111 research outputs found
Transiting exoplanets from the CoRoT space mission III. The spectroscopic transit of CoRoT-Exo-2b with SOPHIE and HARPS
We report on the spectroscopic transit of the massive hot-Jupiter
CoRoT-Exo-2b observed with the high-precision spectrographs SOPHIE and HARPS.
By modeling the radial velocity anomaly occurring during the transit due to the
Rossiter-McLaughlin (RM) effect, we determine the sky-projected angle between
the stellar spin and the planetary orbital axis to be close to zero
lambda=7.2+-4.5 deg, and we secure the planetary nature of CoRoT-Exo-2b. We
discuss the influence of the stellar activity on the RM modeling. Spectral
analysis of the parent star from HARPS spectra are presented.Comment: A&A Letters (in press), 5 pages, 2 figure
Characterization of the HD 17156 planetary system
AIMS : To improve the parameters of the HD 17156 system (peculiar due to the
eccentric and long orbital period of its transiting planet) and constrain the
presence of stellar companions.
METHODS : Photometric data were acquired for 4 transits, and high precision
radial velocity measurements were simultaneously acquired with SARG@TNG for one
transit. The template spectra of HD 17156 was used to derive effective
temperature, gravity, and metallicity. A fit of the photometric and
spectroscopic data was performed to measure the stellar and planetary radii,
and the spin-orbit alignment. Planet orbital elements and ephemeris were
derived from the fit. Near infrared adaptive optic images was acquired with
ADOPT@TNG.
RESULTS: We have found that the star has a radius of R_S = 1.43+/-0.03 R_sun
and the planet R_P =1.02+/-0.08 R_jup. The transit ephemeris is T_c =
2454\756.73134+/-0.00020+N*21.21663+/-0.00045 BJD. The analysis of the
Rossiter-Mclaughlin effect shows that the system is spin orbit aligned with an
angle lambda = 4.8 +/- 5.3 deg. The analysis of high resolution images has not
revealed any stellar companion with projected separation between 150 and 1000
AU from HD 17156.Comment: submitted to A&
Elodie metallicity-biased search for transiting Hot Jupiters IV. Intermediate period planets orbiting the stars HD43691 and HD132406
We report here the discovery of two planet candidates as a result of our
planet-search programme biased in favour of high-metallicity stars, using the
ELODIE spectrograph at the Observatoire de Haute Provence. One of them has a
minimum mass m_2\sin{i} = 2.5 M_Jup and is orbiting the metal-rich star HD43691
with period P = 40 days and eccentricity e = 0.14. The other planet has a
minimum mass m_2\sin{i} = 5.6 M_Jup and orbits the slightly metal-rich star
HD132406 with period P = 974 days and eccentricity e = 0.34. Both stars were
followed up with additional observations using the new SOPHIE spectrograph that
replaces the ELODIE instrument, allowing an improved orbital solution for the
systems.Comment: 6 pages, 4 figures, to be published in A&
SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements
High-precision spectrographs play a key role in exoplanet searches and
Doppler asteroseismology using the radial velocity technique. The 1 m/s level
of precision requires very high stability and uniformity of the illumination of
the spectrograph. In fiber-fed spectrographs such as SOPHIE, the fiber-link
scrambling properties are one of the main conditions for high precision. To
significantly improve the radial velocity precision of the SOPHIE spectrograph,
which was limited to 5-6 m/s, we implemented a piece of octagonal-section fiber
in the fiber link. We present here the scientific validation of the upgrade of
this instrument, demonstrating a real improvement. The upgraded instrument,
renamed SOPHIE+, reaches radial velocity precision in the range of 1-2 m/s. It
is now fully efficient for the detection of low-mass exoplanets down to 5-10
Earth mass and for the identification of acoustic modes down to a few tens of
cm/s.Comment: 12 pages, 11 figures, accepted in Astronomy and Astrophysic
Stellar activity of planetary host star HD 189733
Extra-solar planet search programs require high-precision velocity
measurements. They need to study how to disentangle radial-velocity variations
due to Doppler motion from the noise induced by stellar activity. We monitored
the active K2V star HD 189733 and its transiting planetary companion that has a
2.2-day orbital period. We used the high-resolution spectograph SOPHIE mounted
on the 1.93-m telescope at the Observatoire de Haute-Provence to obtain 55
spectra of HD 189733 over nearly two months. We refined the HD 189733b orbit
parameters and put limits on the eccentricity and on a long-term velocity
gradient. After subtracting the orbital motion of the planet, we compared the
variability of spectroscopic activity indices to the evolution of the
radial-velocity residuals and the shape of spectral lines. The radial velocity,
the spectral-line profile and the activity indices measured in HeI (5875.62
\AA), Halpha (6562.81 \AA) and the CaII H&K lines (3968.47 \AA and 3933.66 \AA,
respectively) show a periodicity around the stellar rotation period and the
correlations between them are consistent with a spotted stellar surface in
rotation. We used such correlations to correct for the radial-velocity jitter
due to stellar activity. This results in achieving high precision on the orbit
parameters, with a semi-amplitude K = 200.56 \pm 0.88 m.s-1 and a derived
planet mass of M_{P}=1.13 \pm 0.03 M.Comment: 9 pages, 2 tables, 9 figures, accepted for publication in A&A on
20/11/200
Rate and nature of false positives in the CoRoT exoplanet search
Context. The CoRoT satellite searches for planets by applying the transit
method, monitoring up to 12 000 stars in the galactic plane for 150 days in
each observation run. This search is contaminated by a large fraction of false
