Millimeter-Wave Aperture Synthesis Imaging of Vega: Evidence for a Ring Arc at 95 AU

We present the first millimeter-wave aperture synthesis map of dust around a main sequence star. A 3'' resolution image of 1.3 mm continuum emission from Vega reveals a clump of emission 12'' from the star at PA 45 deg, consistent with the location of maximum 850 micron emission in a lower resolution JCMT/SCUBA map. The flux density is 4.0+/-0.9 mJy. Adjacent 1.3 mm peaks with flux densities 3.4+/-1.0 mJy and 2.8+/-0.9 mJy are located 14'' and 13'' from the star at PA 67 deg and 18 deg, respectively. An arc-like bridge connects the two strongest peaks. There is an additional 2.4 +/-0.8 mJy peak to the SW 11'' from the star at PA 215 deg and a marginal detection, 1.4+/-0.5 mJy, at the stellar position, consistent with photospheric emission. An extrapolation from the 850 micron flux, assuming F_{1.3mm-0.85mm} proportional to lambda^{-2.8}, agrees well with the total detected flux for Vega at 1.3 mm, and implies a dust emissivity index, beta, of 0.8. We conclude that we have detected all but a very small fraction of the dust imaged by SCUBA in our aperture synthesis map and that these grains are largely confined to segments of a ring of radius 95 AU.Comment: 4 pages, 1 figure, 1 table, accepted for publication in Astrophysical Journal Letter

Empirical Studies on the Economic Impact of Trust

__Abstract__ Generally speaking, would you say that most people can be trusted, or that you cannot be too careful when dealing with strangers?” This survey question is frequently asked to thousands of individuals globally. The aim of this question is to obtain a measure for how trusting individuals are towards people they do not know, but with whom they nonetheless interact. This thesis shows that trust has substantial economic consequences. Currently, in economics trust is often disregarded. It is difficult to reconcile trusting behavior with the classical view of ‘economic man’ as a completely rational, self-interested being. This thesis includes four studies where this behavioral assumption does not hold, however. In fact, they show that more trust is better in various dimensions. From individual income and the location decision of multinational firms to the productivity and technological development of countries: trust matters. Each study identifies how trust generates economic value, and how large the effect of trust is. Furthermore, the development of trust is modeled to explain why there exist such large differences in trust levels between individuals, regions and countries

High-resolution imaging at the SOAR telescope

Bright single and binary stars were observed at the 4.1-m telescope with a fast electron-multiplication camera in the regime of partial turbulence correction by the visible-light adaptive optics system. We compare the angular resolution achieved by simple averaging of AO-corrected images (long-exposure), selection and re-centering (shift-and-add or "lucky" imaging) and speckle interferometry. The effect of partial AO correction, vibrations, and image post-processing on the attained resolution is shown. Potential usefulness of these techniques is evaluated for reaching the diffraction limit in ground-based optical imaging. Measurements of 75 binary stars obtained during these tests are given and objects of special interest are discussed. We report tentative resolution of the astrometric companion to Zeta Aqr B. A concept of advanced high-resolution camera is outlined.Comment: Accepted for publication in PASP. 14 pages, 9 figures, 2 tabl

L- and M-band imaging observations of the Galactic Center region

We present near-infrared H-, K-, L- and M-band photometry of the Galactic Center from images obtained at the ESO VLT in May and August 2002, using the NAOS/CONICA (H and K) and the ISAAC (L and M) instruments. The large field of view (70" x 70") of the ISAAC instrument and the large number of sources identified (L-M data for 541 sources) allows us to investigate colors, infrared excesses and extended dust emission. Our new L-band magnitude calibration reveals an offset to the traditionally used calibrations, which we attribute to the use of the variable star IRS7 as a flux calibrator. Together with new results on the extinction towards the Galactic Center (Scoville et al. 2003; Raab 2000), our magnitude calibration results in stellar color properties expected from standard stars and removes any necessity to modify the K-band extinction. The large number of sources for which we have obtained L-M colors allows us to measure the M-band extinction to A_M=(0.056+-0.006)A_V (approximately =A_L), a considerably higher value than what has so far been assumed. L-M color data has not been investigated previously, due to lack of useful M-band data. We find that this color is a useful diagnostic tool for the preliminary identification of stellar types, since hot and cool stars show a fairly clear L-M color separation. This is especially important if visual colors are not available, as in the Galactic Center. For one of the most prominent dust embedded sources, IRS3, we find extended L- and M-band continuum emission with a characteristic bow-shock shape. An explanation for this appearance is that IRS3 consists of a massive, hot, young mass-losing star surrounded by an optically thick, extended dust shell, which is pushed northwest by wind from the direction of the IRS16 cluster and SgrA*.Comment: 24 pages, 7 figures, 2 tables, accepted for publication in Astronomy & Astrophysic

