- ID:
- ivo://CDS.VizieR/J/A+A/567/A57
- Title:
- HD 161306 H{alpha} and HeI spectra
- Short Name:
- J/A+A/567/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectrum of the Be star HD 161306 is shown to vary periodically with a period of ~100-days. The radial velocity of the HeI 6678{AA} emission peak varying in antiphase to the radial velocity of the H{alpha} emission wings component suggests that the star is a binary similar to {phi} Per, 59 Cyg, or FY CMa, i.e. a radiatively interacting Be binary - a rare case among Be stars. This type of object is also called a {phi} Per-type binary or Be + sdO binaries. The range of radial-velocity variations of the strong emission peak in the helium line observed in HD 161306 is about 180km/s, similar to what is observed for these systems. We therefore conclude that HD 161306 may represent another case of a Be star with a hot subdwarf companion.
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- ID:
- ivo://CDS.VizieR/J/A+A/612/A41
- Title:
- HD 176986 HARPS + HARPS-N data
- Short Name:
- J/A+A/612/A41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a system of two super-Earths orbiting the moderately active K-dwarf HD 176986. This work is part of the RoPES RV program of G- and K-type stars that combines radial velocity from both HARPS and HARPS-N spectrograph to search for short-period terrestrial planets. HD 176986 b and c are super-Earth mass planets with masses of 5.74 and 9.18 Me, with orbital periods of 6.49 and 16.82 days, at a distances of 0.063 and 0.119AU, in orbits that are consistent with circular. The host star is a K2.5 dwarf, and in spite of its modest level of chromospheric activity log(R'hk)=-4.90+/-0.04, shows a complex activity pattern. Along with the discovery of the planets we study the magnetic cycle and rotation of the star. HD 176986 proves to be suitable to test the available techniques of RV analysis and our understanding of stellar activity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/503/1248
- Title:
- HD 13808 HARPS radial velocities
- Short Name:
- J/MNRAS/503/1248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of 10 years of HARPS radial velocities of the K2V dwarf star HD13808, which has previously been reported to host two unconfirmed planet candidates. We use the state-of-the-art nested sampling algorithm PolyChord to compare a wide variety of stellar activity models, including simple models exploiting linear correlations between RVs and stellar activity indicators, harmonic models for the activity signals, and a more sophisticated Gaussian process regression model. We show that the use of overly-simplistic stellar activity models that are not well-motivated physically can lead to spurious `detections' of planetary signals that are almost certainly not real. We also reveal some difficulties inherent in parameter and model inference in cases where multiple planetary signals may be present. Our study thus underlines the importance both of exploring a variety of competing models and of understanding the limitations and precision settings of one's sampling algorithm. We also show that at least in the case of HD 13808, we always arrive at consistent conclusions about two particular signals present in the RV, regardless of the stellar activity model we adopt; these two signals correspond to the previously-reported though unconfirmed planet candidate signals. Given the robustness and precision with which we can characterize these two signals, we deem them secure planet detections. In particular, we find two planets orbiting HD13808 at distances of 0.11, 0.26AU with periods of 14.2, 53.8d, and minimum masses of 11, 10 Earth masses.
