901 research outputs found
Warp propagation in astrophysical discs
Astrophysical discs are often warped, that is, their orbital planes change
with radius. This occurs whenever there is a non-axisymmetric force acting on
the disc, for example the Lense-Thirring precession induced by a misaligned
spinning black hole, or the gravitational pull of a misaligned companion. Such
misalignments appear to be generic in astrophysics. The wide range of systems
that can harbour warped discs - protostars, X-ray binaries, tidal disruption
events, quasars and others - allows for a rich variety in the disc's response.
Here we review the basic physics of warped discs and its implications.Comment: To be published in Astrophysical Black Holes by Haardt et al.,
Lecture Notes in Physics, Springer 2015. 19 pages, 2 figure
Models of hydrostatic magnetar atmospheres at high luminosities
We investigate the possibility of Photospheric Radius Expansion (PRE) during
magnetar bursts. Identification of PRE would enable a determination of the
magnetic Eddington limit (which depends on field strength and neutron star mass
and radius), and shed light on the burst mechanism. To do this we model
hydrostatic atmospheres in a strong radial magnetic field, determining both
their maximum extent and photospheric temperatures. We find that
spatially-extended atmospheres cannot exist in such a field configuration:
typical maximum extent for magnetar-strength fields is ~10 m (as compared to
200 km in the non-magnetic case). Achieving balance of gravitational and
radiative forces over a large range of radii, which is critical to the
existence of extended atmospheres, is rendered impossible in strong fields due
to the dependence of opacities on temperature and field strength. We conclude
that high luminosity bursts in magnetars do not lead to expansion and cooling
of the photosphere, as in the non-magnetic case. We also find the maximum
luminosity that can propagate through a hydrostatic magnetar atmosphere to be
lower than previous estimates. The proximity and small extent of the
photospheres associated with the two different polarization modes also calls
into question the interpretation of two blackbody fits to magnetar burst
spectra as being due to extended photospheres.Comment: Accepted for publication in MNRAS. 14 pages, 6 figures, 2 table
Particle Motion and Electromagnetic Fields of Rotating Compact Gravitating Objects with Gravitomagnetic Charge
The exact solution for the electromagnetic field occuring when the
Kerr-Taub-NUT compact object is immersed (i) in an originally uniform magnetic
field aligned along the axis of axial symmetry (ii) in dipolar magnetic field
generated by current loop has been investigated. Effective potential of motion
of charged test particle around Kerr-Taub-NUT gravitational source immersed in
magnetic field with different values of external magnetic field and NUT
parameter has been also investigated. In both cases presence of NUT parameter
and magnetic field shifts stable circular orbits in the direction of the
central gravitating object. Finally we find analytical solutions of Maxwell
equations in the external background spacetime of a slowly rotating magnetized
NUT star. The star is considered isolated and in vacuum, with monopolar
configuration model for the stellar magnetic field.Comment: 18 pages, 6 figures, new results in section 2 added, section 3 is
revised, 3 references are adde
Ohm's Law for Plasma in General Relativity and Cowling's Theorem
The general-relativistic Ohm's law for a two-component plasma which includes
the gravitomagnetic force terms even in the case of quasi-neutrality has been
derived. The equations that describe the electromagnetic processes in a plasma
surrounding a neutron star are obtained by using the general relativistic form
of Maxwell equations in a geometry of slow rotating gravitational object. In
addition to the general-relativistic effect first discussed by Khanna \&
Camenzind (1996) we predict a mechanism of the generation of azimuthal current
under the general relativistic effect of dragging of inertial frames on radial
current in a plasma around neutron star. The azimuthal current being
proportional to the angular velocity of the dragging of inertial
frames can give valuable contribution on the evolution of the stellar magnetic
field if exceeds (
is the number density of the charged particles, is the conductivity of
plasma). Thus in general relativity a rotating neutron star, embedded in
plasma, can in principle generate axial-symmetric magnetic fields even in
axisymmetry. However, classical Cowling's antidynamo theorem, according to
which a stationary axial-symmetric magnetic field can not be sustained against
ohmic diffusion, has to be hold in the general-relativistic case for the
typical plasma being responsible for the rotating neutron star.Comment: Accepted for publication in Astrophysics & Space Scienc
Orbital characterization of the \beta Pictoris b giant planet
In June 2010, we confirmed the existence of a giant planet in the disk of the
young star Beta Pictoris, located between 8 AU and 15 AU from the star. This
young planet offers the rare opportunity to monitor a large fraction of the
orbit using the imaging technique over a reasonably short timescale. Using the
NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope
(VLT), we obtained repeated follow-up images of the Bpic system in the Ks and
L' filters at four new epochs in 2010 and 2011. Complementing these data with
previous measurements, we conduct a homogeneous analysis, which covers more
than eight yrs, to accurately monitor the Bpic b position relative to the star.
On the basis of the evolution of the planet's relative position with time, we
derive the best-fit orbital solutions for our measurements. More reliable
results are found with a Markov-chain Monte Carlo approach. The solutions favor
a low-eccentricity orbit e < 0.17, with semi-major axis in the range 8--9 AU
corresponding to orbital periods of 17--21 yrs. Our solutions favor a highly
inclined solution with a peak around i=88.5+-1.7 deg, and a longitude of
ascending node tightly constrained at Omega = -147.5+-1.5 deg. These results
indicate that the orbital plane of the planet is likely to be above the
midplane of the main disk, and compatible with the warp component of the disk
being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a
key role in the origin of the inner warped-disk morphology of the Bpic disk.
