2,163 research outputs found
Data calibration for the MASCARA and bRing instruments
Aims: MASCARA and bRing are photometric surveys designed to detect
variability caused by exoplanets in stars with . Such variability
signals are typically small and require an accurate calibration algorithm,
tailored to the survey, in order to be detected. This paper presents the
methods developed to calibrate the raw photometry of the MASCARA and bRing
stations and characterizes the performance of the methods and instruments.
Methods: For the primary calibration a modified version of the coarse
decorrelation algorithm is used, which corrects for the extinction due to the
earth's atmosphere, the camera transmission, and intrapixel variations.
Residual trends are removed from the light curves of individual stars using
empirical secondary calibration methods. In order to optimize these methods, as
well as characterize the performance of the instruments, transit signals were
injected in the data. Results: After optimal calibration an RMS scatter of 10
mmag at is achieved in the light curves. By injecting transit
signals with periods between one and five days in the MASCARA data obtained by
the La Palma station over the course of one year, we demonstrate that MASCARA
La Palma is able to recover 84.0, 60.5 and 20.7% of signals with depths of 2, 1
and 0.5% respectively, with a strong dependency on the observed declination,
recovering 65.4% of all transit signals at versus 35.8% at
. Using the full three years of data obtained by MASCARA La
Palma to date, similar recovery rates are extended to periods up to ten days.
We derive a preliminary occurrence rate for hot Jupiters around A-stars of , knowing that many hot Jupiters are still overlooked. In the era of
TESS, MASCARA and bRing will provide an interesting synergy for finding
long-period ( days) transiting gas-giant planets around the brightest
stars.Comment: 18 pages, 17 figures, accepted for publication in A&
Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: NGC 628 and NGC 6946
We characterize the dust in NGC628 and NGC6946, two nearby spiral galaxies in
the KINGFISH sample. With data from 3.6um to 500um, dust models are strongly
constrained. Using the Draine & Li (2007) dust model, (amorphous silicate and
carbonaceous grains), for each pixel in each galaxy we estimate (1) dust mass
surface density, (2) dust mass fraction contributed by polycyclic aromatic
hydrocarbons (PAH)s, (3) distribution of starlight intensities heating the
dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR
luminosity originating in regions with high starlight intensity. We obtain maps
for the dust properties, which trace the spiral structure of the galaxies. The
dust models successfully reproduce the observed global and resolved spectral
energy distributions (SEDs). The overall dust/H mass ratio is estimated to be
0.0082+/-0.0017 for NGC628, and 0.0063+/-0.0009 for NGC6946, consistent with
what is expected for galaxies of near-solar metallicity. Our derived dust
masses are larger (by up to a factor 3) than estimates based on
single-temperature modified blackbody fits. We show that the SED fits are
significantly improved if the starlight intensity distribution includes a
(single intensity) "delta function" component. We find no evidence for
significant masses of cold dust T<12K. Discrepancies between PACS and MIPS
photometry in both low and high surface brightness areas result in large
uncertainties when the modeling is done at PACS resolutions, in which case
SPIRE, MIPS70 and MIPS160 data cannot be used. We recommend against attempting
to model dust at the angular resolution of PACS.Comment: To be published in Apj, September 2012. See the full version at
http://www.astro.princeton.edu/~ganiano/Papers
Measuring Light Pollution with Fisheye Lens Imagery from A Moving Boat, A Proof of Concept
Near all-sky imaging photometry was performed from a boat on the Gulf of
Aqaba to measure the night sky brightness in a coastal environment. The boat
was not anchored, and therefore drifted and rocked. The camera was mounted on a
tripod without any inertia/motion stabilization. A commercial digital single
lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400,
with the exposure time varied between 0.5 s and 5 s. We find that despite
movement of the vessel the measurements produce quantitatively comparable
results apart from saturation effects. We discuss the potential and limitations
of this method for mapping light pollution in marine and freshwater systems.
This work represents the proof of concept that all-sky photometry with a
commercial DSLR camera is a viable tool to determine light pollution in an
ecological context from a moving boat.Comment: 9 pages, 6 figures, accepted at International Journal of Sustainable
Lightin
Optical identification of X-ray source 1RXS J180431.1-273932 as a magnetic cataclysmic variable
The X-ray source 1RXS J180431.1-273932 has been proposed as a new member of
the symbiotic X-ray binary (SyXB) class of systems, which are composed of a
late-type giant that loses matter to an extremely compact object, most likely a
neutron star. In this paper, we present an optical campaign of imaging plus
spectroscopy on selected candidate counterparts of this object. We also
reanalyzed the available archival X-ray data collected with XMM-Newton. We find
that the brightest optical source inside the 90% X-ray positional error circle
is spectroscopically identified as a magnetic cataclysmic variable (CV), most
likely of intermediate polar type, through the detection of prominent Balmer,
He I, He II, and Bowen blend emissions. On either spectroscopic or statistical
grounds, we discard as counterparts of the X-ray source the other optical
objects in the XMM-Newton error circle. A red giant star of spectral type M5
III is found lying just outside the X-ray position: we consider this latter
object as a fore-/background one and likewise rule it out as a counterpart of
1RXS J180431.1-273932. The description of the X-ray spectrum of the source
using a bremsstrahlung plus black-body model gives temperatures of around 40
keV and around 0.1 keV for these two components, respectively. We estimate a
distance of about 450 pc and a 0.2-10 keV X-ray luminosity of about 1.7e32
erg/s for this system and, using the information obtained from the X-ray
spectral analysis, a mass of about 0.8 solar masses for the accreting white
dwarf (WD). We also confirm an X-ray periodicity of 494 s for this source,
which we interpret as the spin period of the WD. In summary, 1RXS
J180431.1-273932 is identified as a magnetic CV and its SyXB nature is
excluded.Comment: 9 pages, 7 figures, 3 tables, accepted for publication on Astronomy &
Astrophysics, main journal. Version 2 includes the A&A Language Editor's
correction
A search for Earth-crossing asteroids, supplement
