The interaction between low-mass companions and the debris disks they reside in is still not fully understood. A debris disk can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive collisions. On top of this, the presence of a companion could further stir the disk (companion-stirring). Additional information is necessary to understand this fundamental step in the formation and evolution of a planetary system, and at the moment of writing only a handful of systems are known in which both a companion and a debris disk have been detected and studied at the same time. Our primary goal is to augment the sample of such systems and understand the relative importance between self-stirring and companion-stirring. In the course of the VLT/NaCo-ISPY Imaging Survey for Planets around Young stars, we observed HD 193571, an A0 debris disk hosting star at a distance of 68 pc with an age between 60-170Myr. We obtained two sets of observations in L' band and a third epoch in H band using the GPI instrument at Gemini-South. A companion was detected in all three epochs at a projected separation of 11au (0.17-arcsec), and co-motion was confirmed through proper motion analysis. Given the inferred disk size of 120au, the companion appears to reside within the gap between the host star and the disk. Comparison between the L' and H band magnitude and evolutionary tracks suggests a mass of 0.31-0.39M_{sun}_. We discovered a previously unknown M-dwarf companion around HD 193571, making it the third low-mass stellar object discovered within a debris disk. Comparison to self- and companion-stirring models suggests that the companion is likely responsible for the stirring of the disk.
Despite their activity, low-mass stars are of particular importance for the search of exoplanets by the means of Doppler spectroscopy, as planets with lower masses become detectable. We report on the discovery of a planetary companion around HD 180617, a bright J=5.58mag, low-mass M=0.45_{sun}_ star of spectral type M2.5 V. The star, located at a distance of 5.9pc, is the primary of the high proper motion binary system containing vB 10, a star with one of the lowest masses known in most of the twentieth century. Our analysis is based on new radial velocity (RV) measurements made at red-optical wavelengths provided by the high-precision spectrograph CARMENES, which was designed to carry out a survey for Earth-like planets around M dwarfs. The available CARMENES data are augmented by archival Doppler measurements from HIRES and HARPS. Altogether, the RVs span more than 16 years. The modeling of the RV variations, with a semi-amplitude of K=2.85-0.25/+0.16m/s yields a Neptune-like planet with a minimum mass of 12.2-1.4/+1.0M_{Earth}_ on a 105.90-0.10/+0.09d circumprimary orbit, which is partly located in the host star's habitable zone. The analysis of time series of common activity indicators does not show any dependence on the detected RV signal. The discovery of HD 180617 b not only adds information to a currently hardly filled region of the mass-period diagram of exoplanets around M dwarfs, but the investigated system becomes the third known binary consisting of M dwarfs and hosting an exoplanet in an S-type configuration. Its proximity makes it an attractive candidate for future studies.
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. Radial-velocity data were taken at Haute-Provence Observatory (OHP, France) with the ELODIE echelle spectrograph. We report the presence of a planet orbiting HD 196885A, 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 196885B, and give some constraints on its orbit.
Twenty-four years after the first exoplanet discoveries, the radial-velocity (RV) method is still one of the most productive techniques to detect and confirm exoplanets. But stellar magnetic activity can induce RV variations large enough to make it difficult to disentangle planet signals from the stellar noise. In this context, HD 41248 is an interesting planet-host candidate, with RV observations plagued by activity-induced signals. We report on ESPRESSO observations of HD 41248 and analyse them together with previous observations from HARPS, with the goal of evaluating the presence of orbiting planets. Using different noise models within a general Bayesian framework designed for planet detection in RV data, we test the significance of the various signals present in the HD 41248 data set. We use Gaussian processes as well as a first-order moving average component to try to correct for activity-induced signals. At the same time, we analyse photometry from the TESS mission, searching for transits and rotational modulation in the lightcurve. The number of significantly detected Keplerian signals depends on the noise model employed, ranging from 0 with the Gaussian process model to 3 with a white noise model. We find that the Gaussian process alone can explain the RV data and allows for the stellar rotation period and active region evolution timescale to be constrained. The rotation period estimated from the RVs agrees with the value determined from the TESS lightcurve. Based on the currently available data, we conclude that the RV variations of HD 41248 can be explained by stellar activity (using the Gaussian process model) in line with the evidence from activity indicators and the TESS photometry.
We report the radial velocity discovery of a second planetary mass companion to the K0 V star HD 37605, which was already known to host an eccentric, P~55 days Jovian planet, HD 37605b. This second planet, HD 37605c, has a period of ~7.5 years with a low eccentricity and an Msini of ~3.4M_Jup_. Our discovery was made with the nearly 8 years of radial velocity follow-up at the Hobby-Eberly Telescope and Keck Observatory, including observations made as part of the Transit Ephemeris Refinement and Monitoring Survey effort to provide precise ephemerides to long-period planets for transit follow-up. With a total of 137 radial velocity observations covering almost 8 years, we provide a good orbital solution of the HD 37605 system, and a precise transit ephemeris for HD 37605b. Our dynamic analysis reveals very minimal planet-planet interaction and an insignificant transit time variation. Using the predicted ephemeris, we performed a transit search for HD 37605b with the photometric data taken by the T12 0.8m Automatic Photoelectric Telescope (APT) and the MOST satellite. Though the APT photometry did not capture the transit window, it characterized the stellar activity of HD 37605, which is consistent of it being an old, inactive star, with a tentative rotation period of 57.67 days. The MOST photometry enabled us to report a dispositive null detection of a non-grazing transit for this planet. Within the predicted transit window, we exclude an edge-on predicted depth of 1.9% at the {Gt}10{sigma} level, and exclude any transit with an impact parameter b>0.951 at greater than 5{sigma}. We present the BOOTTRAN package for calculating Keplerian orbital parameter uncertainties via bootstrapping. We made a comparison and found consistency between our orbital fit parameters calculated by the RVLIN package and error bars by BOOTTRAN with those produced by a Bayesian analysis using MCMC.
