501 research outputs found
The Moon at thermal infrared wavelengths: A benchmark for asteroid thermal models
Thermal-infrared measurements of asteroids are crucial for deriving the
objects' sizes, albedos, and also the thermophysical properties of the surface
material. Depending on the available data, a range of simple to complex thermal
models are applied to achieve specific science goals. However, testing these
models is often a difficult process and the uncertainties of the derived
parameters are not easy to estimate. Here, we make an attempt to verify a
widely accepted thermophysical model (TPM) against unique thermal infrared
(IR), full-disk, and well-calibrated measurements of the Moon. The data were
obtained by the High-resolution InfraRed Sounder (HIRS) instruments on board a
fleet of Earth weather satellites that serendipitously scan over the Moon. We
found 22 Moon intrusions, taken in 19 channels between 3.75 micron and 15.0
micron, and over a wide phase angle range from -73.1 deg to +73.8 deg. The
similarity between these Moon data and typical asteroid spectral-IR energy
distributions allows us to benchmark the TPM concepts and to point out
problematic aspects. The TPM predictions match the HIRS measurements within 5%
(10% at the shortest wavelengths below 5 micron when using the Moon's known
properties (size, shape, spin, albedo, thermal inertia, roughness) in
combination with a newly established wavelength-dependent hemispherical
emissivity. In the 5-7.5 micron and in the 9.5 to 11 micron ranges, the global
emissivity model deviates considerably from the known lunar sample spectra. Our
findings will influence radiometric studies of near-Earth and main-belt
asteroids in cases where only short-wavelength data (from e.g., NEOWISE, the
warm Spitzer mission, or ground-based M-band measurements) are available. The
new, full-disk IR Moon model will also be used for the calibration of IR
instrumentation on interplanetary missions (e.g., for Hayabusa-2) and weather
satellites.Comment: 21 pages, 9 figures, 7 tables, accepted for publication in Astronomy
& Astrophysics in March 202
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Noise performance of microwave humidity sounders over their lifetime
The microwave humidity sounders Special Sensor Microwave Water Vapor Profiler (SSMT-2), Advanced Microwave Sounding Unit-B (AMSU-B) and Microwave Humidity Sounder (MHS) to date have been providing data records for 25 years. So far, the data records lack uncertainty information essential for constructing consistent long time data series. In this study, we assess the quality of the recorded data with respect to the uncertainty caused by noise. We calculate the noise on the raw calibration counts from the deep space views (DSVs) of the instrument and the noise equivalent differential temperature (NEΔT) as a measure for the radiometer sensitivity. For this purpose, we use the Allan deviation that is not biased from an underlying varying mean of the data and that has been suggested only recently for application in atmospheric remote sensing. Moreover, we use the bias function related to the Allan deviation to infer the underlying spectrum of the noise. As examples, we investigate the noise spectrum in flight for some instruments. For the assessment of the noise evolution in time, we provide a descriptive and graphical overview of the calculated NEΔT over the life span of each instrument and channel. This overview can serve as an easily accessible information for users interested in the noise performance of a specific instrument, channel and time. Within the time evolution of the noise, we identify periods of instrumental degradation, which manifest themselves in an increasing NEΔT, and periods of erratic behaviour, which show sudden increases of NEΔT interrupting the overall smooth evolution of the noise. From this assessment and subsequent exclusion of the aforementioned periods, we present a chart showing available data records with NEΔT < 1 K. Due to overlapping life spans of the instruments, these reduced data records still cover without gaps the time since 1994 and may therefore serve as a first step for constructing long time series. Our method for count noise estimation, that has been used in this study, will be used in the data processing to provide input values for the uncertainty propagation in the generation of a new set of Fundamental Climate Data Records (FCDRs) that are currently produced in the project Fidelity and Uncertainty in Climate data records from Earth Observation (FIDUCEO)
Inferring statistics of planet populations by means of automated microlensing searches
(abridged) The study of other worlds is key to understanding our own, and not
only provides clues to the origin of our civilization, but also looks into its
future. Rather than in identifying nearby systems and learning about their
individual properties, the main value of the technique of gravitational
microlensing is in obtaining the statistics of planetary populations within the
Milky Way and beyond. Only the complementarity of different techniques
