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LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its layer-oriented MCAO systems (one for each arm of the interferometer) are conjugated to the ground layer and an additional layer in the upper atmosphere. In this contribution MCAO wavefront control is discussed in the context of the overall control scheme for LINC-NIRVANA. Special attention is paid to a set of auxiliary control tasks which are mandatory for MCAO operation: The Fields of View of each wavefront sensor in the instrument have to be derotated independent from each other and independently from the science field. Any wavefront information obtained by the sensors has to be matched to the time invariant modes of the deformable mirrors in the system. The tip/tilt control scheme is outlined, in which atmospheric, but also instrumental tip/tilt corrections are sensed with the high layer wavefront sensor and corrected by the adaptive secondary mirror of the LBT. Slow image motion effects on the science detector have to be considered, which are caused by flexure in the non-common path between AO and the science camera, atmospheric differential refraction, and alignment tolerances of the derotators. Last but not least: The sensor optics (pyramids) have to be accurately positioned at the images of natural reference stars.

Characterisation, mitigation and correction of telescope vibrations have proven to be crucial for the performance of astronomical infrared interferometers. The project teams of the interferometers for the LBT, LINC-NIRVANA and LBTI, and LBT Observatory (LBTO) have embarked on a joint effort to implement an accelerometer-based vibration measurement system distributed over the optical elements of the LBT. OVMS, the Optical Path Difference and Vibration Monitoring System will serve to (i) ensure conditions suitable for adaptive optics (AO) and interferometric (IF) observations and (ii) utilize vibration information, converted into tip-tilt and optical path difference data, in the control strategies of the LBT adaptive secondary mirrors and the beam combining interferometers. The system hardware is mainly developed by Steward Observatory's LBTI team and its installation at the LBT is underway. The OVMS software development and associated computer infrastructure is the responsibility of the LINC-NIRVANA team at MPIA Heidelberg. Initially, the OVMS will fill a data archive provided by LBTO that will be used to study vibration data and correlate them with telescope movements and environmental parameters thereby identifiying sources of vibrations and to eliminate or mitigate them. Data display tools will help LBTO staff to keep vibrations within predefined thresholds for quiet conditions for AO and IF observations. Later-on real-time data from the OVMS will be fed into the control loops of the AO systems and IF instruments in order to permit the correction of vibration signals with frequencies up to 450 Hz.

LINC-NIRVANA is the near-infrared Fizeau interferometric imaging camera for the Large Binocular Telescope (LBT). For an efficient interferometric operation of LINC-NIRVANA the Fringe and Flexure Tracking System (FFTS) is mandatory: It is a real-time servo system that allows to compensate atmospheric and instrumental optical pathlength differences (OPD). The thereby produced time-stable interference pattern at the position of the science detector enables long integration times at interferometric angular resolutions. As the development of the FFTS includes tests of control software and robustness of the fringe tracking concept in a realistic physical system a testbed interferometer is set up as laboratory experiment. This setup allows us to generate point-spread functions (PSF) similar to the interferometric PSF of the LBT via a monochromatic (He-Ne laser) or a polychromatic light source (halogen lamp) and to introduce well defined, fast varying phase offsets to simulate different atmospheric conditions and sources of instrumental OPD variations via dedicated actuators. Furthermore it comprises a piston mirror as actuator to counteract the measured OPD and a CCD camera in the focal plane as sensor for fringe acquisition which both are substantial devices for a fringe tracking servo loop. The goal of the setup is to test the performance and stability of different control loop algorithms and to design and optimize the control approaches. We present the design and the realization of the testbed interferometer and comment on the fringe-contrast behavior.

We present the latest status of the fringe detecting algorithms for the LINC-NIRVANA FFTS (Fringe and Flexure Tracker System). The piston and PSF effects of the system from the top of the atmosphere through the telescopes and multi-conjugate AO systems to the detector are discussed and the resulting requirements for the FFTS outlined.

The Fringe and Flexure Tracker System (FFTS) of the LINC-NIRVANA instrument is designed to monitor and correct the atmospheric piston variations and the instrumental vibrations and flexure at the LBT during the NIR interferometric image acquisition. In this contribution, we give an overview of the current FFTS control design, the various subsystems, and their interaction details. The control algorithms are implemented on a realtime computer system with interfaces to the fringe and flexure detector read-out electronics, the OPD vibration monitoring system (OVMS) based on accelerometric sensors at the telescope structure, the piezo-electric actuator for piston compensation, and the AO systems for offloading purposes. The FFTS computer combines data from different sensors with varying sampling rate, noise and delay. This done on the basis of the vibration data and the expected power spectrum of atmospheric conditions. Flexure effects are then separated from OPD signals and the optimal correcting variables are computed and distributed to the actuators. The goal is a 120 nm precision of the correction at a bandwidth of about 50 Hz. An end-to-end simulation including models of atmospheric effects, actuator dynamics, sensor effects, and on-site vibration measurements is used to optimize controllers and filters and to pre-estimate the performance under different observation conditions.

