2,248 research outputs found
Possible Solution of the long-standing discrepancy in the Microlensing Optical Depth Toward the Galactic Bulge by correcting the stellar number count
We find that significant incompleteness in stellar number counts results in a
significant overestimate of the microlensing optical depth and event
rate per star per year toward the Galactic bulge from the first two
years of the MOA-II survey. We find that the completeness in Red Clump Giant
(RCG) counts decreases proportional to the galactic latitude ,
as , ranging between 1 and
0.7 at . The previous measurements using all sources
by Difference Image Analysis (DIA) by MACHO and MOA-I suffer the same bias. On
the other hand, the measurements using a RCG sample by OGLE-II, MACHO and EROS
were free from this bias because they selected only the events associated with
the resolved stars. Thus, the incompleteness both in the number of events and
stellar number count cancel out. We estimate and by correcting
this incompleteness. In the central fields with , we find
star
yr and
for the 427 events with days using all sources brighter
than mag. Our revised all-source measurements are about
2- smaller than the other all-source measurements and are consistent
with the RCG measurements within 1-. We conclude that the long-standing
problem on discrepancy between the high with all-source samples by DIA
and low with RCG samples can probably be explained by the incompleteness
of the stellar number count. A model fit to these measurements predicts
star yr at
and for sources with , where the future space
mission WFIRST will observe.Comment: 39 pages, 15 figures, 5 tables, accepted for publication in ApJ.
arXiv admin note: substantial text overlap with arXiv:1305.018
Measurements of streaming motions of the Galactic bar with Red Clump Giants
We report a measurement of the streaming motion of the stars in the Galactic
bar with the Red Clump Giants (RCGs) using the data of the Optical
Gravitational Lensing Experiment II (OGLE-II). We measure the proper motion of
46,961 stars and divide RCGs into bright and faint sub-samples which on average
will be closer to the near and far side of the bar, respectively. We find that
the far-side RCGs (4,979 stars) have a proper motion of \Delta ~ 1.5 +-
0.11 mas yr^{-1} toward the negative l relative to the near-side RCGs (3,610
stars). This result can be explained by stars in the bar rotating around the
Galactic center in the same direction as the Sun with v_b ~ 100 km s^{-1}. In
the Disc Star (DS) and Red Giant (RG) samples, we do not find significant
difference between bright and faint sub-samples. For those samples \Delta
\~ 0.3 +- 0.14 mas yr^{-1} and ~ 0.03 +- 0.14 mas yr^{-1}, respectively. It is
likely that the average proper motion of RG stars is the same as that of the
Galactic center. The proper motion of DSs with respect to RGs is ~ 3.3 mas
yr^{-1} toward positive l. This value is consistent with the expectations for a
flat rotation curve and Solar motion with respect to local standard of rest.
RGs have proper motion approzimately equal to the average of bright and faint
RCGs, which implies that they are on average near the center of the bar. This
pilot project demonstrates that OGLE-II data may be used to study streaming
motions of stars in the Galactic bar. We intend to extend this work to all 49
OGLE-II fields in the Galactic bulge region.Comment: 7 pages, 9 figures, submitted to MNRA
Possibility to sound the atmospheric ozone by a radiosonde equipped with two temperature sensors, sensitive and non-sensitive to the long wave radiation
The sensitiveness of white coated thermistor sensors and non-sensitiveness of the gold coated over white thermistor sensors (which have been manufactured by a vacuum evaporation process) to long wave radiation were ascertained by some simple experiments in-room and also by analyses of some results of experimental soundings. From results of analyses on the temperature discrepancies caused by long wave radiation, the possibility to sound the atmospheric ozone partial pressure by a radiosonde equipped with two kinds of sensors, sensitive and non-sensitive to the long wave radiation was suggested, and the test results of the newly developed software for the deduction of ozone partial pressure in upper layers was also shown. However, it was found that the following is the necessary condition to realize the purpose. The sounding should be made by a radiosonde equipped with three sensors, instead of two, one being non-sensitive to the long wave radiation perfectly, and the other two also non-sensitive partially to the downward one, with two different angles of exposure upward. It is essential for the realization of the purpose to get two different values of temperature discrepancies simultaneously observed by the three sensors mentioned above and to avoid the troublesome effects of the upward long wave radiation
Large Magellanic Cloud Microlensing Optical Depth with Imperfect Event Selection
