted crust sustaining a slightly larger mountain. We then develop a perturbation formalism for the problem, that allows us to drop the Cowling approximation and have more control over the boundaries. The use of this formalism confirms that there is not much difference between the two cases, but leads to results approximately one order of magnitude larger than those we obtain with the formalism of Ushomirsky et al. [source]

New photometry and astrometry of the isolated neutron star RX J0720.4,3125 using recent VLT/FORS observations,

ASTRONOMISCHE NACHRICHTEN, Issue 3 2010
T. Eisenbeiss
Abstract Since the first optical detection of RX J0720.4,3125 various observations have been performed to determine astrometric and photometric data. We present the first detection of the isolated neutron star in the V Bessel filter to study the spectral energy distribution and derive a new astrometric position. At ESO Paranal we obtained very deep images with FORS 1 (three hours exposure time) of RX J0720.4,3125 in the V Bessel filter in January 2008. We derive the visual magnitude by standard star aperture photometry. Using sophisticated resampling software we correct the images for field distortions. Then we derive an updated position and proper motion value by comparing its position with FORS 1 observations of December 2000. We calculate a visual magnitude of V = 26.81 ± 0.09 mag, which is seven times in excess of what is expected from X-ray data, but consistent with the extant U, B, and R data. Over about a seven year epoch difference we measured a proper motion of , = 105.1 ± 7.4 mas yr,1 towards , = 296.951° ± 0.0063° (NW), consistent with previous data (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Radiative transitions of the helium atom in highly magnetized neutron star atmospheres

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Z. Medin
ABSTRACT Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree,Fock calculations of the polarization-dependent photoionization cross-sections of the He atom in strong magnetic fields ranging from 1012 to 1014 G. Convenient fitting formulae for the cross-sections are given along with the related oscillator strengths for various bound,bound transitions. The effects of finite nucleus mass on the radiative absorption cross-sections are examined using perturbation theory. [source]

Minimal models of cooling neutron stars with accreted envelopes

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
A. D. Kaminker
ABSTRACT We study the ,minimal' cooling scenario of superfluid neutron stars with nucleon cores, where the direct Urca process is forbidden and enhanced cooling is produced by neutrino emission due to the Cooper pairing of neutrons. Extending our recent previous work, we include the effects of surface accreted envelopes of light elements. We employ the phenomenological density-dependent critical temperatures Tcp(,) and Tcnt(,) of singlet-state proton and triplet-state neutron pairing in a stellar core, as well as the critical temperature Tcns(,) of singlet-state neutron pairing in a stellar crust. We show that the presence of accreted envelopes simplifies the interpretation of observations of thermal radiation from isolated neutron stars in the scenario of our recent previous work and widens the class of models for nucleon superfluidity in neutron star interiors consistent with the observations. [source]

PSR J0609+2130: a disrupted binary pulsar?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
D. R. Lorimer
ABSTRACT We report the discovery and initial timing observations of a 55.7-ms pulsar, J0609+2130, found during a 430-MHz drift-scan survey with the Arecibo radio telescope. With a spin-down rate of 3.1 × 10,19 s s,1 and an inferred surface dipole magnetic field of only 4.2 × 109 G, J0609+2130 has very similar spin parameters to the isolated pulsar J2235+1506 found by Camilo, Nice & Taylor. While the origin of these weakly magnetized isolated neutron stars is not fully understood, one intriguing possibility is that they are the remains of high-mass X-ray binary systems which were disrupted by the supernova explosion of the secondary star. [source]