Context. HD 106906AB is the only young binary system so far around which a planet has been imaged and a debris disk has been shown to exist, thanks to a strong IR excess. As such, it represents a ...unique opportunity for studying the dynamics of young planetary systems. Aims. We aim at further investigating the close (tens of au scales) environment of the HD 106906AB system. Methods. We used the extreme adaptive-optics-fed, high-contrast imager SPHERE that has recently been installed on the VLT to observe HD 106906. Both the IRDIS imager and the Integral Field Spectrometer were used. Results. We discovered a highly inclined, ring-like disk at a distance of 65 au from the star. The disk shows a strong brightness asymmetry with respect to its semi-major axis. It shows a smooth outer edge, compatible with ejection of small grains by the stellar radiation pressure. We show furthermore that the planet’s projected position is significantly above the PA of the disk. Given the determined disk inclination, it is not excluded, however, that the planet could still orbit within the disk plane if at a large separation (2000−3000 au). We identified several additional point sources in the SPHERE/IRDIS field of view that appear to be background objects. We compare this system with other debris disks sharing similarities, and we briefly discuss the present results in the framework of dynamical evolution.
The source HD 172555 is a young A7V star surrounded by a debris disk with a gaseous component. Here, we present the detection of variable absorption features detected simultaneously in the Ca II K ...and H doublet lines (at λ3933 Å and λ3968 Å). We identified the presence of these absorption signatures at four different epochs in the 129 HARPS high-resolution spectra gathered between 2004 and 2011. These transient absorption features are most likely due to falling evaporating bodies (FEBs, or exocomets) that produce absorbing gas observed transiting in front of the central star. We also detect a stable Ca II absorption component at the star’s radial velocity. With no corresponding detection in the Na I line, the resulting very low upper limit for the Na I/Ca II ratio suggests that this absorption is due to circumstellar gas.
Context. Accurate stellar parameters are needed in numerous domains of astrophysics. The position of stars on the Hertzsprung-Russell diagram is an important indication of their structure and ...evolution, and it helps improve stellar models. Furthermore, the age and mass of stars hosting planets are required elements for studying exoplanetary systems. Aims. We aim at determining accurate parameters of a set of 18 bright exoplanet host and potential host stars from interferometric measurements, photometry, and stellar models. Methods. Using the VEGA/CHARA interferometer operating in the visible domain, we measured the angular diameters of 18 stars, ten of which host exoplanets. We combined them with their distances to estimate their radii. We used photometry to derive their bolometric flux and, then, their effective temperature and luminosity to place them on the H-R diagram. We then used the PARSEC models to derive their best fit ages and masses, with error bars derived from Monte Carlo calculations. Results. Our interferometric measurements lead to an average of 1.9% uncertainty on angular diameters and 3% on stellar radii. There is good agreement between measured and indirect estimations of angular diameters (either from SED fitting or from surface brightness relations) for main sequence (MS) stars, but not as good for more evolved stars. For each star, we provide a likelihood map in the mass-age plane; typically, two distinct sets of solutions appear (an old and a young age). The errors on the ages and masses that we provide account for the metallicity uncertainties, which are often neglected by other works. From measurements of its radius and density, we also provide the mass of 55 Cnc independently of models. From the stellar masses, we provide new estimates of semi-major axes and minimum masses of exoplanets with reliable uncertainties. We also derive the radius, density, and mass of 55 Cnc e, a super-Earth that transits its stellar host. Our exoplanetary parameters reflect the known population of exoplanets. Conclusions. This work illustrates how precise interferometric measurements of angular diameters and detailled modeling allow fundamental parameters of exoplanet host stars to be constrained at a level permiting analysis of the planet’s parameters.
Context
. Thanks to more than 20 yr of monitoring, the radial velocity (RV) method has detected long-period companions (
P
> 10 yr) around several dozens of stars. Yet, the true nature of these ...companions remains unclear because of the uncertainty as to the inclination of the companion orbital plane.
Aims
. We wish to constrain the orbital inclination and the true mass of long-period single companions.
Methods
. We used a Markov chain Monte Carlo (MCMC) fitting algorithm to combine RV measurements with absolute astrometry and, when available, relative astrometry data.
