1,265 research outputs found
The Observed Seismic Behavior of the Matahina Dam
On 2 March 1987 the 86 m high Matahina earth dam in the Eastern Bay of Plenty region of New Zealand was shaken by a nearby magnitude 6.3 earthquake. The dam response was recorded by five strong motion accelerometers and a maximum crest level acceleration of 0.42 g was measured. The crest level rockfill settled about 100 mm and moved downstream 250 mm during the earthquake. No major leakage has resulted from the earthquake. The results of the damage investigations are described. A condition probably requiring remedial work has been identified on the left abutment
A photometric study of the hot exoplanet WASP-19b
Context: When the planet transits its host star, it is possible to measure
the planetary radius and (with radial velocity data) the planet mass. For the
study of planetary atmospheres, it is essential to obtain transit and
occultation measurements at multiple wavelengths.
Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving
accurate and precise planetary parameters from a dedicated observing campaign
of transits and occultations.
Methods: We have obtained a total of 14 transit lightcurves in the r'-Gunn,
IC, z'-Gunn and I+z' filters and 10 occultation lightcurves in z'-Gunn using
EulerCam on the Euler-Swiss telescope and TRAPPIST. We have also obtained one
lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring
an occultation at 1.19 micron. We have performed a global MCMC analysis of all
new data together with some archive data in order to refine the planetary
parameters and measure the occultation depths in z'-band and at 1.19 micron.
Results: We measure a planetary radius of R_p = 1.376 (+/-0.046) R_j, a
planetary mass of M_p = 1.165 (+/-0.068) M_j, and find a very low eccentricity
of e = 0.0077 (+/-0.0068), compatible with a circular orbit. We have detected
the z'-band occultation at 3 sigma significance and measure it to be dF_z'= 352
(+/-116) ppm, more than a factor of 2 smaller than previously published. The
occultation at 1.19 micron is only marginally constrained at dF_1190 = 1711
(+/-745) ppm.
Conclusions: We have shown that the detection of occultations in the visible
is within reach even for 1m class telescopes if a considerable number of
individual events are observed. Our results suggest an oxygen-dominated
atmosphere of WASP-19b, making the planet an interesting test case for
oxygen-rich planets without temperature inversion.Comment: Published in Astronomy & Astrophysics. 11 pages, 11 figures, 4 table
Pushing the precision limit of ground-based eclipse photometry
Until recently, it was considered by many that ground-based photometry could
not reach the high cadence sub-mmag regime because of the presence of the
atmosphere. Indeed, high frequency atmospheric noises (mainly scintillation)
limit the precision that high SNR photometry can reach within small time bins.
If one is ready to damage the sampling of his photometric time-series, binning
the data (or using longer exposures) allows to get better errors, but the
obtained precision will be finally limited by low frequency noises. To observe
several times the same planetary eclipse and to fold the photometry with the
orbital period is thus generally considered as the only option to get very well
sampled and precise eclipse light curve from the ground. Nevertheless, we show
here that reaching the sub-mmag sub-min regime for one eclipse is possible with
a ground-based instrument. This has important implications for transiting
planets characterization, secondary eclipses measurement and small planets
detection from the ground.Comment: Transiting Planets Proceeding IAU Symposium No.253, 2008. 7 pages, 4
figure
TRAPPIST photometry and imaging monitoring of comet C/2013 R1(Lovejoy): Implications for the origin of daughter species
We report the results of the narrow band photometry and imaging monitoring of
comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla
observatory). We gathered around 400 images over 8 months pre- and
post-perihelion between September 12, 2013 and July 6, 2014. We followed the
evolution of the OH, NH, CN, C3 , and C2 production rates computed with the
Haser model as well as the evolution of the dust production. All five gas
species display an asymmetry about perihelion, the rate of brightening being
steeper than the rate of fading. The study of the coma morphology reveals gas
and dust jets which indicate one or several active zone(s) on the nucleus. The
dust, C2 , and C3 morphologies present some similarities while the CN
morphology is different. OH and NH are enhanced in the tail direction. The
study of the evolution of the comet activity shows that the OH, NH, and C2
production rates evolution with the heliocentric distance is correlated to the
dust evolution. The CN and, to a lesser extent, the C3 do not display such a
correlation with the dust. These evidences and the comparison with parent
species production rates indicate that C2 and C3 on one side and OH and NH on
the other side could be -at least partially- released from organic-rich grains
and icy grains. On the contrary, all evidences point to HCN being the main
parent of CN in this comet.Comment: Accepted for publication in Astronomy & Astrophysics, 10 page
The Spitzer search for the transits of HARPS low-mass planets - I. No transit for the super-Earth HD 40307b
We have used Spitzer and its IRAC camera to search for the transit of the
super-Earth HD 40307b. The transiting nature of the planet could not be firmly
discarded from our first photometric monitoring of a transit window because of
the uncertainty coming from the modeling of the photometric baseline. To obtain
