773 research outputs found
The Gravitational Lensing in Redshift-space Correlation Functions of Galaxies and Quasars
The gravitational lensing, as well as the velocity field and the cosmological
light-cone warp, changes the observed correlation function of high-redshift
objects. We present an analytical expression of 3D correlation function,
simultaneously including those three effects. When two objects are separated
over several hundreds Mpc along a line of sight, the observed correlation
function is dominated by the effect of gravitational lensing rather than the
intrinsic clustering. For a canonical lambda-CDM model, the lensing signals in
the galaxy-galaxy and galaxy-QSO correlations are beyond noise levels in
large-scale redshift surveys like the Sloan Digital Sky Survey.Comment: 10 pages, 1 figure, submitted to ApJ
Photoprocesses in protoplanetary disks
Circumstellar disks are exposed to intense ultraviolet radiation from the
young star. In the inner disks, the UV radiation can be enhanced by more than
seven orders of magnitude compared with the average interstellar field,
resulting in a physical and chemical structure that resembles that of a dense
photon-dominated region (PDR). This intense UV field affects the chemistry, the
vertical structure of the disk, and the gas temperature, especially in the
surface layers of the disk. The parameters which make disks different from
traditional PDRs are discussed, including the shape of the UV radiation field,
grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner
holes. New photorates for selected species, including simple ions, are
presented. Also, a summary of available cross sections at Lyman alpha 1216 A is
made. Rates are computed for radiation fields with color temperatures ranging
from 4000 to 30,000 K, and can be applied to a wide variety of astrophysical
regions including exo-planetary atmospheres. The importance of photoprocesses
is illustrated for a number of representative disk models, including disk
models with grain growth and settling.Comment: A website with the final published version and all photodissociation
cross sections and rates can be found at
http://www.strw.leidenuniv.nl/~ewine/phot
The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems
A transiting extrasolar planet sequentially blocks off the light coming from
the different parts of the disk of the host star in a time dependent manner.
Due to the spin of the star, this produces an asymmetric distortion in the line
profiles of the stellar spectrum, leading to an apparent anomaly of the radial
velocity curves, known as the Rossiter - McLaughlin effect. Here, we derive
approximate but accurate analytic formulae for the anomaly of radial velocity
curves taking account of the stellar limb darkening. The formulae are
particularly useful in extracting information of the projected angle between
the planetary orbit axis and the stellar spin axis, \lambda, and the projected
stellar spin velocity, V sin I_s. We create mock samples for the radial curves
for the transiting extrasolar system HD209458, and demonstrate that constraints
on the spin parameters (V sin I_s, \lambda) may be significantly improved by
combining our analytic template formulae and the precision velocity curves from
high-resolution spectroscopic observations with 8-10 m class telescopes. Thus
future observational exploration of transiting systems using the Rossiter -
McLaughlin effect is one of the most important probes to better understanding
of the origin of extrasolar planetary systems, especially the origin of their
angular momentum.Comment: 39 pages, 16 figures, Accepted to ApJ. To match the published version
(ApJ 623, April 10 issue
The Correlation Function in Redshift Space: General Formula with Wide-angle Effects and Cosmological Distortions
A general formula for the correlation function in redshift space is derived
in linear theory. The formula simultaneously includes wide-angle effects and
cosmological distortions. The formula is applicable to any pair with arbitrary
angle between lines of sight, and arbitrary redshifts, , ,
which are not necessarily small. The effects of the spatial curvature both on
geometry and on fluctuation spectrum are properly taken into account, and thus
our formula holds in a Friedman-Lema\^{\i}tre universe with arbitrary
cosmological parameters and . We illustrate the pattern
of the resulting correlation function with several models, and also show that
validity region of the conventional distant observer approximation is .Comment: 45 pages including 9 figures, To Appear in Astrophys. J. 535 (2000
Large Scale Clustering of Sloan Digital Sky Survey Quasars: Impact of the Baryon Density and the Cosmological Constant
We report the first result of the clustering analysis of Sloan Digital Sky
Survey (SDSS) quasars. We compute the two-point correlation function (2PCF) of
SDSS quasars in redshift space at ,
with particular attention to its baryonic signature. Our sample consists of
19986 quasars extracted from the SDSS Data Release 4 (DR4). The redshift range
of the sample is (the mean redshift is )
and the reddening-corrected -band apparent magnitude range is . Due to the relatively low number density of the
quasar sample, the bump in the power spectrum due to the baryon density,
, is not clearly visible. The effect of the baryon density is,
however, to distort the overall shape of the 2PCF.The degree of distortion
makes it an interesting alternate measure of the baryonic signature. Assuming a
scale-independent linear bias and the spatially flat universe, i.e.,
