55 research outputs found
Small Telescope Exoplanet Transit Surveys: XO
The XO project aims at detecting transiting exoplanets around bright stars
from the ground using small telescopes. The original configuration of XO
(McCullough et al. 2005) has been changed and extended as described here. The
instrumental setup consists of three identical units located at different
sites, each composed of two lenses equipped with CCD cameras mounted on the
same mount. We observed two strips of the sky covering an area of 520 deg
for twice nine months. We build lightcurves for ~20,000 stars up to magnitude
R~12.5 using a custom-made photometric data reduction pipeline. The photometric
precision is around 1-2% for most stars, and the large quantity of data allows
us to reach a millimagnitude precision when folding the lightcurves on
timescales that are relevant to exoplanetary transits. We search for periodic
signals and identify several hundreds of variable stars and a few tens of
transiting planet candidates. Follow-up observations are underway to confirm or
reject these candidates. We found two close-in gas giant planets so far, in
line with the expected yield.Comment: Invited review, 25 pages, 16 figure
Automated analysis of eclipsing binary light curves - I. EBAS - a new Eclipsing Binary Automated Solver with ebop
We present a new algorithm, Eclipsing Binary Automated Solver (EBAS), to analyse light curves of eclipsing binaries. The algorithm is designed to analyse large numbers of light curves, 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 estimatio
Automated analysis of eclipsing binary light curves - II. Statistical analysis of OGLE LMC eclipsing binaries
In the first paper of this series, we presented EBAS - Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that (0.7 ± 0.4) per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope (HST) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LM
Correcting systematic effects in a large set of photometric light curves
We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particula
Correcting systematic effects in a large set of photometric lightcurves
We suggest a new algorithm to remove systematic effects in a large set of
lightcurves obtained by a photometric survey. The algorithm can remove
systematic effects, like the ones associated with atmospheric extinction,
detector efficiency, or PSF changes over the detector. The algorithm works
without any prior knowledge of the effects, as long as they linearly appear in
many stars of the sample. The approach, which was originally developed to
remove atmospheric extinction effects, is based on a lower rank approximation
of matrices, an approach which was already suggested and used in chemometrics,
for example. The proposed algorithm is specially useful in cases where the
uncertainties of the measurements are unequal. For equal uncertainties the
algorithm reduces to the Principal Components Analysis (PCA) algorithm. We
present a simulation to demonstrate the effectiveness of the proposed algorithm
and point out its potential, in search for transit candidates in particular.Comment: 6 pages, 2 figure
Minority Becomes Majority in Social Networks
It is often observed that agents tend to imitate the behavior of their
neighbors in a social network. This imitating behavior might lead to the
strategic decision of adopting a public behavior that differs from what the
agent believes is the right one and this can subvert the behavior of the
population as a whole.
In this paper, we consider the case in which agents express preferences over
two alternatives and model social pressure with the majority dynamics: at each
step an agent is selected and its preference is replaced by the majority of the
preferences of her neighbors. In case of a tie, the agent does not change her
current preference. A profile of the agents' preferences is stable if the
preference of each agent coincides with the preference of at least half of the
neighbors (thus, the system is in equilibrium).
