4,801 research outputs found
(1173) Anchises - Thermophysical and Dynamical Studies of a Dynamically Unstable Jovian Trojan
We have performed detailed thermophysical and dynamical modelling of Jovian
Trojan (1173) Anchises. Our results reveal a most unusual object. By examining
observational data taken by IRAS, Akari and WISE between 11.5 and 60 microns,
along with variations in its optical lightcurve, we find Anchises is most
likely an elongated body, with an axes-ratio of ~1.4. This yields calculated
best-fit dimensions of 170x121x121km (an equivalent diameter of 136+18/-11km).
We find the observations are best fit by Anchises having a retrograde sense of
rotation, and an unusually high thermal inertia (25 to 100 Jm-2s-0.5K-1). The
geometric albedo is found to be 0.027 (+0.006/-0.007). Anchises therefore has
one of the highest published thermal inertias of any object larger than 100km
in diameter, at such large heliocentric distances, and is one of the lowest
albedo objects ever observed. More observations are needed to see if there is a
link between the very shallow phase curve, with almost no opposition effect,
and the derived thermal properties for this large Trojan asteroid. Our
dynamical investigation of Anchises' orbit has revealed it to be dynamically
unstable on timescales of hundreds of Myr, similar to the unstable Neptunian
Trojans 2001 QR322 and 2008 LC18. Unlike those objects, we find that Anchises'
dynamical stability is not a function of its initial orbital elements, the
result of the exceptional precision with which its orbit is known. This is the
first time that a Jovian Trojan has been shown to be dynamically unstable, and
adds weight to the idea that planetary Trojans represent a significant ongoing
contribution to the Centaur population, the parents of the short-period comets.
The observed instability does not rule out a primordial origin for Anchises,
but when taken in concert with the result of our thermophysical analysis,
suggest that it would be a fascinating target for future study.Comment: 5 figures, 3 tables, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
A Detailed Investigation of the Proposed NN Serpentis Planetary System
The post-main sequence eclipsing binary NN Serpentis was recently announced
as the potential host of at least two massive planetary companions. In that
work, the authors put forward two potential architectures that fit the
observations of the eclipsing binary with almost identical precision. In this
work, we present the results of a dynamical investigation of the orbital
stability of both proposed system architectures, finding that they are only
stable for scenarios in which the planets are locked in mutual mean motion
resonance. In the discovery work, the authors artificially fixed the orbital
eccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse
the observational data on NN Serpentis without this artificial constraint, and
derive a new orbital solution for the two proposed planets. We detail the
results of further dynamical simulations investigating the stability of our new
orbital solution, and find that allowing a small non-zero eccentricity for the
outer planet renders the system unstable. We conclude that, although the
original orbits proposed for the NN Serpentis planetary system prove
dynamically feasible, further observations of the system are vital in order to
better constrain the system's true architecture.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society; 5 figures, 2 table
A comparison of leaf crystal macropatterns in the two sister genera Piper and Peperomia (Piperaceae)
Premise of the study: This is the first large-scale study comparing leaf crystal macropatterns of the species-rich sister genera Piper and Peperomia. It focuses on identifying types of calcium oxalate crystals and their macropatterns in leaves of both genera. The Piper results are placed in a phylogenetic context to show evolutionary patterns. This information will expand knowledge about crystals and provide specific examples to help study their form and function. One example is the first-time observation of Piper crystal sand tumbling in chlorenchyma vacuoles.
Methods: Herbarium and fresh leaves were cleared of cytoplasmic content and examined with polarizing microscopy to identify types of crystals and their macropatterns. Selected hydrated herbarium and fresh leaf punches were processed for scanning electron microscopy and x-ray elemental analysis. Vibratome sections of living Piper and Peperomia leaves were observed for anatomical features and crystal movement.
Key results: Both genera have different leaf anatomies. Piper displays four crystal types in chlorenchyma-crystal sand, raphides, styloids, and druses, whereas Peperomia displays three types-druses, raphides, and prisms. Because of different leaf anatomies and crystal types between the genera, macropatterns are completely different. Crystal macropattern evolution in both is characterized by increasing complexity, and both may use their crystals for light gathering and reflection for efficient photosynthesis under low-intensity light environments.