When Interval Analysis Helps Inter-Block Backtracking

International audienceInter-block backtracking (IBB) computes all the solutions of sparse systems of non-linear equations over the reals. This algorithm, introduced in 1998 by Bliek et al., handles a system of equations previously decomposed into a set of (small) k × k sub-systems, called blocks. Partial solutions are computed in the different blocks and combined together to obtain the set of global solutions. When solutions inside blocks are computed with interval-based techniques, IBB can be viewed as a new interval-based algorithm for solving decomposed equation systems. Previous implementations used Ilog Solver and its IlcInterval library. The fact that this interval-based solver was more or less a black box implied several strong limitations. The new results described in this paper come from the integration of IBB with the interval-based library developed by the second author. This new library allows IBB to become reliable (no solution is lost) while still gaining several orders of magnitude w.r.t. solving the whole system. We compare several variants of IBB on a sample of benchmarks, which allows us to better understand the behavior of IBB. The main conclusion is that the use of an interval Newton operator inside blocks has the most positive impact on the robustness and performance of IBB. This modifies the influence of other features, such as intelligent backtracking and filtering strategies

Electron propagation in crossed magnetic and electric fields

Laser-atom interaction can be an efficient mechanism for the production of coherent electrons. We analyze the dynamics of monoenergetic electrons in the presence of uniform, perpendicular magnetic and electric fields. The Green function technique is used to derive analytic results for the field--induced quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi gas of electrons. The method yields the drift current and, at the same time it allows us to quantitatively establish the broadening of the (magnetic) Landau levels due to the electric field: Level number k is split into k+1 sublevels that render the $k$th oscillator eigenstate in energy space. Adjacent Landau levels will overlap if the electric field exceeds a critical strength. Our observations are relevant for quantum Hall configurations whenever electric field effects should be taken into account.Comment: 11 pages, 2 figures, submitte

The Vega Debris Disk -- A Surprise from Spitzer

We present high spatial resolution mid- and far-infrared images of the Vega debris disk obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The disk is well resolved and its angular size is much larger than found previously. The radius of the disk is at least 43" (330 AU), 70"(543 AU), and 105" (815 AU) in extent at 24, 70 and 160 um, respectively. The disk images are circular, smooth and without clumpiness at all three wavelengths. The radial surface brightness profiles imply an inner boundary at a radius of 11"+/-2" (86 AU). Assuming an amalgam of amorphous silicate and carbonaceous grains, the disk can be modeled as an axially symmetric and geometrically thin disk, viewed face-on, with the surface particle number density following an r^-1 power law. The disk radiometric properties are consistent with a range of models using grains of sizes ~1 to ~50 um. We find that a ring, containing grains larger than 180 um and at radii of 86-200 AU from the star, can reproduce the observed 850 um flux, while its emission does not violate the observed MIPS profiles. This ring could be associated with a population of larger asteroidal bodies analogous to our own Kuiper Belt. Cascades of collisions starting with encounters amongthese large bodies in the ring produce the small debris that is blown outward by radiation pressure to much larger distances where we detect its thermal emission. The dust production rate is >~10^15 g/s based on the MIPS results. This rate would require a very massive asteroidal reservoir for the dust to be produced in a steady state throughout Vega's life. Instead, we suggest that the disk we imaged is ephemeral and that we are witnessing the aftermath of a large and relatively recent collisional event, and subsequent collisional cascade.Comment: 13 pages, 17 figures, accepted for publication in ApJ. (Figures 2, 3a, 3b and 4 have been degraded to lower resolutions.

Modifying Anthocyanins Biosynthesis in Tomato Hairy Roots:A Test Bed for Plant Resistance to Ionizing Radiation and Antioxidant Properties in Space

Gene expression manipulation of specific metabolic pathways can be used to obtain bioaccumulation of valuable molecules and desired quality traits in plants. A single-gene approach to impact different traits would be greatly desirable in agrospace applications, where several aspects of plant physiology can be affected, influencing growth. In this work, MicroTom hairy root cultures expressing a MYB-like transcription factor that regulates the biosynthesis of anthocyanins in Petunia hybrida (PhAN4), were considered as a testbed for bio-fortified tomato whole plants aimed at agrospace applications. Ectopic expression of PhAN4 promoted biosynthesis of anthocyanins, allowing to profile 5 major derivatives of delphinidin and petunidin together with pelargonidin and malvidin-based anthocyanins, unusual in tomato. Consistent with PhAN4 features, transcriptomic profiling indicated upregulation of genes correlated to anthocyanin biosynthesis. Interestingly, a transcriptome reprogramming oriented to positive regulation of cell response to biotic, abiotic, and redox stimuli was evidenced. PhAN4 hairy root cultures showed the significant capability to counteract reactive oxygen species (ROS) accumulation and protein misfolding upon high-dose gamma irradiation, which is among the most potent pro-oxidant stress that can be encountered in space. These results may have significance in the engineering of whole tomato plants that can benefit space agriculture