478 research outputs found
Detection of Contact Binaries Using Sparse High Phase Angle Lightcurves
We show that candidate contact binary asteroids can be efficiently identified
from sparsely sampled photometry taken at phase angles >60deg. At high phase
angle, close/contact binary systems produce distinctive lightcurves that spend
most of the time at maximum or minimum (typically >1mag apart) brightness with
relatively fast transitions between the two. This means that a few (~5) sparse
observations will suffice to measure the large range of variation and identify
candidate contact binary systems. This finding can be used in the context of
all-sky surveys to constrain the fraction of contact binary near-Earth objects.
High phase angle lightcurve data can also reveal the absolute sense of the
spin.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in ApJ
Extreme Kuiper Belt Object 2001 QG298 and the Fraction of Contact Binaries
Extensive time-resolved observations of Kuiper Belt object 2001 QG298 show a
lightcurve with a peak-to-peak variation of 1.14 +-0.04 magnitudes and
single-peaked period of 6.8872 +- 0.0002 hr. The mean absolute magnitude is
6.85 magnitudes which corresponds to a mean effective radius of 122 (77) km if
an albedo of 0.04 (0.10) is assumed. This is the first known Kuiper Belt object
and only the third minor planet with a radius > 25 km to display a lightcurve
with a range in excess of 1 magnitude. We find the colors to be typical for a
Kuiper Belt object (B-V = 1.00 +- 0.04, V-R = 0.60 +- 0.02) with no variation
in color between minimum and maximum light. The large light variation,
relatively long double-peaked period and absence of rotational color change
argue against explanations due to albedo markings or elongation due to high
angular momentum. Instead, we suggest that 2001 QG298 may be a very close or
contact binary similar in structure to what has been independently proposed for
the Trojan asteroid 624 Hektor. If so, its rotational period would be twice the
lightcurve period or 13.7744 +- 0.0004 hr. By correcting for the effects of
projection, we estimate that the fraction of similar objects in the Kuiper Belt
is at least 10% to 20% with the true fraction probably much higher. A high
abundance of close and contact binaries is expected in some scenarios for the
evolution of binary Kuiper Belt objects.Comment: 15 text pages,6 figures(Color),5 Tables, Accepted to AJ for May 200
The Origin of (90) Antiope From Component-Resolved Near-Infrared Spectroscopy
The origin of the similary-sized binary asteroid (90) Antiope remains an
unsolved puzzle. To constrain the origin of this unique double system, we
recorded individual spectra of the components using SPIFFI, a near-infrared
integral field spectrograph fed by SINFONI, an adaptive optics module available
on VLT-UT4. Using our previously published orbital model, we requested
telescope time when the separation of the components of (90) Antiope was larger
than 0.087", to minimize the contamination between components, during the
February 2009 opposition. Several multi-spectral data-cubes in J band (SNR=40)
and H+K band (SNR=100) were recorded in three epochs and revealed the two
components of (90) Antiope. After developing a specific photometric extraction
method and running an error analysis by Monte-Carlo simulations, we
successfully extracted reliable spectra of both components from 1.1 to 2.4 um
taken on the night of February 21, 2009. These spectra do not display any
significant absorption features due to mafic mineral, ices, or organics, and
their slopes are in agreement with both components being C- or Cb- type
asteroids. Their constant flux ratio indicates that both components' surface
reflectances are quite similar, with a 1-sigma variation of 7%. By comparison
with 2MASS J, H, K color distribution of observed Themis family members, we
conclude that both bodies were most likely formed at the same time and from the
same material. The similarly-sized system could indeed be the result of the
breakup of a rubble-pile proto-Antiope into two equal-sized bodies, but other
scenarios of formation implying a common origin should also be considered.Comment: 46 pages, 1 table, 11 figures accepted for publication to Icaru
A spectral comparison of (379) Huenna and its satellite
We present near-infrared spectral measurements of Themis family asteroid
(379) Huenna (D~98 km) and its 6 km satellite using SpeX on the NASA IRTF. The
companion was farther than 1.5" from the primary at the time of observations
and was approximately 5 magnitudes dimmer. We describe a method for separating
and extracting the signal of a companion asteroid when the signal is not
entirely resolved from the primary. The spectrum of (379) Huenna has a broad,
shallow feature near 1 {\mu}m and a low slope, characteristic of C-type
asteroids. The secondary's spectrum is consistent with the taxonomic
classification of C-complex or X-complex. The quality of the data was not
sufficient to identify any subtle feature in the secondary's spectrum.Comment: 6 pages, 4 figures, 2 tables - Accepted for publication in Icaru
Atmospheric 81Kr as an integrator of cosmic-ray flux on the hundred-thousand-year timescale
