125 research outputs found
The architecture of the hierarchical triple star KOI 928 from eclipse timing variations seen in Kepler photometry
We present a hierarchical triple star system (KIC 9140402) where a low mass
eclipsing binary orbits a more massive third star. The orbital period of the
binary (4.98829 Days) is determined by the eclipse times seen in photometry
from NASA's Kepler spacecraft. The periodically changing tidal field, due to
the eccentric orbit of the binary about the tertiary, causes a change in the
orbital period of the binary. The resulting eclipse timing variations provide
insight into the dynamics and architecture of this system and allow the
inference of the total mass of the binary ()
and the orbital parameters of the binary about the central star.Comment: Submitted to MNRAS Letters. Additional tables with eclipse times are
included here. The Kepler data that was used for the analysis of this system
(Q1 through Q6) will be available on MAST after June 27, 201
Detection of gravity modes in the massive binary V380 Cyg from Kepler spacebased photometry and high-resolution spectroscopy
We report the discovery of low-amplitude gravity-mode oscillations in the
massive binary star V380 Cyg, from 180 d of Kepler custom-aperture space
photometry and 5 months of high-resolution high signal-to-noise spectroscopy.
The new data are of unprecedented quality and allowed to improve the orbital
and fundamental parameters for this binary. The orbital solution was subtracted
from the photometric data and led to the detection of periodic intrinsic
variability with frequencies of which some are multiples of the orbital
frequency and others are not. Spectral disentangling allowed the detection of
line-profile variability in the primary. With our discovery of intrinsic
variability interpreted as gravity mode oscillations, V380 Cyg becomes an
important laboratory for future seismic tuning of the near-core physics in
massive B-type stars.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS
Letter
Solar-like oscillations in KIC11395018 and KIC11234888 from 8 months of Kepler data
We analyze the photometric short-cadence data obtained with the Kepler
Mission during the first eight months of observations of two solar-type stars
of spectral types G and F: KIC 11395018 and KIC 11234888 respectively, the
latter having a lower signal-to-noise ratio compared to the former. We estimate
global parameters of the acoustic (p) modes such as the average large and small
frequency separations, the frequency of the maximum of the p-mode envelope and
the average linewidth of the acoustic modes. We were able to identify and to
measure 22 p-mode frequencies for the first star and 16 for the second one even
though the signal-to-noise ratios of these stars are rather low. We also derive
some information about the stellar rotation periods from the analyses of the
low-frequency parts of the power spectral densities. A model-independent
estimation of the mean density, mass and radius are obtained using the scaling
laws. We emphasize the importance of continued observations for the stars with
low signal-to-noise ratio for an improved characterization of the oscillation
modes. Our results offer a preview of what will be possible for many stars with
the long data sets obtained during the remainder of the mission.Comment: 39 pages, 9 figures. Accepted for publication in Ap
The complex case of V445 Lyr observed with Kepler: Two Blazhko modulations, a non-radial mode, possible triple mode RR Lyrae pulsation, and more
Rapid and strong changes in the Blazhko modulation of RR Lyrae stars, as they
have recently been detected in high precision satellite data, have become a
crucial topic in finding an explanation of the long-standing mystery of the
Blazhko effect. We present here an analysis of the most extreme case detected
so far, the RRab star V445 Lyr (KIC 6186029) which was observed with the Kepler
space mission. V445 Lyr shows very strong cycle-to-cycle changes in its Blazhko
modulation, which are caused both by a secondary long-term modulation period as
well as irregular variations. In addition to the complex Blazhko modulation,
V445 Lyr also shows a rich spectrum of additional peaks in the frequency range
between the fundamental pulsation and the first harmonic. Among those peaks,
the second radial overtone could be identified, which, combined with a
metallicity estimate of [Fe/H]=-2.0 dex from spectroscopy, allowed to constrain
the mass (0.55-0.65 M_sun) and luminosity (40-50 L_sun) of V445 Lyr through
theoretical Petersen diagrams. A non-radial mode as well as possibly the first
overtone are also excited. Furthermore, V445 Lyr shows signs of the period
doubling phenomenon and a long term period change. A detailed Fourier analysis
along with a study of the O-C variation of V445 Lyr is presented, and the
origin of the additional peaks and possible causes of the changes in the
Blazhko modulation are discussed. The results are then put into context with
those of the only other star with a variable Blazhko effect for which a long
enough set of high precision continuous satellite data has been published so