positives, caused by different binary configurations that might be confused
with a transiting planet. Aims. We evaluate the rates and nature of false
positives in the CoRoT exoplanets search and compare our results with
semiempirical predictions. Methods. We consider the detected binary and planet
candidates in the first three extended CoRoT runs, and classify the results of
the follow-up observations completed to verify their planetary nature. We group
the follow-up results into undiluted binaries, diluted binaries, and planets
and compare their abundances with predictions from the literature. Results. 83%
of the initial detections are classified as false positives using only the
CoRoT light-curves, the remaining 17% require follow-up observations. Finally,
12% of the follow-up candidates are planets. The shape of the overall
distribution of the false positive rate follows previous predictions, except
for candidates with transit depths below about 0.4%. For candidates with
transit depths in the range from 0.1 - 0.4%, CoRoT detections are nearly
complete, and this difference from predictions is probably real and dominated
by a lower than expected abundance of diluted eclipsing binaries.Comment: accepted for A&A special issue on CoRo
The SOPHIE search for northern extrasolar planets. II. A multi-planet system around HD9446
We report the discovery of a planetary system around HD9446, performed from
radial velocity measurements secured with the spectrograph SOPHIE at the 193-cm
telescope of the Haute-Provence Observatory during more than two years. At
least two planets orbit this G5V, active star: HD9446b has a minimum mass of
0.7 M_Jup and a slightly eccentric orbit with a period of 30 days, whereas
HD9446c has a minimum mass of 1.8 M_Jup and a circular orbit with a period of
193 days. As for most of the known multi-planet systems, the HD9446-system
presents a hierarchical disposition, with a massive outer planet and a lighter
inner planet.Comment: 7 pages, 6 figures, 3 tables, accepted for publication in A&
Refined parameters and spectroscopic transit of the super-massive planet HD147506b
In this paper, we report a refined determination of the orbital parameters
and the detection of the Rossiter-McLaughlin effect of the recently discovered
transiting exoplanet HD147506b (HAT-P-2b). The large orbital eccentricity at
the short orbital period of this exoplanet is unexpected and is distinguishing
from other known transiting exoplanets. We performed high-precision radial
velocity spectroscopic observations of HD147506 (HAT-P-2) with the new
spectrograph SOPHIE, mounted on the 1.93 m telescope at the Haute-Provence
observatory (OHP). We obtained 63 new measurements, including 35 on May 14 and
20 on June 11, when the planet was transiting its parent star. The radial
velocity (RV) anomaly observed illustrates that HAT-P-2b orbital motion is set
in the same direction as its parent star spin. The sky-projected angle between
the normal of the orbital plane and the stellar spin axis, \lambda = 0.2 +12.2
-12.5 deg, is consistent with zero. The planetary and stellar radii were
re-determined, yielding R_p = 0.951 +0.039 -0.053 R_Jup, R_s = 1.416 +0.040
-0.062 R_Sun. The mass M_p = 8.62 +0.39 -0.55 M_Jup and radius of HAT-P-2b
indicate a density of 12.5 +2.6 -3.6 g cm^{-3}, suggesting an object in between
the known close-in planets with typical density of the order of 1 g cm^{-3},
and the very low-mass stars, with density greater than 50 g cm^{-3}.Comment: Submitted to A&A; V2: Replaced by accepted versio
The 0.5MJ transiting exoplanet WASP-13b
We report the discovery of WASP-13b, a low-mass M_{\rm p} = 0.46 ^_~M_J transiting exoplanet with an orbital period of 4.35298 0.00004 days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0 < b < 0.46), with radius in the range ~ 1.06-1.21 RJ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M__ ~M_{\odot}) and metallicity ([M/H] = 0.00.2), but is possibly older ( 8.5^_{\rm -4.9} Gyr)
A homogeneous spectroscopic analysis of host stars of transiting planets
The analysis of transiting extra-solar planets provides an enormous amount of
information about the formation and evolution of planetary systems. A precise
knowledge of the host stars is necessary to derive the planetary properties
accurately. The properties of the host stars, especially their chemical
composition, are also of interest in their own right. Information about planet
formation is inferred by, among others, correlations between different
parameters such as the orbital period and the metallicity of the host stars.
The stellar properties studied should be derived as homogeneously as possible.
The present work provides new, uniformly derived parameters for 13 host stars
of transiting planets. Effective temperature, surface gravity, microturbulence
parameter, and iron abundance were derived from spectra of both high
signal-to-noise ratio and high resolution by assuming iron excitation and
ionization equilibria. For some stars, the new parameters differ from previous
determinations, which is indicative of changes in the planetary radii. A
systematic offset in the abundance scale with respect to previous assessments
is found for the TrES and HAT objects. Our abundance measurements are
remarkably robust in terms of the uncertainties in surface gravities. The iron
abundances measured in the present work are supplemented by all previous
determinations using the same analysis technique. The distribution of iron
abundance then agrees well with the known metal-rich distribution of planet
host stars. To facilitate future studies, the spectroscopic results of the
current work are supplemented by the findings for other host stars of
transiting planets, for a total dataset of 50 objects.Comment: accepted for publication in A&A, 7 pages, 6 figure
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