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A. C. M. Correia

Publications and source records attributed to A. C. M. Correia.

At least 73 records · Page 4Linked to original sources
arXiv2016

The ELODIE survey for northern extra-solar planets IV. HD196885, a close binary star with a 3.7-year planet

Aims:We aim to significantly increase the number of detected extra-solar planets in a magnitude-limited sample to improve our knowledge of their orbital element distributions and thus obtain better constraints for planet-formation models. Methods: Radial-velocity data were taken at Haute-Provence Observatory (OHP, France) with the ELODIE echelle spectrograph. Results: We report the presence of a planet orbiting HD 196885 A, with an orbital period of 1349 days. This star was previously suggested to host a 386 -day planet, but we cannot confirm its existence. We also detect the presence of a stellar companion, HD 196885 B, and give some constraints on its orbit.

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arXiv2016

Is the activity level of HD 80606 influenced by its eccentric planet?

Aims: Several studies suggest that the activity level of a planet-host star can be influenced by the presence of a close-by orbiting planet. Moreover, the interaction mechanisms that have been proposed, magnetic interaction and tidal interaction, exhibit a very different dependence on orbital separation between the star and the planet. A detection of activity enhancement and characterization of its dependence on planetary orbital distance can, in principle, allow us to characterize the physical mechanism behind the activity enhancement. Methods: We used the HARPS-N spectrograph to measure the stellar activity level of HD 80606 during the planetary periastron passage and compared the activity measured to that close to apastron. Being characterized by an eccentricity of 0.93 and an orbital period of 111 days, the system's extreme variation in orbital separation makes it a perfect target to test our hypothesis. Results: We find no evidence for a variation in the activity level of the star as a function of planetary orbital distance, as measured by all activity indicators employed log($R'_{HK}$), H$_α$, NaI, and HeI. None of the models employed, whether magnetic interaction or tidal interaction, provides a good description of the data. Conclusions: We find no evidence for star-planet interaction in HD\,80606 at the moment of the periastron passage of its very eccentric planet. The straightforward explanation for the non-detection is the absence of interaction as a result of a low magnetic field strength on either the planet or the star and of the low level of tidal interaction between the two. However, we cannot exclude two scenarios: i) the interaction can be instantaneous and of magnetic origin, being concentrated on the substellar point and its surrounding area, and ii) the interaction can lead to a delayed activity enhancement. (abridged)

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arXiv2016

An extreme planetary system around HD219828. One long-period super Jupiter to a hot-neptune host star

With about 2000 extrasolar planets confirmed, the results show that planetary systems have a whole range of unexpected properties. We present a full investigation of the HD219828 system, a bright metal-rich star for which a hot neptune has previously been detected. We used a set of HARPS, SOPHIE, and ELODIE radial velocities to search for the existence of orbiting companions to HD219828. A dynamical analysis is also performed to study the stability of the system and to constrain the orbital parameters and planet masses. We announce the discovery of a long period (P=13.1years) massive (msini=15.1MJup) companion (HD219828c) in a very eccentric orbit (e=0.81). The same data confirms the existence of a hot-neptune, HD219828b, with a minimum mass of 21 MEarth and a period of 3.83days. The dynamical analysis shows that the system is stable. The HD219828 system is extreme and unique in several aspects. First, among all known exoplanet systems it presents an unusually high mass ratio. We also show that systems like HD219828, with a hot neptune and a long-period massive companion are more frequent than similar systems with a hot jupiter instead. This suggests that the formation of hot neptunes follows a different path than the formation of their hot jovian counterparts. The high mass, long period, and eccentricity of HD219828c also make it a good target for Gaia astrometry as well as a potential target for atmospheric characterisation, using direct imaging or high-resolution spectroscopy. Astrometric observations will allow us to derive its real mass and orbital configuration. If a transit of HD219828b is detected, we will be able to fully characterise the system, including the relative orbital inclinations. With a clearly known mass, HD219828c may become a benchmark object for the range in between giant planets and brown dwarfs.

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arXiv2016

Close-in planets around giant stars. Lack of hot-Jupiters and prevalence of multi-planetary systems

Extrasolar planets abound in almost any possible configuration. However, until five years ago, there was a lack of planets orbiting closer than 0.5 au to giant or subgiant stars. Since then, recent detections have started to populated this regime by confirming 13 planetary systems. We discuss the properties of these systems in terms of their formation and evolution off the main sequence. Interestingly, we find that $70.0\pm6.6$ % of the planets in this regime are inner components of multiplanetary systems. This value is 4.2$σ$ higher than for main-sequence hosts, which we find to be $42.4\pm0.1$ %. The properties of the known planets seem to indicate that the closest-in planets (a < 0.06 au) to main-sequence stars are massive (i.e., hot Jupiters) and isolated and that they are subsequently engulfed by their host as it evolves to the red giant branch, leaving only the predominant population of multiplanetary systems in orbits 0.06 < a < 0.5 au. We discuss the implications of this emerging observational trend in the context of formation and evolution of hot Jupiters.

