5 research outputs found
Auf dem Weg vom Teenager zum Twen
Regionalstatistische Informationssysteme sind aus dem Arbeitsalltag der statistischen LandesĂ€mter nicht mehr wegzudenken: Sie sind gleichrangig neben die klassischen Formen der Bereitstellung statistischer Informationen getreten. Die Vielzahl statistischer Ămter hat indessen auch zu einer Vielzahl verschiedener Lösungen gefunden. Welchen Weg die Informationssysteme bisher gingen, wo sie heute stehen und welchen Weg sie kĂŒnftig einschlagen sollten â diese Fragen werden im Ăberblick untersucht. Am Beispiel der Landesdatenbank Nordrhein-Westfalen wird sodann das Leistungsvermögen eines relativ fortgeschrittenen statistischen Informationssystems dargestellt
Multiple star systems in the Orion nebula
This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for Ξ1 Ori B, Ξ2 Ori B, and Ξ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for Ξ1 Ori A, Ξ1 Ori C, Ξ1 Ori D, and Ξ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary Ξ1 Ori C and we are able to derive a new orbit for Ξ1 Ori D. We find a system mass of 21.7 Mâ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie SkĆodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran
PremiÚre lumiÚre de GRAVITY : une nouvelle Úre pour l'interférométrie optique
International audienceWith the arrival of the second generation instrument GRAVITY, the Very Large Telescope Interferometer (VLTI) has entered a new era of optical interferometry. This instrument pushes the limits of accuracy and sensitivity by orders of magnitude. GRAVITY has achieved phase-referenced imaging at approximately milliarcsecond (mas) resolution and down to ~ 100-microarcsecond astrometry on objects that are several hundred times fainter than previously observable. The cutting-edge design presented in Eisenhauer et al. (2011) has become reality. This article sketches out the basic principles of the instrument design and illustrates its performance with key science results obtained during commissioning: phase-tracking on stars with K ~ 10 mag, phase-referenced interferometry of objects fainter than K âł 17 mag, minute-long coherent integrations, a visibility accuracy of better than 0.25 %, and spectro-differential phase and closure phase accuracy better than 0.5 degrees, corresponding to a differential astrometric precision of a few microarcseconds (ÎŒas).Avec l'arrivĂ©e de l'instrument de deuxiĂšme gĂ©nĂ©ration GRAVITY, qui repousse les limites de prĂ©cision et de sensibilitĂ© en interfĂ©romĂ©trie optique de plusieurs ordres de magnitude, le trĂšs grand interfĂ©romĂštre de l'Observatoire EuropĂ©en Austral (ESO/VLTI) est entrĂ© dans une nouvelle Ăšre. GRAVITY a rĂ©alisĂ© des images en rĂ©fĂ©rence de phase avec une rĂ©solution de l'ordre de la milli-seconde d'arc et des mesures astromĂ©triques avec une prĂ©cision atteignant 100 micro-secondes sur des objets plusieurs centaines de fois moins brillants qu'observable prĂ©cĂ©demment. Le concept de pointe, prĂ©sentĂ© dans [Eisenhauer, F. et al., The Messenger, 143, 16 (2011)] est devenu rĂ©alitĂ©. Cet article esquisse les principes de base de l'instrument et illustre ses performances avec les rĂ©sultats scientifiques clĂ© obtenus pendant les tests de mise en service : asservissement en phase sur des Ă©toiles de magnitude K=10, imagerie en rĂ©fĂ©rence de phase sur des objets de magnitude supĂ©rieure Ă K=17, intĂ©grations cohĂ©rentes de l'ordre de la minute, prĂ©cision de mesure de visibilitĂ© infĂ©rieure Ă 0,25%, et prĂ©cision de mesure sur les phases de clĂŽture ou spectro-diffĂ©rentielles meilleure que 0,5 degrĂ©s, ce qui correspond Ă une prĂ©cision astromĂ©trique diffĂ©rentielle de quelques micro-arcsecondes
Multiple star systems in the Orion nebula