We ask whether there are network topologies that are robust to social
pressure. That is, we ask if there are graphs in which the majority of
preferences in an initial profile always coincides with the majority of the
preference in all stable profiles reachable from that profile. We completely
characterize the graphs with this robustness property by showing that this is
possible only if the graph has no edge or is a clique or very close to a
clique. In other words, except for this handful of graphs, every graph admits
at least one initial profile of preferences in which the majority dynamics can
subvert the initial majority. We also show that deciding whether a graph admits
a minority that becomes majority is NP-hard when the minority size is at most
1/4-th of the social network size.Comment: To appear in WINE 201
Photometric follow-up of the transiting planet WASP-1b
We report on photometric follow-up of the recently discovered transiting
planet WASP-1b. We observed two transits with the Wise Observatory 1m
telescope, and used a variant of the EBOP code together with the Sys-Rem
detrending approach to fit the light curve. Assuming a stellar mass of 1.15
M_sun, we derived a planetary radius of R_p = 1.40 +- 0.06 R_J and mass of M_p
= 0.87 +- 0.07 M_J. An uncertainty of 15% in the stellar mass results in an
additional systematic uncertainty of 5% in the planetary radius and of 10% in
planetary mass. Our observations yielded a slightly better ephemeris for the
center of the transit: T_c [HJD] = (2454013.3127 +- 0.0004) + N_tr * (2.51996
+- 0.00002). The new planet is an inflated, low-density planet, similar to
HAT-P-1b and HD209458b.Comment: Revised version accepted for publication in MNRA
A transiting planet among 23 new near-threshold candidates from the OGLE survey - OGLE-TR-182
By re-processing the data of the second season of the OGLE survey for
planetary transits and adding new mesurements on the same fields gathered in
subsequent years with the OGLE telescope, we have identified 23 new transit
candidates, recorded as OGLE-TR-178 to OGLE-TR-200. We studied the nature of
these objects with the FLAMES/UVES multi-fiber spectrograph on the VLT. One of
the candidates, OGLE-TR-182, was confirmed as a transiting gas giant planet on
a 4-day orbit. We characterised it with further observations using the FORS1
camera and UVES spectrograph on the VLT. OGLE-TR-182b is a typical ``hot
Jupiter'' with an orbital period of 3.98 days, a mass of 1.01 +- 0.15 MJup and
a radius of 1.13 (+0.24-0.08) RJup. Confirming this transiting planet required
a large investment in telescope time with the best instruments available, and
we comment on the difficulty of the confirmation process for transiting planets
in the OGLE survey. We delienate the zone were confirmation is difficult or
impossible, and discuss the implications for the Corot space mission in its
quest for transiting telluric planets.Comment: 7 pages, submitted to Astronomy and Astrophysic
The CORALIE survey for southern extrasolar planets. XVI. Discovery of a planetary system around HD 147018 and of two long period and massive planets orbiting HD 171238 and HD 204313
We report the detection of a double planetary system around HD 140718 as well
as the discovery of two long period and massive planets orbiting HD 171238 and
HD 204313. Those discoveries were made with the CORALIE Echelle spectrograph
mounted on the 1.2-m Euler Swiss telescope located at La Silla Observatory,
Chile. The planetary system orbiting the nearby G9 dwarf HD 147018 is composed
of an eccentric inner planet (e=0.47) with twice the mass of Jupiter (2.1 MJup
) and with an orbital period of 44.24 days. The outer planet is even more
massive (6.6 MJup) with a slightly eccentric orbit (e=0.13) and a period of
1008 days. The planet orbiting HD 171238 has a minimum mass of 2.6 MJup, a
period of 1523 days and an eccentricity of 0.40. It orbits a G8 dwarfs at 2.5
AU. The last planet, HD 204313 b, is a 4.0 MJup -planet with a period of 5.3
years and has a low eccentricity (e = 0.13). It orbits a G5 dwarfs at 3.1 AU.
The three parent stars are metal rich, which further strengthened the case that
massive planets tend to form around metal rich stars.Comment: 6 pages, 6 figures, accepted for publication in A&
Automated analysis of eclipsing binary lightcurves with EBAS. II. Statistical analysis of OGLE LMC eclipsing binaries
In the first paper of this series we presented EBAS, a new fully automated
algorithm to analyse the lightcurves of eclipsing binaries, based on the EBOP
code. Here we apply the new algorithm to the whole sample of 2580 binaries
found in the OGLE LMC photometric survey and derive the orbital elements for
1931 systems. To obtain the statistical properties of the short-period binaries
of the LMC we construct a well defined subsample of 938 eclipsing binaries with
main-sequence B-type primaries. Correcting for observational selection effects,
we derive the distributions of the fractional radii of the two components and
their sum, the brightness ratios and the periods of the short-period binaries.
Somewhat surprisingly, the results are consistent with a flat distribution in
log P between 2 and 10 days. We also estimate the total number of binaries in
the LMC with the same characteristics, and not only the eclipsing binaries, to
be about 5000. This figure leads us to suggest that 0.7 +- 0.4 percent of the
main-sequence B-type stars in the LMC are found in binaries with periods
shorter than 10 days. This frequency is substantially smaller than the fraction
of binaries found by small Galactic radial-velocity surveys of B stars. On the
other hand, the binary frequency found by HST photometric searches within the
late main-sequence stars of 47 Tuc is only slightly higher and still consistent
with the frequency we deduced for the B stars in the LMC.Comment: 28 pages, 11 figures, accepted to MNRA
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