Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “K2”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Two transiting low density sub-saturns from K2

We report the discovery and confirmation of K2-24 b and c, two sub-Saturn planets orbiting a bright (V = 11.3), metal-rich ([Fe/H] = 0.42 ± 0.04 dex) G3 dwarf in the K2 Campaign 2 field. The planets are 5.68 ± 0.56 R{sub ⊕} and 7.82 ± 0.72 R{sub ⊕} and have orbital periods of 20.8851 ± 0.0003 days and 42.3633 ± 0.0006 days, near the 2:1 mean-motion resonance. We obtained 32 radial velocities with Keck/HIRES and detected the reflex motion due to K2-24 b and c. These planets have masses of 21.0 ± 5.4 M{sub ⊕} and 27.0 ± 6.9 M{sub ⊕}, respectively. With low densities of 0.63 ± 0.25 g cm{sup −3} and 0.31 ± 0.12 g cm{sup −3}, respectively, the planets require thick envelopes of H/He to explain their large sizes and low masses. Interior structure models predict that the planets have fairly massive cores of 17.6±4.3 M{sub ⊕} and 16.1±4.2 M{sub ⊕}, respectively. They may have formed exterior to their present locations, accreted their H/He envelopes at large orbital distances, and migrated in as a resonant pair. The proximity to resonance, large transit depths, and host star brightness offers rich opportunities for TTV follow-up. Finally, the low surface gravities of the K2-24 planets make them favorable targets for transmission spectroscopy by Hubble Space Telescope, Spitzer, and James Webb Space Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

TOI-954 b and K2-329 b: Short-period Saturn-mass Planets that Test whether Irradiation Leads to Inflation

We report the discovery of two short-period Saturn-mass planets, one transiting the G subgiant TOI-954 (TIC 44792534, V = 10.343, T = 9.78) observed in TESS sectors 4 and 5 and one transiting the G dwarf K2-329 (EPIC 246193072, V = 12.70, K = 10.67) observed in K2 campaigns 12 and 19. We confirm and characterize these two planets with a variety of ground-based archival and follow-up observations, including photometry, reconnaissance spectroscopy, precise radial velocity, and high-resolution imaging. Combining all available data, we find that TOI-954 b has a radius of 0.852{sub −0.062}{sup +0.053} R{sub J} and a mass of 0.174{sub −0.017}{sup +0.018} M {sub J} and is in a 3.68 day orbit, while K2-329 b has a radius of 0.774{sub −0.024}{sup +0.026} R{sub J} and a mass of 0.260{sub −0.022}{sup +0.020} M {sub J} and is in a 12.46 day orbit. As TOI-954 b is 30 times more irradiated than K2-329 b but more or less the same size, these two planets provide an opportunity to test whether irradiation leads to inflation of Saturn-mass planets and contribute to future comparative studies that explore Saturn-mass planets at contrasting points in their lifetimes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

PROBING TRAPPIST-1-LIKE SYSTEMS WITH K2

The search for small planets orbiting late M dwarfs holds the promise of detecting Earth-size planets for which their atmospheres could be characterized within the next decade. The recent discovery of TRAPPIST-1 entertains hope that these systems are common around hosts located at the bottom of the main sequence. In this Letter, we investigate the ability of the repurposed Kepler mission ( K2 ) to probe planetary systems similar to TRAPPIST-1. We perform a consistent data analysis of 189 spectroscopically confirmed M5.5 to M9 late M dwarfs from Campaigns 1–6 to search for planet candidates and inject transit signals with properties matching TRAPPIST-1b and c. We find no transiting planet candidates across our K2 sample. Our injection tests show that K2 is able to recover both TRAPPIST-1 planets for 10% of the sample only, mainly because of the inefficient throughput at red wavelengths resulting in Poisson-limited performance for these targets. Increasing injected planetary radii to match GJ 1214b’s size yields a recovery rate of 70%. The strength of K2 is its ability to probe a large number of cool hosts across the different campaigns, out of which the recovery rate of 10% may turn into bona fide detections of TRAPPIST-1-like systems within the next two years.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Three Statistically Validated K2 Transiting Warm Jupiter Exoplanets Confirmed as Low-mass Stars