Results
. We have lifted the sin(
i
) indetermination for seven long-period companions. We find true masses in the planetary mass range for the candidate planets detected in the following systems: Epsilon Indi A, HD 13931, HD 115954, and HD 222155. The mass of HD 219077 b is close to the deuterium-burning limit and its nature is uncertain because of the imprecise mass of the host star. Using additional RV measurements, we refine the orbital parameters of HIP 70849 b and find a mass in the planetary range. By combining RV data with absolute and relative astrometry, we significantly improve the characterization of HD 211847 B and properly determine its mass, which appears to be in the low-mass star range. This work illustrates how
Gaia
and H
IPPARCOS
allow for the orbital properties and masses of long-period RV companions to be further constrained.
Context.
HR 8799 is a young planetary system composed of four planets and a double debris belt. Being the first multi-planetary system discovered with the direct imaging technique, it has been ...observed extensively since 1998. This wide baseline of astrometric measurements, counting over 50 observations in 20 years, permits a detailed orbital and dynamical analysis of the system.
Aims.
To explore the orbital parameters of the planets, their dynamical history, and the planet-to-disk interaction, we made follow-up observations of the system during the VLT/SPHERE guaranteed time observation program. We obtained 21 observations, most of them in favorable conditions. In addition, we observed HR 8799 with the instrument LUCI at the Large Binocular Telescope (LBT).
Methods.
All the observations were reduced with state-of-the-art algorithms implemented to apply the spectral and angular differential imaging method. We re-reduced the SPHERE data obtained during the commissioning of the instrument and in three open-time programs to have homogeneous astrometry. The precise position of the four planets with respect to the host star was calculated by exploiting the fake negative companions method. We obtained an astrometric precision of the order of 6 mas in the worst case and 1 mas in the best case. To improve the orbital fitting, we also took into account all of the astrometric data available in the literature. From the photometric measurements obtained in different wavelengths, we estimated the masses of the planets following the evolutionary models.
Results.
We obtained updated parameters for the orbits with the assumption of coplanarity, relatively small eccentricities, and periods very close to the 2:1 resonance. We also refined the dynamical mass of each planet and the parallax of the system (24.49 ± 0.07 mas), which overlap with the recent
Gaia
eDR3/DR3 estimate. Hydrodynamical simulations suggest that inward migration of the planets caused by the interaction with the disk might be responsible for the planets being locked in resonance. We also conducted detailed
N
-body simulations indicating possible positions of a putative fifth planet with a mass below the present detection limits of ≃3
M
Jup
.
Context.
Stellar activity strongly affects and may prevent the detection of Earth-mass planets in the habitable zone of solar-type stars with radial velocity technics. Astrometry is in principle less ...sensitive to stellar activity because the situation is more favourable: the stellar astrometric signal is expected to be fainter than the planetary astrometric signal compared to radial velocities.
Aims.
We quantify the effect of stellar activity on high-precision astrometry when Earth-mass planets are searched for in the habitable zone around old main-sequence solar-type stars.
Methods.
We used a very large set of magnetic activity synthetic time series to characterise the properties of the stellar astrometric signal. We then studied the detectability of exoplanets based on different approaches: first based on the theoretical level of false positives derived from the synthetic time series, and then with blind tests for old main-sequence F6-K4 stars.
Results.
The amplitude of the signal can be up to a few times the solar value depending on the assumptions made for activity level, spectral type, and spot contrast. The detection rates for 1
M
Earth
planets are very good, however, with extremely low false-positive rates in the habitable zone for stars in the F6-K4 range at 10 pc. The standard false-alarm probability using classical bootstrapping on the time series strongly overestimates the false-positive level. This affects the detection rates.
Conclusions.
We conclude that if technological challenges can be overcome and very high precision is reached, astrometry is much more suitable for detecting Earth-mass planets in the habitable zone around nearby solar-type stars than radial velocity, and detection rates are much higher for this range of planetary masses and periods when astrometric techniques are used than with radial velocity techniques.
Aims. Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it ...influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages.Methods. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edgeon. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We analyzed the properties of the RV signal at different activity levels and compared it with commonly used activity indicators such as photometry and the Ca index. We also compared it with the signal that would be produced by an Earth-mass planet in the HZ.Results. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. Short-term variations are also significantly greater than the spot and plage photometric contribution. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet.Conclusions. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators.