LINC-NIRVANA (LN) is a German/Italian interferometric beam combiner camera for the Large Binocular Telescope. Due to homothetic imaging, LN will make use of an exceptionally large field-of-view. As part of LN, the Fringe-and-Flexure-Tracker system (FFTS) will provide real-time, closed-loop measurement and correction of pistonic and flexure signals induced by the atmosphere and inside the telescope-instrument system. Such compensation is essential for achieving coherent light combination over substantial time intervals (~ 10min.). The FFTS is composed of a dedicated near-infrared detector, which can be positioned by three linear stages within the curved focal plane of LN. The system is divided into a cryogenic (detector) and ambient (linear stages) temperature environment, which are isolated from each other by a moving baffle. We give an overview of the current design and implementation stage of the FFTS opto-mechanical and electronic components. We present recent important updates of the system, including the development of separated channels for the tracking of piston and flexure. Furthermore, the inclusion of dispersive elements will allow for the correction of atmospheric differential refraction, as well as the induction of artificial dispersion to better exploit the observational-conditions parameter space (air mass, brightness).

We review the status of hardware developments related to the Linc-Nirvana optical path difference (OPD) control. The status of our telescope vibration measurements is given. We present the design concept of a feed-forward loop to damp the impact of telescope mirror vibrations on the OPD seen by Linc-Nirvana. At the focus of the article is a description of the actuator of the OPD control loop. The weight and vibration optimized construction of this actuator (aka piston mirror) and its mount has a complex dynamical behavior, which prevents classical PI feedback control from delivering fast and precise motion of the mirror surface. Therefore, an H-; optimized control strategy will be applied, custom designed for the piston mirror. The effort of realizing a custom controller on a DSP to drive the piezo is balanced by the outlook of achieving more than 5x faster servo bandwidths. The laboratory set-up to identify the system, and verify the closed loop control performance is presented. Our goal is to achieve 30 Hz closed-loop control bandwidth at a precision of 30 nm.

The LINC-NIRVANA wavefront sensors are in their AIT phase. The first Ground-layerWavefront Sensor (GWS) is shaping in the Adaptive Optics laboratory of the Astronomical Observatory of Padova, while both the Mid- High Wavefront Sensors (MHWSs) have been aligned and tested as stand-alone units in the Observatory of Bologna (MHWS#1 aligned to LINC-NIRVANA post focal relay optics). LINC-NIRVANA is a Fizeau infrared interferometer equipped with advanced, MultiConjugated Adaptive Optics (MCAO) for the Large Binocular Telescope. The aim of the instrument is to allow true interferometric imagery over a 10" square Field of View (FoV), getting the sensitivity of a 12m telescope and the spatial resolution of a 22.8m one. Thanks to the MCAO concept, LINC-NIRVANA will use up to 20 Natural Guide Stars (NGS) which are divided, according to Layer-Oriented Multiple Field of View technique, between the GWSs and the MHWSs. To find such a large number of references, the AO systems will use a wide FoV of 6' in diameter and the light coming from the references used by each WFS will optically sum on its CCD camera. The MHWSs will detect the deformations due to the high layers and will select up to 8 NGSs in the inner 2' FoV. The GWSs, instead, will reconstruct the deformations introduced by the lower atmosphere, which was found out to be the main source of seeing. Their peculiarity is the highest number of references (up to 12) ever used in a single instrument, selected in an annular 2'-6' FoV.

LINC-NIRVANA will realize the interferometric imaging focal station of the Large Binocular Telescope. A double Layer Oriented multi-conjugate adaptive optics system assists the two arms of the interferometer, supplying high order wave-front correction. In order to counterbalance the field rotation, mechanical derotation for the two ground wave-front sensors, and optical derotators for the mid-high layers sensors fix the positions of the focal planes with respect to the pyramids aboard the wave-front sensors. The derotation introduces pupil images rotation on the wavefront sensors: the projection of the deformable mirrors on the sensor consequently change. The proper adjustment of the control matrix will be applied in real-time through numerical computation of the new matrix. In this paper we investigate the temporal and computational aspects related to the pupils rotation, explicitly computing the wave-front errors that may be generated., 6 pages, 2 figures, presented at SPIE Symposium "Astronomical Telescopes and Instrumentation'' conference "Adaptive Optics Systems II'',Sunday 27 June 2010, San Diego, California, USA

The power of the Large Binocular Telescope (LBT) wit h its two 8.4m primary mirrors sharing a common mountwill unfold its full potential with the LINC-NIRVANA (LN) instrument. LINC-NIRVANA is a German-Italianbeam combiner for the LBT and will interfere the light from the two 8.4m mirrors of the LBT in Fizeau mode.More than 140 motors have to be handled by custom developed Motor Controllers (MoCons). One importantfeature of the MoCon is the support of externally computed trajectories. Motion pro“les provide information onthe movement of the motor along a de“ned path over a certain period of time. Such pro“les can be uploadedto the MoCon over Ethernet and can be started at a speci“c time. For “eld derotation it is critical that thederotation trajectories are executed w ith a very precise relative and absolute timing. This raises the problemof the synchronization of the MoCon internal clock with the system time of the servers that are hosting LINC-NIRVANAs Instrument Control Software. The MoCon time should be known by the servers with an uncertaintyof few milliseconds in order to match the start time of the motion pro“le and the “eld rotation trajectory. Inthis paper we will discuss how to synchronize the MoCon internal time and the PC system time.Keywords: LBT, LINC-NIRVANA, MPIA, ICS, Instrument Control Software, Basic Device Application, Time,Synchronization

LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). In close cooperation with the Adaptive Optics systems of LINC-NIRVANA the Fringe and Flexure Tracking System (FFTS) is a fundamental component to ensure a complete and time-stable wavefront correction at the position of the science detector in order to allow for long integration times at interferometric angular resolutions. In this contribution, we present the design and the realization of the ongoing FFTS laboratory tests, taking into account the system requirements. We have to sample the large Field of View and to follow the reference source during science observations to an accuracy of less than 2 microns. In particular, important tests such as cooling tests of cryogenic components and tip - tilt test (the repeatability and the precision under the different inclinations) are presented. The system parameters such as internal flexure and precision are discussed.

