3,774 research outputs found
Cygnus X-2: the Descendant of an Intermediate-Mass X-Ray Binary
The X-ray binary Cygnus X-2 (Cyg X-2) has recently been shown to contain a
secondary that is much more luminous and hotter than is appropriate for a
low-mass subgiant. We present detailed binary-evolution calculations which
demonstrate that the present evolutionary state of Cyg X-2 can be understood if
the secondary had an initial mass of around 3.5 M_sun and started to transfer
mass near the end of its main-sequence phase (or, somewhat less likely, just
after leaving the main sequence). Most of the mass of the secondary must have
been ejected from the system during an earlier rapid mass-transfer phase. In
the present phase, the secondary has a mass of around 0.5 M_sun with a
non-degenerate helium core. It is burning hydrogen in a shell, and mass
transfer is driven by the advancement of the burning shell. Cyg X-2 therefore
is related to a previously little studied class of intermediate-mass X-ray
binaries (IMXBs). We suggest that perhaps a significant fraction of X-ray
binaries presently classified as low-mass X-ray binaries may be descendants of
IMXBs and discuss some of the implications
Temperature variations of the disorder-induced vortex-lattice melting landscape
Differential magneto-optical imaging of the vortex-lattice melting process in
Bi_2Sr_2CaCu_2O_8 crystals reveals unexpected effects of quenched disorder on
the broadening of the first-order phase transition. The melting patterns show
that the disorder-induced melting landscape T_m(H,r) is not fixed, but rather
changes dramatically with varying field and temperature along the melting line.
The changes in both the scale and shape of the landscape are found to result
from the competing contributions of different types of quenched disorder which
have opposite effects on the local melting transition.Comment: 4 pages of text and 3 figures. Accepted for Publication in Physical
Review Letter
Production of Millisecond Dips in Sco X-1 Count Rates by Dead Time Effects
Chang et al. (2006) reported millisecond duration dips in the X-ray intensity
of Sco X-1 and attributed them to occultations of the source by small
trans-Neptunian objects (TNOs). We have found multiple lines of evidence that
these dips are not astronomical in origin, but rather the result of high-energy
charged particle events in the RXTE PCA detectors. Our analysis of the RXTE
data indicates that at most 10% of the observed dips in Sco X-1 could be due to
occultations by TNOs, and, furthermore, we find no positive or supporting
evidence for any of them being due to TNOs. We therefore believe that it is a
mistake to conclude that any TNOs have been detected via occultation of Sco
X-1.Comment: Submitted to ApJ; uses emulateapj.cls, 8 pages with 8 figure
A procedure to analyze nonlinear density waves in Saturn's rings using several occultation profiles
Cassini radio science experiments have provided multiple occultation optical
depth profiles of Saturn's rings that can be used in combination to analyze
density waves. This paper establishes an accurate procedure of inversion of the
wave profiles to reconstruct the wave kinematic parameters as a function of
semi-major axis, in the nonlinear regime. This procedure is achieved from
simulated data in the presence of realistic noise perturbations, to control the
reconstruction error. By way of illustration we have applied our procedure to
the Mimas 5:3 density wave. We were able to recover precisely the kinematic
parameters from the radio experiment occultation data in most of the
propagation region; a preliminary analysis of the pressure-corrected dispersion
allowed us to determine new but still uncertain values for the opacity
( cm/g) and velocity dispersion of ( cm/s) in
the wave region. Our procedure constitutes the first step in our planned
analysis of the density waves of Saturn's rings. It is very accurate and
efficient in the far-wave region. However, improvements are required within the
first wavelength. The ways in which this method can be used to establish
diagnostics of ring physics are outlined.Comment: 50 pages,13 figures, 2 tables. Published in Icarus
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