Author name code: beckers ADS astronomy entries on 2022-09-14 author:"Beckers, Jacques Maurice" ------------------------------------------------------------------------ Title: Charge of clustered microparticles measured in spatial plasma afterglows follows the smallest enclosing sphere model Authors: van Minderhout, B.; van Huijstee, J. C. A.; Rompelberg, R. M. H.; Post, A.; Peijnenburg, A. T. A.; Blom, P.; Beckers, J. Bibcode: 2021NatCo..12.4692V Altcode: The plasma-induced charge of non-spherical microparticles is a crucial parameter in complex plasma physics, aerosol science and astrophysics. Yet, the literature describes this charge by two competing models, neither of which has been experimentally verified or refuted. Here we offer experimental proof that the charge on a two-particle cluster (doublet) in the spatial afterglow of a low-pressure plasma equals the charge that would be obtained by the smallest enclosing sphere and that it should therefore not be based on its geometrical capacitance but rather on the capacitance of its smallest enclosing sphere. To support this conclusion, the size, mass and charge of single particles (singlets) and doublets are measured with high precision. The measured ratio between the plasma-afterglow-induced charges on doublets and singlets is compared to both models and shows perfect agreement with the predicted ratio using the capacitance of the smallest enclosing sphere, while being significantly dissimilar to the predicted ratio based on the particle's geometrical capacitance. Title: Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed Authors: Mossoux, E.; Finociety, B.; Beckers, J. -M.; Vincent, F. H. Bibcode: 2020A&A...636A..25M Altcode: 2020arXiv200306191M Context. The supermassive black hole Sagittarius A* (Sgr A*) is located at the dynamical center of the Milky Way. In a recent study of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton, and Swift observations from 1999 to 2015, it has been argued that the bright flaring rate has increased from 2014 August 31 while the faint flaring rate decreased from around 2013 August.
Aims: We tested the persistence of these changes in the flaring rates with new X-ray observations of Sgr A* performed from 2016 to 2018 (total exposure of 1.4 Ms).
Methods: We reprocessed the Chandra, XMM-Newton, and Swift observations from 2016 to 2018. We detected 9 flares in the Chandra data and 5 flares in the Swift data that we added to the set of 107 previously detected flares. We computed the intrinsic distribution of flare fluxes and durations corrected for the sensitivity bias using a new method that allowed us to take the error on the flare fluxes and durations into account. From this intrinsic distribution, we determined the average flare detection efficiency for each Chandra, XMM-Newton, and Swift observation. After correcting each observational exposure for this efficiency, we applied the Bayesian blocks algorithm on the concatenated flare arrival times. As in the above-mentioned study, we also searched for a flux and fluence threshold that might lead to a change in flaring rate. We improved the previous method by computing the average flare detection efficiencies for each flux and fluence range.
Results: The Bayesian block algorithm did not detect any significant change in flaring rate of the 121 flares. However, we detected an increase by a factor of about three in the flaring rate of the most luminous and most energetic flares that have occurred since 2014 August 30.
Conclusions: The X-ray activity of Sgr A* has increased for more than four years. Additional studies about the overall near-infrared and radio behavior of Sgr A* are required to draw strong results on the multiwavelength activity of the black hole. Title: Tropospheric seeing effects on site selection and the use of adaptive optics for solar telescopes Authors: Beckers, Jacques M. Bibcode: 2018SPIE10703E..6YB Altcode: Because of the very small size of the isoplanatic patch resulting from high altitude, tropopause seeing, the use of the Solar Differential Image Motion Monitor (S-DIMM) for solar seeing observations at large zenith distances is significantly compromised. I examine the resulting limitations and attempt to correct for these in its use for the Advanced Technology Solar Telescope (ATST/DKIST) site survey. Suggestions are given about how one might correct for this altitude seeing by Dual Conjugate and Multi-Conjugate Adaptive Optics (DCAO/MCAO). I also comment on adaptive optics for corona observations with the use of Laser Guide Star aided wavefront sensing. Title: The Effect of Tropopause Seeing on Solar Telescope Site Testing Authors: Beckers, Jacques M. Bibcode: 2017SPD....4811002B Altcode: The site testing for and seeing correction planning of the 4-m solar telescopes has failed to take into account the significant amount of seeing at tropopause levels (10-20 km altitude).The worst aspect of that seeing layer is its small isoplanatic patch size which at low solar elevations can be significantly less than 1 arcsec. The CLEAR/ATST/DKIST SDIMM seeing monitor is insensitive to this type of seeing. A correction for this missed seeing significantly decreases the measured seeing qualities for the sites tested especially in the early morning and