- ID:
- ivo://CDS.VizieR/J/AJ/159/2
- Title:
- K2-19b and c transit times and radial velocities
- Short Name:
- J/AJ/159/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- K2-19b and c were among the first planets discovered by NASA's K2 mission and together stand in stark contrast with the physical and orbital properties of the solar system planets. The planets are between the size of Uranus and Saturn at 7.0+/-0.2 R_{Earth}_ and 4.1+/-0.2 R_{Earth}_, respectively, and reside a mere 0.1% outside the nominal 3:2 mean-motion resonance. They represent a different outcome of the planet formation process than the solar system, as well as the vast majority of known exoplanets. We measured the physical and orbital properties of these planets using photometry from K2, Spitzer, and ground-based telescopes, along with radial velocities from Keck/HIRES. Through a joint photodynamical model, we found that the planets have moderate eccentricities of e~0.20 and well-aligned apsides {Delta}{omega}~0{deg}. The planets occupy a strictly nonresonant configuration: the resonant angles circulate rather than librate. This defies the predictions of standard formation pathways that invoke convergent or divergent migration, both of which predict {Delta}{omega}~180{deg} and eccentricities of a few percent or less. We measured masses of M_p,b_=32.4+/-1.7 M_{Earth}_ and M_p,c_=10.8+/-0.6 M_{Earth}_. Our measurements, with 5% fractional uncertainties, are among the most precise of any sub-Jovian exoplanet. Mass and size reflect a planet's core/envelope structure. Despite having a relatively massive core of M_core_~15 M_{Earth}_, K2-19b is envelope-rich, with an envelope mass fraction of roughly 50%. This planet poses a challenge to standard models of core-nucleated accretion, which predict that cores >~10 M_{Earth}_ will quickly accrete gas and trigger runaway accretion when the envelope mass exceeds that of the core.
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- ID:
- ivo://CDS.VizieR/J/A+A/601/A128
- Title:
- K2-19b and K2-19c radial velocity curves
- Short Name:
- J/A+A/601/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocity follow-up observations of K2-19,a compact planetary system hosting three planets, of which the two larger ones, K2-19b and K2-19c, are close to the 3:2 mean motion resonance. An analysis considering only the radial velocity measurements detects K2-19b, the larger and more massive planet in the system, with a mass of 54.8+/-7.5M_{earth}_ provides a marginal detection of K2-19c, with a mass of Mc,=5.9^+7.6^_-4.3_M_{earth}_. We also used the TRADES code to simultaneously model both our RV measurements and the existing transit timing measurements. We derived a mass of 54.4+/-8.9M_{earth}_ for K2-19b and of 7.5^+3.0^_-1.4_M_{earth}_ for K2-19c. For K2-19b, these masses are consistent with a previous determination that was principally based on a photodynamical analysis of the K2-19 light curve. Differences remain mainly in the mass determination of the more lightweight planet, driven likely by the limited precision of the RV measurements and possibly some as yet unrecognized systematics.
- ID:
- ivo://CDS.VizieR/J/A+A/494/1137
- Title:
- K-band spectral catalog of Quintuplet cluster
- Short Name:
- J/A+A/494/1137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Three very massive clusters are known to reside in the Galactic center region, the Arches cluster, the Quintuplet cluster, and the central parsec cluster, each of them rich in young hot stars. With new infrared instruments, this region is no longer obscured for the observer. For understanding these very massive clusters, it is essential to know their stellar inventory. We provide comprehensive spectroscopic data for the stellar population of the Quintuplet cluster that will form the basis of subsequent spectral analyses. Spectroscopic observations of the Quintuplet cluster were obtained with the Integral Field Spectrograph SINFONI-SPIFFI at the ESO-VLT, with the ESO VLT UT4 (Yepun) telescope between May and July 2006. The inner part of the Quintuplet cluster covered by 22 slightly overlapping fields, each of them of 8"x8" in size. The spectral range comprises the near-IR K-band from 1.94 to 2.45um. The 3D data cubes of the individual fields were flux-calibrated and combined to one contiguous cube, from which the spectra of all detectable point sources were extracted.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/143
- Title:
- K-band spectra of stars within central 1pc of the MW
- Short Name:
- J/ApJ/809/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a metallicity analysis of 83 late-type giants within the central 1pc of the Milky Way. K-band spectroscopy of these stars was obtained with the medium spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guided star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is a large variation in the metallicity, with stars ranging from [M/H]<-1.0 to above solar metallicity. About 6% of the stars have [M/H]<-0.5. This result is in contrast to previous observations with smaller samples that show stars at the Galactic center having approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H]>0, where there are stellar lines not represented in the model. However, the conclusion that there are low-metallicity stars, as well as large variations in metallicity, is robust. The metallicity may be an indicator of the origin of these stars. The low-metallicity population is consistent with that of globular clusters in the Milky Way, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the Milky Way nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, our results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A95
- Title:
- K2-141 b radial velocity and light curve
- Short Name:
