928 research outputs found
Asteroid occultations today and tomorrow: toward the GAIA era
Context: Observation of star occultations is a powerful tool to determine
shapes and sizes of asteroids. This is key information necessary for studying
the evolution of the asteroid belt and to calibrate indirect methods of size
determination, such as the models used to analyze thermal infrared
observations. Up to now, the observation of asteroid occultations is an
activity essentially secured by amateur astronomers equipped with small,
portable equipments. However, the accuracy of the available ephemeris prevents
accurate predictions of the occultation events for objects smaller than ~100
km. Aims: We investigate current limits in predictability and observability of
asteroid occultations, and we study their possible evolution in the future,
when high accuracy asteroid orbits and star positions (such as those expected
from the mission Gaia of the European Space Agency) will be available. Methods:
We use a simple model for asteroid ephemeris uncertainties and numerical
algorithms for estimating the limits imposed by the instruments, assuming
realistic CCD performances and asteroid size distribution, to estimate the
expected occultation rate under different conditions. Results: We show that
high accuracy ephemerides which will be available in the future will extend
toward much smaller asteroids the possibility of observing asteroid
occultations, greatly increasing the number of events and objects involved. A
complete set of size measurements down to ~10 km main belt asteroids could be
obtained in a few years, provided that a small network of ground-based 1m
telescopes are devoted to occultation studies
An optimal Mars Trojan asteroid search strategy
Trojan asteroids are minor planets that share the orbit of a planet about the
Sun and librate around the L4 or L5 Lagrangian points of stability. Although
only three Mars Trojans have been discovered, models suggest that at least ten
times this number should exist with diameters >= 1 km. We derive a model that
constrains optimal sky search areas and present a strategy for the most
efficient use of telescope survey time that maximizes the probability of
detecting Mars Trojans. We show that the Gaia space mission could detect any
Mars Trojans larger than 1 km in diameter, provided the relative motion
perpendicular to Gaia's CCD array is less than 0.40 arcsec per second.Comment: 6 pages, 6 figures, 3 tables, accepted for publication in MNRAS.
arXiv admin note: substantial text overlap with arXiv:1111.112
Should we reconsider competition in residential electricity supply? Survey results in North Carolina
Retail competition has been introduced in many states as part of electricity industry deregulation. Following problems in the electricity market in California in 2000/01 many states, including NC, put deregulation plans on hold. Where retail competition is allowed consumers can choose their electricity supplier, and companies can compete for customers on the basis of rates and/or other options such as green energy choices. The welfare benefits of retail competition depend on consumers’ willingness to switch suppliers, and in many cases people choose to stay with their current supplier even though rivals offer savings. In that sense consumers are ‘sticky’ in the same way they are with other services such as banking and credit. The question then becomes: should states reconsider retail competition or stay with the status quo? To help answer this question we survey residents in two North Carolina counties. Our survey focuses on: (i) households’ knowledge of and interest in retail competition (ii) factors that would encourage them to switch suppliers, with an emphasis on smart meters and (iii) how large the potential savings would have to be to encourage switching. Key Words: electricity supply, retail competition, switching
Detection of inner Solar System Trojan Asteroids by Gaia
The Gaia satellite, planned for launch by the European Space Agency (ESA) in
2013, is the next generation astrometry mission following Hipparcos. While
mapping the whole sky, the Gaia space mission is expected to discover thousands
of Solar System Objects. These will include Near-Earth Asteroids and objects at
Solar elongations as low as 45 degrees, which are difficult to observe with
ground-based telescopes. We present the results of simulations for the
detection of Trojan asteroids in the orbits of Earth and Mars by Gaia.Comment: 4 pages, 3 figures, based on a talk presented at the Gaia-FUN-SSO-2
International Workshop, Paris Observatory, 19-21 September 2012. Part of the
proceedings of that worksho
Australian participation in the Gaia follow-up network for solar system objects
The Gaia satellite, planned for launch by the European Space Agency (ESA) in 2013, is the next-generation astrometry mission following Hipparcos. Gaia’s primary science goal is to determine the kinematics, chemical structure, and evolution of the Milky Way Galaxy. In addition to this core science goal, the Gaia space mission is expected to discover thousands of Solar System objects. Because of orbital constraints, Gaia will only have a limited opportunity for astrometric follow-up of these discoveries. In 2010, the Gaia Data Processing and Analysis Consortium (DPAC) initiated a program to identify ground-based optical telescopes for a Gaia follow-up network for Solar System Objects to perform the following critical tasks: confirmation of discovery, identification of body, object tracking to constrain orbits. To date, this network comprises 37 observing sites (representing 53 instruments). The Zadko Telescope, located in Western Australia, was highlighted as an important network node because of its southern location, longitude, and automated scheduling system. We describe the first follow-up tests using the fast moving Potentially Hazardous Asteroid 2005 YU55 as the target
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
Stellar activity and, in particular, convection-related surface structures,
potentially cause fluctuations that can affect the transit light curves.
Surface convection simulations can help the interpretation of ToV. We used
realistic three-dimensional radiative hydrodynamical simulation of the Sun from
the Stagger-grid and synthetic images computed with the radiative transfer code
Optim3D to provide predictions for the transit of Venus in 2004 observed by the
satellite ACRIMSAT. We computed intensity maps from RHD simulation of the Sun
and produced synthetic stellar disk image. We computed the light curve and
compared it to the ACRIMSAT observations and also to the light curves obtained
with solar surface representations carried out using radial profiles with
different limb-darkening laws. We also applied the same spherical tile imaging
method to the observations of center-to-limb Sun granulation with HINODE. We
managed to explain ACRIMSAT observations of 2004 ToV and showed that the
granulation pattern causes fluctuations in the transit light curve. We
evaluated the contribution of the granulation to the ToV. We showed that the
granulation pattern can partially explain the observed discrepancies between
models and data. This confirms that the limb-darkening and the granulation
pattern simulated in 3D RHD Sun represent well what is imaged by HINODE. In the
end, we found that the Venus's aureole contribution during ToV is less intense
than the solar photosphere, and thus negligible. Being able to explain
consistently the data of 2004 ToV is a new step forward for 3D RHD simulations
that are becoming essential for the detection and characterization of
exoplanets. They show that the granulation have to be considered as an
intrinsic incertitude, due to the stellar variability, on precise measurements
of exoplanet transits of, most likely, planets with small diameters.Comment: Accepted for publication in Astronomy and Astrophysic
On the calibration of the relation between geometric albedo and polarimetric properties for the asteroids
We present a new extensive analysis of the old problem of finding a
satisfactory calibration of the relation between the geometric albedo and some
measurable polarization properties of the asteroids. To achieve our goals, we
use all polarimetric data at our disposal. For the purposes of calibration, we
use a limited sample of objects for which we can be confident to know the
albedo with good accuracy, according to previous investigations of other
authors. We find a new set of updated calibration coefficients for the
classical slope - albedo relation, but we generalize our analysis and we
consider also alternative possibilities, including the use of other
polarimetric parameters, one being proposed here for the first time, and the
possibility to exclude from best-fit analyzes the asteroids having low albedos.
We also consider a possible parabolic fit of the whole set of data.Comment: Accepted by MNRA
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