211 research outputs found
An upper boundary in the mass-metallicity plane of exo-Neptunes
With the progress of detection techniques, the number of low-mass and
small-size exoplanets is increasing rapidly. However their characteristics and
formation mechanisms are not yet fully understood. The metallicity of the host
star is a critical parameter in such processes and can impact the occurence
rate or physical properties of these planets. While a frequency-metallicity
correlation has been found for giant planets, this is still an ongoing debate
for their smaller counterparts. Using the published parameters of a sample of
157 exoplanets lighter than 40 Mearth, we explore the mass-metallicity space of
Neptunes and Super-Earths. We show the existence of a maximal mass that
increases with metallicity, that also depends on the period of these planets.
This seems to favor in situ formation or alternatively a metallicity-driven
migration mechanism. It also suggests that the frequency of Neptunes (between
10 and 40 Mearth) is, like giant planets, correlated with the host star
metallicity, whereas no correlation is found for Super-Earths (<10 Mearth).Comment: Accepted in MNRAS, 11 pages, 5 figure
Radial velocity follow-up for confirmation and characterization of transiting exoplanets
Radial Velocity follow-up is essential to establish or exclude the planetary nature of a transiting companion as well as to accurately determine its mass. Here we present some elements of an efficient Doppler follow-up strategy, based on high-resolution spectroscopy, devoted to the characterization of transiting candidates. Some aspects and results of the radial velocity follow-up of the CoRoT space mission are presented in order to illustrate the strategy used to deal with the zoo of transiting candidate
Observational constraints on tidal effects using orbital eccentricities
We have analysed radial velocity measurements for known transiting exoplanets
to study the empirical signature of tidal orbital evolution for close-in
planets. Compared to standard eccentricity determination, our approach is
modified to focus on the rejection of the null hypothesis of a circular orbit.
We are using a MCMC analysis of radial velocity measurements and photometric
constraints, including a component of correlated noise, as well as Bayesian
model selection to check if the data justifies the additional complexity of an
eccentric orbit. We find that among planets with non-zero eccentricity values
quoted in the literature, there is no evidence for an eccentricity detection
for the 7 planets CoRoT-5b, WASP-5b, WASP-6b, WASP-10b, WASP-12b, WASP-17b, and
WASP-18b. In contrast, we confirm the eccentricity of HAT-P-16b,
e=0.034\pm0.003, the smallest eccentricity that is reliably measured so far for
an exoplanet as well as that of WASP-14b, which is the planet at the shortest
period (P=2.24 d), with a confirmed eccentricity, e= 0.088\pm0.003. As part of
the study, we present new radial velocity data using the HARPS spectrograph for
CoRoT-1, CoRoT-3, WASP-2, WASP-4, WASP-5 and WASP-7 as well as the SOPHIE
spectrograph for HAT-P-4, HAT-P-7, TrES-2 and XO-2.
We show that the dissipative effect of tides raised in the planet by the star
and vice-versa explain all the eccentricity and spin-orbit alignment
measurements available for transiting planets. We revisit the mass-period
relation (Mazeh et al. 2005, Pont 2011) and consider its relation to the
stopping mechanism of orbital migration for hot Jupiters. In addition to
CoRoT-2 and HD 189733 (Pont 2009), we find evidence for excess rotation of the
star in the systems CoRoT-18, HAT-P-20, WASP-19 and WASP-43.Comment: 31 pages, 17 figures. Accepted by MNRAS (Feb 2012
Telluric-line subtraction in high-accuracy velocimetry: a PCA-based approach
Optical velocimetry has led to the detection of more than 500 planets to date
and there is a strong effort to push m/s velocimetry to the near-infrared to
access cooler and lighter stars. The presence of numerous telluric absorption
lines in the nIR brings an important challenge. As the star's barycentric
velocity varies through the year, the telluric absorption lines effectively
varies in velocity relative to the star's spectrum by the same amount leading
to important systematic RV offsets. We present a novel principal component
analysis-based approach for telluric line subtraction and demonstrated its
effectiveness with archival HARPS data for GJ436 and {\tau} Ceti, over parts of
the R-band that contain strong telluric absorption lines. The main results are:
1) a better RV accuracy with excluding only a few percentage of the domain, 2)
better use of the entire spectrum to measure RV and 3) a higher telescope time
efficency by using A0V telluric standard from telescope archive.Comment: Presented at SPIE Astronomical Telescopes + Instrumentation 201
Seismology and activity of the F type star HD 49933
A 10-night asteroseismic observation programme has been conducted in January
2004 with the spectrometer Harps at the ES0 3.6-m telescope. The selected
target, the 6th magnitude F5V star HD 49933, was chosen among the prime
candidates of Corot, the European space mission dedicated to characterize
stellar oscillations mode with high precision photometry measurements. This
star shows important line profiles variations, indicating a surprisingly high
activity with respect to its low rotation rate. However, with the help of tools
developed for disentangling the signatures of activity and oscillations, we are
able to observe its oscillation spectrum in the frequency range [1.2, 2.2 mHz].
