1,713 research outputs found
Probing the Stellar Surface of HD 209458 from Multicolor Transit Observations
Multicolor photometric observations of a planetary transit in the system HD
209458 are analyzed. The observations, made in the Stromgren photometric
system, allowed a recalculation of the basic physical properties of the
star-planet system. This includes derivation of linear limb-darkening values of
HD 209458, which is the first time that a limb-darkening sequence has
observationally been determined for a star other than the Sun. As the derived
physical properties depend on assumptions that are currently known with limited
precision only, scaling relations between derived parameters and assumptions
are given. The observed limb-darkening is in good agreement with theoretical
predictions from evolutionary stellar models combined with ATLAS model
atmospheres, verifying these models for the temperature (Teff ~ 6000K), surface
gravity (log g ~ 4.3) and mass (~ 1.2 Msol) of HD 209458.Comment: 16 pages, 8 figures, uses elsart.cls, accepted for New Astronom
Non-grey dimming events of KIC 8462852 from GTC spectrophotometry
We report ground-based spectrophotometry of KIC 8462852, during its first
dimming events since the end of the Kepler mission. The dimmings show a clear
colour-signature, and are deeper in visual blue wavelengths than in red ones.
The flux loss' wavelength dependency can be described with an \AA ngstr\"om
absorption coefficient of , which is compatible with absorption by
optically thin dust with particle sizes on the order of 0.0015 to 0.15 m.
These particles would be smaller than is required to be resistant against
blow-out by radiation pressure when close to the star. During occultation
events, these particles must be replenished on time-scales of days. If dust is
indeed the source of KIC 8462852's dimming events, deeper dimming events should
show more neutral colours, as is expected from optically thick absorbers.Comment: 5 pages, accepted for A&A letter
Internationalization and Financial Federalism: The United States and Germany at the Crossroads?
In this article, the authors examine some effects of economic internationalization on state structures, especially in regard to the distribution of power and authority within federalist systems. Using an institutional rational choice model, they analyze changes in financial regulation and market structures in Germany and the United States. The focus is on the financial realm because of its high degree of internationalization and because, in both countries, financial markets and regulation have historically exhibited federalist traits. The findings indicate that internationalization has led to significant convergence in financial market structures and regulation across the two countries and that in each case this convergence has been accompanied by centralization of financial regulatory authority. Although both the German type of cooperative federalism and the U.S. model of competitive federalism proved to be vulnerable to the growing international pressures, the two countries took different paths of change that reflected differences in domestic institutions. Thus, the authors conclude that convergence is, and will likely remain, of a limited nature
A Prototype for the PASS Permanent All Sky Survey
A prototype system for the Permanent All Sky Survey (PASS) project is
presented. PASS is a continuous photometric survey of the entire celestial
sphere with a high temporal resolution. Its major objectives are the detection
of all giant-planet transits (with periods up to some weeks) across stars up to
mag 10.5, and to deliver continuously photometry that is useful for the study
of any variable stars. The prototype is based on CCD cameras with short focal
length optics on a fixed mount. A small dome to house it at Teide Observatory,
Tenerife, is currently being constructed. A placement at the antarctic Dome C
is also being considered. The prototype will be used for a feasibility study of
PASS, to define the best observing strategies, and to perform a detailed
characterization of the capabilities and scope of the survey. Afterwards, a
first partial sky surveying will be started with it. That first survey may be
able to detect transiting planets during its first few hundred hours of
operation. It will also deliver a data set around which software modules
dealing with the various scientific objectives of PASS will be developed. The
PASS project is still in its early phase and teams interested in specific
scientific objectives, in providing technical expertise, or in participating
with own observations are invited to collaborate.Comment: Accepted for Astronomische Nachrichten (special issue for 3rd Potsdam
Thinkshop 'Robotic Astronomy' in July 2004). 4 pages, 4 fig
A cool starspot or a second transiting planet in the TrES-1 system?
We investigate the origin of a flux increase found during a transit of
TrES-1, observed with the HST. This feature in the HST light curve cannot be
attributed to noise and is supposedly a dark area on the stellar surface of the
host star eclipsed by TrES-1 during its transit. We investigate the likeliness
of two possible hypothesis for its origin: A starspot or a second transiting
planet. We made use of several transit observations of TrES-1 from space with
the HST and from ground with the IAC-80 telescope. On the basis of these
observations we did a statistical study of flux variations in each of the
observed events, to investigate if similar flux increases are present in other
parts of the data set. The HST observation presents a single clear flux rise
during a transit whereas the ground observations led to the detection of two
such events but with low significance. In the case of having observed a
starspot in the HST data, assuming a central impact between the spot and
TrES-1, we would obtain a lower limit for the spot radius of 42000 km. For this
radius the spot temperature would be 4690 K, 560 K lower then the stellar
surface of 5250 K. For a putative second transiting planet we can set a lower
limit for its radius at 0.37 R and for periods of less than 10.5 days, we
can set an upper limit at 0.72 R. Assuming a conventional interpretation,
then this HST observation constitutes the detection of a starspot.
