154 research outputs found

    Hochauflösende Beobachtungen ultrakompakter HII-Gebiete

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    Die Arbeit präsentiert Ergebnisse von Breit- und Schmalbandbeobachtungen ultrakompakter HII-Gebiete im nahen und mittleren Infrarot. Erstmals kam im NIR ein System adaptiver Optik (ADONIS am 3.6m-Teleskop der ESO) umfassend fuer die Untersuchung dieser Objektklasse zum Einsatz. In der Arbeit werden zunaechst die bestehenden Modellvorstellungen zu ultrakompakten HII-Gebieten zusammengefasst. Dann wird die notwendigkeit hochaufloesender Infrarotbeobachtungen gezeigt sowie - als Loesungsansatz - die Methodik der adaptiven Optik umrissen. Praesentiert werden Ergebnisse zu den Objekten G45.45+0.06, G5.89-0.39 und G5.97-1.17. Darin werden der stellare Inhalt der genannten Gebiete sowie ihre Staubmassen und Ionisationsstrukturen charakterisiert. Hinsichtlich des Sternentstehungsprozesses bestaetigt sich, dass massereiche Sterne in Haufen entstehen. In G45 konnten dank der erreichten Aufloesung 8 Objekte als massereiche Sterne vom Spektraltyp O identifiziert und somit nachgewiesen werden, daß zumindest einige ultrakompakte HII-Gebiete von Haufen ionisiert werden. Die ultrakompakten HII-Gebiete bilden sich in der Regel durch Verschmelzung individueller Ionisationszonen, oder sie gehen auf einzelne Haufenmitglieder zurueck. Warmer Staub ist in allen dr ei Gebieten vorhanden, in G45 ist die Emission dieses Staubes aus denselben Gebieten zu beobachten wie die Frei-frei-Strahlung des ionisierten Plasmas. Ob dies ein Projektionseffekt ist, bedarf noch der Ueberprüfung, auf jeden Fall ist in allen drei Gebi eten warmer Staub an der Grenzschicht zum ionisierten Gas vorhanden. Die Materieverteilung bestimmt bei G45 und G5.89 auch die Morphologie. Bei einer Einordnung in bestehende Modellvorstellungen zu ultrakompakten HII-Gebieten wird entsprechend dargelgt, d aß auf dynamische Modelle kein Hinweis besteht sondern alleine die Staubmengen deren Verteilung zur Loesung des "Lebensdauerproblems" und der Erklaerung der Erscheinungsformen ausreichen

    Frame Combination Techniques for Ultra High-Contrast Imaging

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    We summarize here an experimental frame combination pipeline we developed for ultra high-contrast imaging with systems like the upcoming VLT SPHERE instrument. The pipeline combines strategies from the Drizzle technique, the Spitzer IRACproc package, and homegrown codes, to combine image sets that may include a rotating field of view and arbitrary shifts between frames. The pipeline is meant to be robust at dealing with data that may contain non-ideal effects like sub-pixel pointing errors, missing data points, non-symmetrical noise sources, arbitrary geometric distortions, and rapidly changing point spread functions. We summarize in this document individual steps and strategies, as well as results from preliminary tests and simulations.Comment: 9 pages, 4 figures, SPIE conference pape

    Single conjugate adaptive optics for the ELT instrument METIS

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    The ELT is a 39m large, ground-based optical and near- to mid-infrared telescope under construction in the Chilean Atacama desert. Operation is planned to start around the middle of the next decade. All first light instruments will come with wavefront sensing devices that allow control of the ELT's intrinsic M4 and M5 wavefront correction units, thus building an adaptive optics (AO) system. To take advantage of the ELT's optical performance, full diffraction-limited operation is required and only a high performance AO system can deliver this. Further technically challenging requirements for the AO come from the exoplanet research field, where the task to resolve the very small angular separations between host star and planet, has also to take into account the high-contrast ratio between the two objects. We present in detail the results of our simulations and their impact on high-contrast imaging in order to find the optimal wavefront sensing device for the METIS instrument. METIS is the mid-infrared imager and spectrograph for the ELT with specialised high-contrast, coronagraphic imaging capabilities, whose performance strongly depends on the AO residual wavefront errors. We examined the sky and target sample coverage of a generic wavefront sensor in two spectral regimes, visible and near-infrared, to pre-select the spectral range for the more detailed wavefront sensor type analysis. We find that the near-infrared regime is the most suitable for METIS. We then analysed the performance of Shack-Hartmann and pyramid wavefront sensors under realistic conditions at the ELT, did a balancing with our scientific requirements, and concluded that a pyramid wavefront sensor is the best choice for METIS. For this choice we additionally examined the impact of non-common path aberrations, of vibrations, and the long-term stability of the SCAO system including high-contrast imaging performance.Comment: 37 pages, 27 figures, accepted for publication in Experimental Astronom

