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  • 1
    Electronic Resource
    Electronic Resource
    High-Resolution Near-Infrared Observations of NGC 1068 (1997)
    Springer
    Astrophysics and space science 248 (1997), S. 295-300 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present near-infrared observations of NGC 1068 obtained with the SHARP camera at the ESO 3.5 m telescope, and with SHARP II attached to the COME-ON+ adaptive optics system at the ESO 3.6 m telescope. From the SHARP observations we obtain a K band image of the stellar bar with 0.″4 resolution, and an upper limit to the size of the nuclear K band source of 0.″05 (3.5 pc). The adaptive optics observations are used to determine the position of the infrared nucleus with respect to the visible continuum. The centroid of the 5000 to 9000 Å continuum is displaced 0.″23 ± 0.″10 to the east and 0.″41 ± 0.″10 to the north of the K bank peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000592820834
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  • 2
    Electronic Resource
    Electronic Resource
    High resolution near-IR imaging with arrays (1994)
    Springer
    Experimental astronomy 3 (1994), S. 281-292 
    Details
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The availability of large format, low noise detector arrays has opened the 1 to 20 μm region for sub-arcsecond imaging. Using recent results in the investigation of Galactic star forming regions, the Galactic center and external galaxies as examples, we discuss the various techniques that have been employed. These range from image selection and image sharpening, over speckle techniques and adaptive optics to lunar occultation. These examples demonstrate that sub-arcsecond imaging and spatial interferometry in the near- and mid-infrared has a great future potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00430177
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  • 3
    Electronic Resource
    Electronic Resource
    Sharp images of young stellar objects (1995)
    Springer
    Astrophysics and space science 224 (1995), S. 411-414 
    Details
    ISSN: 1572-946X
    Keywords: high angular resolution imaging ; near infrared - young stellar objects ; polarization ; circumstellar matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present high resolution infrared images of the pre-main sequence star V536 Aql and polarization maps of the reflection nebula IRN Cha observed with the SHARP camera on the ESO NTT. Extended structures are observed near V536 Aql. The polarization pattern of IRN Cha is typical of a centrally illuminated source but with a central band of anomalously oriented polarization believed to occur in an optically thick disk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667882
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  • 4
    Electronic Resource
    Electronic Resource
    High resolution K-band images of the galactic centre (1993)
    Springer
    Astrophysics and space science 205 (1993), S. 1-4 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new near-infrared camera, SHARP (System for High Angular Resolution Pictures), has been used at the 3.5m ESO NTT to produce near-diffraction-limited K-band images of the galactic centre region. The new images show a substantial improvement in resolution and sensitivity over previousK-band images. IRS 16 splits into about 20 compact sources, the extended ridge in IRS16W-E is resolved into at least 5 stellar components, and a faint source (K = 13.7 ± 0.6) is detected at the position of SgrA. Measurement of proper motions of the stellar sources within a few arcseconds of this source will allow us to determine the central mass within the next few years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657949
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  • 5
    Electronic Resource
    Electronic Resource
    The starburst in the Wolf-Rayet nucleus of the Liner NGC 6764 (1993)
    Springer
    Astrophysics and space science 205 (1993), S. 29-35 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present high resolution millimeter, near-infrared, and optical data on the Wolf-Rayet nucleus of the Liner NGC 6764. The millimeter12CO(1-0) maps were obtained using the Nobeyama Millimeter Interferometer. Near-infrared images in the K-band continuum and the 2.12µm H2, 2.06µm He I, 2.17µm Brγ, and 1.64µm [Fe II] lines were taken with the MPE imaging spectrometer FAST at the William Herschel Telescope on La Palma, Spain. The optical data were obtained at the 3.5m telescope on Calar Alto, Spain. The measurements indicate a strong concentration of molecular gas and a massive starburst at the nucleus of NGC 6764. The interferometric position velocity map of the nucleus shows the presence of distinct molecular cloud complexes with an apparently asymmetric velocity field shifted towards the blue with respect to the systemic velocity of 2420 km s−1. The distribution of the 2.12µm H2 line flux exhibits extensions approximately perpendicular to the bar which are in agreement with structural features in VLA radio maps and IRAM 30m maps of the12CO(2–1) line emission. This may represent evidence for combination of a nuclear outflow and a central oval distortion of gas predicted by gas dynamical calculations as a response to a bar like potential. A detailed investigation of the Wolf-Rayet-feature at 466 nm indicates that it is spatially extended on a scale of a few arcseconds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657953
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  • 6
    Electronic Resource
    Electronic Resource
    The ALFA Laser Guide Star: Operation and Results (2000)
    Springer
