A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations

Stellar activity and, in particular, convection-related surface structures, potentially cause fluctuations that can affect the transit light curves. Surface convection simulations can help the interpretation of ToV. We used realistic three-dimensional radiative hydrodynamical simulation of the Sun from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide predictions for the transit of Venus in 2004 observed by the satellite ACRIMSAT. We computed intensity maps from RHD simulation of the Sun and produced synthetic stellar disk image. We computed the light curve and compared it to the ACRIMSAT observations and also to the light curves obtained with solar surface representations carried out using radial profiles with different limb-darkening laws. We also applied the same spherical tile imaging method to the observations of center-to-limb Sun granulation with HINODE. We managed to explain ACRIMSAT observations of 2004 ToV and showed that the granulation pattern causes fluctuations in the transit light curve. We evaluated the contribution of the granulation to the ToV. We showed that the granulation pattern can partially explain the observed discrepancies between models and data. This confirms that the limb-darkening and the granulation pattern simulated in 3D RHD Sun represent well what is imaged by HINODE. In the end, we found that the Venus's aureole contribution during ToV is less intense than the solar photosphere, and thus negligible. Being able to explain consistently the data of 2004 ToV is a new step forward for 3D RHD simulations that are becoming essential for the detection and characterization of exoplanets. They show that the granulation have to be considered as an intrinsic incertitude, due to the stellar variability, on precise measurements of exoplanet transits of, most likely, planets with small diameters.Comment: Accepted for publication in Astronomy and Astrophysic

Solar BaII 4554 A line as Doppler diagnostics: NLTE analysis in 3D hydrodynamical model

The aim of this paper is to analyse the validity of the Dopplergram and lambda-meter techniques for the Doppler diagnostics of solar photospheric velocities using the BaII 4554 A line. Both techniques are evaluated by means of NLTE radiative transfer calculations of the BaII 4554 A line in a three-dimensional hydrodynamical model of solar convection. We consider the cases of spatially unsmeared profiles and the profiles smeared to the resolution of ground-based observations. We find that: (i) Speckle-reconstructed Dopplergram velocities reproduce the ``true'' velocities well at heights around 300 km, except for intergranular lanes with strong downflows where the velocity can be overestimated. (ii) The lambda-meter velocities give a good representation of the ``true'' velocities through the whole photosphere, both under the original and reduced spatial resolutions. The velocities derived from the inner wing of smeared BaII 4554 A line profiles are more reliable than those for the outer wing. Only under high spatial resolution does the inner wing velocities calculated in intergranular regions give an underestimate (or even a sign reversal) compared with the model velocities. (iii) NLTE effects should be taken into account in modelling the BaII 4554 A line profiles. Such effects are more pronounced in intergranular regions. Our analysis supports the opinion that the Dopplergram technique applied to the BaII 4554 A line is a valuable tool for the Doppler diagnostics of the middle photosphere around 300 km. The \lambda-meter technique applied to this line gives us a good opportunity to ``trace'' the non-thermal motions along the whole photosphere up to the temperature minimum and lower chromosphere.Comment: accepted by Astronomy and Astrophysic

A Serum Factor Induces Insulin-Independent Translocation of GLUT4 to the Cell Surface which Is Maintained in Insulin Resistance

In response to insulin, glucose transporter GLUT4 translocates from intracellular compartments towards the plasma membrane where it enhances cellular glucose uptake. Here, we show that sera from various species contain a factor that dose-dependently induces GLUT4 translocation and glucose uptake in 3T3-L1 adipocytes, human adipocytes, myoblasts and myotubes. Notably, the effect of this factor on GLUT4 is fully maintained in insulin-resistant cells. Our studies demonstrate that the serum-induced increase in cell surface GLUT4 levels is not due to inhibition of its internalization and is not mediated by insulin, PDGF, IGF-1, or HGF. Similarly to insulin, serum also augments cell surface levels of GLUT1 and TfR. Remarkably, the acute effect of serum on GLUT4 is largely additive to that of insulin, while it also sensitizes the cells to insulin. In accordance with these findings, serum does not appear to activate the same repertoire of downstream signaling molecules that are implicated in insulin-induced GLUT4 translocation. We conclude that in addition to insulin, at least one other biological proteinaceous factor exists that contributes to GLUT4 regulation and still functions in insulin resistance. The challenge now is to identify this factor

Abnormal Changes in NKT Cells, the IGF-1 Axis, and Liver Pathology in an Animal Model of ALS