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arXiv2016

On the rotation of co-orbital bodies in eccentric orbits

We investigate the resonant rotation of co-orbital bodies in eccentric and planar orbits. We develop a simple analytical model to study the impact of the eccentricity and orbital perturbations on the spin dynamics. This model is relevant in the entire domain of horseshoe and tadpole orbit, for moderate eccentricities. We show that there are three different families of spin-orbit resonances, one depending on the eccentricity, one depending on the orbital libration frequency, and another depending on the pericenter's dynamics. We can estimate the width and the location of the different resonant islands in the phase space, predicting which are the more likely to capture the spin of the rotating body. In some regions of the phase space the resonant islands may overlap, giving rise to chaotic rotation.

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arXiv2016

The SOPHIE search for northern extrasolar planets. X. Detection and characterization of giant planets by the dozen

We present new radial velocity measurements of eight stars secured with the spectrograph SOPHIE at the 193-cm telescope of the Haute-Provence Observatory allowing the detection and characterization of new giant extrasolar planets. The host stars are dwarfs of spectral types between F5 and K0 and magnitudes between 6.7 and 9.6; the planets have minimum masses M_p sin i between 0.4 to 3.8 M_Jup and orbital periods of several days to several months. The data allow only single planets to be discovered around the first six stars (HD143105, HIP109600, HD35759, HIP109384, HD220842, and HD12484), but one of them shows the signature of an additional substellar companion in the system. The seventh star, HIP65407, allows the discovery of two giant planets, just outside the 12:5 resonance in weak mutual interaction. The last star, HD141399, was already known to host a four-planetary system; our additional data and analyses allow new constraints to be put on it. We present Keplerian orbits of all systems, together with dynamical analyses of the two multi-planetary systems. HD143105 is one of the brightest stars known to host a hot Jupiter, which could allow numerous follow-up studies to be conducted despite this is not a transiting system. The giant planets HIP109600b, HIP109384b, and HD141399c are located in the habitable zone of their host star.

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arXiv2015

Detecting ring systems around exoplanets using high resolution spectroscopy: the case of 51Pegb

In this paper we explore the possibility that the recently detected reflected light signal of 51\,Peg\,b could be caused by a ring system around the planet. We use a simple model to compare the observed signal with the expected signal from a short-period giant planet with rings. We also use simple dynamical arguments to understand the possible geometry of such a system. We provide evidence that, to a good approximation, the observations are compatible with the signal expected from a ringed planet, assuming that the rings are non-coplanar with the orbital plane. However, based on dynamical arguments, we also show that this configuration is unlikely. In the case of coplanar rings we then demonstrate that the incident flux on the ring surface is about 2\% the value received by the planet, a value that renders the ring explanation unlikely. The results suggest that the signal observed cannot in principle be explained by a planet+ring system. We discuss, however, the possibility of using reflected light spectra to detect and characterize the presence of rings around short-period planets. Finally, we show that ring systems could have already been detected by photometric transit campaigns, but their signal could have been easily misinterpreted by the expected light curve of an eclipsing binary.

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arXiv2015

Stability of resonant configurations during the migration of planets and constraints on disk-planet interactions

We study the stability of mean-motion resonances (MMR) between two planets during their migration in a protoplanetary disk. We use an analytical model of resonances, and describe the effect of the disk by a migration timescale (T_{m,i}) and an eccentricity damping timescale (T_{e,i}) for each planet (i=1,2 respectively for the inner and outer planet). We show that the resonant configuration is stable if T_{e,1}/T_{e,2} > (e_1/e_2)^2. This general result can be used to put constraints on specific models of disk-planet interactions. For instance, using classical prescriptions for type I migration, we show that when the angular momentum deficit (AMD) of the inner orbit is larger than the outer's orbit AMD, resonant systems must have a locally inverted disk density profile to stay locked in resonance during the migration. This inversion is very untypical of type I migration and our criterion can thus provide an evidence against classical type I migration. That is indeed the case for the Jupiter-mass resonant systems HD 60532b, c (3:1 MMR), GJ 876b, c (2:1 MMR), and HD 45364b, c (3:2 MMR). This result may be an evidence for type II migration (gap opening planets), which is compatible with the large masses of these planets.

