- ID:
- ivo://CDS.VizieR/J/ApJ/900/L44
- Title:
- Kepler TTVs for 6 exomoon candidates
- Short Name:
- J/ApJ/900/L44
- Date:
- 15 Feb 2022 13:03:49
- Publisher:
- CDS
- Description:
- It has been recently claimed that KOIs-268.01, 303.01, 1888.01, 1925.01, 2728.01, and 3320.01 are exomoon candidates, based on an analysis of their transit timing. Here, we perform an independent investigation, which is framed in terms of three questions: (1) Are there significant transit timing variations (TTVs)? (2) Is there a significant periodic TTV? (3) Is there evidence for a nonzero moon mass? We applied rigorous statistical methods to these questions alongside a reanalysis of the Kepler photometry and find that none of the Kepler objects of interest (KOIs) satisfy our three tests. Specifically, KOIs-268.01 and 3220.01 pass none of the tests and KOIs-303.01, 1888.01, and 1925.01 pass a single test each. Only KOI-2728.01 satisfies two, but fails the cross-validation test for predictions. Further, detailed photodynamical modeling reveals that KOI-2728.01 favors a negative-radius moon (as does KOI-268.01). We also note that we find a significant photoeccentric effect for KOI-1925.01 indicating an eccentric orbit of at least e>(0.62+/-0.06). For comparison, we applied the same tests to Kepler-1625b, which reveals that (1) and (3) are passed, but (2) cannot be checked with the cross- validation method used here, due to the limited number of available epochs. In conclusion, we find no compelling evidence for exomoons among the six KOIs. Despite this, we were able to derive exomoon mass upper limits versus semimajor axis, with KOI-3220.01 leading to particularly impressive constraints of MS/MP<0.4% [2{sigma}] at a similar semimajor to that of the Earth-Moon.
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192. K2-38 ESPRESSO RVs
- ID:
- ivo://CDS.VizieR/J/A+A/641/A92
- Title:
- K2-38 ESPRESSO RVs
- Short Name:
- J/A+A/641/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An accurate characterization of the known exoplanet population is key to understand the origin and evolution of planetary systems. The determination of true planetary masses through the radial velocity (RV) method is expected to experience a great improvement thanks to the availability of ultra-stable echelle spectrographs. We took advantage of the extreme precision of the new- generation echelle spectrograph ESPRESSO to characterize the transiting planetary system orbiting the G2V star K2-38 located at 194pc from the Sun with V~11.4. This system is particularly interesting because it could contain the densest planet detected to date. We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets K2-38b and K2-38c with Pb=4.01593+/-0.00050d and Pc=10.56103+/-0.00090d, respectively. Using 43 ESPRESSO high-precision radial velocity measurements taken over 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a Markov Chain Monte Carlo (MCMC) analysis, significantly improving their mass measurements. Using ESPRESSO spectra we derived the stellar paremeters, Teff=5731+/-66K, logg=4.38+/-0.11dex, and [Fe/H]=0.26+/-0.05dex, and thus the mass and radius of K2-38, Ms=1.03^+0.04^_-0.02_M_{sun}_ and Rs=1.06^+0.09^_-0.06_R_[sun}_. We determined new values for the planetary properties of both planets. We characterized K2-38b as a super-Earth with Rp=1.54+/-0.14R_{earth}_ and Mp=7.3^+1.1^_-1.0_M_{earth}_, and K2-38c as a sub-Neptune with Rp=2.29+/-0.26R_{earth}_ and Mp=8.3+/-1.3M_{earth}_. Combining the radius and mass measurements, we derive a mean density of rho_p_=11.0^+4.1^_-2.8_g/cm^3^ for K2-38b and rho_p_=3.8^+1.8^_-1.1_g/cm^3^ for K2-38c, confirming K2-38b as one of the densest planets known to date. The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by an ice-rich model. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the radial velocity time-series whose origin could be linked to a 0.25-3M_Jup_ planet or stellar activity.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A1
- Title:
- 4 K giants velocity curves
- Short Name:
- J/A+A/644/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial-velocity (RV) measurements for the K giant stars HD 25723, 17 Sco, 3 Cnc and 44 UMa, taken at the Lick Observatory between 2000 and 2011. The best Keplerian fits to the data yield minimum masses of 2.5MJup and 4.3M_Jup_ for the planets orbiting HD 25723 and 17 Sco, respectively. The minimum masses of an additional candidate around HD 25723, and of planet candidates around 3 Cnc and 44 UMa, would be 1.3M_Jup_, 20.7M_Jup_ and 12.1M_Jup_, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A90
