3,143 research outputs found
Intense CIII] 1907,1909 emission from a strong Lyman continuum emitting galaxy
We have obtained the first complete ultraviolet (UV) spectrum of a strong
Lyman continuum(LyC) emitter at low redshift -- the compact, low-metallicity,
star-forming galaxy J1154+2443 -- with a Lyman continuum escape fraction of 46%
discovered recently. The Space Telescope Imaging Spectrograph spectrum shows
strong Lya and CIII] 1909 emission, as well as OIII] 1666. Our observations
show that strong LyC emitters can have UV emission lines with a high equivalent
width (e.g. EW(CIII]) rest-frame), although their equivalent
widths should be reduced due to the loss of ionizing photons. The intrinsic
ionizing photon production efficiency of J1154+2443 is high, erg Hz, comparable to that of other recently discovered
LyC emitters. Combining our measurements and earlier
determinations from the literature, we find a trend of increasing with increasing CIII] 1909 equivalent width, which can be understood by
a combination of decreasing stellar population age and metallicity. Simple
ionization and density-bounded photoionization models can explain the main
observational features including the UV spectrum of J1154+2443.Comment: 5 pages, 4 figures. Accepted for publication in A&A Letter
Understanding stellar activity-induced radial velocity jitter using simultaneous K2 photometry and HARPS RV measurements
One of the best ways to improve our understanding of the stellar
activity-induced signal in radial velocity (RV) measurements is through
simultaneous high-precision photometric and RV observations. This is of prime
importance to mitigate the RV signal induced by stellar activity and therefore
unveil the presence of low-mass exoplanets. The K2 Campaign 7 and 8
field-of-views were located in the southern hemisphere, and provided a unique
opportunity to gather unprecedented simultaneous high precision photometric
observation with K2 and high-precision RV measurements with the HARPS
spectrograph to study the relationship between photometric variability and RV
jitter. We observed nine stars with different levels of activity; from quiet to
very active. We probe the presence of any meaningful relation between measured
RV jitter and the simultaneous photometric variation, and also other activity
indicators (e.g. BIS, FWHM, , and F8), by evaluating the strength
and significance of the correlation between RVs and each indicator. We found
that for the case of very active stars, strong and significant correlations
exist between almost all the observables and measured RVs; however, for lower
activity levels the correlations become random. Except for the F8 which its
strong correlation with RV jitter persists over a wide range of stellar
activity level, and thus our result suggests that F8 might be a powerful proxy
for activity induced RV jitter. Moreover, we examine the capability of two
state-of-the-art modeling techniques, namely the FF' method and SOAP2.0, in
accurately predicting the RV jitter amplitude using the simultaneous
photometric observation. We found that for the very active stars both
techniques can reasonably well predict the amplitude of the RV jitter, however,
at lower activity levels the FF' method underpredicts the RV jitter amplitude.Comment: 13 pages, 7 figures, 2 tables, accepted for publication in A&
phase shifts and CP Violation in Decay
In the study of CP violation signals in {\O}\to\pi\Xi nonleptonic decays,
the strong =3/2 and phase shifts for the final-state
interactions are needed. These phases are calculated using an effective
Lagrangian model, including , (1530), and the -term,
in the intermediate states. The -term is calculated in terms of the
scalar form factor of the baryon.Comment: 6 pages, 2 figure
Absolute masses and radii determination in multiplanetary systems without stellar models
The masses and radii of extrasolar planets are key observables for understanding their interior, formation and evolution. While transit photometry and Doppler spectroscopy are used to measure the radii and masses respectively of planets relative to those of their host star, estimates for the true values of these quantities rely on theoretical models of the host star which are known to suffer from systematic differences with observations. When a system is composed of more than two bodies, extra information is contained in the transit photometry and radial velocity data. Velocity information (finite speed-of-light, Doppler) is needed to break the Newtonian MRâ3 degeneracy. We performed a photodynamical modelling of the two-planet transiting system Kepler-117 using all photometric and spectroscopic data available. We demonstrate how absolute masses and radii of single-star planetary systems can be obtained without resorting to stellar models. Limited by the precision of available radial velocities (38msâ1), we achieve accuracies of 20 per cent in the radii and 70 per cent in the masses, while simulated 1msâ1 precision radial velocities lower these to 1 per cent for the radii and 2 per cent for the masses. Since transiting multiplanet systems are common, this technique can be used to measure precisely the mass and radius of a large sample of stars and planets. We anticipate these measurements will become common when the TESS and PLATO mission provide high-precision light curves of a large sample of bright stars. These determinations will improve our knowledge about stars and planets, and provide strong constraints on theoretical model
The Large Aperture GRB Observatory
The Large Aperture GRB Observatory (LAGO) is aiming at the detection of the
high energy (around 100 GeV) component of Gamma Ray Bursts, using the single
particle technique in arrays of Water Cherenkov Detectors (WCD) in high
mountain sites (Chacaltaya, Bolivia, 5300 m a.s.l., Pico Espejo, Venezuela,
4750 m a.s.l., Sierra Negra, Mexico, 4650 m a.s.l). WCD at high altitude offer
a unique possibility of detecting low gamma fluxes in the 10 GeV - 1 TeV range.