    SPOTS: The Search for Planets Orbiting Two Stars. I. Survey description and first observations

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    Direct imaging surveys for exoplanets commonly exclude binary stars from their target lists, leaving a large part of the overall planet demography unexplored. To address this gap in our understanding of planet formation and evolution, we have launched the first direct imaging survey dedicated to circumbinary planets: SPOTS, the Search for Planets Orbiting Two Stars. In this paper, we discuss the theoretical context, scientific merit, and technical feasibility of such observations, describe the target sample and observational strategy of our survey, and report on the first results from our pilot survey of 26 targets with the VLT NaCo facility. While we have not found any confirmed substellar companions to date, a number of promising candidate companions remain to be tested for common proper motion in upcoming follow-up observations. We also report on the astrometry of the three resolved binaries in our target sample. This pilot survey constitutes a successful proof of concept for our survey strategy and paves the way for a second stage of exploratory observations with VLT SPHERE.Comment: 12 pages, 4 figures, 3 tables. Accepted for publication in A&

    Infrared Observation of Hot Cores

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    We report on mid-infrared imaging of hot cores performed with SpectroCam-10 and TIMMI2. The observations aimed at the detection of thermal emission presumably associated with the hot cores. Mid-infrared flux measurements are required to improve the luminosity and optical depth estimates for these sources. Results are presented for W3(H2_2O), G9.62+0.19, G10.47+0.03, and the possible hot core candidate G232.620+0.996. They illustrate that the morphology of these sources cannot be described by simple geometries. Therefore, line-of-sight effects and considerable extinction even at mid-infrared wavelengths must not be neglected.Comment: 6 pages, 4 figures, Conference proceeding "Origins of stars and planets: The VLT view", ESO, Garching, April 24-27 200

    The VLTI/MIDI survey of massive young stellar objects - Sounding the inner regions around intermediate- and high-mass young stars using mid-infrared interferometry

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    We aim to characterize the distribution and composition of circumstellar material around young massive stars, and to investigate exactly which physical structures in these objects are probed by long-baseline mid-infrared interferometric observations. We used the two-telescope interferometric instrument MIDI of the Very Large Telescope Interferometer of the European Southern Observatory to observe a sample of 24 intermediate- and high-mass young stellar objects in the N band (8-13 micron). We had successful fringe detections for 20 objects, and present spectrally-resolved correlated fluxes and visibility levels for projected baselines of up to 128 m. We fit the visibilities with geometric models to derive the sizes of the emitting regions, as well as the orientation and elongation of the circumstellar material. Fourteen objects in the sample show the 10 micron silicate feature in absorption in the total and correlated flux spectra. For 13 of these objects, we were able to fit the correlated flux spectra with a simple absorption model, allowing us to constrain the composition and absorptive properties of the circumstellar material. Nearly all of the massive young stellar objects observed show significant deviations from spherical symmetry at mid-infrared wavelengths. In general, the mid-infrared emission can trace both disks and outflows, and in many cases it may be difficult to disentangle these components on the basis of interferometric data alone, because of the sparse spatial frequency coverage normally provided by current long-baseline interferometers. For the majority of the objects in this sample, the absorption occurs on spatial scales larger than those probed by MIDI. Finally, the physical extent of the mid-infrared emission around these sources is correlated with the total luminosity, albeit with significant scatter.Comment: 36 pages, 22 figures. Accepted to Astronomy and Astrophysic

    Challenges and Practices in Aligning Requirements with Verification and Validation: A Case Study of Six Companies

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    Weak alignment of requirements engineering (RE) with verification and validation (VV) may lead to problems in delivering the required products in time with the right quality. For example, weak communication of requirements changes to testers may result in lack of verification of new requirements and incorrect verification of old invalid requirements, leading to software quality problems, wasted effort and delays. However, despite the serious implications of weak alignment research and practice both tend to focus on one or the other of RE or VV rather than on the alignment of the two. We have performed a multi-unit case study to gain insight into issues around aligning RE and VV by interviewing 30 practitioners from 6 software developing companies, involving 10 researchers in a flexible research process for case studies. The results describe current industry challenges and practices in aligning RE with VV, ranging from quality of the individual RE and VV activities, through tracing and tools, to change control and sharing a common understanding at strategy, goal and design level. The study identified that human aspects are central, i.e. cooperation and communication, and that requirements engineering practices are a critical basis for alignment. Further, the size of an organisation and its motivation for applying alignment practices, e.g. external enforcement of traceability, are variation factors that play a key role in achieving alignment. Our results provide a strategic roadmap for practitioners improvement work to address alignment challenges. Furthermore, the study provides a foundation for continued research to improve the alignment of RE with VV
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