2,863 research outputs found
The pulsation spectrum of VX Hydrae
We present the results of a two-year, multisite observing campaign
investigating the high-amplitude delta Scuti star VX Hydrae during the 2006 and
2007 observing seasons. The final data set consists of nearly 8500 V-band
observations spanning HJD 2453763.6 to 2454212.7 (2006 January 28 to 2007 April
22). Separate analyses of the two individual seasons of data yield 25
confidently-detected frequencies common to both data sets, of which two are
pulsation modes, and the remaining 23 are Fourier harmonics or beat frequencies
of these two modes. The 2006 data set had five additional frequencies with
amplitudes less than 1.5 mmag, and the 2007 data had one additional frequency.
Analysis of the full 2006-2007 data set yields 22 of the 25 frequencies found
in the individual seasons of data. There are no significant peaks in the
spectrum other than these between 0 and 60 c/d. The frequencies of the two main
pulsation modes derived from the 2006 and 2007 observing seasons individually
do not differ at the level of 3-sigma, and thus we find no conclusive evidence
for period change over the span of these observations. However, the amplitude
of f(1) = 5.7898 c/d changed significantly between the two seasons, while the
amplitude of f(0) = 4.4765 c/d remained constant; amplitudes of the Fourier
harmonics and beat frequencies of f(1) also changed. Similar behavior was seen
in the 1950s, and it is clear that VX Hydrae undergoes significant amplitude
changes over time.Comment: 14 pages, 5 figures, published in Publications of the Astronomical
Society of the Pacific, v.121, p.1076 (October 2009
CoRoT's first seven planets: An overview
The up to 150 day uninterrupted high-precision photometry of about 100000
stars - provided so far by the exoplanet channel of the CoRoT space telescope -
gave a new perspective on the planet population of our galactic neighbourhood.
The seven planets with very accurate parameters widen the range of known planet
properties in almost any respect. Giant planets have been detected at low
metallicity, rapidly rotating and active, spotted stars. CoRoT-3 populated the
brown dwarf desert and closed the gap of measured physical properties between
standard giant planets and very low mass stars. CoRoT extended the known range
of planet masses down to 5 Earth masses and up to 21 Jupiter masses, the radii
to less than 2 Earth radii and up to the most inflated hot Jupiter found so
far, and the periods of planets discovered by transits to 9 days. Two CoRoT
planets have host stars with the lowest content of heavy elements known to show
a transit hinting towards a different planet-host-star-metallicity relation
then the one found by radial-velocity search programs. Finally the properties
of the CoRoT-7b prove that terrestrial planets with a density close to Earth
exist outside the Solar System. The detection of the secondary transit of
CoRoT-1 at the -level and the very clear detection of the 1.7 Earth
radii of CoRoT-7b at relative flux are promising evidence of
CoRoT being able to detect even smaller, Earth sized planets.Comment: 8 pages, 19 figures and 3 table
A MICROCOMPUTER MODEL FOR IRRIGATION SYSTEM EVALUATION
ICEASE (Irrigation Cost Estimator and System Evaluator) is a microcomputer model designed and developed to meet the need for conducting economic evaluation of adjustments to irrigation systems and management techniques to improve the use of irrigated water. ICEASE can calculate the annual operating costs for irrigation systems and has five options that can be used to economically evaluate improvements in the pumping plant or the way the irrigation system is used for crop production.Crop Production/Industries,
Where are the Uranus Trojans?
The area of stable motion for fictitious Trojan asteroids around Uranus'
equilateral equilibrium points is investigated with respect to the inclination
of the asteroid's orbit to determine the size of the regions and their shape.
For this task we used the results of extensive numerical integrations of orbits
for a grid of initial conditions around the points L4 and L5, and analyzed the
stability of the individual orbits. Our basic dynamical model was the Outer
Solar System (Jupiter, Saturn, Uranus and Neptune). We integrated the equations
of motion of fictitious Trojans in the vicinity of the stable equilibrium
points for selected orbits up to the age of the Solar system of 5 billion
years. One experiment has been undertaken for cuts through the Lagrange points
for fixed values of the inclinations, while the semimajor axes were varied. The
extension of the stable region with respect to the initial semimajor axis lies
between 19.05 < a < 19.3 AU but depends on the initial inclination. In another
run the inclination of the asteroids' orbit was varied in the range 0 < i < 60
and the semimajor axes were fixed. It turned out that only four 'windows' of
stable orbits survive: these are the orbits for the initial inclinations 0 < i
< 7, 9 < i < 13, 31 < i < 36 and 38 < i < 50. We postulate the existence of at
least some Trojans around the Uranus Lagrange points for the stability window
at small and also high inclinations.Comment: 15 pages, 12 figures, submitted to CMD
Fuzzy Characterization of Near-Earth-Asteroids
Due to close encounters with the inner planets, Near-Earth-Asteroids (NEAs)
can have very chaotic orbits. Because of this chaoticity, a statistical
treatment of the dynamical properties of NEAs becomes difficult or even
impossible. We propose a new way to classify NEAs by using methods from Fuzzy
Logic. We demonstrate how a fuzzy characterization of NEAs can be obtained and
how a subsequent analysis can deliver valid and quantitative results concerning
the long-term dynamics of NEAs.Comment: 11 pages, presented at the 7th Alexander von Humboldt Colloquium on
Celestial Mechanics (2008), accepted for publication in "Celestial Mechanics
and Dynamical Astronomy
Impact inducted surface heating by planetesimals on early Mars
We investigate the influence of impacts of large planetesimals and small
planetary embryos on the early Martian surface on the hydrodynamic escape of an
early steam atmosphere that is exposed to the high soft X-ray and EUV flux of
the young Sun. Impact statistics in terms of number, masses, velocities, and
angles of asteroid impacts onto the early Mars are determined via n-body
integrations. Based on these statistics, smoothed particle hydrodynamics (SPH)
simulations result in estimates of energy transfer into the planetary surface
material and according surface heating. For the estimation of the atmospheric
escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper
atmosphere hydrodynamic model to a magma ocean-related catastrophically
outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11
bar CO2. The estimated impact rates and energy deposition onto an early Martian
surface can account for substantial heating. The energy influx and conversion
rate into internal energy is most likely sufficient to keep a shallow magma
ocean liquid for an extended period of time. Higher surface temperatures keep
the outgassed steam atmosphere longer in vapor form and therefore enhance its
escape to space within about 0.6 Myr after its formation.Comment: submitted to A&
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
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