Do All Flares Have White-Light Emission?

High-cadence, multiwavelength optical observations of a solar active region (NOAA AR 10969), obtained with the Swedish Solar Telescope, are presented. Difference imaging of white light continuum data reveals a white-light brightening, 2 minutes in duration, linked to a cotemporal and cospatial C2.0 flare event. The flare kernel observed in the white-light images has a diameter of 300 km, thus rendering it below the resolution limit of most space-based telescopes. Continuum emission is present only during the impulsive stage of the flare, with the effects of chromospheric emission subsequently delayed by approximate to 2 minutes. The localized flare emission peaks at 300% above the quiescent flux. This large, yet tightly confined, increase in emission is only resolvable due to the high spatial resolution of the Swedish Solar Telescope. An investigation of the line-of-sight magnetic field derived from simultaneous MDI data shows that the continuum brightening is located very close to a magnetic polarity inversion line. In addition, an Ha flare ribbon is directed along a region of rapid magnetic energy change, with the footpoints of the ribbon remaining cospatial with the observed white-light brightening throughout the duration of the flare. The observed flare parameters are compared with current observations and theoretical models for M- and X-class events and we determine the observed white-light emission is caused by radiative back-warming. We suggest that the creation of white-light emission is a common feature of all solar flares.

CSI 2264: Simultaneous Optical and Infrared Light Curves of Young Disk-bearing Stars in NGC 2264 with CoRoT and Spitzer—Evidence for Multiple Origins of Variability

We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30 day multi-wavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes and assess the fractional representation within each class. The largest category (>20%) are optical "dippers" with discrete fading events lasting ~1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with Hα emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk. Based on data from the Spitzer and CoRoT missions. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.

Beamed neutron emission driven by laser accelerated light ions

Highly anisotropic, beam-like neutron emission with peak flux of the order of 10^9 n/sr was obtained from light nuclei reactions in a pitcher–catcher scenario, by employing MeV ions driven by subpetawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHMdivergence angle of ~70 deg, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher–catcher materials indicates the dominant reactions being d(p, n+p)1Hand d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons’ spatial and spectral profiles are most likely related to the directionality and high energy of the projectile ions.

Spectro-imagerie optique à faible flux et comparaison de la cinématique Ha et HI d'un échantillon de galaxies proches

Un nouveau contrôleur de EMCCD (Electron multiplying Charge Coupled Device) est présenté. Il permet de diminuer significativement le bruit qui domine lorsque la puce EMCCD est utilisé pour du comptage de photons: le bruit d'injection de charge. À l'aide de ce contrôleur, une caméra EMCCD scientifique a été construite, caractérisée en laboratoire et testée à l'observatoire du mont Mégantic. Cette nouvelle caméra permet, entre autres, de réaliser des observations de la cinématique des galaxies par spectroscopie de champ intégral par interférométrie de Fabry-Perot en lumière Ha beaucoup plus rapidement, ou de galaxies de plus faible luminosité, que les caméras à comptage de photon basées sur des tubes amplificateurs. Le temps d'intégration nécessaire à l'obtention d'un rapport signal sur bruit donné est environ 4 fois moindre qu'avec les anciennes caméras. Les applications d'un tel appareil d'imagerie sont nombreuses: photométrie rapide et faible flux, spectroscopie à haute résolution spectrale et temporelle, imagerie limitée par la diffraction à partir de télescopes terrestres (lucky imaging), etc. D'un point de vue technique, la caméra est dominée par le bruit de Poisson pour les flux lumineux supérieurs à 0.002 photon/pixel/image. D'un autre côté, la raie d'hydrogène neutre (HI) à 21 cm a souvent été utilisée pour étudier la cinématique des galaxies. L'hydrogène neutre a l'avantage de se retrouver en quantité détectable au-delà du disque optique des galaxies. Cependant, la résolution spatiale de ces observations est moindre que leurs équivalents réalisés en lumière visible. Lors de la comparaison des données HI, avec des données à plus haute résolution, certaines différences étaient simplement attribuées à la faible résolution des observations HI. Le projet THINGS (The HI Nearby Galaxy Survey a observé plusieurs galaxies de l'échantillon SINGS (Spitzer Infrared Nearby Galaxies Survey). Les données cinématiques du projet THIGNS seront comparées aux données cinématiques obtenues en lumière Ha, afin de déterminer si la seule différence de résolution spatiale peut expliquer les différences observées. Les résultats montrent que des différences intrinsèques aux traceurs utilisées (hydrogène neutre ou ionisé), sont responsables de dissemblances importantes. La compréhension de ces particularités est importante: la distribution de la matière sombre, dérivée de la rotation des galaxies, est un test de certains modèles cosmologiques.