late afternoon. It clearly shows the lake site to be superior with mid-day observations much to be preferred. The small tropopause isoplanatic patch size values also complicate the implementation of the solar MCAO systems aimed at large field-of-view sun imaging. Currently planned systems only correct for lower-layer seeing for which the isoplanatic patch size is about one arc minute. To fully achieve the diffraction limit of the 4-meter class (0.025 arcsec at 500 nm), over a large enough field-of-view to be of scientific interest, complicated Multi-Conjugate Adaptive Optics systems will be needed. Title: Isoplanatic patch considerations for solar telescope multi-conjugate adaptive optics Authors: Beckers, Jacques M. Bibcode: 2014SPIE.9148E..60B Altcode: I compare recent site surveys for the future large 4-meter solar and 30-meter nighttime telescopes at the nearby Haleakala and Mauna Kea sites respectively. They show that the outstanding early morning image quality at the solar site corresponds indeed to that observed at the late night one at the nighttime site. That confirms the notion that daytime solar site heating only shows itself later in the morning. The nighttime survey includes observations of the refractive index structure function Cn 2(h) to high altitudes from which the radius of the isoplanatic patch (Ɵ0) can be determined. At zenith (ζ = 00) it equals 2.5 arcsec at 500 nm wavelength. For the early morning (best) seeing at the solar site, which occurs at ζsun = 750 and the cos1.6(ζ) dependence of Θ0,that means an extremely small Ɵ0 (0.26 arcsec). Such small values compromise Adaptive Optics (AO) solar correlation wavefront sensing for which areas are needed equal to about 8"× 8" I suggest options for measuring Cn2(h), and therefore Ɵ0, during the day. These make use of the solar image as well as of daytime images of bright stars and planets. Some use the MASS technique on stars; some use the SHABAR technique using very large detector baselines on the Sun and shorter baselines on planets. It is suggested that these Cn2(h) measurements are made also during regular solar observations. In that way optimal solar observations can be planned using real-time Ɵ0 observations by image selection and optimization of the MCAO configuration. Title: Adaptive Optics for the 8 meter Chinese Giant Solar Telescope Authors: Beckers, Jacques; Liu, Zhong; Deng, Yuanyong; Ji, Haisheng Bibcode: 2013aoel.confE...5B Altcode: Solar ELTs enable diffraction limited imaging of the basic structure of the solar atmosphere. Magneto-hydrodynamic considerations limit their size to about 0.03 arcsec. To observe them in the near-infrared 8-meter class telescopes are needed. The Chinese Giant Solar Telescope, or CGST, is such a NIR solar ELT. It is a Ring Telescope with 8-meter outer diameter and a central clear aperture of about 6-meter diameter. At present various options for such a Gregorian type telescope are under study like a continuous ring made of segments or a multiple aperture ring made of 7 off-axis telescopes. The advantages of such a ring telescope is that its MTF covers all spatial frequencies out to those corresponding to its outer diameter, that its circular symmetry makes it polarization neutral, and that its large central hole helps thermal control and provides ample space for MCAO and Gregorian instrumentation. We present the current status of the design of the CGST. Our thinking is guided by the outstanding performance of the 1-meter vacuum solar telescope of the Yunnan Solar Observatory which like the CGST uses both AO and image reconstruction. Using it with a ring-shape aperture mask the imaging techniques for the CGST are being explored. The CGST will have Multi-Conjugate Adaptive Optics (MCAO). The peculiarities of Atmospheric Wavefront Tomography for Ring Telescopes are aided by the ample availability of guide stars on the Sun. IR MCAO-aided diffraction limited imaging offers the advantage of a large FOV, and high solar magnetic field sensitivity. Site testing is proceeding in western China, (e.g. northern Yunnan Province and Tibet). The CGST is a Chinese solar community project originated by the Yunnan Astronomical Observatory, the National Astronomical Observatories, the Purple Mountain Observatory, the Nanjing University, the Nanjing Institute of Astronomical Optics & Technology and the Beijing Normal University. Title: The History of the Fourier Tachometer Authors: Beckers, J. M.; Brown, T. M. Bibcode: 2013ASPC..478...93B Altcode: Following a suggestion by one of us (T. Brown) we developed in 1978 at the Sacramento Peak Observatory the first version of what we called a Fourier Tachometer which measured the phase of a single frequency component of the Fourier transform of the solar spectrum associated with a specific solar spectrum line (Beckers & Brown 1978). This phase is a direct measure of the wavelength of that Line, its Doppler shift and by using polarization optics, its Zeeman splitting. This first version based on a Michelson interferometer (FT I) was later (Evans 1081) greatly improved by J.W. Evans by using a Solid Polarizing Interferometer (version FT II). The latest version stands out by its ability to: (i) get wavelength measurements over a large 2D field-of-view without the cumbersome