- ID:
- ivo://CDS.VizieR/J/A+A/605/A103
- Title:
- HD20794 HARPS radial velocities
- Short Name:
- J/A+A/605/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the feasibility of detecting Earth analogs around Sun-like stars using the radial velocity method by investigating one of the largest radial velocities datasets for the one of the most stable radial-velocity stars HD20794. We proceed by disentangling the Keplerian signals from correlated noise and activity-induced variability. We diagnose the noise using the differences between radial velocities measured at different wavelength ranges, so-called "differential radial velocities", as well as the combination of radial velocities measured for other stars to account for instrumental effects. We apply this method to the radial velocities measured by HARPS, and identify four signals at 18, 89, 147 and 330d. The two signals at periods of 18 and 89d are previously reported and are better quantified in this work. The signal at a period of about 147d is reported for the first time, and corresponds to a super-Earth with a minimum mass of 4.59 Earth mass located 0.51AU from HD20794. We also find a significant signal at a period of about 330d corresponding to a super-Earth or Neptune in the habitable zone. Since this signal is close to the annual sampling period and significant periodogram power in some noise proxies are found close to this signal, further observations and analyses are required to confirm it. The analyses of the eccentricity and consistency of signals provide weak evidence for the existence of the previously reported 43d signal and a new signal at a period of about 11.9d with a semi amplitude of 0.4m/s. We find that the detection of a number of signals with radial velocity variations around 0.5m/s likely caused by low mass planet candidates demonstrates the important role of noise modeling in searching for Earth analogs.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A9
- Title:
- HD17674, HD29021, and HD42012 radial velocities
- Short Name:
- J/A+A/601/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new radial velocity measurements for three low-metallicity solar-like stars observed with the SOPHIE spectrograph and its predecessor ELODIE, both installed at the 193cm telescope of the Haute-Provence Observatory, allowing the detection and characterization of three new giant extrasolar planets in intermediate periods of 1.7 to 3.7yr. All three stars, HD 17674, HD 42012 and HD 29021 present single giant planetary companions with minimum masses between 0.9 and 2.5M_Jup_. The range of periods and masses of these companions, along with the distance of their host stars, make them good targets to look for astrometric signals over the lifetime of the new astrometry satellite Gaia. We discuss the preliminary astrometric solutions obtained from the first Gaia data release.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A134
- Title:
- HD1461, HD40307, and HD204313 radial velocities
- Short Name:
- J/A+A/585/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of the entire HARPS observations of three stars that host planetary systems: HD1461, HD40307, and HD204313. The data set spans eight years and contains more than 200 nightly averaged velocity measurements for each star. This means that it is sensitive to both long-period and low-mass planets and also to the e ects induced by stellar activity cycles. We modelled the data using Keplerian functions that correspond to planetary candidates and included the short- and long-term effects of magnetic activity. A Bayesian approach was taken both for the data modelling, which allowed us to include information from activity proxies such as log(R'_HK_) in the velocity modelling, and for the model selection, which permitted determining the number of significant signals in the system. The Bayesian model comparison overcomes the limitations inherent to the traditional periodogram analysis. We report an additional super-Earth planet in the HD1461 system. Four out of the six planets previously reported for HD40307 are confirmed and characterised. We discuss the remaining two proposed signals. In particular, we show that when the systematic uncertainty associated with the techniques for estimating model probabilities are taken into account, the current data are not conclusive concerning the existence of the habitable-zone candidate HD40307 g. We also fully characterise the Neptune-mass planet that orbits HD204313 in 34.9 days.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A58
- Title:
- HD20794, HD85512, HD192310 HARPS radial velocities
- Short Name:
- J/A+A/534/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 2009 we started, within the dedicated HARPS-Upgrade GTO program, an intense radial-velocity monitoring of a few nearby, slowly-rotating and quiet solar-type stars. The goal of this campaign is to gather, with high cadence and continuity, very-precise radial-velocity data in order to detect tiny signatures of very-low-mass stars potentially in the habitable zone of their parent stars. 10 stars have been selected among the most stable stars of the original HARPS high-precision program, uniformly spread in hour angle, such that three to four of them are observable at any time of the year. For each star we record 50 data points spread over the observing season. The data point consists of three nightly observations of a total integration time of 10 minutes each and separated by 2 hours. This is an observational strategy adopted to minimize stellar pulsation and granulation noise. In this paper we present the first results of this ambitious program. The radial-velocity data and the orbital parameters of five new and one confirmed low-mass planets around the stars HD 20794, HD 85512 and HD 192310, respectively, are reported and discussed, among which a system of three super-Earths and one harboring a 3.6-Earth-mass planet at the inner edge of the habitable zone. This result already confirms previous indications that low-mass planets seem to be very frequent around solar-type stars and that this occurrence frequency may be higher than 30%.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A6