Laboratory and on-sky experience suggests that the integration of big astronomical instruments, specially of a complex interferometric system, is a challenging process. LINC-NIRVANA is the Fizeau interferometric imager for the Large Binocular Telescope (LBT). Simulating the final operating environment of every system component has shown how critical is the presence of flexures, vibrations and thermal expansion. Assembling and aligning the opto-mechanical sub-systems will require an absolute reference which is not affected by static displacements or positioning errors. A multi-purpose calibration unit has been designed to ensure the quality of the alignment of optics and detectors and the reliability of the mechanical setup. This new compact and light-weighted unit is characterized by sophisticated kinematics, simple mechanical design and composite materials. In addition, the reduced number of motorized axis improves the stiffness and lowers the angular displacements due to moving parts. The modular concept integrates several light sources to provide the proper calibration reference for the different sub-systems of LINC-NIRVANA. For the standard alignment of the optics an absolute reference fiber will be used. For flatfielding of the detectors the unit provides an integrating sphere, and a special rotating multi-fiber plate (infrared and visible) is used to calibrate the advanced adaptive optics and the fringe-tracking systems. A module to control non-common path aberrations (Flattening of Deformable Mirrors) is also provided.

LINC-NIRVANA is the IR Fizeau interferometric imager that will be installed within a couple of years on the Large Binocular Telescope (LBT) in Arizona. Here we present a particular sub-system, the so-called Patrol Camera (PC), which has been now completed, along with the results of the laboratory tests. It images (in the range 600-900 nm) the same 2 arcmin FoV seen by the Medium-High Wavefront Sensor (MHWS), adequately sampled to provide the MHWS star enlargers with the positions of the FoV stars with an accuracy of 0.1 arcsec. To this aim a diffraction-limited performance is not required, while a distortion free focal plane is needed to provide a suitable astrometric output. Two identical systems have been realized, one for each single arm, which corresponds to each single telescope. We give here the details concerning the optical and mechanical layout, as well as the CCD and the control system. The interfaces (mainly software procedures) with LINC-NIRVANA (L-N) are also presented.

The Large Binocular Telescope (LBT) is an international collaboration, with partners from the United States, Italy, and Germany. The telescope uses two 8.4-meter diameter primary mirrors to produce coherent images with the combined light along with adaptive optics. The correct functioning and optimum performance of the LBT is only achieved through a complex interplay of various optical elements. Each of these elements has its individual vibration behaviour, and therefore it is necessary to characterize the LBT as a distributed vibration system. LINC-NIRVANA is a near-infrared image-plane beam combiner with advanced, multi-conjugated adaptive optics, and one of the interferometric instruments for the Large Binocular Telescope (LBT). Its spectral range goes from 1.0 μm to 2.45 μm, therefore the requirements for the maximum optical path difference (OPD) are very tight (λ/10 ~ 100 nm). 1 During two dedicated campaigns, the vibrations introduced by various actuators were measured using different kinds of sensors. The evaluation of the obtained data allows an estimation of the frequency and amplitude contributions of the individual vibration sources. Until the final state of the LBT is reached, further measurements are necessary to optimize and adapt the equipment and also the investigated elements and configurations (measurement points and directions, number of sensors, etc.).

LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). Its Fringe and Flexure Tracking System (FFTS) is mandatory for an effcient interferometric operation of LINC-NIRVANA: the task of this cophasing system is to assure a time-stable interference pattern in the focal plane of the camera. A testbed interferometer, set up as laboratory experiment, is used to develop the FFTS control loop and to test the robustness of the fringe tracking concept. The geometry of the resulting interferometric intensity distribution in the focal plane of the implemented CCD corresponds to that of the LBT PSF. The setup allows to produce monochromatic (He-Ne laser) and polychromatic (halogen lamp) PSFs and allows to actively introduce well defined low-order phase perturbations, namely OPD and differential tip/tilt. Furthermore, all components that are required in a fringe tracking servo loop are included: a sensor for fringe acquisition and an actuator to counteract measured OPD. With this setup it is intended to determine the performance with which a fringe tracking control loop is able to compensate defined OPD sequences, to test different control algorithms, and to optimize the control parameters of an existing servo system. In this contribution we present the design and the realization of the testbed interferometer. Key parameters describing the white light testbed interferometer, such as fringe contrast and thermal sensitivity are discussed. The effects of all controllable phase perturbations are demonstrated.

As a near-infrared (NIR) wide field interferometric imager offering an angular resolution of about 10 milliarcseconds LINC-NIRVANA at the Large Binocular Telescope will be an ideal instrument for imaging the center of the Milky Way especially in conjunction with mm/sub-mm interferometers like CARMA, ATCA or, in the near future, ALMA. Sagittarius A* (Sgr A*) is the electromagnetc manifestation of the ~4×106M super-massive black hole (SMBH) at the Galactic Center. First results from a mult-wavelength campaign focused on Sgr A*, based on the VLT and on CARMA, ATCA, and the IRAM 30m-telescope, in May 2007 show that the NIR data are consistent with partially depolarized non-thermal emission from confined hot spots in relativistic orbits around SgrA*. A 3mm flare following a May 2007 NIR flare is consistent with SSC emission from adiabatically expanding plasma in a wind or jet. With the LBT and ALMA we will be able to study the spectral evolution of NIR/sub-mm/mm flare emission in order to constrain the emission mechanism, the jet/wind physics, and possibly determine the angular momentum of the SMBH. LINC/NIRVANA will also serve to investigate the stellar population and dynamics in the cluster surrounding Sgr A*. A particular emphasis will lie on examining dust embedded and young stars and to unravel the star formation history in the cluster. For the 0.3 parsec core radius central star cluster the investigation of will be investigated.

LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA. It is tailored to compensate low-order phase perturbations in real-time to allow for a time-stable interference pattern in the focal plane of the science camera during the integration. Two independent control loops are realized within FFTS: A cophasing loop continuously monitors and corrects for atmospheric and instrumental differential piston between the two arms of the interferometer. A second loop controls common and differential image motion resulting from changing orientations of the two optical axes of the interferometer. Such changes are caused by flexure but also by atmospheric dispersion. Both loops obtain their input signals from different quadrants of a NIR focal plane array. A piezo-driven piston mirror in front of the beam combining optics serves as actuator in the cophasing loop. Differential piston is determined by fitting a parameterized analytical model to the observed point spread function of a reference target. Tip-tilt corrections in the flexure loop are applied via the secondary mirrors. Image motion is sensed for each optical axis individually in out-of-focus images of the same reference target. In this contribution we present the principles of operation, the latest changes in the opto-mechanical design, the current status of the hardware development.

LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). Its Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA: the task of this cophasing system is to assure a time-stable interference pattern in the focal plane of the camera. Differential piston effects will be detected and corrected in a real-time closed loop by analyzing the PSF of a guide star at a frequency of 100Hz-200Hz. A dedicated piston mirror will then be moved in a corresponding manner by a piezo actuator. The long-term flexure tip/tilt variations will be compensated by the AO deformable mirrors. A testbed interferometer has been designed to simulate the control process of the movement of a scaled piston mirror under disturbances. Telescope vibration and atmospheric variations with arbitrary power spectra are induced into the optical path by a dedicated piezo actuator. Limiting factors of the control bandwith are the sampling frequency and delay of the detector and the resonance frequency of the piston mirror. In our setup we can test the control performance under realistic conditions by considering the real piston mirrors dynamics with an appropriate software filter and inducing a artificial delay of the PSF detector signal. Together with the expected atmospheric OPD variations and a realistic vibration spectrum we are able to quantify the piston control performance for typical observation conditions. A robust control approach is presented as result from in-system control design as provided by the testbed interferometer with simulated dynamics.

7 pags., 3 figs. -- The Universe under the Microscope – Astrophysics at High Angular Resolution, 21–25 April 2008, Bad Honnef, Germany, At the center of the Milky Way, with a distance of 8 kpc, the compact source Sagittarius A* (SgrA*) can be associated with a super massive black hole of 4x 106M⊙. SgrA* shows strong variability from the radio to the X-ray wavelength domains. Here we report on simultaneous NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the IRAM 30m telescope. © 2008 IOP Publishing Ltd., Part of this work was supported by the German Deutsche Forschungsgemeinschaft, DFG via grant SFB 494. L. Meyer, K. Muzic, M. Zamaninasab, D. Kunneriath, and R.-S. Lu, are members of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the MPIfR and the Universities of Bonn and Cologne. RS acknowledges support by the Ramon y Cajal programme by the Ministerio de Ciencia y Innovacion of the government of Spain.

This paper addresses the global molecular gas properties of a representative sample of galaxies hosting low-luminosity quasistellar objects. An abundant supply of gas is necessary to fuel both the active galactic nucleus and any circum-nuclear starburst activity of QSOs. We selected a sample of nearby low-luminosity QSO host galaxies that is free of infrared excess biases. All objects are drawn from the Hamburg-ESO survey for bright UV-excess QSOs, have DEC>-30 degrees and redshifts that do not exceed z=0.06. The IRAM 30m telescope was used to measure the CO(1-0) and CO(2-1) transition in parallel. 27 out of 39 galaxies in the sample have been detected. The molecular gas masses of the detected sources range from 0.4E9 M_sun to 9.7E9 M_sun. We can confirm that the majority of galaxies hosting low-luminosity QSOs are rich in molecular gas. The properties of galaxies hosting brighter type I AGN and circumnuclear starformation regions differ from the properties of galaxies with fainter central regions. The overall supply of molecular gas and the spread of the line width distribution is larger. When comparing the far-infrared with the CO luminosities, the distribution can be separated into two different power-laws: one describing the lower activity Seyfert I population and the second describing the luminous QSO population. The separation in the L_FIR/L'_CO behavior may be explainable with differing degrees of compactness of the emission regions. We provide a simple model to describe the two power-laws. The sample studied in this paper is located in a transition region between the two populations.

The correction of atmospheric differential piston and instrumental flexure effects is mandatory for interferometric operation of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in a real-time closed loop. Being a Fizeau-Interferometer, the LBT provides a large field of view (FoV). The FFTS can make use of the large FoV and increase the sky coverage of the overall instrument if it is able to acquire the light of a suitable fringe tracking reference star within the FoV. For this purpose, the FFTS detector needs to be moved to the position of the reference star PSF in the curved focal plane and needs to precisely follow its trajectory as the field rotates. Sub-pixel (1 pixel = 18.5 micron) positioning accuracy is required over a travel range of 200mm x 300mm x 70mm. Strong are the constraints imposed by the need of a cryogenic environment for the moving detector. We present a mechanical design, in which the Detector Positioning Unit (DPU) is realized with off-the-shelf micro-positioning stages, which can be kept at ambient temperature. A moving baffle will prevent the intrusion of radiation from the ambient temperature environment into the cryogenic interior of the camera. This baffle consists of two nested disks, which synchronously follow any derotation - or repositioning trajectory of the DPU. The detector, its fanout board and a filter wheel are integrated into a housing that is mounted on top of the DPU and that protects the FFTS detector from stray light. Long and flexible copper bands allow heat transfer from the housing to the LINC-NIRVANA heat exchanger.