The atmospheric abundance of 81Kr is a global integrator of cosmic rays. It is insensitive to climate shifts, geographical variations, and short-term solar cycle activity, making it an ideal standard to test models of cosmic-ray flux on the time scale of 105 years. Here we present the first calculation of absolute 81Kr production rates in the atmosphere, and a measurement of the atmospheric 81Kr/Kr abundance via the Atom Trap Trace Analysis method. The measurement result significantly deviates from previously reported values. The agreement between measurement and model prediction supports the current understanding of the production mechanisms. Additionally, the calculated 81Kr atmospheric inventory over the past 1.5 Myr provides a more accurate input function for radiokrypton dating
Introduction to the functional RG and applications to gauge theories
These lectures contain an introduction to modern renormalization group (RG)
methods as well as functional RG approaches to gauge theories. In the first
lecture, the functional renormalization group is introduced with a focus on the
flow equation for the effective average action. The second lecture is devoted
to a discussion of flow equations and symmetries in general, and flow equations
and gauge symmetries in particular. The third lecture deals with the flow
equation in the background formalism which is particularly convenient for
analytical computations of truncated flows. The fourth lecture concentrates on
the transition from microscopic to macroscopic degrees of freedom; even though
this is discussed here in the language and the context of QCD, the developed
formalism is much more general and will be useful also for other systems.Comment: 60 pages, 14 figures, Lectures held at the 2006 ECT* School
"Renormalization Group and Effective Field Theory Approaches to Many-Body
Systems", Trento, Ital
Atmospheric pollution, soil nutrients and climate effects on Mucoromycota arbuscular mycorrhizal fungi
Fine root endophyte mycorrhizal fungi in the Endogonales (Mucoromycota arbuscular mycorrhizal fungi, M-AMF) are now recognized as at least as important globally as Glomeromycota AMF (G-AMF), yet little is known about the environmental factors which influence M-AMF diversity and colonization, partly because they typically only co-colonize plants with G-AMF. Wild populations of Lycopodiella inundata predominantly form mycorrhizas with M-AMF and therefore allow focussed study of M-AMF environmental drivers. Using microscopic examination and DNA sequencing we measured M-AMF colonization and diversity over three consecutive seasons and modelled interactions between these response variables and environmental data. Significant relationships were found between M-AMF colonization and soil S, P, C:N ratio, electrical conductivity, and the previously overlooked micronutrient Mn. Estimated N deposition was negatively related to M-AMF colonization. Thirty-nine Endogonales Operational Taxonomic Units (OTUs) were identified in L. inundata roots, a greater diversity than previously recognized in this plant. Endogonales OTU richness correlated negatively with soil C:N while community composition was mostly influenced by soil P. This study provides first evidence that M-AMF have distinct ecological preferences in response to edaphic variables also related to air pollution. Future studies require site-level atmospheric pollution monitoring to guide critical load policy for mycorrhizal fungi in heathlands and grasslands
Enhanced lithium depletion in Sun-like stars with orbiting planets
The surface abundance of lithium on the Sun is 140 times less than
protosolar, yet the temperature at the base of the surface convective zone is
not hot enough to burn Li. A large range of Li abundances in solar type stars
of the same age, mass and metallicity is observed, but theoretically difficult
to understand. An earlier suggestion that Li is more depleted in stars with
planets was weakened by the lack of a proper comparison sample of stars without
detected planets. Here we report Li abundances for an unbiased sample of
solar-analogue stars with and without detected planets. We find that the
planet-bearing stars have less than 1 per cent of the primordial Li abundance,
while about 50 per cent of the solar analogues without detected planets have on
average 10 times more Li. The presence of planets may increase the amount of
mixing and deepen the convective zone to such an extent that the Li can be
burned.Comment: 13 pages, 2 figure
Rapid, non-invasive, in vivo measurement of tissue mechanical properties using gravitational loading and a nonlinear virtual fields method
Measuring the mechanical properties of soft tissues in vivo is important in biomechanics and for diagnosis and staging of diseases, but challenging because it is difficult to control the boundary conditions. We present a novel, non-invasive method for measuring tissue properties using gravitational loading. MRI images of an organ in different positions are registered to measure tissue displacements due to gravitational forces in different positions. Considering equilibrium between stresses and gravity, we established a nonlinear virtual fields method to identify the tissue properties. The method was applied to the human brain as a proof of concept, using an Ogden model. Sensitivity analysis showed that the bulk modulus could be identified accurately whilst the shear modulus was identified with greater uncertainty; the strains were too small to identify the strain stiffening exponent. The measured properties agreed well with published in vitro data. The technique offers very promising perspectives, allowing the non-invasive measurement of otherwise inaccessible tissues and providing new information such as the bulk modulus under static loading, which has never previously been measured in vivo
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