7,235 research outputs found
The Star Blended with the MOA-2008-BLG-310 Source Is Not the Exoplanet Host Star
High resolution Hubble Space Telescope (HST) image analysis of the
MOA-2008-BLG-310 microlens system indicates that the excess flux at the
location of the source found in the discovery paper cannot primarily be due to
the lens star because it does not match the lens-source relative proper motion,
, predicted by the microlens models. This excess flux is most
likely to be due to an unrelated star that happens to be located in close
proximity to the source star. Two epochs of HST observations indicate proper
motion for this blend star that is typical of a random bulge star, but is not
consistent with a companion to the source or lens stars if the flux is
dominated by only one star, aside from the lens. We consider models in which
the excess flux is due to a combination of an unrelated star and the lens star,
and this yields 95\% confidence level upper limit on the lens star brightness
of and . A Bayesian analysis using a standard
Galactic model and these magnitude limits yields a host star mass , a planet mass of at a projected separation of AU. This result illustrates excess flux in a high
resolution image of a microlens-source system need not be due to the lens. It
is important to check that the lens-source relative proper motion is consistent
with the microlensing prediction. The high resolution image analysis techniques
developed in this paper can be used to verify the WFIRST exoplanet microlensing
survey mass measurements.Comment: Submitted to AJ on March 18, 201
The Imprint of Gravitational Waves on the Cosmic Microwave Background
Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-
Decay of metastable phases in a model for the catalytic oxidation of CO
We study by kinetic Monte Carlo simulations the dynamic behavior of a
Ziff-Gulari-Barshad model with CO desorption for the reaction CO + O
CO on a catalytic surface. Finite-size scaling analysis of the fluctuations
and the fourth-order order-parameter cumulant show that below a critical CO
desorption rate, the model exhibits a nonequilibrium first-order phase
transition between low and high CO coverage phases. We calculate several points
on the coexistence curve. We also measure the metastable lifetimes associated
with the transition from the low CO coverage phase to the high CO coverage
phase, and {\it vice versa}. Our results indicate that the transition process
follows a mechanism very similar to the decay of metastable phases associated
with {\it equilibrium} first-order phase transitions and can be described by
the classic Kolmogorov-Johnson-Mehl-Avrami theory of phase transformation by
nucleation and growth. In the present case, the desorption parameter plays the
role of temperature, and the distance to the coexistence curve plays the role
of an external field or supersaturation. We identify two distinct regimes,
depending on whether the system is far from or close to the coexistence curve,
in which the statistical properties and the system-size dependence of the
lifetimes are different, corresponding to multidroplet or single-droplet decay,
respectively. The crossover between the two regimes approaches the coexistence
curve logarithmically with system size, analogous to the behavior of the
crossover between multidroplet and single-droplet metastable decay near an
equilibrium first-order phase transition.Comment: 27 pages, 22 figures, accepted by Physical Review
Rat mammary carcinogenesis following neutron- or X-radiation
Female 61 to 63 - day - old Sprague-Dawley rats were exposed once to a single dose of either 0.43 - MeV
neutrons or 250 - kVX - rays . For neutrons 23 rats were exposed in plastic tubes rotated around and 31 c m from
a water-cooled tritium impregnated target bombarded with 2.45 - MeV protons from a V a n de Graaff generator.
The mean kerma was measured at the rat location by integrating the response of a rat - sized homogeneous
tissue equivalent ionization chamber of minimum mass. The ratio between absorbed dose and kerma is under
investigation and is anticipated to be approximately 0.7. A compensated GM gamma-ray dosimeter indicated
that the gamma - ray doses were 3.5% of the total dose. All rats were examined weekly for the presence
of breast tumours and these were removed, fixed, stained and verified histologically as mammary neoplasms.
At 10 months after exposure 98<7ο of the rats were a live . The neutron kerma, the per cent of rats with
mammary neoplasia, and the number of rats were, respectively: 0.125 rads, 8.2°}o, 182; 0.5 rads, 9.0^0,
89; 2 rads, 20. 6,68; and 8 rads, 31.1%, 45. The X - ray results were: 30 R, 1.4% 95; 60 R, 27. l°Io, 48;
and 90 R, 35.4%, 48. A 3. O^o incidence was found in 167 control rats. At 10 months after exposure the
mammary neoplastic response after 8 rads of neutrons corresponds approximately to that after 60 - 90 R of
X - rays . Similarly, the response after 2 rads of neutrons was intermediate between 30 and 60 R of X - rays and
the response after 0 . 125 and 0.5 rads of neutrons was similar to that after 30 R of X - rays . This demonstrates
that the RBE for 0.43 - MeV neutrons is much lower at high doses than at low doses. Determination of the
confidence limits for the dose-RBE dependence and dose-incidence relationship will be determined as additional
data are collected
Computing CMB Anisotropy in Compact Hyperbolic Spaces
The measurements of CMB anisotropy have opened up a window for probing the
global topology of the universe on length scales comparable to and beyond the
Hubble radius. For compact topologies, the two main effects on the CMB are: (1)
the breaking of statistical isotropy in characteristic patterns determined by
the photon geodesic structure of the manifold and (2) an infrared cutoff in the
power spectrum of perturbations imposed by the finite spatial extent. We
present a completely general scheme using the regularized method of images for
calculating CMB anisotropy in models with nontrivial topology, and apply it to
the computationally challenging compact hyperbolic topologies. This new
technique eliminates the need for the difficult task of spatial eigenmode
decomposition on these spaces. We estimate a Bayesian probability for a
selection of models by confronting the theoretical pixel-pixel temperature
correlation function with the COBE-DMR data. Our results demonstrate that
strong constraints on compactness arise: if the universe is small compared to
the `horizon' size, correlations appear in the maps that are irreconcilable
with the observations. If the universe is of comparable size, the likelihood
function is very dependent upon orientation of the manifold wrt the sky. While
most orientations may be strongly ruled out, it sometimes happens that for a
specific orientation the predicted correlation patterns are preferred over the
conventional infinite models.Comment: 15 pages, LaTeX (IOP style included), 3 color figures (GIF) in
separate files. Minor revision to match the version accepted in Class.