The Fringe and Flexure Tracking System (FFTS) is designed to correct the atmospheric piston variations and the instrumental flexure during the NIR interferometric image acquisition of the LINC-NIRVANA camera at the LBT. The interferometric image quality depends on the performance of these corrections. Differential piston and flexure effects will be detected and corrected in a real-time closed loop by analyzing the PSF of a guide star at a frequency of up to several hundred Hz. A dedicated piston mirror will then be moved in a corresponding manner by a piezo actuator. The FFTS is expected to provide a residual piston of better then 0.1 λ at the central wavelength of the science band. Thus, the required correction bandwidth is 10-20 Hz as differential piston simulations of different seeing conditions indicate. Therefore, a sampling frequency of 100-200 Hz is required to correct OPD variations. The upper limit for the loop frequency is the resonance frequency of the mirror and the response function respectively. The piston mirror as the actuator and the FFTS detector as the sensor feedback are embedded in a very complex system. Many control loop aspects like sampling frequencies, delays, controller algorithm and control bandwidth have to be identified. With accurate simulations of the system the limits of atmospheric and instrumental conditions for reliable closed loops can be determined against the respective control parameters. We present strategies for the closed-loop control of the piston correction which are suitable to achieve the 0.1 λ requirement and the optimal overall imaging performance with a sufficient "all-purpose" control stability.

LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT). Being able to observe at wavelength bands from J to K (suppported by an adaptive optics system operating at visible light) LINC-NIRVANA will provide an unique and unprecedented combination of high angular resolution (~ 9 milliarcseconds at 1.25μm ), wide field of view (~ 100 arcseconds2 at 1.25μm ), and large collecting area (~ 100m 2). One of the major contributions of the 1. Physikalische Institut of the University of Cologne to this project is the development and provision of the Fringe and Flexure Tracking System (FFTS). In addition to the single-eye adaptive optics systems the FFTS is a crucial component to ensure a time-stable wavefront correction over the full aperture of the double-eye telescope, a mandatory pre-requisite for interferometric observations. Using a independent HAWAII 1 detector array at a combined focus close to the science detector, the Fringe and Flexure Tracking System analyses the complex two-dimensional interferometric point spread function (PSF) of a suitably bright reference source at frame rates of up to several hundred Hertz. By fitting a parameterised theoretical model PSF to the preprocessed image-data the FFTS determines the amount of pistonic phase difference and angular misalignment between the wavefronts of the two optical paths of LINC-NIRVANA. For every exposure the corrective parameters are derived in real-time and transmitted to a dedicated piezo-electric fast linear mirror for simple path lengths adjustments, and/or to the adaptive optics systems of the single-eye telescopes for more complicated corrections. In this paper we present the basic concept and currect status of the opto-mechanical design of the Fringe and Flexure Tracker, the operating principle of the fringe and flexure tracking loops, and the encouraging result of a laboratory test of the piston control loop.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The MPIA is leading an international consortium of institutes in building an instrument called LINC-NIRVANA, the LBT INterferometric Camera and Near-IR / Visible Adaptive INterferometer for Astronomy. LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope doing imaging in the near infrared (J, H, K - band). Multi-conjugated adaptive objects is used to increase sky coverage and to get diffraction limited images over a 2 arcminute field of view. The LN Common Software provides a software infrastructure common to all partners and consists of a documented collection of common patterns in control systems and of services, which implement those patterns. The heart of LCSW is an object model of controlled devices, implemented as ICE network objects. A code generator creates application from templates for these network objects.

Current and future opportunities for interferometric observations of the Galactic Center in the near- and mid-infrared (NIR/MIR) wavelength domain are highlighted. Main emphasis is being put on the Large Binocular Telescope (LBT) and the Very Large Telescope Interferometer (VLTI). The Galactic Center measurements of stellar orbits and strongly variable NIR and X-ray emission from Sagittarius A* (SgrA*) at the center of the Milky Way have provided the strongest evidence so far that the dark mass concentration at this position is associated with a super massive black hole. Similar dark mass concentrations seen in many galactic nuclei are most likely super massive black holes as well. High angular resolution interferometric observations in the NIR/MIR will provide key information on the central massive black hole and the stellar cluster it is embedded in. These observations have already started: Recent results on the luminous dust enshrowded star IRS3 using MIDI at the VLTI are presented and future scientific possibilities in the GC using MIDI at the VLTI in the MIR and GRAVITY in the NIR are highlighted. As a NIR wide field interferometric imager offering an angular resolution of about 10 milliarcseconds LINC/NIRVANA at the Large Binocular Telescope will be an ideal instrument for imaging galactic nuclei including the center of the Milky Way.