use of a high-resolution spectrograph, (ii) have a wide angular field-of-view and étendue, (iii) be mechanically stable and use much real-time digital processing. The FT II was selected for use in Global Oscillation Network Group (GONG) in about 1985 and has since then also been used in the space based helioseismometers — Micheson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (Scherrer et al. 1995) and Helioseismic Magnetic Imager (HMI) onboard Solar Dynamics Observatory (Scherrer et al. 2012). The FT II performance has increased over the years with the current HMI version having 4096 × 4096 pixels, or 0.5 × 0.5 arcsec for the HMI full disk facility, and a cadence of 45 seconds. However, except for some early observations at the Sacramento Peak, the Fourier Tachometer has not appeared to have been applied to non-helioseismology ground-based observations. In ground-based telescopes science full precise line profiles are generally desired making the FT II undesirable since it only measures something close to their center-of-gravity. For future very large diameter (1.5 - 8 m) ground-based solar telescopes that will also be the case. But complimentary FT II observations, for example from the spectrograph reflecting slit-jaws, would provide valuable, high time and spatial resolution complimentary observations. The HMI version would have pixel sizes of about 0.03 × 0.03 arcsec, closely matching the telescope resolution over a 2 × 2 arcmin field-of-view provided by its Multi-Conjugate Adaptive Optics system. Title: Planning the 8-meter Chinese Giant Solar Telescope Authors: Beckers, Jacques M.; Liu, Z.; Deng, Y.; Ji, H. Bibcode: 2013SPD....4440104B Altcode: The Chinese Giant Solar Telescope (CGST) will be a diffraction limited solar telescope optimized for the near-infrared (NIR) spectral region (0.8 - 2.5 microns). Its diffraction limit will be reached by the incorporation of Multi-Conjugate Adaptive Optics (MCAO) enhanced by image restoration techniques to achieve uniform (u.v) plane coverage over the angular spatial frequency region allowed by its 8-meter aperture. Thus it will complement the imaging capabilities of 4-meter telescopes being planned elsewhere which are optimized for the visible (VIS) spectral region (300 - 1000 nm) In the NIR spectral regions the CGST will have access to unique spectral features which will improve the diagnostics of the solar atmosphere. These include the CaII lines near 860 nm , the HeI lines near 1083 nm, the 1074 nm FeXIII coronal lines, the large Zeeman-split FeI line at 1548 nm, and (v) the H- continuum absorption minimum at 1.6 micron. Especially in sunspot umbrae the simultaneous observation of continua and lines across the NIR spectral range will cover a substantial depth range in the solar atmosphere. Of course the mid- and far- infrared regions are also available for unequalled high-angular resolution solar observations, for example, in the Hydrogen Bracket lines, CO molecular bands, and the MgI emission line at 12.3 microns. The CGST is a so-called ring telescope in which the light is captured by a 1 meter wide segmented ring or by a ring of 7 smaller off-axis aperture telescopes. The open central area of the telescope is large. The advantages of such a ring configuration is that (a) it covers all the spatial frequencies out to those corresponding to its outer diameter, (b) its circular symmetry makes it polarization neutral, (c) its large central hole helps thermal control, and (d) it provides ample space for the MCAO system and instrumentation in the Gregorian focus. Even though optimized for the NIR, we expect to use the CGST also at visible wavelengths in the so-called “Partial Adaptive Optics” (PAO) mode (Applied Optics 31,424,1992) to obtain angular resolution twice that of a 4-meter telescope if their observations indicate that higher resolution is desirable. The CGST is a Chinese solar community project. Title: Daytime Observations with ELTs in the Thermal Infrared Using Laser Guide Star Adaptive Optics Authors: Beckers, J. M. Bibcode: 2011aoel.confP..38B Altcode: Using Magneto-Optical Filters (MOFs; also called FADOFs = Faraday Anomalous Dispersion Optical Filters) it is possible to clearly see Sodium Laser Guide Stars in the daytime sky. This makes it possible to use ELT Adaptive Optics systems for diffraction limited observations 24 hours/day. Because of the bright daytime sky this LGS AO application is only of astronomical interest in the mid-infrared wavelength region (4 - 25 microns wavelengths) where the thermal radiation of the atmosphere-telescope system dominates the scattering of sunlight thus making the day- and night- sky background comparable. Incorporating MOFs in the LGS wavefront sensor thus would more than double the ELT observing time for mid-infrared astronomy and would make sources in almost the entire sky available for observation at any time of the year. Even though the AO would increase the brightness of point-sources, it would not compete with the James Webb Space Telescope in terms of detectability. The gain with respect to the JWST lies in the 5 to 6 times better linear angular resolution. The contrast gain in brightness at near-IR wavelengths is sufficient to give sufficient natural guide stars there for tip-tilt