    Experimental astronomy 10 (2000), S. 103-121 
    Details
    ISSN: 1572-9508
    Keywords: Abell Galaxy Clusters ; adaptive optics ; atmospheric turbulence ; Herbig Ae/Be stars ; laser guide star ; sodium profile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The importance of laser guide stars to the practical usefulness ofadaptive optics cannot be understated, and yet there are veryfew working systems.This contribution discusses the current status of the ALFAlaser guide star, with regard to the particular difficulties encounteredwhile observing as well as both the expected performance and that so farachieved from scientific observations.A description is given of a number of experiments involving ALFA whichaim to determine the atmospheric turbulence and sodium layercharateristics, and demonstrate the possibility for tilt recovery fromlaser guide stars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008165517543
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  • 7
    Electronic Resource
    Electronic Resource
    The ALFA Laser and Analysis Tools (2000)
    Springer
    Experimental astronomy 10 (2000), S. 75-88 
    Details
    ISSN: 1572-9508
    Keywords: adaptive optics ; laser guide star ; atmospheric turbulence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The optimal performance of adaptive optics systems can only be maintainedif the wavefront reference is bright and compact.Experience has shown that both of these important criteria are remarkablydifficult to achieve with laser guide stars. This contribution gives an account of the methods by which ALFAattempts to reach them.First, the production of a high quality, high power laser beam isdescribed.However, this quality is unavoidably compromised along the path to thelaunch telescope.In order to rectify this, a new set of diagnostic tools which monitorthe quality of the out-going beam has been installed, and these arealso described.Lastly, we outline a number of possible modifications on which we areworking.If successful, these may allow a substantial improvement in the beamquality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008137214239
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  • 8
    Electronic Resource
    Electronic Resource
    Short timescale variability of the mesospheric sodium layer (2000)
    Springer
    Experimental astronomy 10 (2000), S. 147-156 
    Details
    ISSN: 1572-9508
    Keywords: adaptive optics ; laser guide star ; mesospheric sodium layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this article we investigate the short-term characteristics of the sodium layer and their implications for laser guide star systems. We report measurements of sodium density andcentroid-height variations on timescales of 100 ms upwards. Significant centroid-height variations on short timescales may necessitate frequent refocussing of the beam and wavefront sensor system.We present results from observations of the mesospheric sodium layer taken at the Max Planck observatory in Calar Alto, Spain in September 1997 and August 1998. We describe our experiment which uses the resonant optical backscatter of 589.2 nm laser light from the upper atmosphere as a measure of sodium abundance.Short-term variations are dominated by the formation of dense sporadic layers in the normal sodium layer. Measurements were made on 3 nights in 1997 and on 2 nights in 1998. Somewhat unexpectedly for a mid-latitude site, sporadic sodium layers were seen on 4 of these 5 nights. One of the sporadic layers was observed for its duration. The 2 km wide layer reached a maximum intensity of approximately two and a half times that of the background layer and could be distinguished from the background for over five hours. Centroid height variations of up to 400 m were observed on timescales of 1–2 min. In 1998 we were sensitive to variations of 5% or more in total sodium abundance on timescales of 100 ms upwards. We found no evidencefor variations of this level on these short timescales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008126318786
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  • 9
    Electronic Resource
    Electronic Resource
    The ALFA Laser: Beam Relay and Control System (2000)
    Springer
    Experimental astronomy 10 (2000), S. 89-101 
    Details
    ISSN: 1572-9508
    Keywords: adaptive optics ; hardware ; laser guide star ; software
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ALFA laser subsystem uses a 4 watt continuous wave laser beam to produce an artificial guide star in the mesospheric sodium layer as a reference for wavefront sensing. In this article we describe the system design, focusing on the layout of the beam relay system. It consists of seven mirrors, four of which are motor-controlled in closed loop operation accounting for turbulences inside the dome and flexure of the main telescope.The control system features several computers which are located close to analysis and control units. The distribution of the tasks and their interaction is presented, as well as the graphical user interface used to operate the complete system. This is followed by a discussion of the aircraft detection system ALIENS. This system shuts off the laser beam when an object passes close to the outgoing laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008191103168
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  • 10
    Electronic Resource
    Electronic Resource
    ALFA: The MPIA/MPE Laser Guide Star AO System (2000)
    Springer
    Experimental astronomy 10 (2000), S. 1-3 
    Details
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008119225652
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