The correction of atmospheric differential piston and instrumental flexure effects is mandatory for optimum interferometric performance of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in a real-time closed loop. On a timescale of milliseconds, image data of the order of 4K bytes has to be retrieved from the FFTS detector, analyzed, and the results have to be sent to the control system. The need for a reliable communication between several processes within a confined period of time calls for solutions with good real-time performance. We investigated two soft real-time options for the Linux platform. The design we present takes advantage of several features that follow the POSIX standard with improved real-time performance, which were implemented in the new Linux kernel (2.6.12). Several concepts, such as synchronization, shared memory, and preemptive scheduling are considered and the performance of the most time-critical parts of the FFTS software is tested.

The correction of atmospheric differential piston and instrumental flexure effects is mandatory for interferometric operation of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in real-time. In the fringe tracking concept that we present, differential piston information is gathered in the image plane by analyzing the PSF of a reference star anywhere in the large field of view of the LBT. We have developed and tested a fast PSF analysis algorithm that allows to clearly identify differential piston even in the case of low S/N. We present performance estimates of the algorithm. Since the performance of the FFTS algorithm has a strong impact on the overall sky coverage of LINC-NIRVANA, we studied the required limiting magnitudes of the fringe tracking reference star for different scenarios. As the FFTS may not necessarily operate on the science target, but rather uses a suitable reference star at a certain angular distance to the science target, differences between piston values at the two positions add to the residual piston of the FFTS. We have dealt with the question of differential piston angular anisoplanatism and studied a possible improvement of the isopistonic patch size by the use of multi-conjugate adaptive optics (MCAO). In its final stage, LINC-NIRVANA will be equipped with such a system.

We present near infrared ISAAC VLT observations of nine (0.01, Comment: Accepted by A&A, for higher resolution version, see http://www.ph1.uni-koeln.de/~fischer/fischerAGNinNIR.pdf

We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of ∼0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029-1831, 3C48 and Q0957 + 561. The first two objects belong to the NUGA (NUclei of GAlaxies) project — an international collaboration mainly between Spain, France and Germany — containing about 30 Seyfert and LINER galaxies. Both are at the same distance of ∼14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029-1831 and 3C48 are nearby QSOs. HE10297-1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1-0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1-0) line in Q0957 + 561 — a highly-red-shifted, gravitationally lensed quasar — will be presented as a link to earlier evolutionary stages of active galaxies and their hosts.

We present millimeter CO line emission observations of 12 galaxies within the Abell 262 cluster, together with L_FIR data, in the context of a possible molecular gas deficiency within the region of the cluster center. Several indications of the presence of such a deficiency are highlighted and connected to a model of cirrus-like cloud stripping. The model predicts a drop in the average 100 micron flux density of galaxies in the core of the cluster compared to the average 100 micron flux density in the outer regions, which is actually indicated in the IRAS data of the cluster members. This drop is explained by the decrease in the total hydrogen column density N(H) and, therefore, also includes a decrease in the molecular gas content. In addition to results for the global CO content of the galaxy sample, high-resolution interferometric CO(1-0) observations of one of the cluster members, UGC 1347, exemplify the spatial distribution of the molecular gas in a galaxy of the cluster. With these observations, it was possible to confirm the existence of a bright off-nuclear CO-emission source and to derive molecular masses and line ratios for this source and the nucleus., Comment: 14 pages, 14 figures, accepted by A&A

We present the results of 12CO(1-0) and 12CO(2–1) observations on UGC 1347 obtained with BIMA and the IRAM 30 m telescope. UGC 1347 is a member of the Abell 262 cluster. In Abell 262, a nearby spiral rich cluster, the signs of galaxy interaction and therefore the mechanisms which play an important role in galaxy evolution within clusters can be studied with high spatial resolution. Aside from its bright central region, UGC 1347 features a second prominent source at the southern tip of the bar, which has been identified as region with recent enhanced star formation. The CO observations prove the existence of reservoirs of cold molecular gas at the positions of both bright regions.

On the way to the Extremely Large Telescopes (ELT) the Large Binocular Telescope (LBT) is an intermediate step. The two 8.4m mirrors create a masked aperture of 23m. LINC-NIRVANA is an instrument taking advantage of this opportunity. It will get, by means of Multi-Conjugated Adaptive Optics (MCAO), a moderate Strehl Ratio over a 2 arcmin field of view, which is used for Fizeau (imaging) interferometry in J,H and K. Several MCAO concepts, which are proposed for ELTs, will be proven with this instrument. Studies of sub-systems are done in the laboratory and the option to test them on sky are kept open. We will show the implementation of the MCAO concepts and control aspects of the instrument and present the road map to the final installation at LBT. Major milestones of LINC-NIRVANA, like preliminary design review or final design review are already done or in preparation. LINC-NIRVANA is one of the few MCAO instruments in the world which will see first light and go into operation within the next years.

LINC-NIRVANA is an imaging interferometer for the Large Binocular Telescope (LBT) and will make use of multi-conjugated adaptive optics (MCAO) with two 349 actuators deformable mirrors (DM), two 672 actuator deformable secondary mirrors and a total of 4 wavefront sensors (WFS) by using 8 or 12 natural guide stars each. The goal of the MCAO is to increase sky coverage and achieve a medium Strehl-ratio over the 2 arcmin field of view. To test the concepts and prototypes, a laboratory setup of one MCAO arm is being built. We present the layout of the MCAO prototype, planned and accomplished tests, especially for the used Xinetics DMs, and a possible setup for a test on sky with an existing 8m class telescope.