We measure the large separation (88.7+-0.4 microHz) and the maximum amplitude
(around 0.4+-0.1 m/s rms), respectively in agreement and marginal agreement
with the predicted values.Comment: accepted in A&A Letter
Broadband near-infrared astronomical spectrometer calibration and on-sky validation with an electro-optic laser frequency comb
The quest for extrasolar planets and their characterisation as well as
studies of fundamental physics on cosmological scales rely on capabilities of
high-resolution astronomical spectroscopy. A central requirement is a precise
wavelength calibration of astronomical spectrographs allowing for extraction of
subtle wavelength shifts from the spectra of stars and quasars. Here, we
present an all-fibre, 400 nm wide near-infrared frequency comb based on
electro-optic modulation with 14.5 GHz comb line spacing. Tests on the
high-resolution, near-infrared spectrometer GIANO-B show a photon-noise limited
calibration precision of <10 cm/s as required for Earth-like planet detection.
Moreover, the presented comb provides detailed insight into particularities of
the spectrograph such as detector inhomogeneities and differential spectrograph
drifts. The system is validated in on-sky observations of a radial velocity
standard star (HD221354) and telluric atmospheric absorption features. The
advantages of the system include simplicity, robustness and turn-key operation,
features that are valuable at the observation sites
A Spitzer Search for Water in the Transiting Exoplanet HD189733b
We present Spitzer Space Telescope observations of the extrasolar planet
HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with
the Infrared Array Camera. The system parameters, including planetary radius,
stellar radius, and impact parameter are derived from fits to the transit light
curves at both wavelengths. We measure two consistent planet-to-star radius
ratios, (Rp/Rs)[3.6m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and
(Rp/Rs)[5.8m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include
both the random and systematic errors in the transit baseline. Although planet
radii are determined at 1%-accuracy, if all uncertainties are taken into
account the resulting error bars are still too large to allow for the detection
of atmospheric constituants like water vapour. This illustrates the need to
observe multiple transits with the longest possible out-of-transit baseline, in
order to achieve the precision required by transmission spectroscopy of giant
extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter
A Spitzer Search for Water in the Transiting Exoplanet HD189733b
We present Spitzer Space Telescope observations of the extrasolar planet
HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with
the Infrared Array Camera. The system parameters, including planetary radius,
stellar radius, and impact parameter are derived from fits to the transit light
curves at both wavelengths. We measure two consistent planet-to-star radius
ratios, (Rp/Rs)[3.6m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and
(Rp/Rs)[5.8m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include
both the random and systematic errors in the transit baseline. Although planet
radii are determined at 1%-accuracy, if all uncertainties are taken into
account the resulting error bars are still too large to allow for the detection
of atmospheric constituants like water vapour. This illustrates the need to
observe multiple transits with the longest possible out-of-transit baseline, in
order to achieve the precision required by transmission spectroscopy of giant
extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter
Disentangling stellar activity and planetary signals
High-precision radial-velocimetry (RV) is until now the more efficient way to discover planetary systems. Moreover, photometric transit search missions like CoRoT and Kepler, need spectroscopic RV measurements to establish the planetary nature of a transit candidate and to measure the true mass. An active star has on its photosphere dark spots and bright plages rotating with the star. These inhomogeneities of the stellar surface can induce a variation of the measurement of the RV, due to changes in lines shapes and not to a Doppler motion of the star (e.g. Queloz et al. 2001; Desort et al. 2007; Boisse et al. 2009). We study how the Keplerian fit used to search for planets in RV data is confused by spots and we test an approach to subtract RV jitter based on harmonic decomposition of the star rotation. We use simulations of spectroscopic measurements of rotating spotted stars and validate our approach on active stars monitored by high-precision spectrograph HARPS: CoRoT-7 and ι Ho
CoRoT: harvest of the exoplanet program
One of the objectives of the CoRoT mission is the search for transiting
extrasolar planets using high-precision photometry, and the accurate
characterization of their fundamental parameters. The CoRoT satellite
consecutively observes crowded stellar fields since February 2007, in
high-cadence precise photometry; periodic eclipses are detected and analysed in
the stellar light curves. Then complementary observations using ground-based
facilities allows establishing the nature of the transiting body and its mass.
CoRoT has acquired more than 163,000 light curves and detected about 500 planet
candidates. A fraction of them (5%) are confirmed planets whose masses are
independently measured. Main highlights of the CoRoT discoveries are: i) the
variety of internal structures in close-in giant planets, ii) the
characterisation of the first known transiting rocky planet, CoRoT-7 b, iii)
multiple constraints on the formation, evolution, role of tides in planetary
systems.Comment: Icarus, in press, special issue on Exoplanet
- …