230 research outputs found
Similarities Between the Inner Solar System and the Planetary System of PSR B1257+12
We call attention to the surprising similarity between the newly discovered
planetary system around PSR B1257+12 and the inner solar system. The similarity
is in the ratios of the orbital radii and the masses of the three planets.Comment: 4 pages including 1 figure. uuencoded compressed postscript fil
A Possible Correlation between Mass Ratio and Period Ratio in Multiple Planetary Systems
We report on a possible correlation between the mass ratio and period ratio
of pairs of adjacent planets in extra-solar planetary systems. Monte-Carlo
simulations show that the effect is significant to level of 0.7%, as long as we
exclude two pairs of planets whose periods are at the 1:2 resonance. Only the
next few multiple systems can tell if the correlation is real.Comment: 8 pages, 2 figures, published in The Astrophysical Journal Letter
Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion I. Theory
Some transiting planets discovered by the Kepler mission display transit
timing variations (TTVs) induced by stellar spots that rotate on the visible
hemisphere of their parent stars. An induced TTV can be observed when a planet
crosses a spot and modifies the shape of the transit light curve, even if the
time resolution of the data does not allow to detect the crossing event itself.
We present an approach that can, in some cases, use the derived TTVs of a
planet to distinguish between a prograde and a retrograde planetary motion with
respect to the stellar rotation. Assuming a single spot darker than the stellar
disc, spot crossing by the planet can induce measured positive (negative) TTV,
if the crossing occurs in the first (second) half of the transit. On the other
hand, the motion of the spot towards (away from) the center of the stellar
visible disc causes the stellar brightness to decrease (increase). Therefore,
for a planet with prograde motion, the induced TTV is positive when the local
slope of the stellar flux at the time of transit is negative, and vice versa.
Thus, we can expect to observe a negative (positive) correlation between the
TTVs and the photometric slopes for prograde (retrograde) motion. Using a
simplistic analytical approximation, and also the publicly available SOAP-T
tool to produce light curves of transits with spot-crossing events, we show for
some cases how the induced TTVs depend on the local stellar photometric slopes
at the transit timings. Detecting this correlation in Kepler transiting systems
with high enough signal-to-noise ratio can allow us to distinguish between
prograde and retrograde planetary motions. In coming papers we present analyses
of the KOIs and Kepler eclipsing binaries, following the formalism developed
here.Comment: V2: Major revision, accepted to Ap
Stellar Rotation Periods of the Kepler Objects of Interest: A Dearth of Close-in Planets around Fast Rotators
We present a large sample of stellar rotation periods for Kepler Objects of
Interest (KOIs), based on three years of public Kepler data. These were
measured by detecting periodic photometric modulation caused by star spots,
using an algorithm based on the autocorrelation function (ACF) of the light
curve, developed recently by McQuillan, Aigrain & Mazeh (2013). Of the 1919
main-sequence exoplanet hosts analyzed, robust rotation periods were detected
for 737. Comparing the detected stellar periods to the orbital periods of the
innermost planet in each system reveals a notable lack of close-in planets
around rapid rotators. It appears that only slowly spinning stars, with
rotation periods longer than 5-10 days, host planets on orbits shorter than 3
days, although the mechanism(s) that lead(s) to this is not clear.Comment: Accepted for publication in ApJL on 8th Aug 2013, 5 pages, 3 figures,
1 table. A full machine-readable version of Table 1 is available as an
ancillary fil
Automated analysis of eclipsing binary lightcurves. I. EBAS -- a new Eclipsing Binary Automated Solver with EBOP
We present a new algorithm -- Eclipsing Binary Automated Solver (EBAS), to
analyse lightcurves of eclipsing binaries. The algorithm is designed to analyse
large numbers of lightcurves, and is therefore based on the relatively fast
EBOP code. To facilitate the search for the best solution, EBAS uses two
parameter transformations. Instead of the radii of the two stellar components,
EBAS uses the sum of radii and their ratio, while the inclination is
transformed into the impact parameter. To replace human visual assessment, we
introduce a new 'alarm' goodness-of-fit statistic that takes into account
correlation between neighbouring residuals. We perform extensive tests and
simulations that show that our algorithm converges well, finds a good set of
parameters and provides reasonable error estimation.Comment: 25 pages, 13 figures, accepted to MNRA
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