We have identified three K2 transiting star–planet systems, K2-51 (EPIC 202900527), K2-67 (EPIC 206155547), and K2-76 (EPIC 206432863), as stellar binaries with low-mass stellar secondaries. The three systems were statistically validated as transiting planets, and through measuring their orbits by radial velocity (RV) monitoring we have derived the companion masses to be 0.1459{sub −0.0032}{sup +0.0029} M{sub ⊙} (EPIC 202900527 B), 0.1612{sub −0.0067}{sup +0.0072} M{sub ⊙} (EPIC 206155547 B), and 0.0942 ± 0.0019 M{sub ⊙} (EPIC 206432863 B). Therefore, they are not planets but small stars, part of the small sample of low-mass stars with measured radius and mass. The three systems are at an orbital period range of 12–24 days, and the secondaries have a radius within 0.9–1.9 R{sub J}, not inconsistent with the properties of warm Jupiter planets. These systems illustrate some of the existing challenges in the statistical validation approach. We point out a few possible origins for the initial misclassification of these objects, including poor characterization of the host star, the difficulty in detecting a secondary eclipse in systems on an eccentric orbit, and the difficulty in distinguishing between the smallest stars and gas giant planets as the two populations have indistinguishable radius distributions. Our work emphasizes the need for obtaining medium-precision RV measurements to distinguish between companions that are small stars, brown dwarfs, and gas giant planets.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

K2 & Solar System Science

All of the fields that K2 observes are near the ecliptic plane in order to minimize the spin-up of the spacecraft in response to the effects of solar irradiation. The fields observed by K2 are thus rich in Solar System objects including planets, asteroids and trans-Neptunian objects (TNOs). K2 has already performed observations of Neptune and its large moon Triton, 68 Trojan and Hilda asteroids, 5 TNOs (including Pluto) and Comet C/2013 A1 (Siding Springs). About 10,000 main-belt asteroids that fell into the pixel masks of stars have been serendipitously observed. Observations of small bodies are especially useful for determining rotation periods. Uranus will be observed in a future campaign (C8), as will many more small Solar System bodies. The status of various K2 Solar System studies will be reviewed and placed within the context of our current knowledge of the objects being observed.

trans-Neptunian objects (TNOs).↗
NASA NTRS2019

Discovery and Vetting of Exoplanets. I. Benchmarking K2 Vetting Tools

We have adapted the algorithmic tools developed during the Kepler mission to vet the quality of transit-like signals for use on the K2 mission data. Using the four sets of publicly available light curves at MAST, we produced a uniformly vetted catalog of 772 transiting planet candidates from K2 as listed at the NASA Exoplanet Archive in the K2 Table of Candidates. Our analysis marks 676 of these as planet candidates and 96 as false positives. All confirmed planets pass our vetting tests. Sixty of our false positives are new identifications, effectively doubling the overall number of astrophysical signals mimicking planetary transits in K2 data. Most of the targets listed as false positives in our catalog show either prominent secondary eclipses, transit depths suggesting a stellar companion instead of a planet, or significant photocenter shifts during transit. We packaged our tools into the open-source, automated vetting pipeline Discovery and Vetting of Exoplanets (DAVE), designed to streamline follow-up efforts by reducing the time and resources wasted observing targets that are likely false positives. DAVE will also be a valuable tool for analyzing planet candidates from NASA's TESS mission, where several guest-investigator programs will provide independent light-curve sets—and likely many more from the community. We are currently testing DAVE on recently released TESS planet candidates and will present our results in a follow-up paper.

Kostov, Veselin B.↗
NASA NTRS2018

A Large Ground-Based Observing Campaign of the Disintegrating Planet K2-22b

We present 45 ground-based photometric observations of the K2-22 system collected between 2016 December and 2017 May, which we use to investigate the evolution of the transit of the disintegrating planet K2-22b. Last observed in early 2015, in these new observations we recover the transit at multiple epochs and measure a typical depth of <1.5%. We find that the distribution of our measured transit depths is comparable to the range of depths measured in observations from 2014 and 2015. These new observations also support ongoing variability in the K2-22b transit shape and time, although the overall shallowness of the transit makes a detailed analysis of these transit parameters difficult. We find no strong evidence of wavelength-dependent transit depths for epochs where we have simultaneous coverage at multiple wavelengths, although our stacked Las Cumbres Observatory data collected over days-to-months timescales are suggestive of a deeper transit at blue wavelengths. We encourage continued high-precision photometric and spectroscopic monitoring of this system in order to further constrain the evolution timescale and to aid comparative studies with the other few known disintegrating planets.

