Is the Sun Lighter than the Earth? Isotopic CO in the Photosphere, Viewed through the Lens of 3D Spectrum Synthesis

We consider the formation of solar infrared (2-6 micron) rovibrational bands of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim to refine abundances of the heavy isotopes of carbon (13C) and oxygen (18O,17O), to compare with direct capture measurements of solar wind light ions by the Genesis Discovery Mission. We find that previous, mainly 1D, analyses were systematically biased toward lower isotopic ratios (e.g., R23= 12C/13C), suggesting an isotopically "heavy" Sun contrary to accepted fractionation processes thought to have operated in the primitive solar nebula. The new 3D ratios for 13C and 18O are: R23= 91.4 +/- 1.3 (Rsun= 89.2); and R68= 511 +/- 10 (Rsun= 499), where the uncertainties are 1 sigma and "optimistic." We also obtained R67= 2738 +/- 118 (Rsun= 2632), but we caution that the observed 12C17O features are extremely weak. The new solar ratios for the oxygen isotopes fall between the terrestrial values and those reported by Genesis (R68= 530, R6= 2798), although including both within 2 sigma error flags, and go in the direction favoring recent theories for the oxygen isotope composition of Ca-Al inclusions (CAI) in primitive meteorites. While not a major focus of this work, we derive an oxygen abundance of 603 +/- 9 ppm (relative to hydrogen; 8.78 on the logarithmic H= 12 scale). That the Sun likely is lighter than the Earth, isotopically speaking, removes the necessity to invoke exotic fractionation processes during the early construction of the inner solar system

On The Evolution of Magnetic White Dwarfs

We present the first radiation magnetohydrodynamics simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-beta parameter, the thermal to magnetic pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1-50 kG, which is much smaller than the typical 1-1000 MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have then employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B > 10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (Teff) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection owing to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with Teff < 10,000 K cool significantly slower than non-magnetic degenerates.Comment: 11 pages, 12 figures, accepted for publication in the Astrophysical Journa

Inter-network regions of the Sun at millimetre wavelengths

The continuum intensity at wavelengths around 1 mm provides an excellent way to probe the solar chromosphere. Future high-resolution millimetre arrays, such as the Atacama Large Millimeter Array (ALMA), will thus produce valuable input for the ongoing controversy on the thermal structure and the dynamics of this layer. Synthetic brightness temperature maps are calculated on basis of three-dimensional radiation (magneto-)hydrodynamic (MHD) simulations. While the millimetre continuum at 0.3mm originates mainly from the upper photosphere, the longer wavelengths considered here map the low and middle chromosphere. The effective formation height increases generally with wavelength and also from disk-centre towards the solar limb. The average intensity contribution functions are usually rather broad and in some cases they are even double-peaked as there are contributions from hot shock waves and cool post-shock regions in the model chromosphere. Taking into account the deviations from ionisation equilibrium for hydrogen gives a less strong variation of the electron density and with it of the optical depth. The result is a narrower formation height range. The average brightness temperature increases with wavelength and towards the limb. The relative contrast depends on wavelength in the same way as the average intensity but decreases towards the limb. The dependence of the brightness temperature distribution on wavelength and disk-position can be explained with the differences in formation height and the variation of temperature fluctuations with height in the model atmospheres.Comment: 15 pages, 10 figures, accepted for publication in A&A (15.05.07

High-order aberration compensation with Multi-frame Blind Deconvolution and Phase Diversity image restoration techniques

Context. For accurately measuring intensities and determining magnetic field strengths of small-scale solar (magnetic) structure, knowledge of and compensation for the point spread function is crucial. For images recorded with the Swedish 1-meter Solar Telescope, restoration with Multi-Frame Blind Deconvolution and Joint Phase Diverse Speckle methods lead to remarkable improvements in image quality but granulation contrasts that are too low, indicating additional stray light. Aims. We propose a method to compensate for stray light from high-order atmospheric aberrations not included in MFBD and JPDS processing. Methods. To compensate for uncorrected aberrations, a reformulation of the image restoration process is proposed that allows the average effect of hundreds of high-order modes to be compensated for by relying on Kolmogorov statistics for these modes. The applicability of the method requires simultaneous measurements of Fried's parameter r0. The method is tested with simulations as well as real data and extended to include compensation for conventional stray light. Results. We find that only part of the reduction of granulation contrast in SST images is due to uncompensated high-order aberrations. The remainder is still unaccounted for and attributed to stray light from the atmosphere, the telescope with its re-imaging system and to various high-altitude seeing effects. Conclusions. We conclude that statistical compensation of high-order modes is a viable method to reduce the loss of contrast occurring when a limited number of aberrations is explicitly compensated for with MFBD and JPDS processing. We show that good such compensation is possible with only 10 recorded frames. The main limitation of the method is that already MFBD and JPDS processing introduces high-order compensation that, if not taken into account, can lead to over-compensation.Comment: in press in Astronomy & Astrophysic

Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?