a firm result, two more transit windows were observed and a global Bayesian
analysis of the three IRAC time series and the HARPS radial velocities was
performed. Unfortunately, any transit of the planet during the observed phase
window is firmly discarded, while the probability that the planet transits but
that the eclipse was missed by our observations is nearly negligible (0.26%).Comment: Submitted to A&
TRAPPIST: a robotic telescope dedicated to the study of planetary systems
We present here a new robotic telescope called TRAPPIST (TRAnsiting Planets
and PlanetesImals Small Telescope). Equipped with a high-quality CCD camera
mounted on a 0.6 meter light weight optical tube, TRAPPIST has been installed
in April 2010 at the ESO La Silla Observatory (Chile), and is now beginning its
scientific program. The science goal of TRAPPIST is the study of planetary
systems through two approaches: the detection and study of exoplanets, and the
study of comets. We describe here the objectives of the project, the hardware,
and we present some of the first results obtained during the commissioning
phase.Comment: To appear in Detection and Dynamics of Transiting Exoplanets,
Proceedings of Haute Provence Observatory Colloquium (23-27 August 2010),
eds. F. Bouchy, R.F. Diaz & C.Moutou, Platypus press 201
The Spitzer search for the transits of HARPS low-mass planets - II. Null results for 19 planets
Short-period super-Earths and Neptunes are now known to be very frequent
around solar-type stars. Improving our understanding of these mysterious
planets requires the detection of a significant sample of objects suitable for
detailed characterization. Searching for the transits of the low-mass planets
detected by Doppler surveys is a straightforward way to achieve this goal.
Indeed, Doppler surveys target the most nearby main-sequence stars, they
regularly detect close-in low-mass planets with significant transit
probability, and their radial velocity data constrain strongly the ephemeris of
possible transits. In this context, we initiated in 2010 an ambitious Spitzer
multi-Cycle transit search project that targeted 25 low-mass planets detected
by radial velocity, focusing mainly on the shortest-period planets detected by
the HARPS spectrograph. We report here null results for 19 targets of the
project. For 16 planets out of 19, a transiting configuration is strongly
disfavored or firmly rejected by our data for most planetary compositions. We
derive a posterior probability of 83% that none of the probed 19 planets
transits (for a prior probability of 22%), which still leaves a significant
probability of 17% that at least one of them does transit. Globally, our
Spitzer project revealed or confirmed transits for three of its 25 targeted
planets, and discarded or disfavored the transiting nature of 20 of them. Our
light curves demonstrate for Warm Spitzer excellent photometric precisions: for
14 targets out of 19, we were able to reach standard deviations that were
better than 50ppm per 30 min intervals. Combined with its Earth-trailing orbit,
which makes it capable of pointing any star in the sky and to monitor it
continuously for days, this work confirms Spitzer as an optimal instrument to
detect sub-mmag-deep transits on the bright nearby stars targeted by Doppler
surveys.Comment: Accepted for publication in Astronomy and Astrophysics. 23 pages, 21
figure
An educated search for transiting habitable planets: (Research Note) Targetting M dwarfs with known transiting planets
Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. We investigate here the potential of this approach for the M dwarf GJ 1214 that hosts a transiting super-Earth. For this system, we infer the transit probabilities as a function of orbital periods. Using Monte-Carlo simulations we address both the cases for fully coplanar and for non-coplanar orbits, with three different choices of inclinations distribution for the non-coplanar case. GJ 1214 reveals to be a very promising target for the considered approach. Because of its small size, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring could detect any transiting habitable planet down to the size of Mars. The mass measurement of such a small planet would be out of reach for current facilities, but we emphasize that a planet mass would not be needed to confirm the planetary nature of the transiting object. Furthermore, the radius measurement combined with theoretical arguments would help us to constrain the structure of the planet
Characterization of the hot Neptune GJ 436b with Spitzer and ground-based observations
We present Spitzer Space Telescope infrared photometry of a secondary eclipse
of the hot Neptune GJ436b. The observations were obtained using the 8-micron
band of the InfraRed Array Camera (IRAC). The data spanning the predicted time
of secondary eclipse show a clear flux decrement with the expected shape and
duration. The observed eclipse depth of 0.58 mmag allows us to estimate a
blackbody brightness temperature of T_p = 717 +- 35 K at 8 microns. We compare
this infrared flux measurement to a model of the planetary thermal emission,
and show that this model reproduces properly the observed flux decrement. The
timing of the secondary eclipse confirms the non-zero orbital eccentricity of
the planet, while also increasing its precision (e = 0.14 +- 0.01). Additional
new spectroscopic and photometric observations allow us to estimate the
rotational period of the star and to assess the potential presence of another
planet.Comment: Accepted for publication in A&A on 11/09/2007; 7 pages, 6 figure
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