5,978 research outputs found
Coherence properties of light propagated through a scattering medium
Partially-coherent, quasi-monochromatic optical fields are fully described by
their Mutual Optical Intensity (MOI) or the phase-space equivalent, the
Generalised Radiance (GR). This paper reports on the application of a
propagation-based phase-space tomographic technique for determining both the
MOI and the GR of wavefields. This method is applied to the reconstruction of
the MOI and the GR of an optical wavefield propagated through a suspension of
\~10micrometre diameter polystyrene spheres.Comment: Photonics 2004, 7th International conference on optoelectronics,
fibre optics and photonics, Kochi, Indi
Asteroid family identification using the Hierarchical Clustering Method and WISE/NEOWISE physical properties
Using albedos from WISE/NEOWISE to separate distinct albedo groups within the
Main Belt asteroids, we apply the Hierarchical Clustering Method to these
subpopulations and identify dynamically associated clusters of asteroids. While
this survey is limited to the ~35% of known Main Belt asteroids that were
detected by NEOWISE, we present the families linked from these objects as
higher confidence associations than can be obtained from dynamical linking
alone. We find that over one-third of the observed population of the Main Belt
is represented in the high-confidence cores of dynamical families. The albedo
distribution of family members differs significantly from the albedo
distribution of background objects in the same region of the Main Belt, however
interpretation of this effect is complicated by the incomplete identification
of lower-confidence family members. In total we link 38,298 asteroids into 76
distinct families. This work represents a critical step necessary to debias the
albedo and size distributions of asteroids in the Main Belt and understand the
formation and history of small bodies in our Solar system.Comment: Accepted to ApJ. Full version of Table 3 to be published
electronically in Ap
Oil, Volatility and Institutions:Cross-Country Evidence from Major Oil Producers
This paper examines the long-run effects of oil revenue and its volatility on economic growth as well as the role of institutions in this relationship. We collect annual and monthly data on a sample of 17 major oil producers over the period 1961. 2013, and use the standard panel autoregressive distributed lag (ARDL) approach as well as its cross-sectionally augmented version (CS-ARDL) for estimation. Therefore, in contrast to the earlier literature on the resource curse, we take into account all three key features of the panel: dynamics, heterogeneity and cross-sectional dependence. Our results suggest that (i) there is a significant negative effect of oil revenue volatility on output growth, (ii) higher growth rate of oil revenue significantly raises economic growth, and (iii) better fiscal policy (institutions) can offset some of the negative effects of oil revenue volatility. We therefore argue that volatility in oil revenues combined with poor governmental responses to this volatility drives the resource curse paradox, not the abundance of oil revenues as such
Main Belt Asteroids with WISE/NEOWISE: Near-Infrared Albedos
We present revised near-infrared albedo fits of 2835 Main Belt asteroids
observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010.
These fits are derived from reflected-light near-infrared images taken
simultaneously with thermal emission measurements, allowing for more accurate
measurements of the near-infrared albedos than is possible for visible albedo
measurements. As our sample requires reflected light measurements, it
undersamples small, low albedo asteroids, as well as those with blue spectral
slopes across the wavelengths investigated. We find that the Main Belt
separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um.
Conversely, the 4.6 um albedo distribution spans the full range of possible
values with no clear grouping. Asteroid families show a narrow distribution of
3.4 um albedos within each family that map to one of the three observed
groupings, with the (221) Eos family being the sole family associated with the
16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived
from simultaneous thermal emission and reflected light measurements are an
important indicator of asteroid taxonomy and can identify interesting targets
for spectroscopic followup.Comment: Accepted for publication in ApJ; full version of Table1 to be
published electronically in the journa
A spectroscopically confirmed z=1.327 galaxy-scale deflector magnifying a z~8 Lyman-Break galaxy in the Brightest of Reionizing Galaxies survey
We present a detailed analysis of an individual case of gravitational lensing
of a Lyman-Break galaxy (LBG) in a blank field, identified in Hubble
Space Telescope imaging obtained as part of the Brightest of Reionizing
Galaxies survey. To investigate the close proximity of the bright
() -dropout to a small group of foreground galaxies, we
obtained deep spectroscopy of the dropout and two foreground galaxies using
VLT/X-Shooter. We detect H-, H-, [OIII] and [OII] emission in
the brightest two foreground galaxies (unresolved at the natural seeing of
arcsec), placing the pair at . We can rule out emission lines
contributing all of the observed broadband flux in band at
, allowing us to exclude the candidate as a low redshift
interloper with broadband photometry dominated by strong emission lines. The
foreground galaxy pair lies at the peak of the luminosity, redshift and
separation distributions for deflectors of strongly lensed objects,
and we make a marginal detection of a demagnified secondary image in the
deepest () filter. We show that the configuration can be accurately