K2-22↗
DOE OSTI2015

HAT-P-56b: An INFLATED massive hot jupiter transiting a bright F star followed up with K2 campaign 0 observations

We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F-type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from the Tillinghast Reflector Echelle Spectrograph on the Fred Lawrence Whipple Observatory 1.5 m telescope to determine the physical properties of this system. HAT-P-56b has a mass of 2.18 M{sub J}, radius of 1.47 R{sub J}, and transits its host star on a near-grazing orbit with a period of 2.7908 day. The radius of HAT-P-56b is among the largest known for a planet with M{sub p}>2 M{sub J}. The host star has a V-band magnitude of 10.9, mass of 1.30 M{sub ⊙}, and radius of 1.43 R{sub ⊙}. The periodogram of the K2 light curve suggests that the star is a γ Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A nearby M star with three transiting super-earths discovered by K2

Small, cool planets represent the typical end-products of planetary formation. Studying the architectures of these systems, measuring planet masses and radii, and observing these planets’ atmospheres during transit directly informs theories of planet assembly, migration, and evolution. Here we report the discovery of three small planets orbiting a bright (K{sub s} = 8.6 mag) M0 dwarf using data collected as part of K2, the new ecliptic survey using the re-purposed Kepler spacecraft. Stellar spectroscopy and K2 photometry indicate that the system hosts three transiting planets with radii 1.5–2.1 R{sub ⊕}, straddling the transition region between rocky and increasingly volatile-dominated compositions. With orbital periods of 10–45 days the planets receive just 1.5–10× the flux incident on Earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system’s habitable zone. The bright, low-mass star makes this system an excellent laboratory to determine the planets’ masses via Doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. This discovery demonstrates the ability of K2 and future space-based transit searches to find many fascinating objects of interest.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

K2P{sup 2}—A photometry pipeline for the K2 mission

With the loss of a second reaction wheel, resulting in the inability to point continuously and stably at the same field of view, the NASA Kepler satellite recently entered a new mode of observation known as the K2 mission. The data from this redesigned mission present a specific challenge; the targets systematically drift in position on an ∼6 hr timescale, inducing a significant instrumental signal in the photometric time series—this greatly impacts the ability to detect planetary signals and perform asteroseismic analysis. Here we detail our version of a reduction pipeline for K2 target pixel data, which automatically defines masks for all targets in a given frame; extracts the target’s flux and position time series; corrects the time series based on the apparent movement on the CCD (either in 1D or 2D), combined with the correction of instrumental and/or planetary signals via the Kepler Asteroseismic Science Operations Center (KASOC) filter, thus rendering the time series ready for asteroseismic analysis; computes power spectra for all targets; and identifies potential contaminations between targets. From a test of our pipeline on a sample of targets from the K2 campaign 0, the recovery of data for multiple targets increases the amount of potential light curves by a factor of ⩾10. Our pipeline could be applied to the upcoming TESS and PLATO 2.0 missions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Thermal dissipation studies and Pu238/Li source simulation (MCNP) of the K2 containers (COWS)

The six K2 containers (COWS) have been proposed to be shipped to WIPP in the configuration depicted in Figure 1. Currently, the containers reside in the water bath storage and have not been opened since LANL received them. The K2 containers containing the mound scrap material each have their own unique dose rate and thermal loading. 3 The properties of each container are listed below in Table 1. The problem with loading the K2 container into the proposed configuration is the thermal load the package will experience. Each component within the package has a thermal working limit that should not be exceeded. 2 However, the package must also maintain enough shielding to lower the measured dose rate at the surface of the drum to be accepted by WIPP. Testing the current configuration through simulation LANL can prove heat will not compromise any components and dose can be reduced to a safe configuration.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

TWO HOT JUPITERS FROM K2 CAMPAIGN 4

We confirm the planetary nature of two transiting hot Jupiters discovered by the Kepler spacecraft’s K2 extended mission in its Campaign 4, using precise radial velocity measurements from FIES@NOT, HARPS-N@TNG, and the coudé spectrograph on the McDonald Observatory 2.7 m telescope. K2-29 b (EPIC 211089792b) transits a K1V star with a period of 3.2589263 ± 0.0000015 days; its orbit is slightly eccentric (e=0.084{sub −0.023}{sup +0.032}). It has a radius of R{sub P}=1.000{sub −0.067}{sup +0.071} R{sub J} and a mass of M{sub P}=0.613{sub −0.026}{sup +0.027} M{sub J}. Its host star exhibits significant rotational variability, and we measure a rotation period of P{sub rot}=10.777±0.031 days. K2-30 b (EPIC 210957318 b) transits a G6V star with a period of 4.098503 ± 0.000011 days. It has a radius of R{sub P}=1.039{sub −0.051}{sup +0.050} R{sub J} and a mass of M{sub P}=0.579{sub −0.027}{sup +0.028} M{sub J}. The star has a low metallicity for a hot Jupiter host, [Fe/H]=−0.15±0.05.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ROTATION IN THE PLEIADES WITH K2. III. SPECULATIONS ON ORIGINS AND EVOLUTION

