822 research outputs found
Could the planets around HR 8799 be brown dwarfs?
We consider the limiting case for orbital stability of the companions to HR
8799. This case is only consistent with ages for the system of ~100 Myr, not
with the 1 Gyr age proposed from astroseismology. The discrepancy probably
arises because the inclination of the star is smaller than assumed in analyzing
the astroseismology data. Given this young age, the best estimates of the
companion masses place them by a small margin on the planet side of the
division between planets and brown dwarfs.Comment: 4 pages, 2 figures, accepted by ApJ Letter
On the Solar System-Debris Disk Connecction
This paper emphasizes the connection between solar and extra-solar debris
disks: how models and observations of the Solar System are helping us
understand the debris disk phenomenon, and vice versa, how debris disks are
helping us place our Solar System into context.Comment: 8 pages, Exoplanets: Detection, Formation and Dynamics Proceedings
IAU Symposium No. 249 200
A Study of the Dynamics of Dust from the Kuiper Belt: Spatial Distribution and Spectral Energy Distribution
The dust produced in the Kuiper Belt (KB) spreads throughout the Solar System
forming a dust disk. We numerically model the orbital evolution of KB dust and
estimate its equilibrium spatial distribution and its brightness and spectral
energy distributions (SED), assuming greybody absorption and emission by the
dust grains. We show that the planets modify the KB disk SED, so potentially we
can infer the presence of planets in spatially unresolved debris disks by
studying the shape of their SEDs. We point out that there are inherent
uncertainties in the prediction of structure in the dust disk, owing to the
chaotic dynamics of dust orbital evolution imposed by resonant gravitational
perturbations of the planets.Comment: 19 pages, 14 figures in jpg, accepted to A
High-Mass, Four-Planet Models for HR 8799: Constraining the Orbital Inclination and Age of the System
Debates regarding the age and inclination of the planetary system orbiting HR
8799, and the release of additional astrometric data following the discovery of
the fourth planet prompted us to examine the possibility of constraining these
two quantities by studying the long-term stability of this system at different
orbital inclinations and in its high-mass configuration (7-10-10-10 MJup). We
carried out ~1.5 million N-body integrations for different combinations of
orbital elements of the four planets. The most dynamically stable combinations
survived less than ~5 Myr at inclinations of 0{\deg} and 13{\deg}, and 41, 46,
and 31 Myr at 18{\deg}, 23{\deg}, and 30{\deg}, respectively. Given such short
lifetimes and the location of the system on the age-luminosity diagram for
low-mass objects, the most reasonable conclusion of our study is that the
planetary masses are less than 7-10-10-10 MJup and the system is quite young.
Two trends to note from our work are as follows. (1) In the most stable
systems, the higher the inclination, the more the coordinates for planets b and
c diverge from the oldest archival astrometric data (released after we
completed our N-body integrations), suggesting that either these planets are in
eccentric orbits or have lower orbital inclinations than that of planet d. (2)
The most stable systems place planet e closer to the central star than is
observed, supporting the conclusion that the planets are more massive and the
system is young. We present the details of our simulations and discuss the
implications of the results.Comment: Content: 25 pages, 5 figures, 1 table. Submitted for publication on
2012 January 2. Accepted for publication in the Astrophysical Journal on June
7, 2012. File updated June 9, 201
Country differences in the gender effect on poverty in Europe
This paper evaluates to what extent differences in population and structural characteristics between countries can explain country differences with respect to the gender effect on poverty. Our study aims to advance research on the structural dimension in the predominantly individually-oriented study field of poverty. To facilitate an approach that integrates individual and structural context dimensions we take advantage of multilevel techniques to test differences among a large number of countries regarding the effect of the gender gap on the risk of being poor, entering into poverty, and exiting from poverty. We use the European Union Survey on Income and Living Conditions for the years 2007-2008. From our analyses, we conclude that structural effects seem to be more relevant than individual effects in explaining country differences with regard to the gender poverty gap.The financial support from Spanish Ministry of Education through grant ECO2009-11117 and Junta de Andalucía though grant P07-SEJ-03261
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