currently employed promises to yield a complete picture of planet formation
that has sufficient predictive power to let us understand how habitable worlds
like ours evolve, and how abundant such systems are in the Universe. A
cooperative three-step strategy of survey, follow-up, and anomaly monitoring of
microlensing targets, realized by means of an automated expert system and a
network of ground-based telescopes is ready right now to be used to obtain a
first census of cool planets with masses reaching even below that of Earth
orbiting K and M dwarfs in two distinct stellar populations, namely the
Galactic bulge and disk. The hunt for extra-solar planets acts as a principal
science driver for time-domain astronomy with robotic-telescope networks
adopting fully-automated strategies. Several initiatives, both into facilities
as well as into advanced software and strategies, are supposed to see the
capabilities of gravitational microlensing programmes step-wise increasing over
the next 10 years. New opportunities will show up with high-precision
astrometry becoming available and studying the abundance of planets around
stars in neighbouring galaxies becoming possible. Finally, we should not miss
out on sharing the vision with the general public, and make its realization to
profit not only the scientists but all the wider society.Comment: 10 pages in PDF format. White paper submitted to ESA's Exo-Planet
Roadmap Advisory Team (EPR-AT); typos corrected. The embedded figures are
available from the author on request. See also "Towards A Census of
Earth-mass Exo-planets with Gravitational Microlensing" by J.P. Beaulieu, E.
Kerins, S. Mao et al. (arXiv:0808.0005
Dopaminergic modulation of affective and social deficits induced by prenatal glucocorticoid exposure
Prenatal stress or exposure to elevated levels of glucocorticoids (GCs) can impair specific neurobehavioral circuits leading to alterations in emotional processes later in life. In turn, emotional deficits may interfere with the quality and degree of social interaction. Here, by using a comprehensive behavioral approach in combination with the measurement of ultrasonic vocalizations, we show that in utero GC (iuGC)-exposed animals present increased immobility in the forced swimming test, pronounced anhedonic behavior (both anticipatory and consummatory), and an impairment in social interaction at different life stages. Importantly, we also found that social behavioral expression is highly dependent on the affective status of the partner. A profound reduction in mesolimbic dopaminergic transmission was found in iuGC animals, suggesting a key role for dopamine (DA) in the etiology of the observed behavioral deficits. Confirming this idea, we present evidence that a simple pharmacological approach—acute L-3,4-dihydroxyphenylacetic acid (L-DOPA) oral administration, is able to normalize DA levels in iuGC animals, with a concomitant amelioration of several dimensions of the emotional and social behaviors. Interestingly, L-DOPA effects in control individuals were not so straightforward; suggesting that both hypo- and hyperdopaminergia are detrimental in the context of such complex behaviors.This work was supported by a grant of Institute for the Study of Affective Neuroscience (ISAN) and Janssen Neurosciences Prize. SB and AJR have Fundacao para a Ciencia e Tecnologia (FCT) fellowships (SFRH/BD/89936/2012; SFRH/BPD/33611/2009)
Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope: Early Results on Mrk 1014, Mrk 463, and UGC 5101
We present spectra taken with the Infrared Spectrograph on Spitzer covering
the 5-38micron region of three Ultraluminous Infrared Galaxies (ULIRGs): Mrk
1014 (z=0.163), and Mrk 463 (z=0.051), and UGC 5101 (z=0.039). The continua of
UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant
optical depths to the nuclei at 10microns. UGC 5101 also shows the clear
presence of water ice in absorption. PAH emission features are seen in both Mrk
1014 and UGC 5101, including the 16.4micron line in UGC 5101. The fine
structure lines are consistent with dominant AGN power sources in both Mrk 1014
and Mrk 463. In UGC 5101 we detect the [NeV] 14.3micron emission line providing
the first direct evidence for a buried AGN in the mid-infrared. The detection
of the 9.66micron and 17.03micron H emission lines in both UGC 5101 and
Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the
total molecular gas masses in these galaxies.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 3 figure
ISOPHOT far-infrared serendipity sky survey
