265 research outputs found
Initial Characteristics of Kepler Short Cadence Data
The Kepler Mission offers two options for observations -- either Long Cadence
(LC) used for the bulk of core mission science, or Short Cadence (SC) which is
used for applications such as asteroseismology of solar-like stars and transit
timing measurements of exoplanets where the 1-minute sampling is critical. We
discuss the characteristics of SC data obtained in the 33.5-day long Quarter 1
(Q1) observations with Kepler which completed on 15 June 2009. The truly
excellent time series precisions are nearly Poisson limited at 11th magnitude
providing per-point measurement errors of 200 parts-per-million per minute. For
extremely saturated stars near 7th magnitude precisions of 40 ppm are reached,
while for background limited measurements at 17th magnitude precisions of 7
mmag are maintained. We note the presence of two additive artifacts, one that
generates regularly spaced peaks in frequency, and one that involves additive
offsets in the time domain inversely proportional to stellar brightness. The
difference between LC and SC sampling is illustrated for transit observations
of TrES-2.Comment: 5 pages, 4 figures, ApJ Letters in pres
A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter
In addition to its potential to probe the Inflationary cosmological paradigm,
millimeter-wave polarimetry is a powerful tool for studying the Milky Way
galaxy's composition and magnetic field structure. Towards this end, presented
here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave
polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in
three atmospheric transmission windows centered on 100, 150, and 220 GHz. The
maps sample an optical depth 1 < AV < 30, and are consistent with previous
characterizations of the Galactic millimeter-wave frequency spectrum and the
large-scale magnetic field structure permeating the interstellar medium.
Polarized emission is detected over the entire region within two degrees of the
Galactic plane and indicates that the large-scale magnetic field is oriented
parallel to the plane of the Galaxy. An observed trend of decreasing
polarization fraction with increasing total intensity rules out the simplest
model of a constant Galactic magnetic field throughout the Galaxy. Including
WMAP data in the analysis, the degree-scale frequency spectrum of Galactic
polarization fraction is plotted between 23 and 220 GHz for the first time. A
generally increasing trend of polarization fraction with electromagnetic
frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to
2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component
(synchrotron and dust) model showing that the higher frequency BICEP data are
necessary to tightly constrain the amplitude and spectral index of Galactic
dust. Furthermore, the dust amplitude predicted by this two-component fit is
consistent with model predictions of dust emission in the BICEP bands
CMBPol Mission Concept Study: Prospects for polarized foreground removal
In this report we discuss the impact of polarized foregrounds on a future
CMBPol satellite mission. We review our current knowledge of Galactic polarized
emission at microwave frequencies, including synchrotron and thermal dust
emission. We use existing data and our understanding of the physical behavior
of the sources of foreground emission to generate sky templates, and start to
assess how well primordial gravitational wave signals can be separated from
foreground contaminants for a CMBPol mission. At the estimated foreground
minimum of ~100 GHz, the polarized foregrounds are expected to be lower than a
primordial polarization signal with tensor-to-scalar ratio r=0.01, in a small
patch (~1%) of the sky known to have low Galactic emission. Over 75% of the sky
we expect the foreground amplitude to exceed the primordial signal by about a
factor of eight at the foreground minimum and on scales of two degrees. Only on
the largest scales does the polarized foreground amplitude exceed the
primordial signal by a larger factor of about 20. The prospects for detecting
an r=0.01 signal including degree-scale measurements appear promising, with 5
sigma_r ~0.003 forecast from multiple methods. A mission that observes a range
of scales offers better prospects from the foregrounds perspective than one
targeting only the lowest few multipoles. We begin to explore how optimizing
the composition of frequency channels in the focal plane can maximize our
ability to perform component separation, with a range of typically 40 < nu <
300 GHz preferred for ten channels. Foreground cleaning methods are already in
place to tackle a CMBPol mission data set, and further investigation of the
optimization and detectability of the primordial signal will be useful for
mission design.Comment: 42 pages, 14 figures, Foreground Removal Working Group contribution
to the CMBPol Mission Concept Study, v2, matches AIP versio
Overview of the Kepler Science Processing Pipeline
The Kepler Mission Science Operations Center (SOC) performs several critical
functions including managing the ~156,000 target stars, associated target
tables, science data compression tables and parameters, as well as processing
the raw photometric data downlinked from the spacecraft each month. The raw
data are first calibrated at the pixel level to correct for bias, smear induced
by a shutterless readout, and other detector and electronic effects. A
background sky flux is estimated from ~4500 pixels on each of the 84 CCD
readout channels, and simple aperture photometry is performed on an optimal
aperture for each star. Ancillary engineering data and diagnostic information
extracted from the science data are used to remove systematic errors in the
flux time series that are correlated with these data prior to searching for
signatures of transiting planets with a wavelet-based, adaptive matched filter.