The correction of atmospherical differential piston and instrumental flexure effects is mandatory for full interferometric performance of the LBT NIR interferometric imaging camera LINC-NIRVANA. This is the task of the Fringe and Flexure Tracking System (FFTS), which is part of the contribution of the I. Physikalische Institut of the University of Cologne to the project. Differential piston and flexure effects will be detected and corrected in a real-time closed loop by analyzing the PSF of a guide star at a frequency of up to several hundred Hz. Numerous critical design parameters for both FFTS hardware and control loop have to be derived from simulations. Detailed knowledge of the special shape of the LBT interferometric PSF as a function of a variety of parameters is required to design the fringe tracking control loop. In this paper we will show the results of our software that allows us to generate polychromatic interferometric PSFs for a number of different scenarios. Our fringe detection algorithm is based on an analytic model which is fitted to the acquired PSF. We present the results of the evaluation of the algorithm in terms of speed and residual piston, as well as the first successful implementation of the algorithm in a closed loop system. Simulations of the time evolution of differential piston have been performed in order to investigate necessary correction frequencies and the variation of differential piston across the usable field of view. These simulations are based on the Layer Oriented Adaptive Optics performance simulator "LOST" of the Osservatorio Astriofisico di Arcetri.

We present a 1:3 scale model of the LINC-NIRVANA interferometer. This laboratory Fizeau, or image plane, interferometer allows us to test many aspects of LINC-NIRVANA before the final instrument is integrated. We have used this testbed interferometer to practice alignment procedures, verify the optical design, show that point spread functions with low (10\%) Strehl ratio can maintain high fringe contrast, and test the fringe tracking algorithm by running the interferometer in a closed piston loop.

LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT).Operating at JHK bands LINC-NIRVANA will provide an unique and unprecedented combination of high angularresolution ( 9 milliarcseconds at 1.25 µm ), wide “eld of view ( 100 arcseconds 2 at 1.25 µm ), and largecollecting area ( 100 m 2 ).One of the major contributions of the I. Physikalische Institut of the University of Cologne to this projectisthedevelopmentoftheFringeandFlexureTrackingSystem (FFTS). In close cooperation with the AdaptiveOptics systems of LINC-NIRVANA the FFTS is a fundamental component to ensure a complete and time-stable wavefront correction at the position of the science detector in order to allow for long integration times atinterferometric angular resolutions.Using a dedicated near-infrared det ector array at a combined focus close to the science detector, the Fringeand Flexure Tracking System analyses the interferometric point spread function (PSF) of a suitably brightreference source at frame rates of several hundred Hertz up to 1 kHz. By “tting a parameterized theoreticalmodel PSF to the preprocessed image-data the FFTS determines the amount of pistonic phase dierence andthe amount of an angular misalignment between the wavefronts of the two optical paths of LINC-NIRVANA.For every exposure the correcting parameters are derived in real-time and transmitted to the respective controlelectronics, or the Adaptive Optics syst ems of the single-eye telescopes, which will adjust their optical elementsaccordingly.In this paper we present the opto-mechanical hardware design, the principle of operation of the softwarecontrol algorithms, and the results of “rst numerical simulations and laboratory experiments of the performanceof this Fringe and Flexure Tracking System.Keywords: LBT, instrumentation, interferometry, fringe tracking, piston

As a near-infrared (NIR) wide field interferometric imager offering an angular resolution of about 10 milliarcseconds LINC/NIRVANA at the Large Binocular Telescope will be an ideal instrument for imaging of galactic nuclei including the center of the Milky Way. Recent optical/IR imaging surveys can now quite successfully be used to search for star-galaxy pairs that are suitable for interferometric observation with LINC NIRVANA. These objects can then be used to efficiently investigate galaxy interaction, nuclear activity, and star formation in distant galaxies. In the NIR these investigations will be carried out at scales below 100~pc for z

LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope (LBT) doing imaging in the near infrared (J,H,K - band). Multi-conjugated adaptive optics is used to increase sky coverage and to get diffraction limited images over a 2 arcminute field of view. The control system consists of five independent loops, which are mediated through a master control. Due to the configuration, LINC-NIRVANA has no delay line like other interferometers. To remove residual atmospheric piston, the system must control both the primary and secondary mirrors, in addition to a third, dedicated piston mirror. This leads to a complex and interlocked control scheme and software. We will present parts of the instrument software design, which was developed in an object-oriented manner using UML. Several diagram types were used to structure the overall system and to evaluate the needs and interfaces of each sub-system to each other.

LINC-NIRVANA is a Fizeau interferometer which will be built for the Large Binocular Telescope (LBT). The LBT exists of two 8.4m mirrors on one mounting with a distance of 22.8m between the outer edges of the two mirrors. The interferometric technique used in LINC-NIRVANA provides direct imaging with the resolution of a 23m telescope in one direction and 8.4m in the other. The instrument uses multi-conjugated adaptive optics (MCAO) to increase the sky coverage and achieve the diffraction limit in J, H, K over a moderate Field of View (2 arcmin in diameter). During the preliminary design phase the team faced several problems similar to those for an instrument at a 23m telescope. We will give an overview of the current design, explain problems related to 20m class telescopes and present solutions.