- Title:
- HD 219134 light and RV curves and code
- Short Name:
- J/A+A/635/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By analysing the transit light-curve of a planet-hosting star or the induced radial velocity oscillations, many useful information on the planet may be retrieved. However, inferring the physical parameters of the planet (mass, size, semi-major axis, etc.) requires the preliminary knowledge of some parameters of the host star, especially its mass and/or radius, that are generally inferred through theoretical evolutionary models. The paper aims at presenting and testing a whole algorithm devoted to the complete characterization of an exoplanetary system thanks to the global analysis of photometric and/or radial velocity time-series combined to observational stellar parameters derived either from spectroscopy or photometry. We developed an integrated tool called MCMCI that combines the Markov Chain Monte Carlo (MCMC) approach for analysing photometric and/or radial velocity time-series with a proper interpolation within stellar evolutionary isochrones and tracks (known as Isochrone placement) to be performed at each chain step, to retrieve stellar theoretical parameters, such as age, mass and radius. We tested the MCMCI both on the HD 219134 multiplanetary system hosting two transiting rocky super-Earths and on WASP-4, that hosts a bloated hot Jupiter. Even considering different input approaches, a final convergence was reached within the code, we found good agreement with the results already stated in the literature and we obtained more precise output parameters, especially concerning planetary masses. The MCMCI tool offers the opportunity of performing an integrated analysis of an exoplanetary system, without splitting it into the preliminary stellar characterization through theoretical models, but rather favouring a close interaction between the light-curve analysis and the isochrones, so that the parameters recovered at each step of the MCMC enter as input of the Isochrone placement.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A97
- Title:
- HD 183656 Long-term variations
- Short Name:
- J/A+A/647/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest results of a long-term observational project aimed at observing, collecting from the literature, and homogenising the light, colour, and spectral variations of the well-known emission-line Be star V923 Aql. Our analysis of these parameters confirms that all of the observables exhibit cyclic changes with variable cycle length between about 1800 and 3000 days, so far documented for seven consecutive cycles. We show that these variations can be qualitatively understood within the framework of the model of one-armed oscillation of the circumstellar disk, with a wave of increased density and prograde revolution in space. We confirm the binary nature of the object with a 214.716 day period and estimate the probable system properties. We also confirm the presence of rapid light, and likely also spectral changes. However, we cannot provide any firm conclusions regarding their nature. A quantitative modelling study of long-term changes is planned as a follow-up to this work.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A94
- Title:
- HD 96446 radial velocities
- Short Name:
- J/A+A/626/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HD 96446 is a magnetic B2p He-strong star that has been reported to be a {beta} Cep pulsator. We present a detailed spectroscopic analysis of this object based on an intensive observational data set obtained in a multisite campaign with the spectrographs CORALIE, FEROS, and HARPS (La Silla); UVES (Paranal); HERCULES (Mt. John Observatory); and GIRAFFE (SAAO). Radial velocities were measured by cross-correlations and analysed to detect periodic variations. On the other hand, the mean spectrum was fit with spectral synthesis to derive atmospheric parameters and chemical abundances. From the analysis of radial velocities, HD 96446 was found to be a spectroscopic binary with a period of 799 days. The stellar companion, which contributes only ~5% of the total flux, is an A0-type star. A frequency analysis of the radial velocities allowed us to detect two pulsational modes with periods 2.23h and 2.66h. The main mode is most probably a low-inclination, dipole mode (l, m) = (1, 0), and the second pulsation mode corresponds to (l, m) = (2, 2) or to a pole-on (l, m) = (3, 2) configuration. In addition to radial velocities, the main pulsation mode is evidenced through small variations in the spectral morphology (temperature variations) and the light flux. The rotation period of 23.4d, was detected through the variation in line intensities. Chemical abundances are unevenly distributed over the stellar surface, with helium concentrated at the negative magnetic pole and most metals strengthened at lower latitudes. The mean chemical abundance of helium is strongly abnormal, reaching a value of 0.60 (number fraction).
