164 research outputs found
Transits and secondary eclipses of HD 189733 with Spitzer
We present limits on transit timing variations and secondary eclipse depth
variations at 8 microns with the Spitzer Space Telescope IRAC camera. Due to
the weak limb darkening in the infrared and uninterrupted observing, Spitzer
provides the highest accuracy transit times for this bright system, in
principle providing sensitivity to secondary planets of Mars mass in resonant
orbits. Finally, the transit data provides tighter constraints on the
wavelength- dependent atmospheric absorption by the planet.Comment: 7 pages, 7 figures, submitted to proceedings of IAU Symposium No. 253
"Transiting Planets
Recommended from our members
The influence of the atmospheric boundary layer on nocturnal layers of noctuids and other moths migrating over southern Britain
Insects migrating at high altitude over southern Britain have been continuously monitored by automatically-operating, vertical-looking radars over a period of several years. During some occasions in the summer months, the migrants were observed to form well-defined layer concentrations, typically at heights of 200-400 m, in the stable night-time atmosphere. Under these conditions, insects are likely to have control over their vertical movements and are selecting flight heights which are favourable for long-range migration. We therefore investigated the factors influencing the formation of these insect layers by comparing radar measurements of the vertical distribution of insect density with meteorological profiles generated by the UK Met. Office’s Unified Model (UM). Radar-derived measurements of mass and displacement speed, along with data from Rothamsted Insect Survey light traps provided information on the identity of the migrants. We present here three case studies where noctuid and pyralid moths contributed substantially to the observed layers. The major meteorological factors influencing the layer concentrations appeared to be: (a) the altitude of the warmest air, (b) heights corresponding to temperature preferences or thresholds for sustained migration and (c), on nights when air temperatures are relatively high, wind-speed maxima associated with the nocturnal jet. Back-trajectories indicated that layer duration may have been determined by the distance to the coast. Overall, the unique combination of meteorological data from the UM and insect data from entomological radar described here show considerable promise for systematic studies of high-altitude insect layering
THE AMBIGUITY IN FOREST PROFILES AND XTINCTION ESTIMATED FROM MULTIBASELINE INTERFEROMETRIC SAR
This paper demonstrates by simulation that in the estimation of vegetation profiles from multibaseline interferometric synthetic aperture radar (InSAR), the peak extinction coefficient is poorly determined for typical interferometric coherence and phase accuracies. This coefficient determines overall density and affects the relative density profiles estimated from interferometry. This paper shows that a given radar power profile gives rise to a family of vegetation density profiles, depending on the peak extinction assumed. It is further demonstrated that estimating the peak extinction requires coherence accuracies of better than 0.1% and phase accuracies of better than a few tenths of a degree, both of which exceed the performance of typical or envisioned SAR systems. Two recommended approaches to profile production with InSAR are 1) use the radar power profile instead of the vegetation density profile for biomass estimation and other ecosystem characterization (in analogy to LIDAR power which is most frequently used for lidar studies of biomass) or 2) apply external information to establish the extinction characteristics needed for vegetation density profiles.Esse artigo procura demonstrar, por simulação, que na estimativa de perfis de volume da vegetação por interferometria com múltiplas linhas de base, o pico de extinção não é adequadamente determinado pela coerência interferométrica e fase, com acurácias típicas de InSAR. Esse pico determina a densidade global, afetando os perfis de densidade relativa da vegetação estimados por interferometria. Esse trabalho mostra que para um dado perfil de potência-radar há uma série de perfis de densidade da vegetação, dependendo do pico de extinção assumido. É ainda demonstrado que a estimativa do pico de extinção requer exatidões de coerência melhores que 0,1%, bem como, de acurácias de fases que alguns décimos de graus, valores esses que atualmente excedem o desempenho de sistemas SAR em operação ou aqueles previstos. As duas abordagens recomendadas para a produção de perfis com InSAR são: (1) utilizar o perfil-radar, ao invés do perfil de densidade de vegetação, para estimação de biomassa e outras caracterizações de ecossistema (em nalogia à potência-lidar, a qual é mais frequentemente utilizada nos estudos de biomassa baseados em LIDAR); ou (2) aplicar informação externa para estabelecer as características de extinção necessárias aos perfis de densidade de vegetação
Treetop: A Shiny-based application and R package for extracting forest information from LiDAR data for ecologists and conservationists
Individual tree detection (ITD) and crown delineation are two of the most relevant methods for extracting detailed and reliable forest information from LiDAR (Light Detection and Ranging) datasets. However, advanced computational skills and specialized knowledge have been normally required to extract forest information from LiDAR.The development of accessible tools for 3D forest characterization can facilitate rapid assessment by stakeholders lacking a remote sensing background, thus fostering the practical use of LiDAR datasets in forest ecology and conservation. This paper introduces the treetop application, an open-source web-based and R package LiDAR analysis tool for extracting forest structural information at the tree level, including cutting-edge analyses of properties related to forest ecology and management.We provide case studies of how treetop can be used for different ecological applications, within various forest ecosystems. Specifically, treetop was employed to assess post-hurricane disturbance in natural temperate forests, forest homogeneity in industrial forest plantations and the spatial distribution of individual trees in a tropical forest.treetop simplifies the extraction of relevant forest information for forest ecologists and conservationists who may use the tool to easily visualize tree positions and sizes, conduct complex analyses and download results including individual tree lists and figures summarizing forest structural properties. Through this open-source approach, treetop can foster the practical use of LiDAR data among forest conservation and management stakeholders and help ecological researchers to further understand the relationships between forest structure and function.The authors thank Nicholas L. Crookston for co‐developing the web‐LiDAR treetop tool, and the two anonymous reviewers for their helpful suggestions on the first version of the manuscript. This study is based on the work supported by the Department of Defence Strategic Environmental Research and Development Program (SERDP) under grants No. RC‐2243, RC19‐1064 and RC20‐1346 and USDA Forest Service (grand No. PRO00031122