Finally, these orbital parameters are consistent with the hypothesis that the
planet is responsible for the transit-like event observed in November 1981, and
also linked to the cometary activity observed in the Bpic system.Comment: 10 pages, 12 figures, accepted to A&
Calibrating the Cepheid Period-Luminosity relation from the infrared surface brightness technique I. The p-factor, the Milky Way relations, and a universal K-band relation
We determine Period-Luminosity relations for Milky Way Cepheids in the
optical and near-IR bands. These relations can be used directly as reference
for extra-galactic distance determination to Cepheid populations with solar
metallicity, and they form the basis for a direct comparison with relations
obtained in exactly the same manner for stars in the Magellanic Clouds,
presented in an accompanying paper. In that paper we show that the metallicity
effect is very small and consistent with a null effect, particularly in the
near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC
and SMC to form a best relation. We employ the near-IR surface brightness
(IRSB) method to determine direct distances to the individual Cepheids after we
have recalibrated the projection factor using the recent parallax measurements
to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC
should be independent of pulsation period. We confirm our earlier finding that
the projection factor for converting radial velocity to pulsational velocity
depends quite steeply on pulsation period, p=1.550-0.186*log(P) in disagrement
with recent theoretical predictions. We delineate the Cepheid PL relation using
111 Cepheids with direct distances from the IRSB analysis. The relations are by
construction in agreement with the recent HST parallax distances to Cepheids
and slopes are in excellent agreement with the slopes of apparent magnitudes
versus period observed in the LMC.Comment: Accepted for publication by Astronomy and Astrophysics. 15 pages, 11
figure
Elemental composition of ambient aerosols measured with high temporal resolution using an online XRF spectrometer
The Xact 625 Ambient Metals Monitor was tested during a 3-week field campaign
at the rural, traffic-influenced site Härkingen in Switzerland during the
summer of 2015. The field campaign encompassed the Swiss National Day
fireworks event, providing increased concentrations and unique chemical
signatures compared to non-fireworks (or background) periods. The objective
was to evaluate the data quality by intercomparison with other independent
measurements and test its applicability for aerosol source quantification.
The Xact was configured to measure 24 elements in PM10 with 1 h time
resolution. Data quality was evaluated for 10 24 h averages of Xact data by
intercomparison with 24 h PM10 filter data analysed with ICP-OES for
major elements, ICP-MS for trace elements, and gold amalgamation atomic
absorption spectrometry for Hg. Ten elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn,
Ba, Pb) showed excellent correlation between the compared methods, with
r2 values ≥ 0.95. However, the slopes of the regressions between
Xact 625 and ICP data varied from 0.97 to 1.8 (average 1.28) and thus
indicated generally higher Xact elemental concentrations than ICP for these
elements. Possible reasons for these differences are discussed, but further
investigations are needed. For the remaining elements no conclusions could be
drawn about their quantification for various reasons, mainly detection limit
issues. An indirect intercomparison of hourly values was performed for the
fireworks peak, which brought good agreement of total masses when the Xact
data were corrected with the regressions from the 24 h value
intercomparison. The results demonstrate that multi-metal characterization at
high-time-resolution capability of Xact is a valuable and practical tool for
ambient monitoring
Abortion attitudes: An overview of demographic and ideological differences
Despite being a defining issue in the culture war, the relative importance of the psychological predictors of abortion attitudes are poorly understood. We address this oversight here by reviewing existing findings and providing new evidence for the demographic and ideological correlates of abortion support. Throughout our review, we integrate new analyses of several large-scale, cross-sectional, and longitudinal datasets to provide the most complete empirical examination of abortion attitudes to date. Our review and new analyses indicate that abortion support is increasing (modestly) over time in both the US and New Zealand. We also show that a plurality of respondents (43.8%) in the US indicate that they are “pro-choice” across various elective and traumatic scenarios, whereas only 14.8% report being consistently “pro-life” regardless of why an abortion is sought. Our review and new integrative analyses then demonstrate that age, religiosity, and conservatism correlate negatively, whereas Openness to Experience correlates positively, with abortion support. New analyses of heterosexual couples also reveal that women’s and men’s religiosity uniquely decreases their romantic partner’s abortion support. Finally, noting inconsistent gender differences in abortion support, we review evidence for the impact of traditional gender role attitudes and sexism on abortion support. Our review and theoretical analyses illustrate that, rather than misogyny, benevolent sexism—the belief that women should be cherished and protected—best explains abortion opposition. We conclude that demographic and ideological variables, along with attitudes that revere women and motherhood, continue to undermine women’s interpersonal, intergroup, and societal rights
Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli
Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women) can elicit sex and sexual orientation differences in sexual response. If similar patterns were replicated with non-explicit sexual stimuli (footage of dressed men and women), then pupil dilation could be indicative of automatic sexual response in fully noninvasive designs. We examined this in 325 men and women with varied sexual orientations to determine whether dilation patterns to non-explicit sexual stimuli resembled those to explicit sexual stimuli depicting the same sex or other sex. Sexual orientation differences in pupil dilation to non-explicit sexual stimuli mirrored those to explicit sexual stimuli. However, the relationship of dilation to non-explicit sexual stimuli with dilation to corresponding explicit sexual stimuli was modest, and effect magnitudes were smaller with non-explicit sexual stimuli than explicit sexual stimuli. The prediction that sexual orientation differences in pupil dilation are larger in men than in women was confirmed with explicit sexual stimuli but not with non-explicit sexual stimuli
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