1,282 research outputs found
Circadian patterns of Wikipedia editorial activity: A demographic analysis
Wikipedia (WP) as a collaborative, dynamical system of humans is an
appropriate subject of social studies. Each single action of the members of
this society, i.e. editors, is well recorded and accessible. Using the
cumulative data of 34 Wikipedias in different languages, we try to characterize
and find the universalities and differences in temporal activity patterns of
editors. Based on this data, we estimate the geographical distribution of
editors for each WP in the globe. Furthermore we also clarify the differences
among different groups of WPs, which originate in the variance of cultural and
social features of the communities of editors
Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
We analyze the data of the gravitational microlensing survey carried out by
by the MOA group during 2000 towards the Galactic Bulge (GB). Our observations
are designed to detect efficiently high magnification events with faint source
stars and short timescale events, by increasing the the sampling rate up to 6
times per night and using Difference Image Analysis (DIA). We detect 28
microlensing candidates in 12 GB fields corresponding to 16 deg^2. We use Monte
Carlo simulations to estimate our microlensing event detection efficiency,
where we construct the I-band extinction map of our GB fields in order to find
dereddened magnitudes. We find a systematic bias and large uncertainty in the
measured value of the timescale in our simulations. They are
associated with blending and unresolved sources, and are allowed for in our
measurements. We compute an optical depth tau = 2.59_{-0.64}^{+0.84} \times
10^{-6} towards the GB for events with timescales 0.3<t_E<200 days. We consider
disk-disk lensing, and obtain an optical depth tau_{bulge} =
3.36_{-0.81}^{+1.11} \times 10^{-6}[0.77/(1-f_{disk})] for the bulge component
assuming a 23% stellar contribution from disk stars. These observed optical
depths are consistent with previous measurements by the MACHO and OGLE groups,
and still higher than those predicted by existing Galactic models. We present
the timescale distribution of the observed events, and find there are no
significant short events of a few days, in spite of our high detection
efficiency for short timescale events down to t_E = 0.3 days. We find that half
of all our detected events have high magnification (>10). These events are
useful for studies of extra-solar planets.Comment: 65 pages and 30 figures, accepted for publication in ApJ. A
systematic bias and uncertainty in the optical depth measurement has been
quantified by simulation
MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging
We report the discovery of a microlensing planetâMOA-2016-BLG-227Lbâwith a large planet/host mass ratio of q â 9 Ă 10â3. This event was located near the K2 Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light-curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light-curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar-type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lensâsource relative proper motion
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