We use high-quality K2 light curves for hundreds of stars in the Pleiades to better understand the angular momentum evolution and magnetic dynamos of young low-mass stars. The K2 light curves provide not only rotational periods but also detailed information from the shape of the phased light curve that was not available in previous studies. A slowly rotating sequence begins at (V−K{sub s}){sub 0} ∼ 1.1 (spectral type F5) and ends at (V−K{sub s}){sub 0} ∼ 3.7 (spectral type K8), with periods rising from ∼2 to ∼11 days in that interval. A total of 52% of the Pleiades members in that color interval have periods within 30% of a curve defining the slow sequence; the slowly rotating fraction decreases significantly redward of (V−K{sub s}){sub 0} = 2.6. Nearly all of the slow-sequence stars show light curves that evolve significantly on timescales less than the K2 campaign duration. The majority of the FGK Pleiades members identified as photometric binaries are relatively rapidly rotating, perhaps because binarity inhibits star–disk angular momentum loss mechanisms during pre-main-sequence evolution. The fully convective late M dwarf Pleiades members (5.0 < (V−K{sub s}){sub 0} < 6.0) nearly always show stable light curves, with little spot evolution or evidence of differential rotation. During pre-main-sequence evolution from ∼3 Myr (NGC 2264 age) to ∼125 Myr (Pleiades age), stars of 0.3 M{sub ⊙} shed about half of their angular momentum, with the fractional change in period between 3 and 125 Myr being nearly independent of mass for fully convective stars. Our data also suggest that very low mass binaries form with rotation periods more similar to each other and faster than would be true if drawn at random from the parent population of single stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE K2-ESPRINT PROJECT. V. A SHORT-PERIOD GIANT PLANET ORBITING A SUBGIANT STAR

We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 (EPIC 206247743) is an evolved star with a spectroscopically derived stellar radius and mass of 3.88{sub -0.42}{sup +0.48} R{sub ⊙} and 1.53{sub -0.12}{sup +0.13} M{sub ⊙}, respectively, and a very close-in transiting planet, with a/R{sub •}=3.4. Radial velocity (RV) follow-up using the HARPS, FIES, and PFS instruments leads to a planetary mass of 50.3{sub -9.4}{sup +9.7} M{sub ⊕}. In combination with a radius measurement of 8.3±1.1 R{sub ⊕}, this results in a mean planetary density of 0.50{sub -0.17}{sup +0.29} g cm{sup -3}. We furthermore discover a long-term RV trend, which may be caused by a long-period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Discovery and validation of a high-density sub-neptune from the K2 mission

We report the discovery of K2-56b, a high-density sub-Neptune exoplanet, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission, ground-based radial velocity (RV) follow-up from HARPS and high-resolution lucky and adaptive optics imaging obtained using AstraLux and MagAO, respectively. The host star is a bright (V = 11.04, K {sub s} = 9.37), slightly metal-poor ([Fe/H] = −0.15 ± 0.05 dex) solar analogue located at 152.1{sub −7.4}{sup +9.7} pc from Earth, for which we find a radius of R{sub ∗}=0.928{sub −0.040}{sup +0.055}R{sub ⊙} and a mass of M{sub ∗}=0.961{sub −0.029}{sup +0.032}M{sub ⊙}. A joint analysis of the K2 photometry and HARPS RVs reveal that the planet is in a ≈42 day orbit around its host star, has a radius of 2.23{sub −0.11}{sup +0.14}R{sub ⊕}, and a mass of 16.3{sub −6.1}{sup +6.0}M{sub ⊕}. Although the data at hand put the planet in the region of the mass–radius diagram where we could expect planets with a pure rock (i.e., magnesium silicate) composition using two-layer models (i.e., between rock/iron and rock/ice compositions), we discuss more realistic three-layer composition models which can explain the high density of the discovered exoplanet. The fact that the planet lies in the boundary between “possibly rocky” and “non-rocky” exoplanets makes it an interesting planet for future RV follow-up.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Study of the Kepler K2 Variable EPIC 211957146 Exhibiting a Variable O’ Connell Effect

