The discrepancy in G-band contrast: Where is the quiet Sun?

We compare the rms contrast in observed speckle reconstructed G-band images with synthetic filtergrams computed from two magneto-hydrodynamic simulation snapshots. The observations consist of 103 bursts of 80 frames each taken at the Dunn Solar Telescope (DST), sampled at twice the diffraction limit of the telescope. The speckle reconstructions account for the performance of the Adaptive Optics (AO) system at the DST to supply reliable photometry. We find a considerable discrepancy in the observed rms contrast of 14.1% for the best reconstructed images, and the synthetic rms contrast of 21.5% in a simulation snapshot thought to be representative of the quiet Sun. The areas of features in the synthetic filtergrams that have positive or negative contrast beyond the minimum and maximum values in the reconstructed images have spatial scales that should be resolved. This leads us to conclude that there are fundamental differences in the rms G-band contrast between observed and computed filtergrams. On the basis of the substantially reduced granular contrast of 16.3% in the synthetic plage filtergram we speculate that the quiet-Sun may contain more weak magnetic field than previously thought.Comment: 16 pages, 8 figure

Stratification of sunspot umbral dots from inversion of Stokes profiles recorded by Hinode

This work aims to constrain the physical nature of umbral dots (UDs) using high-resolution spectropolarimetry. Full Stokes spectra recorded by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the disk center are analyzed. The height dependence of the temperature, magnetic field vector, and line-of-sight velocity across each UD is obtained from an inversion of the Stokes vectors of the two FeI lines at 630 nm. No difference is found at higher altitudes (-3 <= log(tau) <= -2) between the UDs and the diffuse umbral background. Below that level the difference rapidly increases, so that at the continuum formation level (log(tau) = 0) we find on average a temperature enhancement of 570 K, a magnetic field weakening of 510 G, and upflows of 800 m/s for peripheral UDs, whereas central UDs display an excess temperature of on average 550 K, a field weakening of 480 G, and no significant upflows. The results for, in particular, the peripheral UDs, including cuts of magnetic vector and velocity through them, look remarkably similar to the output of recent radiation MHD simulations. They strongly suggest that UDs are produced by convective upwellings

Association between computed tomography obstruction index and mortality in elderly patients with acute pulmonary embolism: A prospective validation study.

Computed tomography pulmonary angiography (CTPA) has not only become the method of choice for diagnosing acute pulmonary embolism (PE), it also allows for risk stratification of patients with PE. To date, no study has specifically examined the predictive value of CTPA findings to assess short-term prognosis in elderly patients with acute PE who are particularly vulnerable to adverse outcomes. We studied 291 patients aged ≥65 years with acute symptomatic PE in a prospective multicenter cohort. Outcomes were 90-day overall and PE-related mortality, recurrent venous thromboembolism (VTE), and length of hospital stay (LOS). We examined associations of the computed tomography obstruction index (CTOI) and the right ventricular (RV) to left ventricular (LV) diameter ratio with mortality and VTE recurrence using survival analysis, adjusting for provoked VTE, Pulmonary Embolism Severity Index (PESI), and anticoagulation as a time-varying covariate. Overall, 15 patients died within 90 days. There was no association between the CTOI and 90-day overall mortality (adjusted hazard ratio per 10% CTOI increase 0.92; 95% confidence interval [CI] 0.70-1.21; P = 0.54), but between the CTOI and PE-related 90-day mortality (adjusted sub-hazard ratio per 10% CTOI increase 1.36; 95% CI 1.03-1.81; P = 0.03). The RV/LV diameter ratio was neither associated with overall nor PE-related 90-day mortality. The CTOI and the RV/LV diameter ratio were significantly associated with VTE recurrence and LOS. In elderly patients with acute PE, the CTOI was associated with PE-related 90-day mortality but not with overall 90-day mortality. The RV/LV diameter ratio did not predict mortality. Both measures predicted VTE recurrence and LOS. The evaluated CTPA findings do not appear to offer any advantage over the PESI in terms of mortality prediction