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arXiv2014

Spin-orbit resonances and rotation of coorbital bodies in quasi-circular orbits

The rotation of asymmetric bodies in eccentric Keplerian orbits can be chaotic when there is some overlap of spin-orbit resonances. Here we show that the rotation of two coorbital bodies (two planets orbiting a star or two satellites of a planet) can also be chaotic even for quasi-circular orbits around the central body. When dissipation is present, the rotation period of a body on a nearly circular orbit is believed to always end synchronous with the orbital period. Here we demonstrate that for coorbital bodies in quasi-circular orbits, stable non-synchronous rotation is possible for a wide range of mass ratios and body shapes. We further show that the rotation becomes chaotic when the natural rotational libration frequency, due to the axial asymmetry, is of the same order of magnitude as the orbital libration frequency.

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arXiv2014

SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly eccentric three-month period transiting exoplanet

In this paper we report a new transiting warm giant planet: KOI-1257 b. It was first detected in photometry as a planet-candidate by the ${\it Kepler}$ space telescope and then validated thanks to a radial velocity follow-up with the SOPHIE spectrograph. It orbits its host star with a period of 86.647661 d $\pm$ 3 s and a high eccentricity of 0.772 $\pm$ 0.045. The planet transits the main star of a metal-rich, relatively old binary system with stars of mass of 0.99 $\pm$ 0.05 Msun and 0.70 $ \pm $ 0.07 Msun for the primary and secondary, respectively. This binary system is constrained thanks to a self-consistent modelling of the ${\it Kepler}$ transit light curve, the SOPHIE radial velocities, line bisector and full-width half maximum (FWHM) variations, and the spectral energy distribution. However, future observations are needed to confirm it. The PASTIS fully-Bayesian software was used to validate the nature of the planet and to determine which star of the binary system is the transit host. By accounting for the dilution from the binary both in photometry and in radial velocity, we find that the planet has a mass of 1.45 $ \pm $ 0.35 Mjup, and a radius of 0.94 $ \pm $ 0.12 Rjup, and thus a bulk density of 2.1 $ \pm $ 1.2 g.cm$^{-3}$. The planet has an equilibrium temperature of 511 $\pm$ 50 K, making it one of the few known members of the warm-jupiter population. The HARPS-N spectrograph was also used to observe a transit of KOI-1257 b, simultaneously with a joint amateur and professional photometric follow-up, with the aim of constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin effect was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet.

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arXiv2014

Resonance breaking due to dissipation in planar planetary systems

We study the evolution of two planets around a star, in mean-motion resonance and undergoing tidal effect. We derive an integrable analytical model of mean-motion resonances of any order which reproduce the main features of the resonant dynamics. Using this simplified model, we obtain a criterion showing that depending on the balance of the tidal dissipation in both planets, their final period ratio may stay at the resonant value, increase above, or decrease below the resonant value. Applying this criterion to the two inner planets orbiting GJ163, we deduce that the current period ratio (2.97) could be the outcome of dissipation in the 3:1 MMR provided that the innermost planet is gaseous (slow dissipation) while the second one is rocky (faster dissipation). We perform N-body simulations with tidal dissipation to confirm the results of our analytical model. We also apply our criterion on GJ581b, c (5:2 MMR) and reproduce the current period ratio (2.4) if the inner planet is gaseous and the outer is rocky (as for GJ163). Finally, we apply our model to the Kepler mission's statistics. We show that the excess of planets pairs close to first order MMR but in external circulation, i.e., with period ratios P_out/P_in > (p+1)/p for the resonance (p+1):p, can be reproduced by tidal dissipation in the inner planet. There is no need for any other dissipative mechanism, provided that these systems left the resonance with non-negligible eccentricities.

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arXiv2013

Orbital and physical properties of planets and their hosts: new insights on planet formation and evolution

We explore the relations between physical and orbital properties of planets and properties of their host stars to identify the main observable signatures of the formation and evolution processes of planetary systems. We use a large sample of FGK dwarf planet hosts with stellar parameters derived in a homogeneous way from the SWEET-Cat database to study the relation between stellar metallicity and position of planets in the period-mass diagram. In the second part we use all the RV-detected planets orbiting FGK stars to explore the role of planet-disk and planet-planet interaction on the evolution of orbital properties of planets with masses above 1MJup. We show that planets orbiting metal-poor stars have longer periods than those in metal-rich systems. This trend is valid for masses at least from 10MEarth to 4MJup. Earth-like planets orbiting metal-rich stars always show shorter periods (fewer than 20 days) than those orbiting metal-poor stars. We also found statistically significant evidence that very high mass giants have on average more eccentric orbits than giant planets with lower mass.Finally, we show that the eccentricity of planets with masses higher than 4MJup tends to be lower for planets with shorter periods. Our results suggest that the planets in the P-MP diagram are evolving differently because of a mechanism that operates over a wide range of planetary masses. This mechanism is stronger or weaker depending on the metallicity of the respective system. One possibility is that planets in metal-poor disks form farther out from their central star and/or they form later and do not have time to migrate as far as the planets in metal-rich systems. The trends and dependencies obtained for very high mass planetary systems suggest that planet-disk interaction is a very important and orbit-shaping mechanism for planets in the high-mass domain. Shortened.