The ISOPHOT Serendipity Survey utilizes the slew time between ISO's pointed observations with strip scanning measurements of the sky in the far-IR at 170 micrometers . The slews contain information about two fundamentally different types of objects, namely unresolved galactic and extragalactic far-IR sources as well as extended regions of galactic cirrus emission. Since the structure of the obtained data is almost unique, the development of dedicated software to extract astrophysically interesting parameters for the crossed sources is mandatory. Data analysis is currently in its early stages and concentrates on the detection of point sources. First results from an investigation of a high galactic latitude field near the North Galactic Pole indicate that the detection completeness with respect to previously known IRAS sources will be almost 100 percent for sources with f(subscript 100micrometers > 2 Jy, dropping below approximately equals 50 percent for f(subscript 100micrometers < 1.5 Jy. Nevertheless, even faint sources down to a level of f(subscript 170micrometers approximately equals 1 Jy can be detected. Since the majority of the detected point sources are galaxies, the Serendipity Survey will result in a large database of approximately equals 2000 galaxies
RoboTAP: Target priorities for robotic microlensing observations
Context. The ability to automatically select scientifically-important transient events from an alert stream of many such events, and to conduct follow-up observations in response, will become increasingly important in astronomy. With wide-angle time domain surveys pushing to fainter limiting magnitudes, the capability to follow-up on transient alerts far exceeds our follow-up telescope resources, and effective target prioritization becomes essential. The RoboNet-II microlensing program is a pathfinder project, which has developed an automated target selection process (RoboTAP) for gravitational microlensing events, which are observed in real time using the Las Cumbres Observatory telescope network.
Aims. Follow-up telescopes typically have a much smaller field of view compared to surveys, therefore the most promising microlensing events must be automatically selected at any given time from an annual sample exceeding 2000 events. The main challenge is to select between events with a high planet detection sensitivity, with the aim of detecting many planets and characterizing planetary anomalies.
Methods. Our target selection algorithm is a hybrid system based on estimates of the planet detection zones around a microlens. It follows automatic anomaly alerts and respects the expected survey coverage of specific events.
Results. We introduce the RoboTAP algorithm, whose purpose is to select and prioritize microlensing events with high sensitivity to planetary companions. In this work, we determine the planet sensitivity of the RoboNet follow-up program and provide a working example of how a broker can be designed for a real-life transient science program conducting follow-up observations in response to alerts; we explore the issues that will confront similar programs being developed for the Large Synoptic Survey Telescope (LSST) and other time domain surveys
I. Flux and color variations of the quadruply imaged quasar HE 0435-1223
aims: We present VRi photometric observations of the quadruply imaged quasar
HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla
Observatory. Our aim was to monitor and study the magnitudes and colors of each
lensed component as a function of time. methods: We monitored the object during
two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data
with two independent techniques: difference imaging and PSF (Point Spread
Function) fitting.results: Between these two seasons, our results show an
evident decrease in flux by ~0.2-0.4 magnitudes of the four lensed components
in the three filters. We also found a significant increase (~0.05-0.015) in
their V-R and R-i color indices. conclusions: These flux and color variations
are very likely caused by intrinsic variations of the quasar between the
observed epochs. Microlensing effects probably also affect the brightest "A"
lensed component.Comment: 10 pages, 8 figure
The Transiting System GJ1214: High-Precision Defocused Transit Observations and a Search for Evidence of Transit Timing Variation
Aims: We present 11 high-precision photometric transit observations of the
transiting super-Earth planet GJ1214b. Combining these data with observations
from other authors, we investigate the ephemeris for possible signs of transit
timing variations (TTVs) using a Bayesian approach.
Methods: The observations were obtained using telescope-defocusing
techniques, and achieve a high precision with random errors in the photometry
as low as 1mmag per point. To investigate the possibility of TTVs in the light
curve, we calculate the overall probability of a TTV signal using Bayesian
methods.
Results: The observations are used to determine the photometric parameters
and the physical properties of the GJ1214 system. Our results are in good
agreement with published values. Individual times of mid-transit are measured
with uncertainties as low as 10s, allowing us to reduce the uncertainty in the
orbital period by a factor of two.
Conclusions: A Bayesian analysis reveals that it is highly improbable that
the observed transit times is explained by TTV, when compared with the simpler
alternative of a linear ephemeris.Comment: Submitted to A&
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