The status of the Observatory and data collected from 2007 to date will be
presented.Comment: 4 pages, proceeding of 31st ICRC 200
Water Cherenkov Detectors response to a Gamma Ray Burst in the Large Aperture GRB Observatory
In order to characterise the behaviour of Water Cherenkov Detectors (WCD)
under a sudden increase of 1 GeV - 1 TeV background photons from a Gamma Ray
Burst (GRB), simulations were conducted and compared to data acquired by the
WCD of the Large Aperture GRB Observatory (LAGO). The LAGO operates arrays of
WCD at high altitude to detect GRBs using the single particle technique. The
LAGO sensitivity to GRBs is derived from the reported simulations of the gamma
initiated particle showers in the atmosphere and the WCD response to
secondaries.Comment: 5 pages, proceeding of the 31st ICRC 200
New Physics and CP Violation in Hyperon Nonleptonic Decays
The sum of the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in
hyperon nonleptonic decays is presently being measured by the E871 experiment.
We evaluate contributions to the asymmetries induced by chromomagnetic-penguin
operators, whose coefficients can be enhanced in certain models of new physics.
Incorporating recent information on the strong phases in Xi->Lambda pi decay,
we show that new-physics contributions to the two asymmetries can be
comparable. We explore how the upcoming results of E871 may constrain the
coefficients of the operators. We find that its preliminary measurement is
already better than the epsilon parameter of K-Kbar mixing in bounding the
parity-conserving contributions.Comment: 12 pages, 2 figure
Chinaâs rising hydropower demand challenges water sector
Demand for hydropower is increasing, yet the water footprints (WFs) of reservoirs and hydropower, and their contributions to water scarcity, are poorly understood. Here, we calculate reservoir WFs (freshwater that evaporates from reservoirs) and hydropower WFs (the WF of hydroelectricity) in China based on data from 875 representative reservoirs (209 with power plants). In 2010, the reservoir WF totaled 27.9âĂâ109âm3â(Gm3), or 22% of Chinaâs total water consumption. Ignoring the reservoir WF seriously underestimates human water appropriation. The reservoir WF associated with industrial, domestic and agricultural WFs caused water scarcity in 6 of the 10 major Chinese river basins from 2 to 12 months annually. The hydropower WF was 6.6âGm3 yrâ1 or 3.6âm3 of water to produce a GJ (109âJ) of electricity. Hydropower is a water intensive energy carrier. As a response to global climate change, the Chinese government has promoted a further increase in hydropower energy by 70% by 2020 compared to 2012. This energy policy imposes pressure on available freshwater resources and increases water scarcity. The water-energy nexus requires strategic and coordinated implementations of hydropower development among geographical regions, as well as trade-off analysis between rising energy demand and water use sustainability
Assessment of surface temperatures of buffalo bulls (Bubalus bubalis) raised under tropical conditions using infrared thermography.
O presente trabalho visou avaliar as temperaturas superficiais de diferentes regiĂ”es anatĂŽmicas de bĂșfalos ao longo do tempo, por meio da termografia infravermelha, e correlacionĂĄ-las a Ăndices bioclimatolĂłgicos de conforto tĂ©rmico. O ensaio foi realizado em regiĂŁo de clima tropical Ășmido (Afi de Köppen), de abril a agosto. Dez touros (n=10) foram avaliados a cada 25 dias (manhĂŁ: seis-nove horas; tarde: 12-15h), quanto Ă frequĂȘncia respiratĂłria (FR), temperatura retal (TR) e imagens termogrĂĄficas da Ăłrbita ocular (ORB), flanco direito (FLd), flanco esquerdo (FLe) e escroto (ESC). Os dados climatolĂłgicos foram ininterruptamente monitorados, e calculados o Ăndice de temperatura e umidade (ITU) e o Ăndice de conforto de Benezra (ICB). O ITU foi ?78, com diferença entre turnos (P<0,05). JĂĄ o ICB variou de 1,96 a 2,25 e apresentou diferenças ao longo dos meses e entre turnos (P<0,05). As temperaturas observadas foram de TR=38,2±0,5ÂșC, ORB=36,1±0,8ÂșC, FLd=33,5±2,5ÂșC, FLe=35,4±1,7ÂșC e ESC=33,3±1,1ÂșC, as quais variaram significativamente ao longo dos meses e entre turnos (P<0,05). O ITU apresentou correlaçÔes positivas com ORB (0,72), FLd (0,77), FLe (0,75) e ESC (0,41) (P<0,0001). A temperatura mĂĄxima de ORB apresentou a maior correlação com a TR (0,58; P<0,0001). Portanto, as temperaturas superficiais dos animais sofrem interferĂȘncias das variaçÔes climĂĄticas e se elevam ao longo do dia, devido Ă variação nos Ăndices de conforto tĂ©rmico; a temperatura mĂĄxima de ORB foi o parĂąmetro mais condicionado Ă temperatura retal. TambĂ©m, as oscilaçÔes de temperatura de superfĂcie de ORB, FLd, FLe e ESC podem ser aferidas em bubalinos com o uso da termografia infravermelha, de modo preciso e nĂŁo invasivo
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