- Title:
- K2-138 HARPS radial velocities
- Short Name:
- J/A+A/631/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0M_{Earth}_ with a precision of 34%, 20%, 18%, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8g/cm^3^, ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A49
- Title:
- K2-18 HARPS time-series
- Short Name:
- J/A+A/621/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In an earlier campaign to characterize the mass of the transiting temperate super-Earth K2-18b with HARPS, a second, non-transiting planet was posited to exist in the system at ~9-days. Further radial velocity follow-up with the CARMENES spectrograph visible channel revealed a much weaker signal at 9-days, which also appeared to vary chromatically and temporally, leading to the conclusion that the origin of the 9-day signal was more likely related to stellar activity than to a planetary presence. Here we conduct a detailed re-analysis of all available RV time-series -- including a set of 31 previously unpublished HARPS measurements -- to investigate the effects of time-sampling and of simultaneous modelling of planetary plus activity signals on the existence and origin of the curious 9-day signal. We conclude that the 9-day signal is real and was initially seen to be suppressed in the CARMENES data due to a small number of anomalous measurements, although the exact cause of these anomalies remains unknown. Investigation of the signal's evolution in time with wavelength and detailed model comparison reveals that the 9-day signal is most likely planetary in nature. Using this analysis we reconcile the conflicting HARPS and CARMENES results and measure precise and self-consistent planet masses of m_p,b_=8.63+/-1.35 and m_p,c_sin(i_c_)=5.62+/-0.84 Earth masses. This work, along with the previously published RV papers on the K2-18 planetary system, highlights the importance of understanding the time-sampling and of modelling the simultaneous planet plus stochastic activity, particularly when searching for sub-Neptune-sized planets with radial velocities.
- ID:
- ivo://CDS.VizieR/J/AJ/155/173
- Title:
- K2 light curve for K2-231
- Short Name:
- J/AJ/155/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify a sub-Neptune exoplanet (R_p_=2.5+/-0.2R_{Earth}_) transiting a solar twin in the Ruprecht 147 star cluster (3Gyr, 300pc, [Fe/H]=+0.1dex). The ~81 day light curve for EPIC 219800881 (V=12.71) from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ~0.06%, and a duration of ~4hr. Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: M_*_=1.01+/-0.03M_{sun}_, R_*_=0.95+/-0.03R_{sun}_, and T_eff_=5695+/-50K. This star appears to be single based on our modeling of the photometry, the low radial velocity (RV) variability measured over nearly 10yr, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass-radius relation, we estimate that the mass of this planet is M_p_=7+5-3M_{Earth}_, which would cause an RV semi-amplitude of K=2+/-1m/s that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231b, making it the second substellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 22 other planets and three candidates found in open clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A90
- Title:
- KMT-2018-BLG-1025Lb I light curve
- Short Name:
- J/A+A/649/A90
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data. For this purpose, we conduct a systematic inspection of high-magnification microlensing events, with peak magnifications Apeak>~30, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identify an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens. We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close-wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is q~0.8x10^-4^ for the solution A and q~1.6x10^-4^ for the solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are (Mp, Mh, DL)~(6.1M_{sun}_, 0.22M_Earth_, 6.7kpc) for the solution A and ~(4.4M_{sun}_, 0.08M_Earth_, 7.5kpc) for the solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar system's ice giants, discovered by microlensing.