Stars with signatures exceeding 7.1 sigma are subjected to a suite of
statistical tests including an examination of each star's centroid motion to
reject false positives caused by background eclipsing binaries. Physical
parameters for each planetary candidate are fitted to the transit signature,
and signatures of additional transiting planets are sought in the residual
light curve. The pipeline is operational, finding planetary signatures and
providing robust eliminations of false positives.Comment: 8 pages, 3 figure
Discovery and Rossiter-McLaughlin Effect of Exoplanet Kepler-8b
We report the discovery and the Rossiter-McLaughlin effect of Kepler-8b, a
transiting planet identified by the NASA Kepler Mission. Kepler photometry and
Keck-HIRES radial velocities yield the radius and mass of the planet around
this F8IV subgiant host star. The planet has a radius RP = 1.419 RJ and a mass,
MP = 0.60 MJ, yielding a density of 0.26 g cm^-3, among the lowest density
planets known. The orbital period is P = 3.523 days and orbital semima jor axis
is 0.0483+0.0006/-0.0012 AU. The star has a large rotational v sin i of 10.5
+/- 0.7 km s^-1 and is relatively faint (V = 13.89 mag), both properties
deleterious to precise Doppler measurements. The velocities are indeed noisy,
with scatter of 30 m s^-1, but exhibit a period and phase consistent with the
planet implied by the photometry. We securely detect the Rossiter-McLaughlin
effect, confirming the planet's existence and establishing its orbit as
prograde. We measure an inclination between the projected planetary orbital
axis and the projected stellar rotation axis of lambda = -26.9 +/- 4.6 deg,
indicating a moderate inclination of the planetary orbit. Rossiter-McLaughlin
measurements of a large sample of transiting planets from Kepler will provide a
statistically robust measure of the true distribution of spin-orbit
orientations for hot jupiters in general.Comment: 26 pages, 8 figures, 2 tables; In preparation for submission to the
Astrophysical Journa
Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25
We present the Kepler Object of Interest (KOI) catalog of transiting
exoplanets based on searching four years of Kepler time series photometry (Data
Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet
candidates with periods between 0.25 and 632 days. Of these candidates, 219 are
new and include two in multi-planet systems (KOI-82.06 and KOI-2926.05), and
ten high-reliability, terrestrial-size, habitable zone candidates. This catalog
was created using a tool called the Robovetter which automatically vets the
DR25 Threshold Crossing Events (TCEs, Twicken et al. 2016). The Robovetter also
vetted simulated data sets and measured how well it was able to separate TCEs
caused by noise from those caused by low signal-to-noise transits. We discusses
the Robovetter and the metrics it uses to sort TCEs. For orbital periods less
than 100 days the Robovetter completeness (the fraction of simulated transits
that are determined to be planet candidates) across all observed stars is
greater than 85%. For the same period range, the catalog reliability (the
fraction of candidates that are not due to instrumental or stellar noise) is
greater than 98%. However, for low signal-to-noise candidates between 200 and
500 days around FGK dwarf stars, the Robovetter is 76.7% complete and the
catalog is 50.5% reliable. The KOI catalog, the transit fits and all of the
simulated data used to characterize this catalog are available at the NASA
Exoplanet Archive.Comment: 61 pages, 23 Figures, 9 Tables, Accepted to The Astrophysical Journal
Supplement Serie
Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller
In the spring of 2009, the Kepler Mission commenced high-precision photometry
on nearly 156,000 stars to determine the frequency and characteristics of small
exoplanets, conduct a guest observer program, and obtain asteroseismic data on
a wide variety of stars. On 15 June 2010 the Kepler Mission released data from
the first quarter of observations. At the time of this publication, 706 stars
from this first data set have exoplanet candidates with sizes from as small as
that of the Earth to larger than that of Jupiter. Here we give the identity and
characteristics of 306 released stars with planetary candidates. Data for the
remaining 400 stars with planetary candidates will be released in February
2011. Over half the candidates on the released list have radii less than half
that of Jupiter. The released stars include five possible multi-planet systems.
