Search

Start Over Subject stellar radii Capability Type Simple Cone Search
91. Kepler planet candidates radii
ID:
ivo://CDS.VizieR/J/ApJ/770/69
Title:
Kepler planet candidates radii
Short Name:
J/ApJ/770/69
Date:
21 Oct 2021
Publisher:
CDS
Description:
We carry out an independent search of Kepler photometry for small transiting planets with sizes 0.5-8.0 times that of Earth and orbital periods between 5 and 50 days, with the goal of measuring the fraction of stars harboring such planets. We use a new transit search algorithm, TERRA, optimized to detect small planets around photometrically quiet stars. We restrict our stellar sample to include the 12000 stars having the lowest photometric noise in the Kepler survey, thereby maximizing the detectability of Earth-size planets. We report 129 planet candidates having radii less than 6R_E_ found in three years of Kepler photometry (quarters 1-12). Forty-seven of these candidates are not in Batalha et al. (J/ApJS/204/24), which only analyzed photometry from quarters 1-6. We gather Keck HIRES spectra for the majority of these targets leading to precise stellar radii and hence precise planet radii. We make a detailed measurement of the completeness of our planet search. We inject synthetic dimmings from mock transiting planets into the actual Kepler photometry. We then analyze that injected photometry with our TERRA pipeline to assess our detection completeness for planets of different sizes and orbital periods. We compute the occurrence of planets as a function of planet radius and period, correcting for the detection completeness as well as the geometric probability of transit, R_*_/a. The resulting distribution of planet sizes exhibits a power law rise in occurrence from 5.7R_E_ down to 2R_E_, as found in Howard et al. (2012ApJS..201...15H). That rise clearly ends at 2R_E_. The occurrence of planets is consistent with constant from 2R_E_ toward 1R_E_. This unexpected plateau in planet occurrence at 2R_E_ suggests distinct planet formation processes for planets above and below 2R_E_.
92. 139 Kepler planets transit time variations
ID:
ivo://CDS.VizieR/J/ApJ/787/80
Title:
139 Kepler planets transit time variations
Short Name:
J/ApJ/787/80
Date:
21 Oct 2021
Publisher:
CDS
Description:
We extract densities and eccentricities of 139 sub-Jovian planets by analyzing transit time variations (TTVs) obtained by the Kepler mission through Quarter 12. We partially circumvent the degeneracies that plague TTV inversion with the help of an analytical formula for the TTV. From the observed TTV phases, we find that most of these planets have eccentricities of the order of a few percent. More precisely, the rms eccentricity is 0.018_-0.004_^+0.005^, and planets smaller than 2.5 R_{earth}_ are around twice as eccentric as those bigger than 2.5 R_{earth}_. We also find a best-fit density-radius relationship {rho}~3 g/cm^3^x(R/3 R_{earth}_)^-2.3^ for the 56 planets that likely have small eccentricity and hence small statistical correction to their masses. Many planets larger than 2.5 R_{earth}_are less dense than water, implying that their radii are largely set by a massive hydrogen atmosphere.
93. Kepler-80 transit timing observations
ID:
ivo://CDS.VizieR/J/AJ/152/105
Title:
Kepler-80 transit timing observations
Short Name:
J/AJ/152/105
Date:
21 Oct 2021
Publisher:
CDS
Description:
Kepler has discovered hundreds of systems with multiple transiting exoplanets which hold tremendous potential both individually and collectively for understanding the formation and evolution of planetary systems. Many of these systems consist of multiple small planets with periods less than ~50 days known as Systems with Tightly spaced Inner Planets, or STIPs. One especially intriguing STIP, Kepler-80 (KOI-500), contains five transiting planets: f, d, e, b, and c with periods of 1.0, 3.1, 4.6, 7.1, and 9.5 days, respectively. We provide measurements of transit times and a transit timing variation (TTV) dynamical analysis. We find that TTVs cannot reliably detect eccentricities for this system, though mass estimates are not affected. Restricting the eccentricity to a reasonable range, we infer masses for the outer four planets (d, e, b, and c) to be 6.75_-0.51_^+0.69^, 4.13_-0.95_^+0.81^, 6.93_-0.70_^+1.05^, and 6.74_-0.86_^+1.23^ Earth masses, respectively. The similar masses but different radii are consistent with terrestrial compositions for d and e and ~2% H/He envelopes for b and c. We confirm that the outer four planets are in a rare dynamical configuration with four interconnected three-body resonances that are librating with few degree amplitudes. We present a formation model that can reproduce the observed configuration by starting with a multi-resonant chain and introducing dissipation. Overall, the information-rich Kepler-80 planets provide an important perspective into exoplanetary systems.
94. 106 Kepler ultra-short-period planets
ID:
ivo://CDS.VizieR/J/ApJ/787/47
Title:
106 Kepler ultra-short-period planets
Short Name:
J/ApJ/787/47
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a survey aimed at discovering and studying transiting planets with orbital periods shorter than one day (ultra-short-period, or USP, planets), using data from the Kepler spacecraft. We computed Fourier transforms of the photometric time series for all 200000 target stars, and detected transit signals based on the presence of regularly spaced sharp peaks in the Fourier spectrum. We present a list of 106 USP candidates, of which 18 have not previously been described in the literature. This list of candidates increases the number of planet candidates with orbital periods shorter than about six hours from two to seven. In addition, among the objects we studied, there are 26 USP candidates that had been previously reported in the literature which do not pass our various tests. All 106 of our candidates have passed several standard tests to rule out false positives due to eclipsing stellar systems. A low false positive rate is also implied by the relatively high fraction of candidates for which more than one transiting planet signal was detected. By assuming these multi-transit candidates represent coplanar multi-planet systems, we are able to infer that the USP planets are typically accompanied by other planets with periods in the range 1-50 days, in contrast with hot Jupiters which very rarely have companions in that same period range. Another clear pattern is that almost all USP planets are smaller than 2 R_{earth}_, possibly because gas giants in very tight orbits would lose their atmospheres by photoevaporation when subject to extremely strong stellar irradiation. Based on our survey statistics, USP planets exist around approximately (0.51+/-0.07)% of G-dwarf stars, and (0.83+/-0.18)% of K-dwarf stars.