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing fatal neurodegenerative disorder characterized by the selective death of motor neurons (MN) in the spinal cord, and is associated with local neuroinflammation. Circulating CD4+ T cells are required for controlling the local detrimental inflammation in neurodegenerative diseases, and for supporting neuronal survival, including that of MN. T-cell deficiency increases neuronal loss, while boosting T cell levels reduces it. Here, we show that in the mutant superoxide dismutase 1 G93A (mSOD1) mouse model of ALS, the levels of natural killer T (NKT) cells increased dramatically, and T-cell distribution was altered both in lymphoid organs and in the spinal cord relative to wild-type mice. The most significant elevation of NKT cells was observed in the liver, concomitant with organ atrophy. Hepatic expression levels of insulin-like growth factor (IGF)-1 decreased, while the expression of IGF binding protein (IGFBP)-1 was augmented by more than 20-fold in mSOD1 mice relative to wild-type animals. Moreover, hepatic lymphocytes of pre-symptomatic mSOD1 mice were found to secrete significantly higher levels of cytokines when stimulated with an NKT ligand, ex-vivo. Immunomodulation of NKT cells using an analogue of α-galactosyl ceramide (α-GalCer), in a specific regimen, diminished the number of these cells in the periphery, and induced recruitment of T cells into the affected spinal cord, leading to a modest but significant prolongation of life span of mSOD1 mice. These results identify NKT cells as potential players in ALS, and the liver as an additional site of major pathology in this disease, thereby emphasizing that ALS is not only a non-cell autonomous, but a non-tissue autonomous disease, as well. Moreover, the results suggest potential new therapeutic targets such as the liver for immunomodulatory intervention for modifying the disease, in addition to MN-based neuroprotection and systemic treatments aimed at reducing oxidative stress

Global gene expression analysis in time series following N-acetyl L-cysteine induced epithelial differentiation of human normal and cancer cells in vitro

BACKGROUND: Cancer prevention trials using different types of antioxidant supplements have been carried out at several occasions and one of the investigated compounds has been the antioxidant N-acetyl-L-cysteine (NAC). Studies at the cellular level have previously demonstrated that a single supplementation of NAC induces a ten-fold more rapid differentiation in normal primary human keratinocytes as well as a reversion of a colon carcinoma cell line from neoplastic proliferation to apical-basolateral differentiation [1]. The investigated cells showed an early change in the organization of the cytoskeleton, several newly established adherens junctions with E-cadherin/β-catenin complexes and increased focal adhesions, all features characterizing the differentiation process. METHODS: In order to investigate the molecular mechanisms underlying the proliferation arrest and accelerated differentiation induced by NAC treatment of NHEK and Caco-2 cells in vitro, we performed global gene expression analysis of NAC treated cells in a time series (1, 12 and 24 hours post NAC treatment) using the Affymetrix GeneChip™ Human Genome U95Av2 chip, which contains approximately 12,000 previously characterized sequences. The treated samples were compared to the corresponding untreated culture at the same time point. RESULTS: Microarray data analysis revealed an increasing number of differentially expressed transcripts over time upon NAC treatment. The early response (1 hour) was transient, while a constitutive trend was commonly found among genes differentially regulated at later time points (12 and 24 hours). Connections to the induction of differentiation and inhibition of growth were identified for a majority of up- and down-regulated genes. All of the observed transcriptional changes, except for seven genes, were unique to either cell line. Only one gene, ID-1, was mutually regulated at 1 hour post treatment and might represent a common mediator of early NAC action. The detection of several genes that previously have been identified as stimulated or repressed during the differentiation of NHEK and Caco-2 provided validation of results. In addition, real-time kinetic PCR analysis of selected genes also verified the differential regulation as identified by the microarray platform. CONCLUSION: NAC induces a limited and transient early response followed by a more consistent and extensively different expression at later time points in both the normal and cancer cell lines investigated. The responses are largely related to inhibition of proliferation and stimulation of differentiation in both cell types but are almost completely lineage specific. ID-1 is indicated as an early mediator of NAC action

Distribution of magnetic fields in the quiet Sun

Context. The distribution of magnetic fields in the atmosphere of the quiet Sun has been extensively studied with various methods, but it is still a matter of debate. Previous analyses mostly rely on the inversion of spectro-polarimetric data and different methods lead to somewhat different results. Aims. Here we do not intend to determine the magnetic field vector, but we use total polarization images as tracers of the magnetic field distribution and we study their cross-correlations with granulation and reversed-granulation images. Methods. We used high-resolution spectro-polarimetric scans obtained in the 630 nm FeI line pair at varying heliocentric angles along the north-south polar axis of the Sun, with the Solar Optical Telescope (SOT) onboard Hinode. We obtain polarization images by summing the total polarization (linear and circular) in each line. We compute the 2D correlation of polarization images and their cross-correlations with images of the granulation observed simultaneously in the line wings and with the reversed granulation observed in the line cores, and we examine their center-to-limb variations. Results. The correlation-widths of polarization images have on the average, the same value (1.3′′) as the correlation-width of the granulation, showing that the granular scale is a characteristic scale of the quiet Sun magnetic field distribution. At disk center the cross-correlation between total polarization and the granulation shows a negative peak. Out of disk-center both a negative and a positive peak are detected. The cross-correlation of polarization images with the reversed granulation always shows a positive peak. We assign these cross-correlation signals to the presence of two kinds of magnetized regions spatially separated, one of them is located in the intergranular lanes (anti-correlated with the granulation), the other one lies within the bright granules. For images obtained out of disk center, the correlation and anti-correlation peaks are shifted along the north-south direction and the shifts measured at the same limb-distance in the southern and northern hemispheres have opposite values. A consistent interpretation of these shifts is proposed in terms of a perspective effect arising when two images formed at different heights are observed at an angle. We were able to measure the perspective effect for the magnetic component correlated with the reversed granulation. Its polarization signals observed in the FeI 630.25 nm line and in the 630.15 nm line, are formed respectively 100 km and 150 km below the bright features seen at line centers