I present a new analysis of the MACHO Project 5.7 year Large Magellanic Cloud
(LMC) microlensing data set that incorporates the effects of contamination of
the microlensing event sample by variable stars. Photometric monitoring of
MACHO LMC microlensing event candidates by the EROS and OGLE groups has
revealed that one of these events is likely to be a variable star, while
additional data has confirmed that many of the other events are very likely to
be microlensing. This additional data on the nature of the MACHO microlensing
candidates is incorporated into a simple likelihood analysis to derive a
probability distribution for the number of MACHO microlens candidates that are
true microlensing events. This analysis shows that 10-12 of the 13 events that
passed the MACHO selection criteria are likely to be microlensing events, with
the other 1-3 being variable stars. This likelihood analysis is also used to
show that the main conclusions of the MACHO LMC analysis are unchanged by the
variable star contamination. The microlensing optical depth toward the LMC is =
1.0 +/- 0.3 * 10^{-7}. If this is due to microlensing by known stellar
populations, plus an additional population of lens objects in the Galactic
halo, then the new halo population would account for 16% of the mass of a
standard Galactic halo. The MACHO detection exceeds the expected background of
2 events expected from ordinary stars in standard models of the Milky Way and
LMC at the 99.98% confidence level. The background prediction is increased to 3
events if maximal disk models are assumed for both the MilkyWay and LMC, but
this model fails to account for the full signal seen by MACHO at the 99.8%
confidence level.Comment: 20 pages, 2 postscript figues, accepted by Ap
About the maximal rank of 3-tensors over the real and the complex number field
High dimensional array data, tensor data, is becoming important in recent
days. Then maximal rank of tensors is important in theory and applications. In
this paper we consider the maximal rank of 3 tensors. It can be attacked from
various viewpoints, however, we trace the method of Atkinson-Stephens(1979) and
Atkinson-Lloyd(1980). They treated the problem in the complex field, and we
will present various bounds over the real field by proving several lemmas and
propositions, which is real counterparts of their results.Comment: 13 pages, no figure v2: correction and improvemen
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
Retours d'expérience d'Asie et Europe pour le développement de systèmes de transparence pour le transport solide dans des projets de barrage hydro-électrique
HydroAsia, Vietiane, LAO, 01-/03/2016 - 03/03/2016International audienceSediment trapping in reservoirs is a serious concern for dam operators as it usually induces a series of adverse impacts upstream, within and downstream impoundments. Many strategies can be applied in order to avoid sediment continuity disruption. Such challenge is all the more important in mountainous and tropical basins that sediment-laden flows are particularly intense there. Among possible strategies, drawdown routing aims at minimizing sediment deposition while drawdown flushing is favored to recover storage volume. However, those options require designing suitable gate arrangement and operation rules, so as to achieve in particular following objectives: (1) recover natural-like flow conditions in the reservoir as soon as high flows and flood events are experienced in the basin, (2) allow a wide range of sediments extending from silt to gravel to pass as much as possible through the dam and (3) regulate if necessary solid fluxes released from the reservoir according to eco-friendly flushing principles. Through several examples taken in Japan and France on the Mimikawa and Rhône River basins respectively, the purpose of this communication is to present a series of case studies for which such successful strategies have been applied either from the very beginning of the design stage of the project or after several years of operation in the frame of retrofitting operations. Experience shows that many factors have to be taken into account to design appropriate operation rules and optimize the vertical distribution of hydraulic facilities contributing to pass sediment-laden flows. Those are in particular the catchment size, the stream slope, the hydrological and sediment regimes of the river, the possible existence of upstream reservoirs, the relative importance of each sediment transportation process at reservoir inlet, the different issues at stake along the stream, the range of target-particles to be passed through the dam as well as the dam height. Concerning that latter criterion in particular, suggestions resulting from proved feedbacks are proposed so as to specify, according to the dam height, the possible needs for including bottom outlets, low level outlets and/or surface spillways
- …