6,451 research outputs found
Determination of new coefficients in the angular momentum and energy fluxes at infinity to 9PN for eccentric Schwarzschild extreme-mass-ratio inspirals using mode-by-mode fitting
We present an extension of work in an earlier paper showing high precision
comparisons between black hole perturbation theory and post-Newtonian (PN)
theory in their region of overlapping validity for bound, eccentric-orbit,
Schwarzschild extreme-mass-ratio inspirals. As before we apply a numerical
fitting scheme to extract eccentricity coefficients in the PN expansion of the
gravitational wave fluxes, which are then converted to exact analytic form
using an integer-relation algorithm. In this work, however, we fit to
individual modes to exploit simplifying factorizations that lie therein.
Since the previous paper focused solely on the energy flux, here we concentrate
initially on analyzing the angular momentum flux to infinity. A first step
involves finding convenient forms for hereditary contributions to the flux at
low-PN order, analogous to similar terms worked out previously for the energy
flux. We then apply the upgraded techniques to find new PN terms through 9PN
order and (at many PN orders) to in the power series in eccentricity.
With the new approach applied to angular momentum fluxes, we return to the
energy fluxes at infinity to extend those previous results. Like before, the
underlying method uses a \textsc{Mathematica} code based on use of the
Mano-Suzuki-Takasugi (MST) function expansion formalism to represent
gravitational perturbations and spectral source integration (SSI) to find
numerical results at arbitrarily high precision.Comment: 36 pages, 1 figur
A New Feature in the Spectrum of the Superluminous LMC Supergiant HDE 269896
We have found strong selective emission of the N II 5000A complex in the
spectrum of the LMC hypergiant HDE 269896, ON9.7 Ia. Since this object also
has anomalously strong He II 4686 emission for its spectral type, an
unusually wide range of ionization in its extended atmosphere is indicated. The
published model of this spectrum does not reproduce these emission features,
but we show that increased nitrogen and helium abundances, together with small
changes in other model parameters, can do so. The morphological and possible
evolutionary relationships of HDE 269896, as illuminated by the new spectral
features, to other denizens of the OB Zoo are discussed. This object may be in
an immediate pre-WNVL (Very Late WN) state, which is in turn the quiescent
state of at least some Luminous Blue Variables.
More generally, the N II spectrum in HDE 269896 provides a striking
demonstration of the occurrence of two distinctly different kinds of line
behavior in O-type spectra: normal absorption lines that develop P Cygni
profiles at high wind densities, and selective emission lines from the same
ions that do not. Further analysis of these features will advance understanding
of both atomic physics and extreme stellar atmospheres.Comment: 12 pages, 2 tables, 4 figures (quality downgraded due to size
constraints); to appear in PASP January 200
Fowl communicate the size, speed and proximity of avian stimuli through graded structure in referential alarm calls
Many animals produce alarm calls that warn conspecifics about predators. In some species, alarm calls communicate continuous traits associated with a predator encounter, such as its level of threat. In other species, alarm calls communicate categorical traits, such as predator class (e.g. avian versus terrestrial), and are consequently considered functionally referential. In theory, functionally referential alarm calls can simultaneously communicate continuously distributed traits, though examples of such calls are rare. Such dual-function calls could be adaptive because they would enable receivers to tailor their responses to a specific predator class, as well as to more subtle characteristics of individual attacks. Here, we tested whether male fowl (Gallus gallus) communicate continuous variation in avian stimuli through graded structure in their functionally referential aerial alarm calls. In the first experiment, we held male fowl in an indoor test cage and allowed them to view wild birds flying past a window. We recorded their alarm calls and compared the structure to the size, speed, and proximity of the eliciting stimuli. Stimuli that appeared closer, larger, and faster elicited alarm calls that were shorter, louder, clearer, and lower in
frequency. In the second experiment, we broadcast alarm calls to foraging females and compared their responses to the graded structural changes documented earlier. Females exhibited greater initial responses and finished feeding later in response to louder alarm calls. Together, these results show that fowl communicate the size, speed and proximity of avian stimuli through graded variation in their functionally referential aerial alarm calls
Two-dimensional colloidal fluids exhibiting pattern formation
Fluids with competing short range attraction and long range repulsive
interactions between the particles can exhibit a variety of microphase
separated structures. We develop a lattice-gas (generalised Ising) model and
analyse the phase diagram using Monte Carlo computer simulations and also with
density functional theory (DFT). The DFT predictions for the structures formed
are in good agreement with the results from the simulations, which occur in the
portion of the phase diagram where the theory predicts the uniform fluid to be
linearly unstable. However, the mean-field DFT does not correctly describe the
transitions between the different morphologies, which the simulations show to
be analogous to micelle formation. We determine how the heat capacity varies as
the model parameters are changed. There are peaks in the heat capacity at state
points where the morphology changes occur. We also map the lattice model onto a
continuum DFT that facilitates a simplification of the stability analysis of
the uniform fluid.Comment: 13 pages, 15 figure
Tidal heating and torquing of the primary black hole in eccentric-orbit, non-spinning extreme-mass-ratio inspirals to 22PN order
We calculate the high-order post-Newtonian (PN) expansion of the energy and