Solar-cycle variations of the internetwork magnetic field

Context. The quiet Sun exhibits a rich and complex magnetic structuring that is still not fully resolved or understood. Aims. We intend to contribute to the debate about the origin of the internetwork magnetic fields and whether or not they are related to the global solar dynamo. Methods. We analyzed center-to-limb polarization measurements obtained with the SOT/SP spectropolarimeter onboard the Hinode satellite outside active regions in 2007 and 2013, that is, at a minimum and a maximum of the solar cycle, respectively. We examined 10′′ × 10′′ maps of the unsigned circular and linear polarization in the FeI 630.25 nm line in regions located away from network elements. The maps were corrected for bias and focus variations between the two data sets. Then we applied a Fourier spectral analysis to examine wether the spatial structuring of the internetwork magnetic fields shows significant differences between the minimum and maximum of the cycle. Results. Neither the mean values of the unsigned circular and linear polarizations in the selected 10′′ × 10′′ maps nor their spatial fluctuation power spectra show significant center-to-limb variations. For the unsigned circular polarization the power of the spatial fluctuations is lower in 2013 than in 2007, but the spectral slope is unchanged. The linear polarization spectra show no significant differences in 2013 and 2007, but the spectrum of 2013 is more strongly affected by noise. Conclusions. The small-scale magnetic structuring in the internetwork is different in our 2013 and 2007 data. Surprisingly, we find a lower spatial fluctuation power at the solar maximum in the internetwork magnetic structuring. This indicates some complex interactions between the small-scale magnetic structures in the quiet Sun and the global dynamo, as predicted by recent numerical simulations. This result has to be confirmed by further statistical studies with larger data sets

Magnetic flux structuring of the quiet Sun internetwork

International audienceContext. The small-scale magnetism of the quiet Sun has been investigated by various means in recent decades. It is now well established that the quiet Sun contains in total more magnetic flux than active regions and represents an important reservoir of magnetic energy. But the nature and evolution of these fields remain largely unknown. Aims. We investigate the solar-cycle and center-to-limb variations of magnetic-flux structures at small scales in internetwork regions of the quiet Sun. Methods. We used Hinode SOT/SP data from the irradiance program between 2008 and 2016. Maps of the magnetic-flux density are derived from the center-of gravity method applied to the circular polarization profiles in the FeI 630.15 nm and FeI 630.25 nm lines. To correct the maps from the instrumental smearing of the telescope, we applied a deconvolution method based on a principal component analysis of the line profiles and on a Richardson-Lucy deconvolution of their coefficients. We took defocus effects and the diffraction of the SOT telescope into account. We then performed a spectral analysis of the spatial fluctuations of the magnetic-flux density in 10″ × 10″ internetwork regions spanning a wide range of latitudes from ±70° to the equator. Results. At low and mid latitudes the power spectra normalized by the mean value of the unsigned flux in the regions do not vary significantly with the solar cycle. However at solar maximum for one scan in the activity belt showing an enhanced network, a marginal increase in the power of the magnetic fluctuations is observed at granular and larger scales in the internetwork. At high latitudes, we observe variations at granular and larger scales where the power decreases at solar maximum. At all the latitudes the power of the magnetic fluctuations at scales smaller than 0.5″ remains constant throughout the solar cycle. Conclusions. At the equator the unsigned flux density is related to the vertical component of the magnetic field, whereas at high latitudes this flux density is mainly related to the horizontal component and probe higher altitudes. Our results favor a small-scale dynamo that operates in the internetwork, but they show that the global dynamo also contributes to the internetwork fields. At solar maximum the high-latitude horizontal internetwork fields seem to be depleted from the structures at granular and larger scales that are seen at solar minimum, whereas the internetwork within enhanced network regions show more structures at those scales than at solar minimum

A cross-correlation method for measuring line formation heights in the solar photosphere

Context. Detailed 3D-simulations of magneto-convection in the solar photosphere are now available. They intend to capture the main physical mechanisms at play in this boundary layer, where complex physical phenomena, such as convective overshooting and small scale magnetic dynamo take place. But numerical limitations in spatial resolution and in box-size are likely to affect the description of some relevant physical scales, so simulations need to be compared to independent observations allowing us to explore the full height range of the photosphere. Aims. Here we focus on a model-independent method for measuring line formation depths. We construct images of the photosphere at constant continuum opacity levels from the low to the upper photosphere and we show how they can be used to measure systematic displacements of granular structures with height. The method is applied to determine the formation height of the 630 nm Fe