- ID:
- ivo://CDS.VizieR/J/A+A/624/A123
- Title:
- Gl 49 radial velocities and activity indicators
- Short Name:
- J/A+A/624/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Small planets around low-mass stars often show orbital periods in a range that corresponds to the temperate zones of their host stars which are therefore of prime interest for planet searches. Surface phenomena such as spots and faculae create periodic signals in radial velocities and in observational activity tracers in the same range, so they can mimic or hide true planetary signals. We aim to detect Doppler signals corresponding to planetary companions, determine their most probable orbital configurations, and understand the stellar activity and its impact on different datasets. We analyzed 22 years of data of the M1.5V-type star Gl 49 (BD+61 195) including HARPS-N and CARMENES spectrographs, complemented by APT2 and SNO photometry. Activity indices are calculated from the observed spectra, and all datasets are analyzed with periodograms and noise models. We investigated how the variation of stellar activity imprints on our datasets. We further tested the origin of the signals and investigate phase shifts between the different sets. To search for the best-fit model we maximize the likelihood function in a Markov chain Monte Carlo approach. As a result of this study, we are able to detect the super-Earth Gl 49b with a minimum mass of 5.6M_{earth}_. It orbits its host star with a period of 13.85d at a semi-major axis of 0.090au and we calculate an equilibrium temperature of 350K and a transit probability of 2.0%. The contribution from the spot-dominated host star to the different datasets is complex, and includes signals from the stellar rotation at 18.86d, evolutionary timescales of activity phenomena at 40-80d, and a long-term variation of at least four years.
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- ID:
- ivo://CDS.VizieR/J/A+A/622/A193
- Title:
- Gl686 RV curves and BVR photometry
- Short Name:
- J/A+A/622/A193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HArps-n red Dwarf Exoplanet Survey is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial velocity measurements in a narrow range of spectral sub-types. Using the HARPS-N spectrograph we reach the precision needed to detect small planets with a few earth masses. Our survey is mainly focused on the M-dwarf population of the northern hemisphere. As part of that programme, we obtained radial velocity measurements of Gl686, an M1 dwarf at d=8.2pc. These measurements show a dispersion much in excess of their internal errors. The analysis of data obtained within an intensive observing campaign, demonstrates that the excess dispersion is due to a coherent signal, with a period of 15.53d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programmes to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We used a Bayesian framework to estimate the orbital parameters and the planet minimum mass, and to properly treat the activity noise. We took advantage of the available radial velocity measurements for this target from other observing campaigns. The analysis of the radial velocity composite time series from the HIRES, HARPS and HARPS-N spectrographs, consisting of 198 measurements taken over 20 years, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature and rotation). We report the discovery of a super-Earth orbiting at a distance of 0.092AU from the host star Gl686. Gl686 b has a minimum mass of 7.1+/-0.9M_{Earth} and an orbital period of 15.532+/-0.002d. The analysis of the activity indexes, correlated noise through a Gaussian process framework and photometry, provides an estimate of the stellar rotation period at 37d, and highlights the variability of the spot configuration during the long timespan covering 20yrs. The observed periodicities around 2000d likely point to the existence of an activity cycle.
- ID:
- ivo://CDS.VizieR/J/AJ/157/21
- Title:
- Ground-based spectroscopy of the exoplanet XO-2b
- Short Name:
- J/AJ/157/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanets orbiting close to their host star are expected to support a large ionosphere, which extends to larger pressures than witnessed in our solar system. These ionospheres can be investigated with ground-based transit observations of the optical signatures of alkali metals, which are the source of the ions. However, most ground-based transit spectra do not systematically resolve the wings of the features and continuum, as needed to constrain the alkali abundances. Here we present new observations and analyses of optical transit spectra that cover the Na doublet in the atmosphere of the exoplanet XO-2b. To assess the consistency of our results, observations were obtained from two separate platforms: Gemini/GMOS and Mayall/KOSMOS. To mitigate the systematic errors, we chose XO-2, because it has a binary companion of the same brightness and stellar type, which provides an ideal reference star to model Earth's atmospheric effects. We find that interpretation of the data is highly sensitive to time-varying translations along the detector, which change according to wavelength and differ between the target and reference star. It was necessary to employ a time-dependent cross-correlation to align our wavelength bins and correct for atmospheric differential refraction. This approach allows us to resolve the wings of the Na line across five wavelength bins at a resolution of ~1.6 nm and limit the abundance of Na. We obtain consistent results from each telescope with an Na amplitude of 521+/-161 and 403+/-186 ppm for GMOS and KOSMOS, respectively. The results are analyzed with a radiative transfer model that includes the effects of ionization. The data are consistent with a clear atmosphere between ~1 and 100 mbar that establishes a lower limit on Na at 0.4_-0.3_^+2^ ppm ([Na/H]=-0.64_-0.6_^+0.78^), consistent with solar. However, we cannot rule out the presence of clouds at ~10 mbar that allow for higher Na abundances, which would be consistent with the stellar metallicity measured for the host star ([Na/H]=0.485+/-0.043).