95. KIC star parallaxes from asteroseismology vs Gaia
ID:
ivo://CDS.VizieR/J/ApJ/844/102
Title:
KIC star parallaxes from asteroseismology vs Gaia
Short Name:
J/ApJ/844/102
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red-giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived from asteroseismology and eclipsing binaries have likely been overestimated for parallaxes <~5-10mas (~90%-98% of the TGAS sample). The observed differences in our sample can furthermore be partially compensated by adopting a hotter Teff scale (such as the infrared flux method) instead of spectroscopic temperatures for dwarfs and subgiants. Residual systematic differences are at the ~2% level in parallax across three orders of magnitude. We use TGAS parallaxes to empirically demonstrate that asteroseismic radii are accurate to ~5% or better for stars between ~0.8-8R_{sun}_. We find no significant offset for main- sequence (<~1.5R_{sun}_) and low-luminosity RGB stars (~3-8R_{sun}_), but seismic radii appear to be systematically underestimated by ~5% for subgiants (~1.5-3R_{sun}_). We find no systematic errors as a function of metallicity between [Fe/H]~-0.8 to +0.4dex, and show tentative evidence that corrections to the scaling relation for the large frequency separation ({Delta}{nu}) improve the agreement with TGAS for RGB stars. Finally, we demonstrate that beyond ~3kpc asteroseismology will provide more precise distances than end-of-mission Gaia data, highlighting the synergy and complementary nature of Gaia and asteroseismology for studying galactic stellar populations.
96. KIC stars properties in NGC 6791 and NGC 6819
ID:
ivo://CDS.VizieR/J/ApJ/729/L10
Title:
KIC stars properties in NGC 6791 and NGC 6819
Short Name:
J/ApJ/729/L10
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present initial results on some of the properties of open clusters NGC 6791 and NGC 6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating the mass, radius, and log g of stars on the red giant branch (RGB) of these clusters, we estimate the distance to the clusters and their ages. Our model-independent estimate of the distance modulus of NGC 6791 is (m-M)_0_=13.11+/-0.06. We find (m-M)_0_=11.85+/-0.05 for NGC 6819. The average mass of stars on the RGB of NGC 6791 is 1.20+/-0.01M_{sun}_, while that of NGC 6819 is 1.68+/-0.03M_{sun}_. It should be noted that we do not have data that cover the entire RGB and the actual mass will be somewhat lower. We have determined model-dependent estimates of ages of these clusters. We find ages between 6.8 and 8.6Gyr for NGC 6791, however, most sets of models give ages around 7Gyr. We obtain ages between 2 and 2.4Gyr for NGC 6819.
97. K2 planetary syst. around low-mass stars. I.
ID:
ivo://CDS.VizieR/J/ApJ/836/167
Title:
K2 planetary syst. around low-mass stars. I.
Short Name:
J/ApJ/836/167
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3-M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13R_{sun}_ (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.
98. K2 planetary systems orbiting low-mass stars
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.
99. K2 star parameters from Gaia & LAMOST
ID:
ivo://CDS.VizieR/J/ApJS/247/28
Title:
K2 star parameters from Gaia & LAMOST
Short Name:
J/ApJS/247/28
Date:
21 Oct 2021
Publisher:
CDS
Description:
Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog (EPIC) largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26838 K2 stars. For 195250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1-13, elucidating a distinct planet radius valley around 1.9R_{Earth}_, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates.
100. K2 & TESS Synergy. I. Parameters & LC, 4 stars
ID:
ivo://CDS.VizieR/J/AJ/160/209
Title:
K2 & TESS Synergy. I. Parameters & LC, 4 stars
Short Name:
J/AJ/160/209
Date:
21 Oct 2021
Publisher:
CDS
Description:
Although the Transiting Exoplanet Survey Satellite (TESS) primary mission observed the northern and southern ecliptic hemispheres, generally avoiding the ecliptic, and the Kepler space telescope during the K2 mission could only observe near the ecliptic, many of the K2 fields extend far enough from the ecliptic plane that sections overlap with TESS fields. Using photometric observations from both K2 and TESS, combined with archival spectroscopic observations, we globally modeled four known planetary systems discovered by K2 that were observed in the first year of the primary TESS mission. Specifically, we provide updated ephemerides and system parameters for K2-114b, K2-167b, K2-237b, and K2-261b. These were some of the first K2 planets to be observed by TESS in the first year and include three Jovian sized planets and a sub-Neptune with orbital periods less than 12 days. In each case, the updated ephemeris significantly reduces the uncertainty in prediction of future times of transit, which is valuable for planning observations with the James Webb Space Telescope and other future facilities. The TESS extended mission is expected to observe about half of the K2 fields, providing the opportunity to perform this type of analysis on a larger number of systems.

Limit your search

more »

  • 2237