The I. Physikalische Institut of the University of Cologne is participating in an international collaboration with the Max-Planck-Institut fur Astronomie in Heidelberg and the Osservatorio Astrofisico di Arcetri for the development of LINC/NIRVANA, the Near-Infrared/Visible Interferometric Camera for the Large Binocular Telescope (LBT). LINC/NIRVANA will be one of the two interferometric camera systems of the LBT and will operate at wavelengths from 0.6 μm to 2.4 μm, with the long wavelength regime between 1.0 μm and 2.5 μm being covered by LINC (LBT INterferometric Camera} and the shorter wavelengths part from 0.6 μm to 1.0 μm being processed by NIRVANA (Near-InfraRed/Visible Adaptive iNterferometer for Astronomy}. The main contributions of the Cologne institute to this camera will be the 77K dewar and the Fringe and Flexure Tracker (FFT) for the near-infrared part on the system. Detecting and correcting the fast pistonic aberrations of the atmosphere and the slow flexure of the instrument in a closed-loop operation, the presence and proper function of the FFT is mandatory for a time-stable image quality at highest interferometic resolutions. In order to get the best possible image correction for LINC, the FFT will be located inside the camera dewar at an interferometric focus close the one of the near-infrared science detector. Using simple optical elements it will continuously monitor the time-variable phase difference and pupil locations of the incoming wavefronts from the two arms of the twin-telescope. In this article we give a short overview of the camera concept of LINC and present the current status of the design and development of the FFT going on at our institute at the University of Cologne.

VLTI interferometry will allow imaging of galactic and extragalactic sources with milliarcsecond angular resolution. For moderately bright sources the spectral resolution will be of the order of 10000. These capabilities will allow detailed studies of solar system objects, stars, protoplanetary systems and the detection of hot extra-solar planets. The observations of galactic nuclei will allow unprecedented measurements of physical parameters in these systems. VLTI will be a prime instrument to study the immediate environment of the massive black hole at the center of the Milky Way. With the exception of a few ‘self-referencing’ sources the observations of extragalactic nuclei will benefit from an extended capability for simultaneous measurements of nearby reference sources for fringe tracking. With beam combination instruments like AMBER, MIDI, PRIMA, and GENIE the VLTI will reach full maturity at a time when other interferometric instruments at different wavelengths will be fully operational. Most important are ALMA (in the mm- and sub-mm-domain), LOFAR and SKA (in the radio meter to centimeter domain) and of course VLB-networks in the radio, and other — at that time — well developed interferometers in the optical. A major scientific potential of future scientific VLTI programs will lie in an efficient combination of these high angular resolution capabilities.

Stellar proper motions, radial velocities and accelarations obtained with high angular resolution techniques over the past decade have convincingly proven the presence of a central compact dark mass of 3x10 6 M. This mass is most likely associated with the compact radio source Sagittarius A* and represents one of the best candidates for a super massive Black Hole. This contribution summarizes some important observational facts and outlines the future possibilities for interferometric observations of the Galactic Center. In the near future interferometric observations of that region with the LBT, VLTI and the Keck Interferometer will be possible. Detailed measurements of the stellar orbits close to the center will allow us to precisely determine the compactness, extent and shape of any extended mass contribution e.g. due to a central stellar cusp. Emphasis will be put on the potential of the NIR LBT interferometric camera LINC. Given the combination of large telescope apertures, adaptive optics, and interferometry it is likely that stars with orbital time scales of the order of one year will be detected. Theses sources, however, will most likely not be on simple Keplerian orbits. The effects of measurable prograde relativistic and retrograde Newtonian periastron shifts will result in rosetta shaped orbits. An increased interferometric point source sensitivity will also allow for an effective search and monitoring of an IR counterpart of SgrA*.

In this article we present the basic principle of operation and the current status of LINC-NIRVANA, the upcoming interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT). Using the exceptional optical design of the LBT for homothetic mapping at a large scale twin-telescope, LINC-NIRVANA will provide an unique combination of high angular resolution (≈ 9 mas), wide field of view (≈ 100 arcsec 2 - both values given for J-band) and large collecting area (≈ 100 m 2 ).

LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the large binocular telescope (LBT) on Mt. Graham, Arizona (elevation of 3267 m). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy in Heidelberg, Germany. It will combine the radiation from both 8.4 m primary mirrors of LBT in such a way that the sensitivity of a 11.9 m telescope and the spatial resolution of a 22.8 m telescope will be obtained within a 10.5×10.5 arcsec 2 scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5 arcmin. In addition, both incoming beams are individually corrected by LN’s multiconjugate adaptive optics system to reduce atmospheric image distortion over a circular field of up to 6 arcmin in diameter. A comprehensive technical overview of the instrument is presented, comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the near infrared range of 1 to 2.4 μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 to 0.9 μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration, and verification process are discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.

5 pags., 7 figs. -- The Universe under the Microscope – Astrophysics at High Angular Resolution, 21–25 April 2008, Bad Honnef, Germany, We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the ∼4x106M⊙ super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8x1033 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to differential rotation within the disk. © 2008 IOP Publishing Ltd., Part of this work was supported by the German Deutsche Forschungsgemeinschaft, DFG via grant SFB 494. L. Meyer, K. Muzic, M. Zamaninasab, D. Kunneriath, and R.-S. Lu, are members of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the MPIfR and the Universities of Bonn and Cologne. RS acknowledges support by the Ramon y Cajal programme by the Ministerio de Ciencia y Innovación of the government of Spain.

It is difficult to measure the mechanical properties of physical vapor deposition coatings owing to their small layer thickness. This report c describes a special four-point bending device that makes it possible to determine quantitative critical tensile or compressive failure stresses and shear stresses in thin coatings. The bending test was also used to carry out measurements of hardness and critical loads (scratch test) under stress, excluding other influences such as microstructure changes. The material parameters determined form the basis of a finite element model of the indentation process, and this offers new possibilities for mechanical characterization of coated materials.