411 research outputs found
Renormalized 2PN spin contributions to the accumulated orbital phase for LISA sources
We give here a new third post-Newtonisn (3PN) spin-spin contribution (in the
PN parameter ) to the accumulated orbital phase of a compact binary,
arising from the spin-orbit precessional motion of the spins. In the equal mass
case this contribution vanishes, but LISA sources of merging supermassive
binary black holes have typically a mass ratio of 1:10. For such non-equal
masses this 3PN correction is periodic in time, with period approximately
times larger than the period of gravitational waves. We derive
a renormalized and simpler expression of the spin-spin coefficient at 2PN, as
an average over the time-scale of this period of the combined 2PN and 3PN
contribution. We also find that for LISA sources the quadrupole-monopole
contribution to the phase dominates over the spin-spin contribution, while the
self-spin contribution is negligible even for the dominant spin. Finally we
define a renormalized total spin coefficient to be employed in
the search for gravitational waves emitted by LISA sources.Comment: v2: 14 pages, 6 figures, 2 animated gifs; new section on the
comparison of the analytical results with numerical evolution; published
versio
Should we adjust for seasonality in food consumption surveys? The answer in Switzerland.
Background : Due to market globalization and high availability of various foods throughout the year, adjustment for seasonality at food level may have become unnecessary.
Objective : To describe food consumption across seasons using data from the first National Nutrition Survey in Switzerland.
Methods : National population-based cross-sectional survey included the three linguistic regions of Switzerland
Magnetospheric Gap and Accumulation of Giant Planets Close to the Star
The bunching of giant planets at a distance of several stellar radii may be
explained by the disruption of the inner part of the disk by the magnetosphere
of the star during the T Tauri stage of evolution. The rotating magnetic field
of the star gives rise to a low density magnetospheric gap where stellar
migration is strongly suppressed. We performed full 3D magnetohydrodynamic
simulations of the disk-magnetosphere interaction and examined conditions for
which the magnetospheric gap is "empty", by changing the misalignment angle
between magnetic and rotational axes of the star, Theta, and by lowering the
adiabatic index gamma, which mocks up the effect of heat conductivity and
cooling. Our simulations show that for a wide range of plausible conditions the
gap is essentially empty. However, in the case of large misalignment angles
Theta, part of the funnel stream is located in the equatorial plane and the gap
is not empty. Furthermore, if the adiabatic index is small (gamma=1.1) and the
rotational and magnetic axes are almost aligned, then matter penetrates through
the magnetosphere due to 3D instabilities forming high-density equatorial
funnels. For these two limits there is appreciable matter density in the
equatorial plane of the disk so that a planet may migrate into the star.Comment: 6 pages, 6 figures, Accepted to the ApJ Letters. See version of the
paper with higher resolution plots at
http://astrosun2.astro.cornell.edu/us-rus/planets.ht
Locking of the Rotation of Disk-Accreting Magnetized Stars
We investigate the rotational equilibrium state of a disk accreting
magnetized stars using axisymmetric magnetohydrodynamic (MHD) simulations. In
this ``locked'' state, the spin-up torque balances the spin-down torque so that
the net average torque on the star is zero. We investigated two types of
initial conditions, one with a relatively weak stellar magnetic field and a
high coronal density, and the other with a stronger stellar field and a lower
coronal density. We observed that for both initial conditions the rotation of
the star is locked to the rotation of the disk. In the second case, the radial
field lines carry significant angular momentum out of the star. However, this
did not appreciably change the condition for locking of the rotation of the
star. We find that in the equilibrium state the corotation radius is
related to the magnetospheric radius as for
case (1) and for case (2). We estimated periods of
rotation in the equilibrium state for classical T Tauri stars, dwarf novae and
X-ray millisecond pulsars.Comment: 10 pages, 9 figures. Accepted by ApJ, will appear in vol. 634, 2005
December
On the Nature of Part Time Radio Pulsars
The recent discovery of rotating radio transients and the quasi-periodicity
of pulsar activity in the radio pulsar PSR B193124 has challenged the
conventional theory of radio pulsar emission. Here we suggest that these
phenomena could be due to the interaction between the neutron star
magnetosphere and the surrounding debris disk. The pattern of pulsar emission
depends on whether the disk can penetrate the light cylinder and efficiently
quench the processes of particle production and acceleration inside the
magnetospheric gap. A precessing disk may naturally account for the
switch-on/off behavior in PSR B193124.Comment: 9 pages, accepted to ApJ
Helical motion and the origin of QPO in blazar-type sources
Recent observations and analysis of blazar sources provide strong evidence
for (i) the presence of significant periodicities in their lightcurves and (ii)
the occurrence of helical trajectories in their radio jets. In scenarios, where
the periodicity is caused by differential Doppler boosting effects along a
helical jet path, both of these facts may be naturally tied together. Here we
discuss four possible driving mechanisms for the occurrence of helical
trajectories: orbital motion in a binary system, Newtonian-driven jet
precession, internal jet rotation and motion along a global helical magnetic
field. We point out that for non-ballistic helical motion the observed period
may appear strongly shortened due to classical travel time effects. Finally,
the possible relevance of the above mentioned driving mechanisms is discussed
for Mkn~501, OJ 287 and AO 0235+16.Comment: 6 pages, 1 figure; presented at the 5th Microquasar Workshop,
Beijing, June 2004. Accepted for publication in the Chinese Journal of
Astronomy and Astrophysic
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
INTEGRAL observations of SS433, a supercritically accreting microquasar with hard spectrum
Observations of SS433 by INTEGRAL carried out in March -- May 2003 are
presented. SS433 is evidently detected on the INTEGRAL images of the
corresponding sky region in the energy bands 25-50 and 50-100 keV. The
precessional variability of the hard X-ray flux is clearly seen. The X-ray
eclipse caused by the binary orbital motion is also detected. A possible origin
of the hard continuum is briefly discussed.Comment: 5 pages, 6 figures. Accepted to A&A INTEGRAL special volum
Spectropolarimetry of the Classical T Tauri Star TW Hydrae
We present high resolution (R ~ 60,000) circular spectropolarimetry of the
classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines
and measure the net longitudinal magnetic field for 6 consecutive nights. While
no net polarization is detected the first five nights, a significant
photospheric field of Bz = 149 \pm 33 G is found on the sixth night. To rule
out spurious instrumental polarization, we apply the same analysis technique to
several non-magnetic telluric lines, detecting no significant polarization. We
further demonstrate the reality of this field detection by showing that the
splitting between right and left polarized components in these 12 photospheric
lines shows a linear trend with Lande g-factor times wavelength squared, as
predicted by the Zeeman effect. However, this longitudinal field detection is
still much lower than that which would result if a pure dipole magnetic
geometry is responsible for the mean magnetic field strength of 2.6 kG
previously reported for TW Hya. We also detect strong circular polarization in
the He I 5876 and the Ca II 8498 emission lines, indicating a strong field in
the line formation region of these features. The polarization of the Ca II line
is substantially weaker than that of the He I line, which we interpret as due
to a larger contribution to the Ca II line from chromospheric emission in which
the polarization signals cancel. However, the presence of polarization in the
Ca II line indicates that accretion shocks on Classical T Tauri stars do
produce narrow emission features in the infrared triplet lines of Calcium.Comment: One tar file. The paper has 22 pages, 5 figures. Accepted by AJ on
Sep 10, 200
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