- J/A+A/612/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of K2-141 b (EPIC 246393474 b), an ultra-short-period super-Earth on a 6.7-hour orbit transiting an active K7 V star based on data from K2 campaign 12. We confirmed the planet's existence and measured its mass with a series of follow-up observations: seeing-limited MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS high-precision radial-velocity monitoring. K2-141 b has a mass of 5.31+/-0.46M_{Earth}_ and radius of 1.54+0.10-0.09R_{Earth}_, yielding a mean density of 8.00^+1.83^_-1.45_g/cm^3^ and suggesting a rocky-iron composition. Models indicate that iron cannot exceed ~70% of the total mass. With an orbital period of only 6.7 hours, K2-141 b is the shortest-period planet known to date with a precisely determined mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/175
- Title:
- Keck and APF radial velocities of HD7924
- Short Name:
- J/ApJ/805/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two super-Earth-mass planets orbiting the nearby K0.5 dwarf HD 7924, which was previously known to host one small planet. The new companions have masses of 7.9 and 6.4M_{Earth}_, and orbital periods of 15.3 and 24.5 days. We perform a joint analysis of high-precision radial velocity data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to robustly detect three total planets in the system. We refine the ephemeris of the previously known planet using 5yr of new Keck data and high-cadence observations over the last 1.3yr with the APF. With this new ephemeris, we show that a previous transit search for the inner-most planet would have covered 70% of the predicted ingress or egress times. Photometric data collected over the last eight years using the Automated Photometric Telescope shows no evidence for transits of any of the planets, which would be detectable if the planets transit and their compositions are hydrogen-dominated. We detect a long-period signal that we interpret as the stellar magnetic activity cycle since it is strongly correlated with the CaII H and K activity index. We also detect two additional short-period signals that we attribute to rotationally modulated starspots and a one-month alias. The high-cadence APF data help to distinguish between the true orbital periods and aliases caused by the window function of the Keck data. The planets orbiting HD 7924 are a local example of the compact, multi-planet systems that the Kepler Mission found in great abundance.
- ID:
- ivo://CDS.VizieR/J/AJ/158/136
- Title:
- Keck & APF radial velocities for HD 200964
- Short Name:
- J/AJ/158/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of mean-motion resonances (MMRs) complicates analysis and fitting of planetary systems that are observed through the radial velocity (RV) technique. MMR can allow planets to remain stable in regions of phase space where strong planet-planet interactions would otherwise destabilize the system. These stable orbits can occupy small phase space volumes, allowing MMRs to strongly constrain system parameters, but making searches for stable orbital parameters challenging. Furthermore, libration of the resonant angle and dynamical interaction between the planets introduces another long-period variation into the observed RV signal, complicating analysis of the periods of the planets in the system. We discuss this phenomenon using the example of HD 200964. By searching through parameter space and numerically integrating each proposed set of planetary parameters to test for long-term stability, we find stable solutions in the 7:5 and 3:2 MMRs in addition to the originally identified 4:3 MMR. The 7:5 configuration provides the best match to the data, while the 3:2 configuration provides the most easily understood formation scenario. In reanalysis of the originally published shorter-baseline data, we find fits in both the 4:3 and 3:2 resonances, but not in the 7:5. Because the time baseline of the data is shorter than the resonant libration period, the current best fit to the data may not reflect the actual resonant configuration. In the absence of a full sample of the longer libration period, we find that it is of paramount importance to incorporate long-term stability when the orbital configuration of the system is fit.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/109
- Title:
- Keck HIRES obs. of 245 subgiants (retired A stars)
- Short Name:
- J/ApJ/860/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass (M*). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a -0.12M_{sun}_ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with M*>=1.6M_{sun}_ (the "retired A stars") have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0M_{sun}_. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk M* 10^[Fe/H]. This correlation provides additional support for the core accretion mechanism of planet formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/L2
- Title:
- Keck/HIRES radial velocities for HD 97658
- Short Name:
- J/ApJ/772/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements. The mid-transit times are 5.6{sigma} earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth together with our determined stellar radius (R_{star}_=0.703_-0.034_^+0.039^R_{sun}_) indicates a 2.34_-0.15_^0.18^R_{Earth}_ super-Earth. When combined with the radial velocity determined mass of 7.86+/-0.73M_{Earth}_, our radius measure allows us to derive a planet density of 3.44_-0.82_^+0.91^g/cm3. Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating follow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/104
- Title:
- Keck/HIRES radial velocity obs. of HD32963
- Short Name:
- J/ApJ/817/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a set of 109 new, high-precision Keck/HIRES radial velocity (RV) observations for the solar-type star HD 32963. Our data set reveals a candidate planetary signal with a period of 6.49+/-0.07yr and a corresponding minimum mass of 0.7+/-0.03 Jupiter masses. Given Jupiter's crucial role in shaping the evolution of the early Solar System, we emphasize the importance of long-term RV surveys. Finally, using our complete set of Keck radial velocities and correcting for the relative detectability of synthetic planetary candidates orbiting each of the 1122 stars in our sample, we estimate the frequency of Jupiter analogs across our survey at approximately 3%.