modelled by a singular isothermal ellipsoidal deflector and a S\'{e}rsic source
magnified by a factor of . The reconstructed source in the
best-fitting model is consistent with luminosities and morphologies of
LBGs in the literature. The lens model yields a group mass of
and a stellar mass-to-light ratio for the
brightest deflector galaxy of within its effective radius. The foreground galaxies'
redshifts would make this one of the few strong lensing deflectors discovered
at .Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 3 table
Solar limb darkening function and solar diameter with eclipses observations
We introduce a new method to perform high resolution astrometry of the solar
diameter from the ground, through the observations of eclipses. A discussion of
the solar diameter and its variations is linked to the Limb Darkening Function
(LDF) using the luminosity evolution of a Baily's Bead and the profile of the
lunar limb available from satellite data. The inflexion point of the LDF is
defined as the solar limb. The method proposed is applied for the videos of the
eclipse in January, 15, 2010 recorded by Richard Nugent in Uganda and Andreas
Tegtmeier in India. An upper limit for the inflexion point position has been
set for that eclipse.Comment: 3 pages, 2 figures. Proceedings of the Fourth French-Chinese meeting
on Solar Physics Understanding Solar Activity: Advances and Challenges, 15 -
18 November, 2011 Nice, Franc
NEOWISE Reactivation Mission Year Three: Asteroid Diameters and Albedos
The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
reactivation mission has completed its third year of surveying the sky in the
thermal infrared for near-Earth asteroids and comets. NEOWISE collects
simultaneous observations at 3.4 um and 4.6 um of solar system objects passing
through its field of regard. These data allow for the determination of total
thermal emission from bodies in the inner solar system, and thus the sizes of
these objects. In this paper we present thermal model fits of asteroid
diameters for 170 NEOs and 6110 MBAs detected during the third year of the
survey, as well as the associated optical geometric albedos. We compare our
results with previous thermal model results from NEOWISE for overlapping sample
sets, as well as diameters determined through other independent methods, and
find that our diameter measurements for NEOs agree to within 26% (1-sigma) of
previously measured values. Diameters for the MBAs are within 17% (1-sigma).
This brings the total number of unique near-Earth objects characterized by the
NEOWISE survey to 541, surpassing the number observed during the fully
cryogenic mission in 2010.Comment: Accepted for publication in A
The Rising Light Curves of Type Ia Supernovae
We present an analysis of the early, rising light curves of 18 Type Ia
supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the
La Silla-QUEST variability survey (LSQ). We fit these early data flux using a
simple power-law to determine the time of first
light , and hence the rise-time from first light to
peak luminosity, and the exponent of the power-law rise (). We find a mean
uncorrected rise time of days, with individual SN rise-times
ranging from to days. The exponent n shows significant
departures from the simple 'fireball model' of (or ) usually assumed in the literature. With a mean value of , our data also show significant diversity from event to event. This
deviation has implications for the distribution of 56Ni throughout the SN
ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The
range of n found also confirms that the 56Ni distribution is not standard
throughout the population of SNe Ia, in agreement with earlier work measuring
such abundances through spectral modelling. We also show that the duration of
the very early light curve, before the luminosity has reached half of its
maximal value, does not correlate with the light curve shape or stretch used to
standardise SNe Ia in cosmological applications. This has implications for the
cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA
Spectral Models for Early Time SN 2011fe Observations
We use observed UV through near IR spectra to examine whether SN 2011fe can
be understood in the framework of Branch-normal SNe Ia and to examine its
individual peculiarities. As a benchmark, we use a delayed-detonation model
with a progenitor metallicity of Z_solar/20. We study the sensitivity of
features to variations in progenitor metallicity, the outer density profile,
and the distribution of radioactive nickel. The effect of metallicity
variations in the progenitor have a relatively small effect on the synthetic
spectra. We also find that the abundance stratification of SN 2011fe resembles
closely that of a delayed detonation model with a transition density that has
been fit to other Branch-normal Type Ia supernovae. At early times, the model
photosphere is formed in material with velocities that are too high, indicating
that the photosphere recedes too slowly or that SN 2011fe has a lower specific
energy in the outer ~0.1 M_sun than does the model. We discuss several
explanations for the discrepancies. Finally, we examine variations in both the
spectral energy distribution and in the colors due to variations in the
progenitor metallicity, which suggests that colors are only weak indicators for
the progenitor metallicity, in the particular explosion model that we have
studied. We do find that the flux in the U band is significantly higher at
maximum light in the solar metallicity model than in the lower metallicity
model and the lower metallicity model much better matches the observed
spectrum.Comment: 9 pages, 14 figures, MNRAS, in press, fixed typ
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