, where
and denote the density parameters of dark matter and the
cosmological constant, we combine the observed quasar 2PCF and the predicted
matter 2PCF to put constraints on and . Our
result is fitted as at the 2 confidence level, which is consistent with
results from other cosmological observations such as WMAP. (abridged)Comment: 26 pages, 12 figures, Accepted for publication in the PAS
Demonstrating Discreteness and Collision Error in Cosmological N-body Simulations of Dark Matter Gravitational Clustering
Two-body scattering and other discreteness effects are unimportant in
cosmological gravitational clustering in most scenarios, since the dark matter
has a small particle mass. The collective field should determine evolution:
Two-body scattering in simulations violates the Poisson-Vlasov equations. We
test this in PM, PM, Tree, and NGPM codes, noting that a collisionless code
will preserve the one-dimensional character of plane wave collapse. We find
collisionality vanishing as the softening parameter approaches the mean
interparticle separation. Solutions for the problem are suggested, involving
greater computer power, PM-based nested grid codes, and a more conservative
approach to resolution claims.Comment: Final version accepted for ApJ Letters. Minor revisions, including
due to bug fix in tree code. Uses aasms4.sty. 15 pages. Higher resolution
figures available at ftp://kusmos.phsx.ukans.edu/preprints/discret
Perturbative analysis of disordered Ising models close to criticality
We consider a two-dimensional Ising model with random i.i.d. nearest-neighbor
ferromagnetic couplings and no external magnetic field. We show that, if the
probability of supercritical couplings is small enough, the system admits a
convergent cluster expansion with probability one. The associated polymers are
defined on a sequence of increasing scales; in particular the convergence of
the above expansion implies the infinite differentiability of the free energy
but not its analyticity. The basic tools in the proof are a general theory of
graded cluster expansions and a stochastic domination of the disorder
The Prograde Orbit of Exoplanet TrES-2b
We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of
its giant planet. The anomalous Doppler shift due to stellar rotation (the
Rossiter-McLaughlin effect) is discernible in the data, with a signal-to-noise
ratio of 2.9, even though the star is a slow rotator. By modeling this effect
we find that the planet's trajectory across the face of the star is tilted by
-9 +/- 12 degrees relative to the projected stellar equator. With 98%
confidence, the orbit is prograde.Comment: ApJ, in press [15 pages
Two-Dimensional Molecular Patterning by Surface-Enhanced Zn-Porphyrin Coordination
In this contribution, we show how zinc-5,10,15,20-meso-tetradodecylporphyrins (Zn-TDPs) self-assemble into stable organized arrays on the surface of graphite, thus positioning their metal center at regular distances from each other, creating a molecular pattern, while retaining the possibility to coordinate additional ligands. We also demonstrate that Zn-TDPs coordinated to 3-nitropyridine display a higher tendency to be adsorbed at the surface of highly oriented pyrolytic graphite (HOPG) than noncoordinated ones. In order to investigate the two-dimensional (2D) self-assembly of coordinated Zn-TDPs, solutions with different relative concentrations of 3-nitropyridine and Zn-TDP were prepared and deposited on the surface of HOPG. STM measurements at the liquid-solid interface reveal that the ratio of coordinated Zn-TDPs over noncoordinated Zn-TDPs is higher at the n-tetradecane/HOPG interface than in n-tetradecane solution. This enhanced binding of the axial ligand at the liquid/solid interface is likely related to the fact that physisorbed Zn-TDPs are better binding sites for nitropyridines.
Probability Distribution Function of Cosmological Density Fluctuations from Gaussian Initial Condition: Comparison of One- and Two-point Log-normal Model Predictions with N-body Simulations
We quantitatively study the probability distribution function (PDF) of
cosmological nonlinear density fluctuations from N-body simulations with
Gaussian initial condition. In particular, we examine the validity and
limitations of one-point and two-point log-normal PDF models against those
directly estimated from the simulations. We find that the one-point log-normal
PDF describes very accurately the cosmological density distribution even in the
nonlinear regime (the rms variance \sigma_{nl} \simlt 4 and the over-density
\delta \simlt 100). Furthermore the two-point log-normal PDFs are also in good
agreement with the simulation data from linear to fairly nonlinear regime,
while slightly deviate from them for \delta \simlt -0.5. Thus the log-normal
PDF can be used as a useful empirical model for the cosmological density
fluctuations. While this conclusion is fairly insensitive to the shape of the
underlying power spectrum of density fluctuations P(k), models with substantial
power on large scales, i.e., n\equiv d\ln P(k)/d \ln k \simlt -1, are better
described by the log-normal PDF. On the other hand, we note that the one-to-one
mapping of the initial and the evolved density fields consistent with the
log-normal model does not approximate the broad distribution of their mutual
correlation even on average. Thus the origin of the phenomenological log-normal
PDF approximation still remains to be understood.Comment: 25 pages, 8 figures, Accepted for publication in Ap
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