Visible-light-mediated synthesis of helicenes in batch and continuous flow systems

Le présent mémoire décrit le développement d’une méthode de synthèse des hélicènes catalysée par la lumière visible. Les conditions pour la formation de [5]hélicène ont été établies par une optimisation du photocatalyseur, du solvant, du système d’oxydation et du temps réactionnel. Suite aux études mécanistiques préliminaires, un mécanisme oxydatif est proposé. Les conditions optimisées ont été appliquées à la synthèse de [6]hélicènes pour laquelle la régiosélectivité a été améliorée en ajoutant des substituants sur la colonne hélicale. La synthèse de thiohélicènes a aussi été testée en utilisant les mêmes conditions sous irradiation par la lumière visible. La méthode a été inefficace pour la formation de benzodithiophènes et de naphtothiophènes, par contre elle permet la formation du phenanthro[3,4-b]thiophène avec un rendement acceptable. En prolongeant la surface-π de la colonne hélicale, le pyrène a été fusionné aux motifs de [4]- et [5]hélicène. Trois dérivés de pyrène-hélicène ont été synthétisés en utilisant les conditions optimisées pour la photocyclisation et leurs caractéristiques physiques ont été étudiées. La méthode de cyclisation sous l’action de la lumière visible a aussi été étudiée en flux continu. Une optimisation du montage expérimental ainsi que de la source lumineuse a été effectuée et les meilleures conditions ont été appliquées à la formation de [5]hélicène et des trois dérivés du pyrène-hélicène. Une amélioration ou conservation des rendements a été observée pour la plupart des produits formés en flux continu comparativement à la synthèse en batch. La concentration de la réaction a aussi été conservée et le temps réactionnel a été réduit par un facteur de dix toujours en comparaison avec la synthèse en batch.

Tracking the momentum flux of a CME and quantifying its influence on geomagnetically induced currents at Earth

We investigate a coronal mass ejection (CME) propagating toward Earth on 29 March 2011. This event is specifically chosen for its predominately northward directed magnetic field, so that the influence from the momentum flux onto Earth can be isolated. We focus our study on understanding how a small Earth-directed segment propagates. Mass images are created from the white-light cameras onboard STEREO which are also converted into mass height-time maps (mass J-maps). The mass tracks on these J-maps correspond to the sheath region between the CME and its associated shock front as detected by in situ measurements at L1. A time series of mass measurements from the STEREO COR-2A instrument is made along the Earth propagation direction. Qualitatively, this mass time series shows a remarkable resemblance to the L1 in situ density series. The in situ measurements are used as inputs into a three-dimensional (3-D) magnetospheric space weather simulation from the Community Coordinated Modeling Center. These simulations display a sudden compression of the magnetosphere from the large momentum flux at the leading edge of the CME, and predictions are made for the time derivative of the magnetic field (dB/dt) on the ground. The predicted dB/dt values were then compared with the observations from specific equatorially located ground stations and showed notable similarity. This study of the momentum of a CME from the Sun down to its influence on magnetic ground stations on Earth is presented as a preliminary proof of concept, such that future attempts may try to use remote sensing to create density and velocity time series as inputs to magnetospheric simulations.

Reduced-order modeling of light transport in tissue for real-time monitoring of brain hemodynamics using diffuse optical tomography

This paper proposes a new reconstruction method for diffuse optical tomography using reduced-order models of light transport in tissue. The models, which directly map optical tissue parameters to optical flux measurements at the detector locations, are derived based on data generated by numerical simulation of a reference model. The reconstruction algorithm based on the reduced-order models is a few orders of magnitude faster than the one based on a finite element approximation on a fine mesh incorporating a priori anatomical information acquired by magnetic resonance imaging. We demonstrate the accuracy and speed of the approach using a phantom experiment and through numerical simulation of brain activation in a rat's head. The applicability of the approach for real-time monitoring of brain hemodynamics is demonstrated through a hypercapnic experiment. We show that our results agree with the expected physiological changes and with results of a similar experimental study. However, by using our approach, a three-dimensional tomographic reconstruction can be performed in ∼3  s per time point instead of the 1 to 2 h it takes when using the conventional finite element modeling approach

An evaluation of the correlation between open solar flux and total solar irradiance

The correlation between the coronal source flux F_{S} and the total solar irradiance I_{TS} is re-evaluated in the light of an additional 5 years' data from the rising phase of solar cycle 23 and also by using cosmic ray fluxes detected at Earth. Tests on monthly averages show that the correlation with F_{S} deduced from the interplanetary magnetic field (correlation coefficient, r = 0.62) is highly significant (99.999%), but that there is insufficient data for the higher correlation with annual means (r = 0.80) to be considered significant. Anti-correlations between I_{TS} and cosmic ray fluxes are found in monthly data for all stations and geomagnetic rigidity cut-offs (r ranging from −0.63 to −0.74) and these have significance levels between 85% and 98%. In all cases, the t is poorest for the earliest data (i.e., prior to 1982). Excluding these data improves the anticorrelation with cosmic rays to r = −0:93 for one-year running means. Both the interplanetary magnetic field data and the cosmic ray fluxes indicate that the total solar irradiance lags behind the open solar flux with a delay that is estimated to have an optimum value of 2.8 months (and is within the uncertainty range 0.8-8.0 months at the 90% level).

Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions

Observations are presented of the response of the dayside cusp/cleft aurora to changes in both the clock and elevation angles of the interplanetary magnetic field (IMF) vector, as monitored by the WIND spacecraft. The auroral observations are made in 630 nm light at the winter solstice near magnetic noon, using an all-sky camera and a meridian-scanning photometer on the island of Spitsbergen. The dominant change was the response to a northward turning of the IMF which caused a poleward retreat of the dayside aurora. A second, higher-latitude band of aurora was seen to form following the northward turning, which is interpreted as the effect of lobe reconnection which reconfigures open flux. We suggest that this was made possible in the winter hemisphere, despite the effect of the Earth's dipole tilt, by a relatively large negative X component of the IMF. A series of five events then formed in the poleward band and these propagated in a southwestward direction and faded at the equatorward edge of the lower-latitude band as it migrated poleward. It is shown that the auroral observations are consistent with overdraped lobe flux being generated by lobe reconnection in the winter hemisphere and subsequently being re-closed by lobe reconnection in the summer hemisphere. We propose that the balance between the reconnection rates at these two sites is modulated by the IMF elevation angle, such that when the IMF points more directly northward, the summer lobe reconnection site dominates, re-closing all overdraped lobe flux and eventually becoming disconnected from the Northern Hemisphere.

Precession and nutation in the eta Carinae binary system: evidence from the X-ray light curve

It is believed that eta Carinae is actually a massive binary system, with the wind-wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and the short quasi-periodic oscillations seen at those epochs have not yet been accounted for. In this paper we explain these features assuming that the rotation axis of eta Carinae is not perpendicular to the orbital plane of the binary system. As a consequence, the companion star will face eta Carinae on the orbital plane at different latitudes for different orbital phases and, since both the mass-loss rate and the wind velocity are latitude dependent, they would produce the observed asymmetries in the X-ray flux. We were able to reproduce the main features of the X-ray light curve assuming that the rotation axis of eta Carinae forms an angle of 29 degrees +/- 4 degrees with the axis of the binary orbit. We also explained the short quasi-periodic oscillations by assuming nutation of the rotation axis, with an amplitude of about 5 degrees and a period of about 22 days. The nutation parameters, as well as the precession of the apsis, with a period of about 274 years, are consistent with what is expected from the torques induced by the companion star.

Do European starlings prefer light environments containing UV?

Many captive birds are kept in artificial lighting that is typically deficient in ultraviolet (UV) wavelengths. Most birds can perceive the range of light that humans see but also have an additional retinal cone type that is tuned to UV wavelengths. Consequently, artificial lighting may be detrimental as it might limit the functionality of their vision. We examined the preferences of European starlings, Sturnus vulgaris, for various artificial light environments. In our first experiment, groups of starlings showed a preference for environments that contained UV (UV+) over those where UV wavelengths had been removed (UV -). This preference was not affected by the sex of the individuals within the group or, as shown in a later experiment, by whether the birds had been previously housed in UV+ or UV - conditions. In contrast, individual starlings showed no preference for UV+ over UV - environments, although the power of our test was low. In a subsequent experiment, starling groups preferred the higher of two light intensities that were presented; however, equalizing the overall quantal flux between UV+ and UV - extinguished any preference for UV+ over UV -. The group preference for UV+ conditions in the first experiment may therefore have resulted from a preference for brighter conditions rather than a specific preference for UV. However, equalizing the quantal flux may not equalize perceived brightness, because it is not known how birds' visual systems weight input from each cone type. We conclude that, for nonbreeding, group-housed captive starlings, there is no positive evidence of a preference for the presence of UV as a specific wavelength. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Mercury Redox Chemistry in the Negro River Basin, Amazon: The Role of Organic Matter and Solar Light

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Confusing the extragalactic neutrino flux limit with a neutrino propagation limit

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Morphological and physiological responses of Cedrela Fissilis Vellozo (Meliaceae) seedlings to light

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

CO2 assimilation, photosynthetic light response curves, and water relations of 'Pêra' sweet orange plants infected with Xylella fastidiosa

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)