Quantum Grav.: Proc. of Topology and Cosmology, Cleveland, 1997. The paper
can be also downloaded from
http://www.cita.utoronto.ca/~pogosyan/cwru_proc.ps.g
THE EFFECTS OF 2.0-Bev PROTONS IN MICE
The biological effects of proton beams of 2.0 to 2.2 Bev were studied in mice. Physical studies of particle distribution and depth dosimetry are described. Data are presented on lethal dosage measurements and studies of light element activation in tissues through proton reactions (p,pn) as determined by whole-body counting of gamma activity. (C.H.
The cloud-in-cloud problem for non-Gaussian density fields
The cloud-in-cloud problem is studied in the context of the extension to
non-Gaussian density fields of the Press-Schechter approach for the calculation
of the mass function. As an example of a non-Gaussian probability distribution
functions (PDFs) we consider the Chi-square, with various degrees of freedom.
We generate density fields in cubic boxes with periodic boundary conditions and
then determine the number of points considered collapsed at each scale through
an hierarchy of smoothing windows. We find that the mass function we obtain
differs from that predicted using the Extended Press-Schechter formalism,
particularly for low values of and for those PDFs most distinct from a
Gaussian.Comment: 5 pages, LaTex using mn.sty, matches published version, results for
the Inverted Chi-square distribution withdraw
The Sunyaev-Zeldovich effect in CMB-calibrated theories applied to the Cosmic Background Imager anisotropy power at l > 2000
We discuss the nature of the possible high-l excess in the Cosmic Microwave
Background (CMB) anisotropy power spectrum observed by the Cosmic Background
Imager (CBI). We probe the angular structure of the excess in the CBI deep
fields and investigate whether it could be due to the scattering of CMB photons
by hot electrons within clusters, the Sunyaev-Zeldovich (SZ) effect. We
estimate the density fluctuation parameters for amplitude, sigma_8, and shape,
Gamma, from CMB primary anisotropy data and other cosmological data. We use the
results of two separate hydrodynamical codes for Lambda-CDM cosmologies,
consistent with the allowed sigma_8 and Gamma values, to quantify the expected
contribution from the SZ effect to the bandpowers of the CBI experiment and
pass simulated SZ effect maps through our CBI analysis pipeline. The result is
very sensitive to the value of sigma_8, and is roughly consistent with the
observed power if sigma_8 ~ 1. We conclude that the CBI anomaly could be a
result of the SZ effect for the class of Lambda-CDM concordance models if
sigma_8 is in the upper range of values allowed by current CMB and Large Scale
Structure (LSS) data.Comment: Accepted by The Astrophysical Journal; 17 pages including 12 color
figures. v2 matches accepted version. Additional information at
http://www.astro.caltech.edu/~tjp/CBI
How exactly did the Universe become neutral?
We present a refined treatment of H, He I, and He II recombination in the
early Universe. The difference from previous calculations is that we use
multi-level atoms and evolve the population of each level with redshift by
including all bound-bound and bound-free transitions. In this framework we
follow several hundred atomic energy levels for H, He I, and He II combined.
The main improvements of this method over previous recombination calculations
are: (1) allowing excited atomic level populations to depart from an
equilibrium distribution; (2) replacing the total recombination coefficient
with recombination to and photoionization from each level directly at each
redshift step; and (3) correct treatment of the He I atom, including the
triplet and singlet states. We find that the ionization fraction x_e = n_e/n_H
is approximately 10% smaller at redshifts <~800 than in previous calculations,
due to the non-equilibrium of the excited states of H, which is caused by the
strong but cool radiation field at those redshifts. In addition we find that He
I recombination is delayed compared with previous calculations, and occurs only
just before H recombination. These changes in turn can affect the predicted
power spectrum of microwave anisotropies at the few percent level. Other
improvements such as including molecular and ionic species of H, including
complete heating and cooling terms for the evolution of the matter temperature,
including collisional rates, and including feedback of the secondary spectral
distortions on the radiation field, produce negligible change to x_e. The lower
x_e at low z found in this work affects the abundances of H molecular and ionic
species by 10-25%. However this difference is probably not larger than other
uncertainties in the reaction rates.Comment: 24 pages, including 18 figures, using emulateapj.sty, to appear in
ApJ, the code recfast can be obtained at
http://www.astro.ubc.ca/people/scott/recfast.html (in FORTRAN) and
http://cfa-www.harvard.edu/~sasselov/rec/ (in C
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