- ID:
- ivo://CDS.VizieR/J/A+A/622/A172
- Title:
- GTC transit light curves of HAT-P-11b
- Short Name:
- J/A+A/622/A172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rayleigh scattering in a hydrogen-dominated exoplanet atmosphere can be detected using ground- or space-based telescopes. However, stellar activity in the form of spots can mimic Rayleigh scattering in the observed transmission spectrum. Quantifying this phenomena is key to our correct interpretation of exoplanet atmospheric properties. We obtained Gran Telescopio Canarias (GTC) long-slit optical spectroscopy of two transits of HAT-P-11b with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) on August 30, 2016 and September 25, 2017. By fitting both transits together, we find a slope in the transmission spectrum showing an increase of the planetary radius towards blue wavelengths. Closer inspection of the transmission spectrum of the individual data sets reveals that the first transit presents this slope while the transmission spectrum of the second data set is flat. Additionally, we detect hints of Na absorption on the first night, but not on the second. We conclude that the transmission spectrum slope and Na absorption excess found in the first transit observation are caused by unocculted stellar spots. Modeling the contribution of unocculted spots to reproduce the results of the first night we find a spot filling factor of delta=0.62^+0.20^_-0.17_ and a spot-to-photosphere temperature difference of {Delta}T=429^+184^_-299_K.
- ID:
- ivo://CDS.VizieR/J/AJ/160/129
- Title:
- HARPS, HIRES and AAT Radial Velocities of HD 136352
- Short Name:
- J/AJ/160/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some of the most scientifically valuable transiting planets are those that were already known from radial velocity (RV) surveys. This is primarily because their orbits are well characterized and they preferentially orbit bright stars that are the targets of RV surveys. The Transiting Exoplanet Survey Satellite (TESS) provides an opportunity to survey most of the known exoplanet systems in a systematic fashion to detect possible transits of their planets. HD136352 (Nu Lupi) is a naked-eye (V=5.78) G-type main-sequence star that was discovered to host three planets with orbital periods of 11.6, 27.6, and 108.1days via RV monitoring with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. We present the detection and characterization of transits for the two inner planets of the HD136352 system, revealing radii of 1.482_-0.056_^+0.058^ R{Earth} and 2.608_-0.077_^+0.078^ R{Earth} for planets b and c, respectively. We combine new HARPS observations with RV data from the Keck/High Resolution Echelle Spectrometer and the Anglo-Australian Telescope, along with TESS photometry from Sector 12, to perform a complete analysis of the system parameters. The combined data analysis results in extracted bulk density values of {rho}_b_=7.8_-1.1_^+1.2^g/cm3 and {rho}_c_=3.50_-0.36_^+0.41^g/cm3 for planets b and c, respectively, thus placing them on either side of the radius valley. The combination of the multitransiting planet system, the bright host star, and the diversity of planetary interiors and atmospheres means this will likely become a cornerstone system for atmospheric and orbital characterization of small worlds.
- ID:
- ivo://CDS.VizieR/J/AJ/155/107
- Title:
- HARPS-N observations of K2-141 planetary system
- Short Name:
- J/AJ/155/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51+/-0.05 R_{Earth}_ and a mass of 5.08+/-0.41 M_{Earth}_, consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30+/-0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ~3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios.
- ID:
- ivo://CDS.VizieR/J/AJ/154/237
- Title:
- HARPS-N radial velocities of WASP-47
- Short Name:
- J/AJ/154/237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present precise radial velocity observations of WASP-47, a star known to host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional transiting planets in short-period orbits: a super-Earth in a ~19 hr orbit, and a Neptune in a ~9 day orbit. We analyze our observations from the HARPS-N spectrograph along with previously published data to measure the most precise planet masses yet for this system. When combined with new stellar parameters and reanalyzed transit photometry, our mass measurements place strong constraints on the compositions of the two small planets. We find that, unlike most other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83+/-0.66 M_{Earth}_) and a radius (1.810+/-0.027 R_{Earth}_) that are inconsistent with an Earth-like composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding an Earth-like core and mantle. We also perform a dynamical analysis to constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This planet likely orbits close to the plane of the inner three planets, suggesting a quiet dynamical history for the system. Our dynamical constraints also imply that WASP-47 c is much more likely to transit than a geometric calculation would suggest. We calculate a transit probability for WASP-47 c of about 10%, more than an order of magnitude larger than the geometric transit probability of 0.6%.