angular momentum fluxes onto the horizon of a nonspinning black hole primary in
eccentric-orbit extreme-mass-ratio inspirals. The first-order black hole
perturbation theory calculation uses \textsc{Mathematica} and makes an analytic
expansion of the Regge-Wheeler-Zerilli functions using the Mano-Suzuki-Takasugi
formalism. The horizon absorption, or tidal heating and torquing, is calculated
to 18PN relative to the leading horizon flux (i.e., 22PN order relative to the
leading quadrupole flux at infinity). Each PN term is a function of
eccentricity and is calculated as a series to . A second expansion,
to 10PN horizon-relative order (or 14PN relative to the flux at infinity), is
computed deeper in eccentricity to . A number of resummed closed-form
functions are found for the low PN terms in the series. Using a separate
Teukolsky perturbation code, numerical comparisons are made to test how
accurate the PN expansion is when extended to a close orbit. We find
that the horizon absorption expansion is not as convergent as a previously
computed infinity-side flux expansion. However, given that the horizon
absorption is suppressed by 4PN, useful results can be obtained even with an
orbit as tight as this for . Combining the present results with our
earlier expansion of the fluxes to infinity makes the knowledge of the total
dissipation known to 19PN for eccentric-orbit nonspinning EMRIs.Comment: 19 pages, 1 figur
Relativistic Corrections in White Dwarf Asteroseismology
With the precision now afforded by modern space-based photometric
observations from the retired K2 and current TESS missions, the effects of
general relativity (GR) may be detectable in the light curves of pulsating
white dwarfs (WDs). Almost all WD models are calculated using a Newtonian
description of gravity and hydrodynamics. To determine if inclusion of GR leads
to observable effects, we used idealized models of compact stars and made
side-by-side comparison of mode periods computed using a (i) Newtonian and (ii)
GR description of the equilibrium structure and nonradial pulsations. For
application to white dwarfs, it is only necessary to include the first
post-Newtonian (1PN) approximation to GR. The mathematical nature of the linear
nonradial pulsation problem is then qualitatively unchanged and the GR
corrections can be written as extensions of the classic Dziembowski equations.
As such, GR effects might easily be included in existing asteroseismology
codes. The idealized stellar models are (i) \pn1 relativistic polytropes and
(ii) stars with cold degenerate-electron equation of state featuring a
near-surface chemical transition from to , simulating a
surface hydrogen layer. Comparison of Newtonian and 1PN normal mode periods
reveals fractional differences on the order of the surface gravitational
redshift . For a typical WD, this fractional difference is
and is greater than the period uncertainty of many white
dwarf pulsation modes observed by TESS. A consistent theoretical modeling of
periods observed in these stars should in principle include GR effects to 1PN
order
The Protostellar Mass Function
The protostellar mass function (PMF) is the Present-Day Mass Function of the
protostars in a region of star formation. It is determined by the initial mass
function weighted by the accretion time. The PMF thus depends on the accretion
history of protostars and in principle provides a powerful tool for
observationally distinguishing different protostellar accretion models. We
consider three basic models here: the Isothermal Sphere model (Shu 1977), the
Turbulent Core model (McKee & Tan 2003), and an approximate representation of
the Competitive Accretion model (Bonnell et al. 1997, 2001a). We also consider
modified versions of these accretion models, in which the accretion rate tapers
off linearly in time. Finally, we allow for an overall acceleration in the rate
of star formation. At present, it is not possible to directly determine the PMF
since protostellar masses are not currently measurable. We carry out an
approximate comparison of predicted PMFs with observation by using the theory
to infer the conditions in the ambient medium in several star-forming regions.
Tapered and accelerating models generally agree better with observed
star-formation times than models without tapering or acceleration, but
uncertainties in the accretion models and in the observations do not allow one
to rule out any of the proposed models at present. The PMF is essential for the
calculation of the Protostellar Luminosity Function, however, and this enables
stronger conclusions to be drawn (Offner & McKee 2010).Comment: 16 pages, 8 figures, published in Ap
Quantitative Spectroscopy of Blue Supergiants in Metal-Poor Dwarf Galaxy NGC 3109
We present a quantitative analysis of the low-resolution (4.5 A) spectra of
12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy
NGC 3109. A modified method of analysis is presented which does not require use
of the Balmer jump as an independent temperature indicator, as used in previous
studies. We determine stellar effective temperatures, gravities, metallicities,
reddening, and luminosities, and combine our sample with the early-B type BSGs
analyzed by Evans et al. (2007) to derive the distance to NGC 3109 using the
Flux-weighted Gravity-Luminosity Relation (FGLR). Using primarily Fe-group
elements, we find an average metallicity of [Z] = -0.67 +/- 0.13, and no
evidence of a metallicity gradient in the galaxy. Our metallicities are higher
than those found by Evans et al. (2007) based on the oxygen abundances of
early-B supergiants ([Z] = -0.93 +/- 0.07), suggesting a low alpha/Fe ratio for
the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy
mass-metallicity relation accordingly and compare it to metallicity studies of
HII regions in star-forming galaxies. We derive an FGLR distance modulus of
25.55 +/- 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red
giant branch (TRGB) distances. The FGLR itself is consistent with those found
in other galaxies, demonstrating the reliability of this method as a measure of
extragalactic distances.Comment: 50 pages, 23 figures; Accepted for publication in The Astrophysical
Journa
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