52,437 research outputs found
The young, active binary star EK Draconis
EK Dra (HD 129333) is a young, active, nearby star that is orbited by a low
mass companion. By combining new speckle observations with old and new radial
velocity measurements we find that the orbit is highly eccentric with
e=0.82\pm0.03, and we derive the true masses of both components. The masses are
and , for the primary and
secondary, respectively. From high resolution spectra we derive a new of K, and a of , which is different to
previous estimates. However, the new spectroscopic distance differs by only
5.8% to the distance derived by parallax measurement of the Hipparcos satellite
and thus the stellar parameters are presumably more realistic than older
determinations. We derive a somewhat higher value for the metallicity of
. EK Dra turns out to be one of the few nearby young stars
which will evolve similar to the sun. The precise radial velocity measurements
taken in the course of this program also allows us to shed more light on to the
activity of this star. In 2001 and 2002 we find a periodic signal of the radial
velocity variations with a period of days which we interpret as
the rotation period. This signal vanishes in 2003. However the signal can be
recovered if only the spectra in which the photospheric lines are asymmetric
are used. On the other hand, we do not find a close correlation between the
asymmetry of photospheric lines and the radial velocity.Comment: 10 pages, 11 figures, accepted by A&
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âUnfairâ Discrimination in Two-sided Peering? Evidence from LINX
âUnfairâ Discrimination in Two-sided Peering? Evidence from LINX
Abstract: Does asymmetry between Internet Providers affect the âfairnessâ of their interconnection contracts?
While recent game theoretic literature provides contrasting answers to this question, there is a lack of empirical research.
We introduce a novel dataset on micro-interconnection policies and provide an econometric analysis of the determinants
of peering decisions amongst the Internet Service Providers interconnecting at the London Internet Exchange Point (LINX).
Our key result shows that two different metrics, introduced to capture asymmetry, exert opposite effects. Asymmetry in
âmarket sizeâ enhances the quality of the link, while asymmetry in ânetwork centralityâ induces quality degradation, hence
âunfairerâ interconnection conditions
Beyond Caustic Crossings: Properties of Binary Microlensing Light Curves
Binary microlensing light curves have a variety of morphologies. Many are
indistinguishable from point lens light curves. Of those that deviate from the
point lens form, caustic crossing light curves have tended to dominate
identified binary lens events. Other distinctive signatures of binary lenses
include significant asymmetry, multiple peaks, and repeating events. We have
quantified, using high resolution simulations, the theoretically expected
relative numbers of each type of binary lens event, based on its measurable
characteristics. We find that a microlensing survey with current levels of
photometric uncertainty and sampling should find at least as many non-caustic
crossing binary lens events as caustic crossing events; in future surveys with
more sensitive photometry, the contribution of distinctive non-caustic crossing
events will be even greater. To try to explain why caustic crossing light
curves appear to be so dominant among the published binary lensing events, we
investigate the influence of several physical effects, including blending,
sampling rate, and various binary populations.Comment: 17 pages, 17 figures, submitted to Ap
PASTIS: Bayesian extrasolar planet validation II. Constraining exoplanet blend scenarios using spectroscopic diagnoses
The statistical validation of transiting exoplanets proved to be an efficient
technique to secure the nature of small exoplanet signals which cannot be
established by purely spectroscopic means. However, the spectroscopic diagnoses
are providing us with useful constraints on the presence of blended stellar
contaminants. In this paper, we present how a contaminating star affects the
measurements of the various spectroscopic diagnoses as function of the
parameters of the target and contaminating stars using the model implemented
into the PASTIS planet-validation software. We find particular cases for which
a blend might produce a large radial velocity signal but no bisector variation.
It might also produce a bisector variation anti-correlated with the radial
velocity one, as in the case of stellar spots. In those cases, the full width
half maximum variation provides complementary constraints. These results can be
used to constrain blend scenarios for transiting planet candidates or radial
velocity planets. We review all the spectroscopic diagnoses reported in the
literature so far, especially the ones to monitor the line asymmetry. We
estimate their uncertainty and compare their sensitivity to blends. Based on
that, we recommend the use of BiGauss which is the most sensitive diagnosis to
monitor line-profile asymmetry. In this paper, we also investigate the
sensitivity of the radial velocities to constrain blend scenarios and develop a
formalism to estimate the level of dilution of a blended signal. Finally, we
apply our blend model to re-analyse the spectroscopic diagnoses of HD16702, an
unresolved face-on binary which exhibits bisector variations.Comment: Accepted for publication in MNRA
Understanding confounding effects in linguistic coordination: an information-theoretic approach
We suggest an information-theoretic approach for measuring stylistic
coordination in dialogues. The proposed measure has a simple predictive
interpretation and can account for various confounding factors through proper
conditioning. We revisit some of the previous studies that reported strong
signatures of stylistic accommodation, and find that a significant part of the
observed coordination can be attributed to a simple confounding effect - length
coordination. Specifically, longer utterances tend to be followed by longer
responses, which gives rise to spurious correlations in the other stylistic
features. We propose a test to distinguish correlations in length due to
contextual factors (topic of conversation, user verbosity, etc.) and
turn-by-turn coordination. We also suggest a test to identify whether stylistic
coordination persists even after accounting for length coordination and
contextual factors
Eclipsing Light-Curve Asymmetry for Black-Hole Accretion Flows
We propose an eclipsing light-curve diagnosis for black-hole accretion flows.
When emission from an inner accretion disk around a black hole is occulted by a
companion star, the observed light curve becomes asymmetric at ingress and
egress on a time scale of 0.1-1 seconds. This light-curve analysis provides a
means of verifying the relativistic properties of the accretion flow, based on
the special/general relativistic effects of black holes. The ``skewness'' for
the eclipsing light curve of a thin disk is , whereas that of a slim
disk is , since the innermost part is self-occulted by the disk's outer
rim.Comment: 7 pages, 4 figures, PASJ accepte
Post-Mortem Examination of the International Financial Network
As the recent crisis has forcefully suggested, understanding financial-market interconnectedness is of a paramount importance to explain systemic risk, stability and economic dynamics. In this paper, we address these issues along two related perspectives. First, we explore the statistical properties of the International Financial Network (IFN), defined as the weighted-directed multigraph where nodes are world countries and links represent debtor-creditor relationships in equities and short/long-run debt. We investigate whether the 2008 financial crisis has resulted in a significant change in the topological properties of the IFN. Our findings suggest that the crisis caused not only a reduction in the amount of securities traded, but also induced changes in the topology of the network and in the time evolution of its statistical properties. This has happened, however, without changing the disassortative, core-periphery structure of the IFN architecture. Second, we perform an econometric study to examine the ability of network-based measures to explain cross-country differences in crisis intensity. We investigate whether the conclusion of previous studies showing that international connectedness is not a relevant predictor of crisis intensity may be reversed, once one explicitly accounts for the position of each country within the IFN. We show that higher interconnectedness reduces the severity of the crisis, as it allows adverse shocks to dissipate quicker. However, the systemic risk hypothesis cannot be completely dismissed and being central in the network, if the node is not a member of a rich club, puts the country in an adverse and risky position in times of crises. Finally, we find strong evidence of nonlinear effects, once the high degree of heterogeneity that characterizes the IFN is taken into account.financial networks, crisis, early warning systems
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