- ID:
- ivo://CDS.VizieR/J/AJ/155/203
- Title:
- HARPS-N RVs & activity indicators for Kepler-1655
- Short Name:
- J/AJ/155/203
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the confirmation of a small, moderately irradiated (F=155+/-7 F_{Earth}_) Neptune with a substantial gas envelope in a P=11.8728787+/-0.0000085 day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b's radius to be 2.213+/-0.082 R_{Earth}_. We acquired 95 high-resolution spectra with Telescopio Nazionale Galileo/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0_-2.8_^+3.1^ M_{Earth}_ via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98% confidence. Kepler-1655b falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further.
- ID:
- ivo://CDS.VizieR/J/AJ/158/100
- Title:
- HARPS radial velocities for HD 181433
- Short Name:
- J/AJ/158/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the orbital stability of the HD 181433 planetary system, finding it to exhibit strong dynamical instability across a wide range of orbital eccentricities, semimajor axes, and mutual inclinations. We also analyze the behavior of an alternative system architecture, proposed by Campanella, and find that it offers greater stability than the original solution, as a result of the planets being trapped in strong mutual resonance. We take advantage of more recent observations to perform a full refit of the system, producing a new planetary solution. The best-fit orbit for HD 181433 d now places the planet at a semimajor axis of 6.60+/-0.22 au, with an eccentricity of 0.469+/-0.013. Extensive simulations of this new system architecture reveal it to be dynamically stable across a broad range of potential orbital parameter space, increasing our confidence that the new solution represents the ground truth of the system. Our work highlights the advantage of performing dynamical simulations of candidate planetary systems in concert with the orbital fitting process, as well as supporting the continuing monitoring of radial velocity planet search targets.
- ID:
- ivo://CDS.VizieR/J/A+A/636/A74
- Title:
- HARPS radial velocity database
- Short Name:
- J/A+A/636/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph is mounted since 2003 at the ESO 3.6m telescope in La Silla and provides state-of-the-art stellar radial velocity (RV) measurements with a precision down to ~1m/s. The spectra are extracted with a dedicated data-reduction software (DRS) and the RVs are computed by cross correlating with a numerical mask. The aim of this study is three-fold: (i) Create an easy access to the public HARPS RV data set. (ii) Apply the new public SpEctrum Radial Velocity AnaLyser (SERVAL) pipeline to the spectra, and produce a more precise RV data set. (iii) Check whether the precision of the RVs can be further improved by correcting for small nightly systematic effects. For each star observed with HARPS, we downloaded the publicly available spectra from the ESO archive, and recomputed the RVs with SERVAL. This was based on fitting each observed spectrum with a high signal-to-noise ratio template created by co-adding all the available spectra of that star. We then computed nightly zero points (NZPs) by averaging the RVs of quiet stars. Analysing the RVs of the most RV-quiet stars, whose RV scatter is <5m/s, we find that SERVAL RVs are on average more precise than DRS RVs by a few percent. Investigating the NZP time series, we find three significant systematic effects, whose magnitude is independent of the software used for the RV derivation: (i) stochastic variations with a magnitude of ~1m/s; (ii) longterm variations, with a magnitude of ~1m/s and a typical timescale of a few weeks; and (iii) 20-30NZPs significantly deviating by few m/s. In addition, we find small (<~1m/s) but significant intra-night drifts in DRS RVs before the 2015 intervention, and in SERVAL RVs after it. We confirm that the fibre exchange in 2015 caused a discontinuous RV jump, which strongly depends on the spectral type of the observed star: from ~14m/s for late F-type stars, to ~-3m/sx for M dwarfs. The combined effect of extracting the RVs with SERVAL and correcting them for the systematics we find is an improved average RV precision: ~5% improvement for spectra taken before the 2015 intervention, and ~15% improvement for spectra taken after it. To demonstrate the quality of the new RV data set, we present an updated orbital solution of the GJ 253 two-planet system. Our NZP-corrected SERVAL RVs can be retrieved from a user-friendly, public database. It provides more than 212000 RVs for about 3000 stars along with many auxiliary information, such as the NZP corrections, various activity indices, and DRS-CCF products.