One of these has two Neptune-size (2.3 and 2.5 Earth-radius) candidates with
near-resonant periods.Comment: Paper to accompany Kepler's June 15, 2010 data release; submitted to
Astrophysical Journal Figures 1,2,& 3 revised. Improved labeling on all
figures. Slight changes to planet frequencies in result
3D Structure Prediction of TAS2R38 Bitter Receptors Bound to Agonists Phenylthiocarbamide (PTC) and 6-n-Propylthiouracil (PROP)
Malleable Machines in Transcription Regulation: The Mediator Complex
The Mediator complex provides an interface between gene-specific regulatory proteins and the general transcription machinery including RNA polymerase II (RNAP II). The complex has a modular architecture (Head, Middle, and Tail) and cryoelectron microscopy analysis suggested that it undergoes dramatic conformational changes upon interactions with activators and RNAP II. These rearrangements have been proposed to play a role in the assembly of the preinitiation complex and also to contribute to the regulatory mechanism of Mediator. In analogy to many regulatory and transcriptional proteins, we reasoned that Mediator might also utilize intrinsically disordered regions (IDRs) to facilitate structural transitions and transmit transcriptional signals. Indeed, a high prevalence of IDRs was found in various subunits of Mediator from both Saccharomyces cerevisiae and Homo sapiens, especially in the Tail and the Middle modules. The level of disorder increases from yeast to man, although in both organisms it significantly exceeds that of multiprotein complexes of a similar size. IDRs can contribute to Mediator's function in three different ways: they can individually serve as target sites for multiple partners having distinctive structures; they can act as malleable linkers connecting globular domains that impart modular functionality on the complex; and they can also facilitate assembly and disassembly of complexes in response to regulatory signals. Short segments of IDRs, termed molecular recognition features (MoRFs) distinguished by a high protein–protein interaction propensity, were identified in 16 and 19 subunits of the yeast and human Mediator, respectively. In Saccharomyces cerevisiae, the functional roles of 11 MoRFs have been experimentally verified, and those in the Med8/Med18/Med20 and Med7/Med21 complexes were structurally confirmed. Although the Saccharomyces cerevisiae and Homo sapiens Mediator sequences are only weakly conserved, the arrangements of the disordered regions and their embedded interaction sites are quite similar in the two organisms. All of these data suggest an integral role for intrinsic disorder in Mediator's function
Kepler Mission Design, Realized Photometric Performance, and Early Science
The Kepler Mission, launched on Mar 6, 2009 was designed with the explicit
capability to detect Earth-size planets in the habitable zone of solar-like
stars using the transit photometry method. Results from just forty-three days
of data along with ground-based follow-up observations have identified five new
transiting planets with measurements of their masses, radii, and orbital
periods. Many aspects of stellar astrophysics also benefit from the unique,
precise, extended and nearly continuous data set for a large number and variety
of stars. Early results for classical variables and eclipsing stars show great
promise. To fully understand the methodology, processes and eventually the
results from the mission, we present the underlying rationale that ultimately
led to the flight and ground system designs used to achieve the exquisite
photometric performance. As an example of the initial photometric results, we
present variability measurements that can be used to distinguish dwarf stars
from red giants.Comment: 16 pages, 5 figures, 1 table 26 Jan revision replaced Subject
headings with keywords from approved lis
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