Alternatively, this flux rise might also be caused by an additional transiting
planet. The true nature of the origin can be revealed if a wavelength
dependency of the flux rise can be shown or discarded with a higher certainty.
Additionally, the presence of a second planet can also be detected by radial
velocity measurements.Comment: 8 pages, 6 figures, accepted for publication in A&
Catena: Collaboration, Cohesion and Continuity in Design Thinking and Making
In the interests of enhanced collaborative methods of design thinking, design communication,
representation and rapid ideation, this article examines how a series of related activities and events,
‘catenated’ together, or forming a ‘catena’1 of design thinking, could create a clearer, more meaningful
and more efficient portfolio of work for a beginning design studio. Drawing inspiration upon the
operative verbs found in the work of sculptor Richard Serra,2 and using the artefacts from such activities
to create generative design products and iterations across a semester schedule, this paper chronicles a
series of active in-class collaborations over the course of a semester that allowed a cohort of students
to connect a series of design projects together, rather than experience a series of unconnected learning
objectives as was typical. References to learning theories including Jerome Bruner’s spiral curriculum
and David Kolb’s theory of experiential learning3 informed the inquiry. Student feedback and reflection
informed the areas of success and areas of improvement
Cost-effectiveness of etanercept in patients with severe ankylosing spondylitis in Germany
Objectives. To estimate the cost-effectiveness of etanercept (ETN) plus usual care (including NSAIDs) compared with usual care alone (including NSAIDs) in patients with severe AS in Germany. Methods. A mathematical model previously applied to the UK was adapted using resource use and cost data (for 2007) from the national database of the German Collaborative Arthritis Centres. Social health insurance (SHI) and societal perspectives were analysed. Assumptions on initial response and changes in health-related quality of life were based on Phase III randomized controlled trials. Initial treatment response according to British Society for Rheumatology guidelines were assumed as a conservative estimate in the German context. Long-term disease progression was based on the available literature. Incremental cost-effectiveness ratios (ICERs) were expressed as euros/quality-adjusted life year (QALY), for a cohort of 1000 patients over 25 years. Sensitivity analyses explored uncertainty in results. Results. In the base case, ETN plus usual care (including NSAIDs) yielded 1475 more QALYs at an additional cost of €80 827 668 (SHI) or €32 657 590 (societal) leading to an ICER of €54 815/QALY and €22 147/QALY, respectively. Over a shorter time horizon of 10 years, the ICERs were €59 006 and €29 815 for SHI and societal viewpoints, respectively. Assumptions having the largest impact on results included withdrawal rates from ETN, quality of life, disease costs and initial response. Conclusions. Cost-effectiveness for ETN in patients with severe AS in Germany differs according to the cost perspective. Study estimates were higher than in the UK but comparable with reported cost-effectiveness of anti-TNF treatments in patients with RA in German
TRUFAS, a wavelet based algorithm for the rapid detection of planetary transits
Aims: We describe a fast, robust and automatic detection algorithm, TRUFAS,
and apply it to data that are being expected from the CoRoT mission. Methods:
The procedure proposed for the detection of planetary transits in light curves
works in two steps: 1) a continuous wavelet transformation of the detrended
light curve with posterior selection of the optimum scale for transit
detection, and 2) a period search in that selected wavelet transformation. The
detrending of the light curves are based on Fourier filtering or a discrete
wavelet transformation. TRUFAS requires the presence of at least 3 transit
events in the data. Results: The proposed algorithm is shown to identify
reliably and quickly the transits that had been included in a standard set of
999 light curves that simulate CoRoT data. Variations in the pre-processing of
the light curves and in the selection of the scale of the wavelet transform
have only little effect on TRUFAS' results. Conclusions: TRUFAS is a robust and
quick transit detection algorithm, especially well suited for the analysis of
very large volumes of data from space or ground-based experiments, with long
enough durations for the target-planets to produce multiple transit events.Comment: 9 pages, 10 figures, accepted by A&
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