- ID:
- ivo://CDS.VizieR/J/AJ/160/255
- Title:
- KMTNet & OGLE I-band photometry of KMT-2019-BLG-0842
- Short Name:
- J/AJ/160/255
- Date:
- 09 Mar 2022
- Publisher:
- CDS
- Description:
- We report the discovery of a cold planet with a very low planet/host mass ratio of q=(4.09{+/-}0.27)x10^-5^, which is similar to the ratio of Uranus/Sun (q=4.37x10^-5^) in the solar system. The Bayesian estimates for the host mass, planet mass, system distance, and planet-host projected separation are M_host_=0.76{+/-}0.40M{sun}, M_planet_=10.3{+/-}5.5M{Earth}, D_L_=3.3{+/-}1.3kpc, and a{perp}=3.3{+/-}1.4 au, respectively. The consistency of the color and brightness expected from the estimated lens mass and distance with those of the blend suggests the possibility that the most blended light comes from the planet host, and this hypothesis can be established if high-resolution images are taken during the next (2020) bulge season. We discuss the importance of conducting optimized photometry and aggressive follow-up observations for moderately or very high magnification events to maximize the detection rate of planets with very low mass ratios.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A79
- Title:
- KOINet. Study of exoplanet systems via TTVs
- Short Name:
- J/A+A/615/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During its four years of photometric observations, the Kepler space telescope detected thousands of exoplanets and exoplanet candidates. One of Kepler's greatest heritages has been the confirmation and characterization of hundreds of multi-planet systems via transit timing variations (TTVs). However, there are many interesting candidate systems displaying TTVs on such long timescales that the existing Kepler observations are of insufficient length to confirm and characterize them by means of this technique. To continue with Kepler's unique work, we have organized the "Kepler Object of Interest Network" (KOINet), a multi-site network formed of several telescopes located throughout America, Europe, and Asia. The goals of KOINet are to complete the TTV curves of systems where Kepler did not cover the interaction timescales well, to dynamically prove that some candidates are true planets (or not), to dynamically measure the masses and bulk densities of some planets, to find evidence for non-transiting planets in some of the systems, to extend Kepler's baseline adding new data with the main purpose of improving current models of TTVs, and to build a platform that can observe almost anywhere on the northern hemisphere, at almost any time. KOINet has been operational since March 2014. Here we show some promising first results obtained from analyzing seven primary transits of KOI-0410.01, KOI-0525.01, KOI-0760.01, and KOI-0902.01, in addition to the Kepler data acquired during the first and second observing seasons of KOINet. While carefully choosing the targets we set demanding constraints on timing precision (at least 1 min) and photometric precision (as good as one part per thousand) that were achieved by means of our observing strategies and data analysis techniques. For KOI-0410.01, new transit data revealed a turnover of its TTVs. We carried out an in-depth study of the system, which is identified in the NASA Data Validation Report as a false positive. Among others, we investigated a gravitationally bound hierarchical triple star system and a planet-star system. While the simultaneous transit fitting of ground- and space-based data allowed for a planet solution, we could not fully reject the three-star scenario. New data, already scheduled in the upcoming 2018 observing season, will set tighter constraints on the nature of the system.
- ID:
- ivo://CDS.VizieR/J/AJ/154/207
- Title:
- K2 planetary systems orbiting low-mass stars
- Short Name:
- J/AJ/154/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We recently used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets. 29 of these worlds were new discoveries that had not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new transit-like events and three previously reported events as false positives. We also statistically validate 17 planets (7 of which were previously unpublished), confirm the earlier validation of 22 planets, and announce 17 newly discovered planet candidates. Revising the properties of the associated planet candidates based on the updated host star characteristics and refitting the transit photometry, we find that our sample contains 21 planets or planet candidates with radii smaller than 1.25 R_{Earth}_, 18 super-Earths (1.25-2 R_{Earth}_), 21 small Neptunes (2-4 R_{Earth}_), three large Neptunes (4-6 R_{Earth}_), and eight giant planets (>6 R_{Earth}_). Most of these planets are highly irradiated, but EPIC 206209135.04 (K2-72e, 1.29_-0.13_^+0.14^ R_{Earth}_), EPIC 211988320.01 (R_p_=2.86_-0.15_^+0.16^ R_{Earth}_), and EPIC 212690867.01 (2.20_-0.18_^+0.19^ R_{Earth}_) orbit within optimistic habitable zone boundaries set by the "recent Venus" inner limit and the "early Mars" outer limit. In total, our planet sample includes eight moderately irradiated 1.5-3 R_{Earth}_ planet candidates (F_p_~<20 F_{Earth}_) orbiting brighter stars (Ks<11) that are well-suited for atmospheric investigations with the Hubble, Spitzer, and/or James Webb Space Telescopes. Five validated planets orbit relatively bright stars (Kp<12.5) and are expected to yield radial velocity semi-amplitudes of at least 2 m/s. Accordingly, they are possible targets for radial velocity mass measurement with current facilities or the upcoming generation of red optical and near-infrared high-precision RV spectrographs.