We present the multi-band photometric and spectroscopic study of an over-contact binary system, EPIC 211957146. The light curves exhibit a variable O’ Connell effect, confirmed from our observational data and the Kepler K2 data. The best photometric solution incorporating a dark spot over the primary component unveils that the system has a low-mass ratio ( q ∼ 0.17) and a high inclination ( i ∼ 85°). To confirm the solution and constrain the uncertainty, Monte-Carlo simulations are performed and the results are reported. Based on the O–C diagram analysis, we see that the variable shows a period increase at the rate of dP / dt ∼ 1.06 × 10{sup −6} days yr{sup −1}, which is higher than the theoretically predicted value. Presence of a third body having a period of ∼16.23 years is evident from the O–C diagram. No filled-in effect is observed in the H α line, while the effect is vividly present in the Na line. From the Kepler K2 data, we found that the primary and secondary minima exhibit an anti-correlated O–C variation followed by an erratic behavior. This is possibly caused by the longitudinal motion of the spot, and hence, we set a lower limit of ∼40 days for the spot modulation. We also observe a possibly associated photometric difference in the primary depth by comparing our light curves with Kepler K2 normalized light curves. This system has a low-mass ratio and a high fill-out factor, and, theoretically, such a physical configuration would lead to a merger.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Rotation of Low-mass Stars in Upper Scorpius and ρ Ophiuchus with K2

We present an analysis of K2 light curves (LCs) for candidate members of the young Upper Sco (USco) association (∼8 Myr) and the neighboring ρ Oph embedded cluster (∼1 Myr). We establish ∼1300 stars as probable members, ∼80% of which are periodic. The phased LCs have a variety of shapes which can be attributed to physical causes ranging from stellar pulsation and stellar rotation to disk-related phenomena. We identify and discuss a number of observed behaviors. The periods are ∼0.2–30 days with a peak near 2 days and the rapid period end nearing breakup velocity. M stars in the young USco region rotate systematically faster than GK stars, a pattern also present in K2 data for the older Pleiades and Praesepe systems. At higher masses (types FGK), the well-defined period–color relationship for slowly rotating stars seen in the Pleiades and Praesepe systems is not yet present in USco. Circumstellar disks are present predominantly among the more slowly rotating M stars in USco, with few disks in the subday rotators. However, M dwarfs with disks rotate faster on average than FGK systems with disks. For four of these disked M dwarfs, we provide direct evidence for disk locking based on the K2 LC morphologies. Our preliminary analysis shows a relatively mass-independent spin-up by a factor of ∼3.5 between USco and the Pleiades, then mass-dependent spin-down between Pleiades and Praesepe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

An Improved Transit Measurement for a 2.4 R{sub ⊕} Planet Orbiting A Bright Mid-M Dwarf K2–28

We present a new Spitzer transit observation of K2–28b, a sub-Neptune (R {sub p} = 2.45 ± 0.28 R {sub ⊕}) orbiting a relatively bright (V {sub mag} = 16.06, K {sub mag} = 10.75) metal-rich M4 dwarf (EPIC 206318379). This star is one of only seven with masses less than 0.2 M{sub ⊙} known to host transiting planets, and the planet appears to be a slightly smaller analogue of GJ 1214b (2.85±0.20 R{sub ⊕}). Our new Spitzer observations were taken two years after the original K2 discovery data and have a significantly higher cadence, allowing us to derive improved estimates for this planet’s radius, semimajor axis, and orbital period, which greatly reduce the uncertainty in the prediction of near future transit times for the James Webb Space Telescope (JWST) observations. We also evaluate the system’s suitability for atmospheric characterization with JWST and find that it is currently the only small (<3 R{sub ⊕}) and cool (<600 K) planet aside from GJ 1214b with a potentially detectable secondary eclipse. We also note that this system is a favorable target for near-infrared radial velocity instruments on larger telescopes (e.g., the Habitable Planet Finder on the Hobby–Eberly Telescope), making it one of only a handful of small, cool planets accessible with this technique. Finally, we compare our results with the simulated catalog of the Transiting Exoplanet Survey Satellite (TESS) and find K2–28b to be representative of the kind of mid-M systems that should be detectable in the TESS sample.

79 ASTRONOMY AND ASTROPHYSICS↗