25 research outputs found
Tight constraints on the existence of additional planets around HD 189733
We report a transit timing study of the transiting exoplanetary system HD
189733. In total we observed ten transits in 2006 and 2008 with the 2.6-m
Nordic Optical Telescope, and two transits in 2007 with the 4.2-m William
Herschel Telescope. We used Markov-Chain Monte Carlo simulations to derive the
system parameters and their uncertainties, and our results are in a good
agreement with previously published values. We performed two independent
analyses of transit timing residuals to place upper mass limits on putative
perturbing planets. The results show no evidence for the presence of planets
down to 1 Earth mass near the 1:2 and 2:1 resonance orbits, and planets down to
2.2 Earth masses near the 3:5 and 5:3 resonance orbits with HD 189733b. These
are the strongest limits to date on the presence of other planets in this
system.Comment: 10 pages, 4 figures, accepted by MNRA
A transit timing analysis of nine RISE light curves of the exoplanet system TrES-3
We present nine newly observed transits of TrES-3, taken as part of a transit
timing program using the RISE instrument on the Liverpool Telescope. A
Markov-Chain Monte-Carlo analysis was used to determine the planet-star radius
ratio and inclination of the system, which were found to be
Rp/Rstar=0.1664^{+0.0011}_{-0.0018} and i = 81.73^{+0.13}_{-0.04} respectively,
consistent with previous results. The central transit times and uncertainties
were also calculated, using a residual-permutation algorithm as an independent
check on the errors. A re-analysis of eight previously published TrES-3 light
curves was conducted to determine the transit times and uncertainties using
consistent techniques. Whilst the transit times were not found to be in
agreement with a linear ephemeris, giving chi^2 = 35.07 for 15 degrees of
freedom, we interpret this to be the result of systematics in the light curves
rather than a real transit timing variation. This is because the light curves
that show the largest deviation from a constant period either have relatively
little out-of-transit coverage, or have clear systematics. A new ephemeris was
calculated using the transit times, and was found to be T_c(0) = 2454632.62610
+- 0.00006 HJD and P = 1.3061864 +- 0.0000005 days. The transit times were then
used to place upper mass limits as a function of the period ratio of a
potential perturbing planet, showing that our data are sufficiently sensitive
to have probed for sub-Earth mass planets in both interior and exterior 2:1
resonances, assuming the additional planet is in an initially circular orbit.Comment: 21 pages, 4 figures, Accepted for publication in Ap
Transit timing variation in exoplanet WASP-3b
Photometric follow-ups of transiting exoplanets may lead to discoveries of
additional, less massive bodies in extrasolar systems. This is possible by
detecting and then analysing variations in transit timing of transiting
exoplanets. We present photometric observations gathered in 2009 and 2010 for
exoplanet WASP-3b during the dedicated transit-timing-variation campaign. The
observed transit timing cannot be explained by a constant period but by a
periodic variation in the observations minus calculations diagram. Simplified
models assuming the existence of a perturbing planet in the system and
reproducing the observed variations of timing residuals were identified by
three-body simulations. We found that the configuration with the hypothetical
second planet of the mass of about 15 Earth masses, located close to the outer
2:1 mean motion resonance is the most likely scenario reproducing observed
transit timing. We emphasize, however, that more observations are required to
constrain better the parameters of the hypothetical second planet in WASP-3
system. For final interpretation not only transit timing but also photometric
observations of the transit of the predicted second planet and the high
precision radial-velocity data are needed.Comment: MNRAS accepte
WASP-3b: a strongly irradiated transiting gas-giant planet
We report the discovery of WASP-3b, the third transiting exoplanet to be discovered by the WASP and SOPHIE collaboration. WASP-3b transits its host star USNO-B1.0 1256−0285133 every 1.846 834 ± 0.000 002 d. Our high-precision radial velocity measurements present a variation with amplitude characteristic of a planetary-mass companion and in phase with the light curve. Adaptive optics imaging shows no evidence for nearby stellar companions, and line-bisector analysis excludes faint, unresolved binarity and stellar activity as the cause of the radial velocity variations. We make a preliminary spectroscopic analysis of the host star and find it to have Teff= 6400 ± 100 K and log g= 4.25 ± 0.05 which suggests it is most likely an unevolved main-sequence star of spectral type F7-8V. Our simultaneous modelling of the transit photometry and reflex motion of the host leads us to derive a mass of 1.76+0.08−0.14MJ and radius 1.31+0.07−0.14RJ for WASP-3b. The proximity and relative temperature of the host star suggests that WASP-3b is one of the hottest exoplanets known, and thus has the potential to place stringent constraints on exoplanet atmospheric model
Reliable elimination of telluric lines from stellar spectra
We demonstrate that the powerful disentangling
technique used to separate the individual spectra of binary
components and telluric lines can also be used to remove telluric lines from the
spectrum of a single star by treating the telluric spectrum
as a second star. We tested that on the spectra of
α Boo (=Arcturus) secured with a Reticon detector in the coudé
focus of the Ondřejov 2-m telescope. We demonstrate that the
method works well and is invaluable especially for the spectra of
red stars which are heavily blended with the telluric lines. The
disadvantage of the method is that one needs a number of spectra
of the star in question, secured at different months of the year.
The advantage is that one obtains the final disentangled stellar
spectrum with a high ratio
Scale-imprecision space
It is argued that image measurements should satisfy two requirements of physical plausibility: the measurements are of non-zero scale and non-zero imprecision; and two required invariances, nothing is lost by expanding the image and nothing is lost by increasing the contrast of the image. A model of measurements satisfying these constraints, based on blurring the graph of the incident luminance, is described. Within this framework, several types of filtering can be expressed: mean filtering (ordinary scale space); median filtering; and mode filtering. It is found that of these possibilities, a system based on mode filtering produces interesting results. In particular, edges-defined as discontinuities-naturally appear, and their behaviour over scale and imprecision is presented
Updated parameters for the transiting exoplanet WASP-3b using RISE, a new fast camera for the Liverpool Telescope
Some of the first results are reported from RISE - a new fast camera mounted
on the Liverpool Telescope primarily designed to obtain high time resolution
light curves of transiting extrasolar planets for the purpose of transit
timing. A full and partial transit of WASP-3 are presented, and a Monte Carlo
Markov Chain analysis is used to update the parameters from the discovery
paper. This results in a planetary radius of 1.29^{+0.05}_{-0.12} R_J and
therefore a density of 0.82^{+0.14}_{-0.09} p_J, consistent with previous
results. The inclination is 85.07^{+0.15}_{-0.16} deg, in agreement (but with a
significant improvement in the precision) with the previously determined value.
Central transit times are found to be consistent with the ephemeris given in
the discovery paper. However, a new ephemeris calculated using the longer
baseline results in T_c(0) = 2454605.55915 +- 0.00023 HJD and P = 1.846835 +-
0.000002 days.Comment: 5 pages, 2 figures, Accepted for publication in A&