far, the CoRoT star 105288363.Comment: 19 pages, 20 figuers, accepted for publication in MNRA
Period and light curve fluctuations of the Kepler Cepheid V1154 Cyg
We present a detailed period analysis of the bright Cepheid-type variable
star V1154 Cygni (V =9.1 mag, P~4.9 d) based on almost 600 days of continuous
observations by the Kepler space telescope. The data reveal significant
cycle-to-cycle fluctuations in the pulsation period, indicating that classical
Cepheids may not be as accurate astrophysical clocks as commonly believed:
regardless of the specific points used to determine the O-C values, the cycle
lengths show a scatter of 0.015-0.02 days over the 120 cycles covered by the
observations. A very slight correlation between the individual Fourier
parameters and the O-C values was found, suggesting that the O - C variations
might be due to the instability of the light curve shape. Random fluctuation
tests revealed a linear trend up to a cycle difference 15, but for long term,
the period remains around the mean value. We compare the measurements with
simulated light curves that were constructed to mimic V1154 Cyg as a perfect
pulsator modulated only by the light travel time effect caused by low-mass
companions. We show that the observed period jitter in V1154 Cyg represents a
serious limitation in the search for binary companions. While the Kepler data
are accurate enough to allow the detection of planetary bodies in close orbits
around a Cepheid, the astrophysical noise can easily hide the signal of the
light-time effect.Comment: published in MNRAS: 8 pages, 7 figure
Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on The Entire 48 Month Dataset (Q1-Q17 DR24)
We present the seventh Kepler planet candidate catalog, which is the first to
be based on the entire, uniformly processed, 48 month Kepler dataset. This is
the first fully automated catalog, employing robotic vetting procedures to
uniformly evaluate every periodic signal detected by the Q1-Q17 Data Release 24
(DR24) Kepler pipeline. While we prioritize uniform vetting over the absolute
correctness of individual objects, we find that our robotic vetting is overall
comparable to, and in most cases is superior to, the human vetting procedures
employed by past catalogs. This catalog is the first to utilize artificial
transit injection to evaluate the performance of our vetting procedures and
quantify potential biases, which are essential for accurate computation of
planetary occurrence rates. With respect to the cumulative Kepler Object of
Interest (KOI) catalog, we designate 1,478 new KOIs, of which 402 are
dispositioned as planet candidates (PCs). Also, 237 KOIs dispositioned as false
positives (FPs) in previous Kepler catalogs have their disposition changed to
PC and 118 PCs have their disposition changed to FP. This brings the total
number of known KOIs to 8,826 and PCs to 4,696. We compare the Q1-Q17 DR24 KOI
catalog to previous KOI catalogs, as well as ancillary Kepler catalogs, finding
good agreement between them. We highlight new PCs that are both potentially
rocky and potentially in the habitable zone of their host stars, many of which
orbit solar-type stars. This work represents significant progress in accurately
determining the fraction of Earth-size planets in the habitable zone of
Sun-like stars. The full catalog is publicly available at the NASA Exoplanet
Archive.Comment: Accepted to the Astrophysical Journal Supplement Series. 30 pages, 9
figures, 7 tables. We make the DR24 robovetter decision code publicly
available at http://github.com/JeffLCoughlin/robovetter, with input and
output examples provided using the same data as contained in the full paper's
table
Two Earth-sized planets orbiting Kepler-20
Since the discovery of the first extrasolar giant planets around Sun-like
stars, evolving observational capabilities have brought us closer to the
detection of true Earth analogues. The size of an exoplanet can be determined
when it periodically passes in front of (transits) its parent star, causing a
decrease in starlight proportional to its radius. The smallest exoplanet
hitherto discovered has a radius 1.42 times that of the Earth's radius (R
Earth), and hence has 2.9 times its volume. Here we report the discovery of two
planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth
(0.87R Earth), orbiting the star Kepler-20, which is already known to host
three other, larger, transiting planets. The gravitational pull of the new
planets on the parent star is too small to measure with current
instrumentation. We apply a statistical method to show that the likelihood of
the planetary interpretation of the transit signals is more than three orders
of magnitude larger than that of the alternative hypothesis that the signals
result from an eclipsing binary star. Theoretical considerations imply that
these planets are rocky, with a composition of iron and silicate. The outer
planet could have developed a thick water vapour atmosphere.Comment: Letter to Nature; Received 8 November; accepted 13 December 2011;
Published online 20 December 201
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