The ground based electro-optical deep space surveillance program involves a network of computer controlled 40 inch 1m telescopes equipped with large format, low light level, television cameras of the intensified silicon diode array type which is to replace the Baker-Nunn photographic camera system for artificial satellite tracking. A prototype observatory was constructed where distant artificial satellites are discriminated from stars in real time on the basis of the satellites' proper motion. Hardware was modified and the technique was used to observe and search for minor planets. Asteroids are now routinely observed and searched. The complete observing cycle, including the 2"-3" measurement of position, requires about four minutes at present. The commonality of asteroids and artificial satellite observing, searching, data reduction, and orbital analysis is stressed. Improvements to the hardware and software as well as operational techniques are considered
Vision technology/algorithms for space robotics applications
The thrust of automation and robotics for space applications has been proposed for increased productivity, improved reliability, increased flexibility, higher safety, and for the performance of automating time-consuming tasks, increasing productivity/performance of crew-accomplished tasks, and performing tasks beyond the capability of the crew. This paper provides a review of efforts currently in progress in the area of robotic vision. Both systems and algorithms are discussed. The evolution of future vision/sensing is projected to include the fusion of multisensors ranging from microwave to optical with multimode capability to include position, attitude, recognition, and motion parameters. The key feature of the overall system design will be small size and weight, fast signal processing, robust algorithms, and accurate parameter determination. These aspects of vision/sensing are also discussed
VLT Suzaku observations of the Fermi pulsar PSR J1028-5819
We used optical images taken with the Very Large Telescope (VLT) in the B and
V bands to search for the optical counterpart of PSR J1028-5819 or constrain
its optical brightness. At the same time, we used an archival Suzaku
observation to confirm the preliminary identification of the pulsar's X-ray
counterpart obtained by Swift. Due to the large uncertainty on the pulsar's
radio position and the presence of a bright (V = 13.2) early F-type star at <
4", we could not detect its counterpart down to flux limits of B~25.4 and V
~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku
observations, we found that the X-ray spectrum of the pulsar's candidate
counterpart is best-fit by a power-law with spectral index 1.7 +/- 0.2 and an
absorption column density NH < 10^21 cm-2, which would support the proposed
X-ray identification. Moreover, we found possible evidence for the presence of
diffuse emission around the pulsar. If real, and associated with a pulsar wind
nebula (PWN), its surface brightness and angular extent would be compatible
with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
Multiple View Geometry For Video Analysis And Post-production
Multiple view geometry is the foundation of an important class of computer vision techniques for simultaneous recovery of camera motion and scene structure from a set of images. There are numerous important applications in this area. Examples include video post-production, scene reconstruction, registration, surveillance, tracking, and segmentation. In video post-production, which is the topic being addressed in this dissertation, computer analysis of the motion of the camera can replace the currently used manual methods for correctly aligning an artificially inserted object in a scene. However, existing single view methods typically require multiple vanishing points, and therefore would fail when only one vanishing point is available. In addition, current multiple view techniques, making use of either epipolar geometry or trifocal tensor, do not exploit fully the properties of constant or known camera motion. Finally, there does not exist a general solution to the problem of synchronization of N video sequences of distinct general scenes captured by cameras undergoing similar ego-motions, which is the necessary step for video post-production among different input videos. This dissertation proposes several advancements that overcome these limitations. These advancements are used to develop an efficient framework for video analysis and post-production in multiple cameras. In the first part of the dissertation, the novel inter-image constraints are introduced that are particularly useful for scenes where minimal information is available. This result extends the current state-of-the-art in single view geometry techniques to situations where only one vanishing point is available. The property of constant or known camera motion is also described in this dissertation for applications such as calibration of a network of cameras in video surveillance systems, and Euclidean reconstruction from turn-table image sequences in the presence of zoom and focus. We then propose a new framework for the estimation and alignment of camera motions, including both simple (panning, tracking and zooming) and complex (e.g. hand-held) camera motions. Accuracy of these results is demonstrated by applying our approach to video post-production applications such as video cut-and-paste and shadow synthesis. As realistic image-based rendering problems, these applications require extreme accuracy in the estimation of camera geometry, the position and the orientation of the light source, and the photometric properties of the resulting cast shadows. In each case, the theoretical results are fully supported and illustrated by both numerical simulations and thorough experimentation on real data
Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO
High-precision astrometry requires accurate point-spread function modeling
and accurate geometric-distortion corrections. This paper demonstrates that it
is possible to achieve both requirements with data collected at the high acuity
wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth
focus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3
mas per coordinate for a well-exposed star in a single image with a systematic
error less than 0.1 mas. We constructed calibrated astro-photometric catalogs
and atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,
NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in the
Large Magellanic Cloud. We make these catalogs and images electronically
available to the community. Furthermore, as a demonstration of the efficacy of
our approach, we combined archival material taken with the optical wide-field
imager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are able
to achieve an excellent separation between cluster members and field objects
for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both
HST and HAWK-I data, we also study the radial distribution of the SGB
populations in NGC 6656 and conclude that the radial trend is flat within our
uncertainty. We also provide membership probabilities for most of the stars in
NGC 6656 and NGC 6121 catalogs and estimate membership for the published
variable stars in these two fields.Comment: 36 pages (included appendix), 13 tables, 35 figures (26 in low
resolution), accepted for publication in Astronomy and Astrophysics. Online
materials will be soon available on CDS. Meanwhile, online materials can be
requested directly to the first autho
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