211 research outputs found
Assessing Sustainability at Farm Level using RISE Tool: Results from Armenia
Environmental Economics and Policy, Farm Management,
High-contrast Imaging with Spitzer: Deep Observations of Vega, Fomalhaut, and epsilon Eridani
Stars with debris disks are intriguing targets for direct imaging exoplanet
searches, both due to previous detections of wide planets in debris disk
systems, as well as commonly existing morphological features in the disks
themselves that may be indicative of a planetary influence. Here we present
observations of three of the most nearby young stars, that are also known to
host massive debris disks: Vega, Fomalhaut, and eps Eri. The Spitzer Space
Telescope is used at a range of orientation angles for each star, in order to
supply a deep contrast through angular differential imaging combined with
high-contrast algorithms. The observations provide the opportunity to probe
substantially colder bound planets (120--330 K) than is possible with any other
technique or instrument. For Vega, some apparently very red candidate point
sources detected in the 4.5 micron image remain to be tested for common proper
motion. The images are sensitive to ~2 Mjup companions at 150 AU in this
system. The observations presented here represent the first search for planets
around Vega using Spitzer. The upper 4.5 micron flux limit on Fomalhaut b could
be further constrained relative to previous data. In the case of eps Eri,
planets below both the effective temperature and the mass of Jupiter could be
probed from 80 AU and outwards, although no such planets were found. The data
sensitively probe the regions around the edges of the debris rings in the
systems where planets can be expected to reside. These observations validate
previous results showing that more than an order of magnitude improvement in
performance in the contrast-limited regime can be acquired with respect to
conventional methods by applying sophisticated high-contrast techniques to
space-based telescopes, thanks to the high degree of PSF stability provided in
this environment.Comment: 11 pages, 12 figures, accepted for publication in A&
SPOTS: The Search for Planets Orbiting Two Stars: II. First constraints on the frequency of sub-stellar companions on wide circumbinary orbits
A large number of direct imaging surveys for exoplanets have been performed
in recent years, yielding the first directly imaged planets and providing
constraints on the prevalence and distribution of wide planetary systems.
However, like most of the radial velocity ones, these surveys generally focus
on single stars, hence binaries and higher-order multiples have not been
studied to the same level of scrutiny. This motivated the SPOTS (Search for
Planets Orbiting Two Stars) survey, which is an ongoing direct imaging study of
a large sample of close binaries, started with VLT/NACO and now continuing with
VLT/SPHERE. To complement this survey, we have identified the close binary
targets in 24 published direct imaging surveys. Here we present our statistical
analysis of this combined body of data. We analysed a sample of 117 tight
binary systems, using a combined Monte Carlo and Bayesian approach to derive
the expected values of the frequency of companions, for different values of the
companion's semi-major axis. Our analysis suggest that the frequency of
sub-stellar companions in wide orbit is moderately low (13% with a
best value of 6% at 95% confidence level) and not significantly different
between single stars and tight binaries. One implication of this result is that
the very high frequency of circumbinary planets in wide orbits around
post-common envelope binaries, implied by eclipse timing (up to 90% according
to Zorotovic & Schreiber 2013), can not be uniquely due to planets formed
before the common-envelope phase (first generation planets), supporting instead
the second generation planet formation or a non-Keplerian origin of the timing
variations.Comment: 21 pages, 3 figure
A dual-mask coronagraph for observing faint companions to binary stars
Observations of binary stars for faint companions with conventional
coronagraphic methods are challenging, as both targets will be bright enough to
obscure any nearby faint companions if their scattered light is not suppressed.
We propose coronagraphic examination of binary stars using an apodized pupil
Lyot coronagraph and a pair of actively-controlled image plane masks to
suppress both stars simultaneously. The performance is compared to imaging with
a band-limited mask, a dual-mask Lyot coronagraph and with no coronagraph at
all. An imaging procedure and control system for the masks are also described.Comment: 17 pages, 6 figure
Effects of defoliation by horse chestnut leafminer ( Cameraria ohridella ) on reproduction in Aesculus hippocastanum
In large parts of Europe horse chestnut trees (Aesculus hippocastanum) suffer from severe defoliation by an alien invasive species, the specialist leaf mining moth Cameraria ohridella (Lepidoptera; Gracillariidae). Heavily infested trees have a drastically shortened period for photosynthesis. We quantified the effect of moth infestation on reproduction of horse chestnut trees in two different cities in central Europe, Bern and Munich. C. ohridella negatively affected seed and fruit weight of A. hippocastanum at both locations. In Munich, seed weight of heavily damaged trees was reduced by almost half. However, the number of seeds per fruit, the number of fruits per inflorescence, and the number of inflorescences per tree did not change due to herbivory. We conclude that C. ohridella mining affects seed quality but not seed quantity. The reduced seed weight may severely impair growth and survival of horse chestnut seedlings and thus may endanger the long-term persistence of A. hippocastanum in its endemic forests in south-east Europ
An Approach for Secure Data Transmission in a Distributed Production Environment
The exchange of data along the supply chain can be viewed as one of the key characteristics of advanced manufacturing concepts, frequently labeled as industry 4.0 . Intelligent products produced in shorter life cycles, increasing cost and quality pressures from global supply chains, increasingly complex regulatory requirements, as well as decreasing costs of advanced sensors are major drivers for this trend. Large amounts of data generated as a by-product of this trend represents an opportunity for advanced data analytics. However, the exchange of data across organizational boundaries bears also the risks of being in the focus of cyber-attacks. In this paper, we tackle the challenge of securing the data transfer in an Industry 4.0 environment. We first identify the security requirements within our use case. Based on these requirements, we present an approach for secure data transmission and discuss how our solution meets the identified requirements
Knowledge Protection for Digital Innovations: Integrating Six Perspectives
New ways of combining digital and physical innovations, as well as intensified inter-organizational collaborations, create new challenges to the protection of organizational knowledge. Existing research on knowledge protection is at an early stage and scattered among various research domains. This research-in-progress paper presents a plan for a structured literature review on knowledge protection, integrating the perspectives of the six base domains of knowledge, strategic, risk, intellectual property rights, innovation, and information technology security management. We define knowledge protection as a set of capabilities comprising and enforcing technical, organizational, and legal mechanisms to protect tacit and explicit knowledge necessary to generate or adopt innovations
Reduction of polarimetric data using Mueller calculus applied to Nasmyth instruments
We present a method based on Mueller calculus to calibrate linear
polarimetric observations. The key advantages of the proposed way of
calibration are: (1) that it can be implemented in a data reduction pipeline,
(2) that it is possible to do accurate polarimetry also for
telescopes/instruments with polarimetric non-friendly architecture (e.g.
Nasmyth instruments) and (3) that the proposed strategy is much less time
consuming than standard calibration procedures. The telescope/instrument will
polarimetrically be described by a train of Mueller matrices. The components of
these matrices are dependent on wavelength, incident angle of the incoming
light and surface properties.Comment: 2 figure
On-sky speckle nulling demonstration at small angular separation with SCExAO
This paper presents the first on-sky demonstration of speckle nulling, which
was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic
Extreme Adaptive Optics (SCExAO) Project. Despite the absence of a high-order
high-bandwidth closed-loop AO system, observations conducted with SCExAO show
that even in poor-to-moderate observing conditions, speckle nulling can be used
to suppress static and slow speckles even in the presence of a brighter dynamic
speckle halo, suggesting that more advanced high-contrast imaging algorithms
developed in the laboratory can be applied to ground-based systems.Comment: 5 figures, accepted for publication by PAS
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