The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
We present observations of seven transits and seven eclipses of the
transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use
a new correction for the detector ramp variation with a double-exponential
function. Our main findings are: (1) an upper limit on the variability of the
day-side planet flux of 2.7% (68% confidence); (2) the most precise set of
transit times measured for a transiting planet, with an average accuracy of 3
seconds; (3) a lack of transit-timing variations, excluding the presence of
second planets in this system above 20% of the mass of Mars in low-order
mean-motion resonance at 95% confidence; (4) a confirmation of the planet's
phase variation, finding the night side is 64% as bright as the day side, as
well as an upper limit on the night-side variability of 17% (68% confidence);
(5) a better correction for stellar variability at 8 micron causing the phase
function to peak 3.5 hrs before secondary eclipse, confirming that the
advection and radiation timescales are comparable at the 8 micron photosphere;
(6) variation in the depth of transit, which possibly implies variations in the
surface brightness of the portion of the star occulted by the planet, posing a
fundamental limit on non-simultaneous multi-wavelength transit absorption
measurements of planet atmospheres; (7) a measurement of the infrared
limb-darkening of the star, in agreement with stellar atmosphere models; (8) an
offset in the times of secondary eclipse of 69 sec, which is mostly accounted
for by a 31 sec light travel time delay and 33 sec delay due to the shift of
ingress and egress by the planet hot spot; this confirms that the phase
variation is due to an offset hot spot on the planet; (9) a retraction of the
claimed eccentricity of this system due to the offset of secondary eclipse; and
(10) high precision measurements of the parameters of this system.Comment: 18 pages, 19 figures, accepted for publication in the Astrophysical
Journa
The Science Case for an Extended Spitzer Mission
Although the final observations of the Spitzer Warm Mission are currently
scheduled for March 2019, it can continue operations through the end of the
decade with no loss of photometric precision. As we will show, there is a
strong science case for extending the current Warm Mission to December 2020.
Spitzer has already made major impacts in the fields of exoplanets (including
microlensing events), characterizing near Earth objects, enhancing our
knowledge of nearby stars and brown dwarfs, understanding the properties and
structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to
study galaxy birth and evolution. By extending Spitzer through 2020, it can
continue to make ground-breaking discoveries in those fields, and provide
crucial support to the NASA flagship missions JWST and WFIRST, as well as the
upcoming TESS mission, and it will complement ground-based observations by LSST
and the new large telescopes of the next decade. This scientific program
addresses NASA's Science Mission Directive's objectives in astrophysics, which
include discovering how the universe works, exploring how it began and evolved,
and searching for life on planets around other stars.Comment: 75 pages. See page 3 for Table of Contents and page 4 for Executive
Summar
Properties and Evolution of the Redback Millisecond Pulsar Binary PSR J2129-0429
PSR J2129−0429 is a "redback" eclipsing millisecond pulsar binary with an unusually long 15.2 hr orbit. It was discovered by the Green Bank Telescope in a targeted search of unidentified Fermi gamma-ray sources. The pulsar companion is optically bright (mean m_R = 16.6 mag), allowing us to construct the longest baseline photometric data set available for such a system. We present 10 years of archival and new photometry of the companion from the Lincoln Near-Earth Asteroid Research Survey, the Catalina Real-time Transient Survey, the Palomar Transient Factory, the Palomar 60 inch, and the Las Cumbres Observatory Global Telescope. Radial velocity spectroscopy using the Double-Beam Spectrograph on the Palomar 200 inch indicates that the pulsar is massive: 1.74 ± 0.18 M_☉. The G-type pulsar companion has mass 0.44 ± 0.04 M_☉, one of the heaviest known redback companions. It is currently 95 ± 1% Roche-lobe filling and only mildly irradiated by the pulsar. We identify a clear 13.1 mmag yr^(−1) secular decline in the mean magnitude of the companion as well as smaller-scale variations in the optical light curve shape. This behavior may indicate that the companion is cooling. Binary evolution calculations indicate that PSR J2129−0429 has an orbital period almost exactly at the bifurcation period between systems that converge into tighter orbits as black widows and redbacks and those that diverge into wider pulsar–white dwarf binaries. Its eventual fate may depend on whether it undergoes future episodes of mass transfer and increased irradiation
Gene Activation Using FLP Recombinase in C. elegans
The FLP enzyme catalyzes recombination between specific target sequences in DNA. Here we use FLP to temporally and spatially control gene expression in the nematode C. elegans. Transcription is blocked by the presence of an “off cassette” between the promoter and the coding region of the desired product. The “off cassette” is composed of a transcriptional terminator flanked by FLP recognition targets (FRT). This sequence can be excised by FLP recombinase to bring together the promoter and the coding region. We have introduced two fluorescent reporters into the system: a red reporter for promoter activity prior to FLP expression and a green reporter for expression of the gene of interest after FLP expression. The constructs are designed using the multisite Gateway system, so that promoters and coding regions can be quickly mixed and matched. We demonstrate that heat-shock-driven FLP recombinase adds temporal control on top of tissue specific expression provided by the transgene promoter. In addition, the temporal switch is permanent, rather than acute, as is usually the case for heat-shock driven transgenes. Finally, FLP expression can be driven by a tissue specific promoter to provide expression in a subset of cells that can only be addressed as the intersection of two available promoters. As a test of the system, we have driven the light chain of tetanus toxin, a protease that cleaves the synaptic vesicle protein synaptobrevin. We show that we can use this to inactivate synaptic transmission in all neurons or a subset of neurons in a FLP-dependent manner
- …