452 research outputs found
Validating Phasing and Geometry of Large Focal Plane Arrays
The Kepler Mission is designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-sized and smaller planets in or near the habitable zone. The Kepler photometer is an array of 42 CCDs (charge-coupled devices) in the focal plane of a 95-cm Schmidt camera onboard the Kepler spacecraft. Each 50x25-mm CCD has 2,200 x 1,024 pixels. The CCDs accumulate photons and are read out every six seconds to prevent saturation. The data is integrated for 30 minutes, and then the pixel data is transferred to onboard storage. The data is subsequently encoded and transmitted to the ground. During End-to-End Information System (EEIS) testing of the Kepler Mission System (KMS), there was a need to verify that the pixels requested by the science team operationally were correctly collected, encoded, compressed, stored, and transmitted by the FS, and subsequently received, decoded, uncompressed, and displayed by the Ground Segment (GS) without the outputs of any CCD modules being flipped, mirrored, or otherwise corrupted during the extensive FS and GS processing. This would normally be done by projecting an image on the focal plane array (FPA), collecting the data in a flight-like way, and making a comparison between the original data and the data reconstructed by the science data system. Projecting a focused image onto the FPA through the telescope would normally involve using a collimator suspended over the telescope opening. There were several problems with this approach: the collimation equipment is elaborate and expensive; as conceived, it could only illuminate a limited section of the FPA (.25 percent) during a given test; the telescope cover would have to be deployed during testing to allow the image to be projected into the telescope; the equipment was bulky and difficult to situate in temperature-controlled environments; and given all the above, test setup, execution, and repeatability were significant concerns. Instead of using this complicated approach of projecting an optical image on the FPA, the Kepler project developed a method using known defect features in the CCDs to verify proper collection and reassembly of the pixels, thereby avoiding the costs and risks of the optical projection approach. The CCDs composing the Kepler FPA, as all CCDs, had minor defects. At ambient temperature, some pixels look far brighter than they should. These ghot h pixels have a higher rate of charge leakage than the others due to manufacturing variations. They are usually stable over time, and appear at temperatures above 5 oC. The hot pixels on the Kepler FPA were mapped before photometer assembly during module testing. Selected hot pixels were used as target gstars h for the purposes of EEIS testing. gDead h pixels are permanently off, producing a permanently black pixel. These can also be used if there is some illumination of the FPA. During EEIS testing, Dark Current Full Frame Images (FFIs) taken at room temperature were used to create the hot pixel maps for all 84 Kepler photometer CCD channels. Data from two separate nights were used to create two hot pixel maps per channel, which were cross-correlated to remove cosmic ray events which appear to be hot pixels. These hot pixel maps obtained during EEIS testing were compared to the maps made during module testing to verify that the end-to-end data flow was correct
Caltech Faint Field Galaxy Redshift Survey IX: Source detection and photometry in the Hubble Deep Field Region
Detection and photometry of sources in the U_n, G, R, and K_s bands in a 9x9
arcmin^2 region of the sky, centered on the Hubble Deep Field, are described.
The data permit construction of complete photometric catalogs to roughly
U_n=25, G=26, R=25.5 and K_s=20 mag, and significant photometric measurements
somewhat fainter. The galaxy number density is 1.3x10^5 deg^{-2} to R=25.0 mag.
Galaxy number counts have slopes dlog N/dm=0.42, 0.33, 0.27 and 0.31 in the
U_n, G, R and K_s bands, consistent with previous studies and the trend that
fainter galaxies are, on average, bluer. Galaxy catalogs selected in the R and
K_s bands are presented, containing 3607 and 488 sources, in field areas of
74.8 and 59.4 arcmin^2, to R=25.5 and and K_s=20 mag.Comment: Accepted for publication in ApJS; some tables and slightly nicer
figures available at http://www.sns.ias.edu/~hogg/deep
Far Infrared Prperties of M Dwarfs
We report the mid- and far-infrared properties of nearby M dwarfs.
Spitzer/MIPS measurements were obtained for a sample of 62 stars at 24 um, with
subsamples of 41 and 20 stars observed at 70 um and 160 um respectively. We
compare the results with current models of M star photospheres and look for
indications of circumstellar dust in the form of significant deviations of
K-[24 um] colors and 70 um / 24 um flux ratios from the average M star values.
At 24 um, all 62 of the targets were detected; 70 um detections were achieved
for 20 targets in the subsample observed; and no detections were seen in the
160 um subsample. No clear far-infrared excesses were detected in our sample.
The average far infrared excess relative to the photospheric emission of the M
stars is at least four times smaller than the similar average for a sample of
solar-type stars. However, this limit allows the average fractional infrared
luminosity in the M-star sample to be similar to that for more massive stars.
We have also set low limits for the maximum mass of dust possible around our
stars.Comment: 28 pages, 4 figures, to be published in The Astrophysical Journa
Spitzer-MIPS Observations of the eta Cha Young Association
We have mapped the eta Chamaeleontis young stellar association in the
far-infrared with the Multiband Imaging Photometer for Spitzer (MIPS) on the
Spitzer Space Telescope. All sixteen members within the map region were
detected at 24 um, along with five members at 70 um and two at 160 um. Ten
stars show far-infrared excess emission indicating the presence of
circumstellar disks; six of these have central clearings as evidenced by the
onset of excess emission at >5 um. No new infrared excess sources are
identified among the 113 2MASS field stars with 24 um photometry but not seen
as X-ray sources, indicating that membership lists derived from X-ray surveys
are reasonably complete. Circumstellar disks in the eta Cha association span
the range from 1e-1 to 1e-4 in their fractional infrared luminosity, with a
median Ldust /Lstar of 0.04. The presence of optically thick, optically thin,
and intermediate optical depth disks within the same stellar group, in
combination with the large fraction of disks with inner holes, indicates that
the Cha association represents a crucial stage in circumstellar disk evolution.Comment: To appear in The Astrophysical Journa
Closed-loop separation control over a sharp edge ramp using Genetic Programming
We experimentally perform open and closed-loop control of a separating
turbulent boundary layer downstream from a sharp edge ramp. The turbulent
boundary layer just above the separation point has a Reynolds number
based on momentum thickness. The goal of the
control is to mitigate separation and early re-attachment. The forcing employs
a spanwise array of active vortex generators. The flow state is monitored with
skin-friction sensors downstream of the actuators. The feedback control law is
obtained using model-free genetic programming control (GPC) (Gautier et al.