Context. In June 2010, we confirmed the existence of a giant planet in the disk of the young star βPictoris located between 8 AU and 15 AU from the star. This young planet offers the rare ...opportunity to monitor a large fraction of the orbit using the imaging technique over a reasonably short timescale. It also offers the opportunity to study its atmospheric properties using spectroscopy and multi-band photometry, and possibly derive its dynamical mass by combining imaging with radial velocity data to set tight constraints on giant planet formation theories. Aims. We aim to measure the evolution of the planet’s position relative to the star βPictoris to determine the planetary orbital properties. Our ultimate goal is to relate both the planetary orbital configuration and physical properties to either the disk structure or the cometary activity observed for decades in the βPictoris system. Methods. Using the NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope (VLT), we obtained repeated follow-up images of the βPictoris system in the Ks and L′ filters at four new epochs in 2010 and 2011. Complementing these data with previous measurements, we conduct a homogeneous analysis, which covers more than eight yrs, to accurately monitor the βPictoris b position relative to the star. We then carefully consider the various sources of uncertainties that may affect the orbital parameter determination. Results. On the basis of the evolution of the planet’s relative position with time, we derive the best-fit orbital solutions for our measurements using two fitting methods, a least squares Levenberg-Marquardt algorithm and a Markov-chain Monte Carlo approach. More reliable results are found with the second approach as our measurements do not cover the complete planetary orbit, and are biased toward the most recent epochs since the planet recovery. The solutions favor a low-eccentricity orbit e ≲ 0.17, with semi-major axis in the range 8–9 AU corresponding to orbital periods of 17–21 yrs. Our solutions favor a highly inclined solution with a peak around i = 88.5 ± 1.7°, and a longitude of ascending node tightly constrained at Ω = −147.5 ± 1.5°. These results indicate that the orbital plane of the planet is likely to be above the midplane of the main disk, and compatible with the warp component of the disk being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a key role in the origin of the inner warped-disk morphology of the β Pic disk. Finally, these orbital parameters are consistent with the hypothesis that the planet is responsible for the transit-like event observed in November 1981, and also linked to the cometary activity observed in the β Pic system.
The transiting extrasolar planet XO-3b is remarkable, with a high mass and eccentric orbit. These unusual characteristics make it interesting to test whether its orbital plane is parallel to the ...equator of its host star, as it is observed for other transiting planets. We performed radial velocity measurements of XO-3 with the SOPHIE spectrograph at the 1.93 m telescope of Haute-Provence Observatory during a planetary transit and at other orbital phases. This allowed us to observe the Rossiter-McLaughlin effect and, together with a new analysis of the transit light curve, to refine the parameters of the planet. The unusual shape of the radial velocity anomaly during the transit provides a hint of a nearly transverse Rossiter-McLaughlin effect. The sky-projected angle between the planetary orbital axis and the stellar rotation axis should be λ = 70° ± 15° to be compatible with our observations. This suggests that some close-in planets might result from gravitational interaction between planets and/or stars rather than migration due to interaction with the accretion disk. This surprising result requires confirmation by additional observations, especially at lower airmass, to fully exclude the possibility that the signal is due to systematic effects.
We present deep VLT/NACO infrared imaging and spectroscopic observations of the brown dwarf 2MASSWJ 1207334-393254, obtained during our on-going adaptive optics survey of southern young, nearby ...associations. This similar to 25 M sub(Jup) brown dwarf, located similar to 70 pc from Earth, has been recently identified as a member of the TW Hydrae Association (age similar to 8 Myr). Using adaptive optics infrared wavefront sensing to acquire sharp images of its circumstellar environment, we discovered a very faint and very red object at a close separation of similar to 780 mas ( similar to 55 AU). Photometry in the H, K sub(s) and L' bands and upper limit in J-band are compatible with a spectral type L5-L9.5. Near-infrared spectroscopy is consistent with this spectral type estimate. Different evolutionary models predict an object within the planetary regime with a mass of M = 5 plus or minus 2 M sub(Jup) and an effective temperature of T sub(eff) = 1250 plus or minus 200 K.
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