We compare the abundances of various chemical species as derived with 3D hydrodynamical and classical 1D stellar atmosphere codes in a late-type giant characterized by T_eff=3640K, log g = 1.0, [M/H] = 0.0. For this particular set of atmospheric parameters the 3D-1D abundance differences are generally small for neutral atoms and molecules but they may reach up to 0.3-0.4 dex in case of ions. The 3D-1D differences generally become increasingly more negative at higher excitation potentials and are typically largest in the optical wavelength range. Their sign can be both positive and negative, and depends on the excitation potential and wavelength of a given spectral line. While our results obtained with this particular late-type giant model suggest that 1D stellar atmosphere models may be safe to use with neutral atoms and molecules, care should be taken if they are exploited with ions.Comment: Poster presented at the IAU Symposium 265 "Chemical Abundances in the Universe: Connecting First Stars to Planets", Rio de Janeiro, 10-14 August 2009; 2 pages, 1 figur

Entwicklung eines situationsbezogenen Konzeptes zur Regulation des Erbsenwicklers in Gemüse- und Körnererbsen

Das Ziel des Projektes war es, ein Konzept zur Risikobewertung des Erbsenwicklerbefalls in Anbauregionen von Gemüseerbsen zu entwickeln, in dem präventive Maßnahmen und eine bedarfsgerechte Option zur Direktbekämpfung integriert sind. Die Datenerfassung zur Beurteilung von Risikolagen erfolgte in Erbsenanbaugebieten in Hessen und Sachsen, beide mit Schwerpunkt auf ökologischen Landbau. Die Risikobewertung umfasste die Abschätzung der Schlaggefährdung durch den Erbsenwickler innerhalb der Anbaugebiete mittels zeitlich-räumlicher Analysen und die Berücksichtigung phänologischer Daten zum Erscheinen, Flugaktivität und Entwicklung des Erbsenwicklers in Abhängigkeit von Temperatur und Photoperiode. Basierend auf der Risikobewertung sollten Entscheidungen zum Einsatz ökologischer Regulierungsverfahren getroffen werden können, die in einem zweiten Projektteil bearbeitet wurden. Die Regulierung des Erbsenwicklers wurde in einem Parzellenversuch über die präventiven Maßnahmen Sortenwahl und Aussaatzeitpunkt und eine bedarfsgerechte Direktbekämpfung untersucht. Als Ergebnis konnten die wesentlichen Faktoren, die für eine Risikobewertung zum Erbsenwicklerbefall notwendig sind, definiert werden: a) ein zeitlich-räumlicher Zusammenhang zwischen den vorjährigen Erbsenflächen und dem Erbsenwicklerauftreten im Folgejahr b) ein Einfluss von Photoperiode und Temperatur auf die Entwicklung der Überwinterungsstadien von C. nigricana, sowie Erscheinen und Flugaktivität der adulten Erbsenwickler c) eine Steuerung der zeitlichen Koinzidenzvermeidung von empfindlichen Entwicklungsstadien der Erbsenpflanze und dem Erbsenwicklerauftreten durch Sortenwahl und Aussaatzeitpunkt. Der Einsatz einer Pyrethrin-Rapsöl Formulierung hat eine variable Wirkung in der Regulierung des Erbsenwicklers gezeigt. Der Befall konnte nur bei geringem Befallsdruck unterhalb der sehr niedrigen Schadtoleranzgrenze von 0,5% geschädigter Ernteerbsen gehalten werden; bei einer starken Schädlingsdichte konnte keine ausreichende Befallsreduktion erreicht werden

Clinical Relevance of Transjugular Liver Biopsy in Comparison with Percutaneous and Laparoscopic Liver Biopsy

Background. Transjugular liver biopsy (TJLB) is frequently used to obtain liver specimens in high-risk patients. However, TJLB sample size possibly limits their clinical relevance. Methods. 102 patients that underwent TJLB were included. Clinical parameters and outcome of TJLB were analyzed. Control samples consisted of 112 minilaparoscopic liver biopsies (mLLBs) and 100 percutaneous liver biopsies (PLBs). Results. Fewer portal tracts were detected in TJLB (4.3 ± 0.3) in comparison with PLB (11.7 ± 0.5) and mLLB (11.0 ± 0.6). No difference regarding the specification of indeterminate liver disease and staging/grading of chronic hepatitis was observed. In acute liver failure (n = 32), a proportion of hepatocellular necrosis beyond 25% was associated with a higher rate of death or liver transplantation. Conclusions. Despite smaller biopsy samples the impact on the clinical decision process was found to be comparable to PLB and mLLB. TJLB represents a helpful tool to determine hepatocellular necrosis rates in patients with acute liver failure

Impact of granulation effects on the use of Balmer lines as temperature indicators

Balmer lines serve as important indicators of stellar effective temperatures in late-type stellar spectra. One of their modelling uncertainties is the influence of convective flows on their shape. We aim to characterize the influence of convection on the wings of Balmer lines. We perform a differential comparison of synthetic Balmer line profiles obtained from 3D hydrodynamical model atmospheres and 1D hydrostatic standard ones. The model parameters are appropriate for F,G,K dwarf and subgiant stars of metallicity ranging from solar to 1/1000 solar. The shape of the Balmer lines predicted by 3D models can never be exactly reproduced by a 1D model, irrespective of its effective temperature. We introduce the concept of a 3D temperature correction, as the effective temperature difference between a 3D model and a 1D model which provides the closest match to the 3D profile. The temperature correction is different for the different members of the Balmer series and depends on the adopted mixing-length parameter in the 1D model. Among the investigated models, the 3D correction ranges from -300K to +300K. Horizontal temperature fluctuations tend to reduce the 3D correction. Accurate effective temperatures cannot be derived from the wings of Balmer lines, unless the effects of convection are properly accounted for. The 3D models offer a physically well justified way of doing so. The use of 1D models treating convection with the mixing-length theory do not appear to be suitable for this purpose. In particular, there are indications that it is not possible to determine a single value of the mixing-length parameter which will optimally reproduce the Balmer lines for any choice of atmospheric parameters.Comment: 6 pages, 3 figures, accepted for publication in A&