Commissioning of the Adaptive Optics System NAOS-CONICA for the VLT : the way to First Light

In October 2002 NAOS-CONICA, one of the most powerful adaptive optics systems was offered to the astronomical community. The instrument is installed at the Very Large Telescope in Chile and operated by the European Southern Observatory. The adaptive optics system NAOS corrects for atmospheric turbulence and provides the near-infrared multi-mode camera and spectrograph CONICA with diffraction limited images. Development of NAOS was achieved by a French consortium, while CONICA was developed by a German consortium under the leadership of the Max-Planck-Institut für Astronomie, Heidelberg. In the context of this PhD thesis several critical contributions to the successful commissioning were made. The major test and calibration results obtained on the way to First Light, i.e., during the laboratory, integration and commissioning periods are presented. They cover cryogenics, mechanics, optics and detector characteristics of CONICA. A major achievement was the development and implementation of a technique for the calibration of static optical aberrations. Since the instrument is designed to achieve absolute Strehl ratios higher than 70%, even the accumulation of residual static wavefront perturbations arising from optical components in the imaging path, critically affect the overall performance. The technique has been completely implemented for the instrument, and the adaptive optics system automatically corrects the static aberrations according to the different instrument configurations. The presented technique will be of great importance for future adaptive optics systems. Particular attention is payed to the calibration of CONICA's high resolution imaging spectroscopy mode, realized by a cold tunable Fabry-Perot interferometer. A detailed guideline is given of how to process a phase-shift map and the capabilities for 3-dimensional structure analysis are demonstrated at Eta Carinae. A first, high-spatial resolution velocity map is created

Sub-systems in nearby solar-type wide binaries

We conducted a deep survey of resolved sub-systems among wide binaries with solar-type components within 67 pc from the Sun. Images of 61 stars in the K and H bands were obtained with the NICI adaptive-optics instrument on the 8-m Gemini-South telescope. Our maximum detectable magnitude difference is about 5mag and 7.8mag at 0.15" and 0.9" separations, respectively. This enables a complete census of sub-systems with stellar companions in the projected separation range from 5 to 100 AU. Out of 7 such companions found in our sample, only one was known previously. We determine that the fraction of sub-systems with projected separations above 5 AU is 0.12 +- 0.04 and that the distribution of their mass ratio is flat, with a power-law index 0.2 +- 0.5. Comparing this with the properties of closer spectroscopic sub-systems (separations below 1 AU), it appears that the mass-ratio distribution does not depend on the separation. The frequency of sub-systems in the separation ranges below 1 AU and between 5 and 100 AU is similar, about 0.15. Unbiased statistics of multiplicity higher than two, advanced by this work, provide constraints on star-formation theory.Comment: Accepted by Astronomical Journal. 13 pages, 5 figure

Revealing companions to nearby stars with astrometric acceleration

A subset of 51 Hipparcos astrometric binaries among FG dwarfs within 67pc has been surveyed with the NICI adaptive optics system at Gemini-S, directly resolving for the first time 17 sub-arcsecond companions and 7 wider ones. Using these data together with published speckle interferometry of 57 stars, we compare the statistics of resolved astrometric companions with those of a simulated binary population. The fraction of resolved companions is slightly lower than expected from binary statistics. About 10% of astrometric companions could be "dark" (white dwarfs and close pairs of late M-dwarfs). To our surprise, several binaries are found with companions too wide to explain the acceleration. Re-analysis of selected intermediate astrometric data shows that some acceleration solutions in the original Hipparcos catalog are spurious.Comment: Accepted by The Astronomical Journal. 15 pages, 6 figures, 4 table

MBMS—IP Multicast/Broadcast in 3G Networks

In this article, the Multimedia Broadcast and Multicast Service (MBMS) as standardized in 3GPP is presented. With MBMS, multicast and broadcast capabilities are introduced into cellular networks. After an introduction into MBMS technology, MBMS radio bearer realizations are presented. Different MBMS bearer services like broadcast mode, enhanced broadcast mode and multicast mode are discussed. Streaming and download services over MBMS are presented and supported media codecs are listed. Service layer components as defined in Open Mobile Alliance (OMA) are introduced. For a Mobile TV use case capacity improvements achieved by MBMS are shown. Finally, evolution of MBMS as part of 3GPP standardization is presented

Approximate model for analyzing band structures of single-ring hollow-core anti-resonant fibers

Precise knowledge of modal behavior is of essential importance for understanding light guidance, particularly in hollow-core fibers. Here we present a semi-analytical model that allows determination of bands formed in revolver-type anti-resonant hollow-core fibers. The approach is independent of the actual arrangement of the anti-resonant elements, does not enforce artificial lattice arrangements and allows determination of the effective indices of modes of preselected order. The simulations show two classes of modes: (i) low-order modes exhibiting effective indices with moderate slopes and (ii) a high number of high-order modes with very strong effective index dispersion, forming a quasi-continuum of modes. It is shown that the mode density scales with the square of the normalized frequency, being to some extent similar to the behavior of multimode fibers

Observing Strategies for the NICI Campaign to Directly Image Extrasolar Planets

We discuss observing strategy for the Near Infrared Coronagraphic Imager (NICI) on the 8-m Gemini South telescope. NICI combines a number of techniques to attenuate starlight and suppress superspeckles: 1) coronagraphic imaging, 2) dual channel imaging for Spectral Differential Imaging (SDI) and 3) operation in a fixed Cassegrain rotator mode for Angular Differential Imaging (ADI). NICI will be used both in service mode and for a dedicated 50 night planet search campaign. While all of these techniques have been used individually in large planet-finding surveys, this is the first time ADI and SDI will be used with a coronagraph in a large survey. Thus, novel observing strategies are necessary to conduct a viable planet search campaign.Comment: 12 pages, 10 figures, submitted to Proceedings of the SPI

NICI: combining coronagraphy, ADI, and SDI

The Near-Infrared Coronagraphic Imager (NICI) is a high-contrast AO imager at the Gemini South telescope. The camera includes a coronagraphic mask and dual channel imaging for Spectral Differential Imaging (SDI). The instrument can also be used in a fixed Cassegrain Rotator mode for Angular Differential Imaging (ADI). While coronagraphy, SDI, and ADI have been applied before in direct imaging searches for exoplanets. NICI represents the first time that these 3 techniques can be combined. We present preliminary NICI commissioning data using these techniques and show that combining SDI and ADI results in significant gains.Comment: Proc. SPIE, Vol. 7014, 70141Z (2008