2015). The resulting flow is assessed using the momentum coefficient, pressure
distribution and skin friction over the ramp and stereo PIV. The PIV yields
vector field statistics, e.g. shear layer growth, the backflow area and vortex
region. GPC is benchmarked against the best periodic forcing. While open-loop
control achieves separation reduction by locking-on the shedding mode, GPC
gives rise to similar benefits by accelerating the shear layer growth.
Moreover, GPC uses less actuation energy.Comment: 24 pages, 24 figures, submitted to Experiments in Fluid
Architecture of Kepler's Multi-transiting Systems: II. New investigations with twice as many candidates
We report on the orbital architectures of Kepler systems having multiple
planet candidates identified in the analysis of data from the first six
quarters of Kepler data and reported by Batalha et al. (2013). These data show
899 transiting planet candidates in 365 multiple-planet systems and provide a
powerful means to study the statistical properties of planetary systems. Using
a generic mass-radius relationship, we find that only two pairs of planets in
these candidate systems (out of 761 pairs total) appear to be on Hill-unstable
orbits, indicating ~96% of the candidate planetary systems are correctly
interpreted as true systems. We find that planet pairs show little statistical
preference to be near mean-motion resonances. We identify an asymmetry in the
distribution of period ratios near first-order resonances (e.g., 2:1, 3:2),
with an excess of planet pairs lying wide of resonance and relatively few lying
narrow of resonance. Finally, based upon the transit duration ratios of
adjacent planets in each system, we find that the interior planet tends to have
a smaller transit impact parameter than the exterior planet does. This finding
suggests that the mode of the mutual inclinations of planetary orbital planes
is in the range 1.0-2.2 degrees, for the packed systems of small planets probed
by these observations.Comment: Accepted to Ap
The Kepler Follow-up Observation Program
The Kepler Mission was launched on March 6, 2009 to perform a photometric
survey of more than 100,000 dwarf stars to search for terrestrial-size planets
with the transit technique. Follow-up observations of planetary candidates
identified by detection of transit-like events are needed both for
identification of astrophysical phenomena that mimic planetary transits and for
characterization of the true planets and planetary systems found by Kepler. We
have developed techniques and protocols for detection of false planetary
transits and are currently conducting observations on 177 Kepler targets that
have been selected for follow-up. A preliminary estimate indicates that between
24% and 62% of planetary candidates selected for follow-up will turn out to be
true planets.Comment: 12 pages, submitted to the Astrophysical Journal Letter
Caltech Faint Galaxy Redshift Survey. IX. Source Detection and Photometry in the Hubble Deep Field Region
Detection and photometry of sources in the U_n, G, ℛ, and K_s bands in a 9 × 9 arcmin^2 region of the sky, centered on the Hubble Deep Field, are described. The data permit construction of complete photometric catalogs to roughly U_n = 25, G = 26, ℛ = 25.5, K_s = 20 mag and significant photometric measurements somewhat fainter. The galaxy number density is 1.3 × 10^5 deg^(-2) to ℛ = 25.0 mag. Galaxy number counts have slopes d log N/dm = 0.42, 0.33, 0.27, and 0.31 in the U_n, G, ℛ, and K_s bands, consistent with previous studies and the trend that fainter galaxies are, on average, bluer. Galaxy catalogs selected in the ℛ and K_s bands are presented, containing 3607 and 488 sources in field areas of 74.8 and 59.4 arcmin^2, to ℛ = 25.5 and K_s = 20 mag
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Kepler-4B: A Hot Neptune-Like Planet of A G0 Star Near Main-Sequence Turnoff
Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19(h)02(m)27.(s)68, delta = +50 degrees 08'08 '' 7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10(-3) and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3(-1.9)(+1.1) m s(-1), consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223(-0.091)(+0.053) M(circle dot) and 1.487(-0.084)(+0.071) R(circle dot).We estimate the planet mass and radius to be {M(P), R(P)} = {24.5 +/- 3.8 M(circle plus), 3.99 +/- 0.21 R(circle plus)}. The planet's density is near 1.9 g cm(-3); it is thus slightly denser and more massive than Neptune, but about the same size.W. M. Keck FoundationNASA's Science Mission DirectorateAstronom
Kepler Observations of Transiting Hot Compact Objects
Kepler photometry has revealed two unusual transiting companions orbiting an
early A-star and a late B-star. In both cases the occultation of the companion
is deeper than the transit. The occultation and transit with follow-up optical
spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a
companion in a 5.2 day orbit with a radius of 0.08 Rsun and a 10000 K late
B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a
radius of 0.2 Rsun. We infer a temperature of 12250 K for KOI-74b and 13500 K
for KOI-81b.
We present 43 days of high duty cycle, 30 minute cadence photometry, with
models demonstrating the intriguing properties of these object, and speculate
on their nature.Comment: 12 pages, 3 figures, submitted to ApJL (updated to correct KOI74
lightcurve
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