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arXiv2013

A semi-empirical stability criterion for real planetary systems

We test a crossing orbit stability criterion for eccentric planetary systems, based on Wisdom's criterion of first order mean motion resonance overlap (Wisdom, 1980). We show that this criterion fits the stability regions in real exoplanet systems quite well. In addition, we show that elliptical orbits can remain stable even for regions where the apocenter distance of the inner orbit is larger than the pericenter distance of the outer orbit, as long as the initial orbits are aligned. The analytical expressions provided here can be used to put rapid constraints on the stability zones of multi-planetary systems. As a byproduct of this research, we further show that the amplitude variations of the eccentricity can be used as a fast-computing stability indicator.

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arXiv2013

The HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone

The meter-per-second precision achieved by today velocimeters enables the search for 1-10 M_Earth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting GJ163 (HIP19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ163 over a period of 8 years. We searched the RV time series for coherent signals and found 5 distinct periodic variabilities. We investigated the stellar activity and casted doubts on the planetary interpretation for 2 signals. Before more data can be acquired we concluded that at least 3 planets are orbiting GJ163. They have orbital periods of P_b=8.632+-0.002, P_c=25.63+-0.03 and P_d=604+-8 days and minimum masses msini = 10.6+-0.6, 6.8+-0.9, and 29+-3 M_Earth, respectively. We hold our interpretations for the 2 additional signals with periods P_(e)=19.4 and P_(f)=108 days. The inner pair presents an orbital period ratio of 2.97, but a dynamical analysis of the system shows that it lays outside the 3:1 mean motion resonance. GJ163c, in particular, is a super-Earth with an equilibrium temperature of T_eq = (302+-10) (1-A)^(1/4) K and may lie in the so called habitable zone for albedo values (A=0.34-0.89) moderately higher than that of Earth (A_Earth=0.2-0.3).

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arXiv2013

Tidal damping of the mutual inclination in hierachical systems

Hierarchical two-planet systems, in which the inner body's semi-major axis is between 0.1 and 0.5 AU, usually present high eccentricity values, at least for one of the orbits. As a result of the formation process, one may expect that planetary systems with high eccentricities also have high mutual inclinations. However, here we show that tidal effects combined with gravitational interactions damp the initial mutual inclination to modest values in timescales that are shorter than the age of the system. This effect is not a direct consequence of tides on the orbits, but it results from a secular forcing of the inner planet's flattening. We then conclude that these hierarchical planetary systems are unlikely to present very high mutual inclinations, at least as long as the orbits remain outside the Lidov-Kozai libration areas. The present study can also be extended to systems of binary stars and to planet-satellite systems.

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arXiv2012

Dissipation in planar resonant planetary systems

Close-in planetary systems detected by the Kepler mission present an excess of periods ratio that are just slightly larger than some low order resonant values. This feature occurs naturally when resonant couples undergo dissipation that damps the eccentricities. However, the resonant angles appear to librate at the end of the migration process, which is often believed to be an evidence that the systems remain in resonance. Here we provide an analytical model for the dissipation in resonant planetary systems valid for low eccentricities. We confirm that dissipation accounts for an excess of pairs that lie just aside from the nominal periods ratios, as observed by the Kepler mission. In addition, by a global analysis of the phase space of the problem, we demonstrate that these final pairs are non-resonant. Indeed, the separatrices that exist in the resonant systems disappear with the dissipation, and remains only a circulation of the orbits around a single elliptical fixed point. Furthermore, the apparent libration of the resonant angles can be explained using the classical secular averaging method. We show that this artifact is only due to the severe damping of the amplitudes of the eigenmodes in the secular motion.

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arXiv2012

Stellar wobble in triple star systems

The radial velocity method for detecting extra-solar planets relies on measuring the star's wobble around the system's center of mass. Since this is an indirect method, we may ask if there are other dynamical effects that can mimic such wobble. In recent articles\cite{1,2,3}, we modeled the effect of a nearby binary system on a star's radial velocity. We showed that, if we are unaware of this nearby binary, for instance because one component is unresolved or both components are faint stars, the binary's effect may mimic a planet. Here, we review this work, explaining in which circumstances the binary's effect may mimic a planet and we discuss what can be done in practice in order to distinguish between these two scenarios (planet or nearby binary).

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