This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for theta(1) Ori B, theta(2) Ori B, and theta(2) Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for theta(1) Ori A, theta(1) Ori C, theta(1) Ori D, and theta(2) Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary theta(1) Ori C and we are able to derive a new orbit for theta(1) Ori D. We find a system mass of 21.7 M-circle dot and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion
PremiÚre lumiÚre de GRAVITY : interférométrie optique avec référence de phase pour le mode interférométrique du TrÚs Grand Télescope européen
International audienceGRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m2. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as mK â 10âmag, phase-referenced interferometry of objects fainter than mK â 15âmag with a limiting magnitude of mK â 17âmag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than tenâmicroarcseconds (ÎŒas). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 ÎŒas when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the âGalactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BPâCru and the active galactic nucleus of PDSâ456 for a few ÎŒas spectro-differential astrometry, the TâTauri star SâCrA for a spectro-differential visibility analysis, ΟâTel and 24âCap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.GRAVITY est un nouvel instrument permettant la recombinaison interfĂ©romĂ©trique des tĂ©lescopes du VLT (Very Large Telescope) de l'ESO (European Southern Observatory) pour former un tĂ©lescope avec une limite de rĂ©solution Ă©quivalente Ă un diamĂštre 130 m et une surface collectrice de 200 mÂČ. L'instrument inclut un dispositif en optique intĂ©grĂ© alimentĂ© par fibre pour recombinaison des faisceaux, un spectromĂštre Ă haute rĂ©solution, des dispositifs intĂ©grĂ©s d'analyse et de contrĂŽle, un analyse de surface d'onde en infrarouge (IR) proche, un suiveur de frange, un mode double champ et une mĂ©trologie laser. GRAVITY fait office de prĂ©curseur en introduisant en interfĂ©romĂ©trie optique/IR les techniques de rĂ©fĂ©rence de phase et d'astromĂ©trie Ă faible champ, inspirĂ©es des concepts dĂ©veloppĂ©s en radio-interfĂ©romĂ©trie. Cet article donne un aperçu de GRAVITY et rend compte des performances et des premiĂšres observations astronomiques lors de la mise en service en 2015/16. Nous dĂ©montrons le suivi de phase sur des Ă©toiles aussi faible que mK â 10 mag, l'interfĂ©romĂ©trie par rĂ©fĂ©rence de phase sur des objets plus faibles que mK â 15 mag avec une magnitude limite de mK â 17 mag, des intĂ©grations cohĂ©rentes pendant une minute, une prĂ©cision de mesure de visibilitĂ© meilleure que 0,25%, et une prĂ©cision sur la mesure des phases diffĂ©rentielles spectrales ou des clĂŽtures de phase meilleure que 0,5 °, correspondant Ă une prĂ©cision astromĂ©trique diffĂ©rentielle meilleure que dix microsecondes d'arc (ÎŒas). L'astromĂ©trie Ă double champ, mesurant la diffĂ©rence de phase entre deux objets avec mĂ©trologie laser, est encore en cours de test. Les premiĂšres observations montrent des rĂ©sidus aussi bas que 50 ÎŒas en suivant des objets sur plusieurs mois. Nous illustrons la performance de l'instrument avec les observations d'objets archĂ©typiques pour les diffĂ©rents modes d'instrument. Les exemples comprennent le trou noir supermassif du centre galactique et son Ă©toile S2 en orbite rapide pour les observations Ă double champ avec rĂ©fĂ©rence de phase et analyse de front d'onde IR, l'Ă©toile binaire massive BP Cru Ă Ă©mission X et le noyau galactique actif de PDS 456 pour quelques cas de spectro-astromĂ©trie diffĂ©rentielle avec quelques ÎŒas de prĂ©cision, l'Ă©toile S CrA (de type T Tauri) pour une analyse spectro-diffĂ©rentielle de visibilitĂ©, les Ă©toiles Ο Tel et 24 Cap pour des observations de visibilitĂ© de haute prĂ©cision, et η Car pour une imagerie interfĂ©romĂ©trique avec GRAVITY