As part of the Transit Ephemeris Refinement and Monitoring Survey, we present new radial velocities and photometry of the HD 192263 system. Our analysis of the already available Keck-HIRES and CORALIE radial velocity measurements together with the five new Keck measurements we report in this paper results in improved orbital parameters for the system. We derive constraints on the size and phase location of the transit window for HD 192263b, a Jupiter-mass planet with a period of 24.3587+/-0.0022 days. We use 10 years of Automated Photoelectric Telescope photometry to analyze the stellar variability and search for planetary transits. We find continuing evidence of spot activity with periods near 23.4 days. The shape of the corresponding photometric variations changes over time, giving rise to not one but several Fourier peaks near this value. However, none of these frequencies coincides with the planet's orbital period and thus we find no evidence of star-planet interactions in the system. We attribute the ~23 day variability to stellar rotation. There are also indications of spot variations on longer (8 years) timescales. Finally, we use the photometric data to exclude transits for a planet with the predicted radius of 1.09R_J_, and as small as 0.79R_J_.
Our red-wavelength spectroscopic observations of HD 131861, a previously known single-line multiple system, span 20 years. Now lines of two components, the short-period F5 V primary and G8 V secondary, have been detected. The inner orbit is circular with a period of 3.5507439-days, while the outer orbit of the system has a period of 1642 days or 4.496-yr and a relatively low eccentricity of 0.10. Analysis of the Hipparcos data produces a well-determined astrometric orbit for the long-period system that has an inclination of 52{deg}. Our photometric observations show shallow primary and secondary eclipses of the short-period pair, and eclipse solutions result in an inclination of 81{deg}. Thus, the long- and short-period orbits are not coplanar. The mass of the unseen third component is 0.7M_{dot}_, corresponding to a mid-K dwarf. The total mass of the system, 3.08M_{dot}_, leads to a semimajor axis of 4AU for the outer orbit. The F5 V primary is rotating more slowly than it would if it were synchronously rotating, while the G8 V secondary may be synchronously rotating. The lithium abundance of the F5 V primary is similar to the initial lithium abundance found for Population I dwarfs and so indicates no significant dilution.
In the frame of the search for extrasolar planets and brown dwarfs around early-type main-sequence stars, we present the detection of a giant planet around the young F-type star HD113337. We estimated the age of the system to be 150^+100^_-50_Myr. Interestingly, an IR excess attributed to a cold debris disk was previously detected on this star. The SOPHIE spectrograph on the 1.93m telescope at the Observatoire de Haute-Provence (OHP) was used to obtain ~300 spectra over 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A and F stars, to derive the radial velocity variations. The data reveal a 324.0^+1.7^_-3.3_days period that we attribute to a giant planet with a minimum mass of 2.83+/-0.24MJup in an eccentric orbit with e=0.46+/-0.04. A long-term quadratic drift, that we assign to be probably of stellar origin, is superimposed to the Keplerian solution.
With about 2000 extrasolar planets confirmed, the results show that planetary systems have a whole range of unexpected properties. This wide diversity provides fundamental clues to the processes of planet formation and evolution. We present a full investigation of the HD 219828 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 HD 219828. The spectra were used to characterise the star and its chemical abundances, as well as to check for spurious, activity induced signals. 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=13.1-years) massive (msini=15.1M_{Jup}_) companion (HD 219828 c) in a very eccentric orbit (e=0.81). The same data confirms the existence of a hot-neptune, HD 219828 b, with a minimum mass of 21M_{sun}_ and a period of 3.83-days. The dynamical analysis shows that the system is stable, and that the equilibrium eccentricity of planet $b$ is close to zero. The HD 219828 system is extreme and unique in several aspects. First, ammong all known exoplanet systems it presents an unusually high mass ratio. We also show that systems like HD 219828, 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 HD 219828 c 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 HD 219828 b is detected, we will be able to fully characterise the system, including the relative orbital inclinations. With a clearly known mass, HD 219828 c may become a benchmark object for the range in between giant planets and brown dwarfs.
The presence of a small-mass planet (M_p_<0.1M_{Jup}_) seems, to date, not to depend on metallicity. However, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths. In this paper we present the analysis of HD175607, an old G6 star with metallicity [Fe/H]=-0.62. We gathered 119 radial velocity measurements in 110 nights over a timespan of more than 9 years. The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov-Chain Monte-Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities. We find evidence for the presence of a small Neptune-mass planet (M_p_sini=8.98+/-1.10M_{sun}_) orbiting this star with an orbital period P=29.01+/-0.02days in a slightly eccentric orbit (e=0.11+/-0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed due to the presence of a planetary companion rather than stellar related. An additional longer period signal (P~1400d) is present in the data, for which more measurements are needed to constrain its nature and its properties. HD175607 is the most metal-poor FGK dwarf with a detected low mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories.