Conclusions: Both genera have different leaf anatomies, types of crystals and crystal macropatterns. Based on Piper crystals associated with photosynthetic tissues and low-intensity light, further study of their function and association with surrounding chloroplasts is warranted, especially active crystal movement
Stable habitable zones of single Jovian planet systems
With continued improvement in telescope sensitivity and observational
techniques, the search for rocky planets in stellar habitable zones is entering
an exciting era. With so many exoplanetary systems available for follow-up
observations to find potentially habitable planets, one needs to prioritise the
ever-growing list of candidates. We aim to determine which of the known
planetary systems are dynamically capable of hosting rocky planets in their
habitable zones, with the goal of helping to focus future planet search
programs. We perform an extensive suite of numerical simulations to identify
regions in the habitable zones of single Jovian planet systems where Earth mass
planets could maintain stable orbits, specifically focusing on the systems in
the Catalog of Earth-like Exoplanet Survey Targets (CELESTA). We find that
small, Earth-mass planets can maintain stable orbits in cases where the
habitable zone is largely, or partially, unperturbed by a nearby Jovian, and
that mutual gravitational interactions and resonant mechanisms are capable of
producing stable orbits even in habitable zones that are significantly or
completely disrupted by a Jovian. Our results yield a list of 13 single Jovian
planet systems in CELESTA that are not only capable of supporting an Earth-mass
planet on stable orbits in their habitable zone, but for which we are also able
to constrain the orbits of the Earth-mass planet such that the induced radial
velocity signals would be detectable with next generation instruments.Comment: 15 pages, 12 figures, Accepted for publication by MNRA
Decoding sequential vs non-sequential two-photon double ionization of helium using nuclear recoil
Above 54.4 eV, two-photon double ionization of helium is dominated by a
sequential absorption process, producing characteristic behavior in the single
and triple differential cross sections. We show that the signature of this
process is visible in the nuclear recoil cross section, integrated over all
energy sharings of the ejected electrons, even below the threshold for the
sequential process. Since nuclear recoil momentum imaging does not require
coincident photoelectron measurement, the predicted images present a viable
target for future experiments with new short-pulse VUV and soft X-ray sources.Comment: 4 pages, 3 figure
The Iowa Academy of Science Parish Farm: Its Past, Present and Future - A 25 Year Overview
This article focuses on the Iowa Academy of Science Parish Farm celebration of its 25th anniversary in 1985 at the Farm. The celebration provided an opportunity to view the progress made in establishing the Farm as a model for both farming and non-farming conservation practices. The celebration also included opportunities to review the history of the Farm, the life of Jessie A. Parish, and the interactions of the Iowa Academy of Science with the Parish Farm management, tenants, and Grundy County Conservation Board. These activities are followed by an in-depth account of the struggles which have occurred within the Board of Directors and Finance, Farm, and Social Implications committees to rationalize owning and operating a farm versus selling it and investing the principle for general Academy use. All of these accounts are placed in perspective with the growth and development of the Academy during the past 25 years to the present. What the role of the Farm will be in the future of the Academy is discussed in light of a changing and active membership and the continued growth of the Academy within the realms of science and science education
Origin and Dynamical Evolution of Neptune Trojans - II: Long Term Evolution
We present results examining the fate of the Trojan clouds produced in our
previous work. We find that the stability of Neptunian Trojans seems to be
strongly correlated to their initial post-migration orbital elements, with
those objects that survive as Trojans for billions of years displaying
negligible orbital evolution. The great majority of these survivors began the
integrations with small eccentricities (e < 0.2) and small libration amplitudes
(A < 30 - 40{\deg}). The survival rate of "pre-formed" Neptunian Trojans (which
in general survived on dynamically cold orbits (e < 0.1, i < 5 - 10{\deg}))
varied between ~5 and 70%. By contrast, the survival rate of "captured" Trojans
(on final orbits spread across a larger region of e-i element space) were
markedly lower, ranging between 1 and 10% after 4 Gyr. Taken in concert with
our earlier work, we note that planetary formation scenarios which involve the
slow migration (a few tens of millions of years) of Neptune from an initial
planetary architecture that is both resonant and compact (aN < 18 AU) provide
the most promising fit of those we considered to the observed Trojan
population. In such scenarios, we find that the current day Trojan population
would number ~1% of that which was present at the end of the planet's
migration, with the bulk being sourced from captured, rather than pre-formed
objects. We note, however, that even those scenarios still fail to reproduce
the currently observed portion of the Neptune Trojan population moving on
orbits with e 20{\deg}. Dynamical integrations of the currently
observed Trojans show that five out of the seven are dynamically stable on 4
Gyr timescales, while 2001 QR322, exhibits significant dynamical instability.
The seventh Trojan object, 2008 LC18, has such large orbital uncertainties that
only future studies will be able to determine its stability.Comment: 24 pages, 6 figures, accepted for publication in MNRAS (The abstract
was shortened. Original version can be found in the pdf file
MAGSAT data processing: A report for investigators
The in-flight attitude and vector magnetometer data bias recovery techniques and results are described. The attitude bias recoveries are based on comparisons with a magnetic field model and are thought to be accurate to 20 arcsec. The vector magnetometer bias recoveries are based on comparisons with the scalar magnetometer data and are thought to be accurate to 3 nT or better. The MAGSAT position accuracy goals of 60 m radially and 300 m horizontally were achieved for all but the last 3 weeks of Magsat lifetime. This claim is supported by ephemeris overlap statistics and by comparisons with ephemerides computed with an independent orbit program using data from an independent tracking network. MAGSAT time determination accuracy is estimated at 1 ms. Several errors in prelaunch assumptions regarding data time tags, which escaped detection in prelaunch data tests, and were discovered and corrected postlaunch are described. Data formats and products, especially the Investigator-B tapes, which contain auxiliary parameters in addition to the basic magnetometer and ephemeris data, are described
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