control. MOFs have been shown to function with Na lasers in LIDAR applications (see Beckers and Cacciani, Experimental Astronomy 11, 133, 2001). The main complication associated with incorporating MOFs in ELT AO system is likely the requirement to make the telescope and its enclosure robust in the daytime environment. I refer to SPIE Proceedings 6986 (2008) for a recent reference on this topic. Title: Satellite Calibration And Validation Experiments Over Arctic Sea Ice In The Vicinity Of Svalbard Authors: Gerland, S.; Brandt, O.; Hansen, E.; Rnner, A. H. H.; Granskog, M.; Forsstrom, S.; Eltoft, T.; Fors Schwenke, A.; Moen, M. -A.; Doulgeris, A.; Haas, C.; Beckers, J.; Hughes, N. Bibcode: 2011ESASP.693E..22G Altcode: In late summer 2010, in situ observations on Arctic sea ice were performed at the end of the melting season north of Svalbard, and in the Fram Strait. High resolution Radarsat-2 SAR images were obtained. Simultaneously, data about sea ice and snow thickness, ice topography, and melt ponds was collected. A helicopter performed ice thickness surveys using an electromagnetic (EM) device, accompanied with automatic photography and laser altimetry. The EM method is also used for the calibration and validation of data from the new CryoSat-2 radar altimetry satellite. Data on snow and ice properties have been collected over several years for satellite altimetry calibration. These are necessary for estimating the sea ice thickness from measured freeboard. Preliminary results indicate the improved possibilities for ice type classification from SAR satellite imagery. Data collected for CryoSat- 2 calibration and validation will contribute to improve data quality of CryoSat-2 products. Title: Enhanced ocean temperature forecast skills through 3-D super-ensemble multi-model fusion Authors: Lenartz, F.; Mourre, B.; Barth, A.; Beckers, J. -M.; Vandenbulcke, L.; Rixen, M. Bibcode: 2010GeoRL..3719606L Altcode: An innovative multi-model fusion technique is proposed to improve short-term ocean temperature forecasts: the three-dimensional super-ensemble. In this method, a Kalman Filter is used to adjust three-dimensional model weights over a past learning period, allowing to give more importance to recent observations, and take into account spatially varying model skills. The predictive performance is evaluated against SST analyses, CTD casts and gliders tracks collected during the Ligurian Sea Cal/Val 2008 experiment. Statistical results not only show a very significant bias reduction of this multi-model forecast in comparison with the individual models, their ensemble mean and a single-weight-per-model version of the super-ensemble, but also the improvement of other pattern-related skills. In a 48-h forecast experiment, and with respect to the ensemble mean, surface and subsurface root-mean-square differences with observations are reduced by 57% and 35% respectively, making this new technique a suitable non-intrusive post-processing method for multi-model operational forecasting systems. Title: Optical Turbulence in High Angular Resolution Techniques in Astronomy Authors: Beckers, Jacques M. Bibcode: 2009otam.conf....1B Altcode: All astronomical observations are done best from space where the absorption by and turbulence in the Earth atmosphere are absent. One has access to the entire electromagnetic radiation spectrum and the absence of seeing allows unlimited angular resolution. However, the cost of facilities in space and their operation is 3 orders of magnitude of similar sized facilities on Earth. Experimental astrophysicists have therefore in the past decades pursued the development of techniques to overcome the seeing limitations by the atmosphere. So far they have been very successful at this and much more is almost certain to come. Adaptive Optics (AO) will make very large (8 - 10-meters diameter) and extremely large (30 - 42 meters diameter) telescopes diffraction limited first at infrared wavelengths and eventually at visible wavelengths. The development of fast optical turbulence/seeing wavefront sensing techniques using artificial sources (Laser Beacons) will enable doing that over the entire sky. Atmospheric Tomography (AT) needed for Multi-Conjugate Adaptive Optics (MCAO) will give 3D maps of the rapidly variable atmospheric turbulence. Large interferometers with baselines of hundreds of meters will further enhance the angular resolution using fringe tracking for both co-phasing and coherent operation. Ground-based astronomy is therefore entering a new era in which milli-arcsecond observations and better are foreseen even of objects at the edge of the universe. The astronomical techniques will result in information of atmospheric optical turbulence which is likely to be of interest for meteorologists. Title: Pupil Slicing Adaptive Optics:. Making Extremely Large Telescopes Diffraction Limited at Short Wavelengths Authors: Beckers, Jacques M. Bibcode: 2009otam.conf..307B Altcode: Extremely Large Telescopes (ELTs) will have aperture diameters up to 42 meters. Adaptive Optics (AO) at short wavelengths (< 1 micron) will be very hard to implement at these wavelengths because of the limited number of actuators on state-of-the-art deformable mirrors and because of the limited brightness of Laser Guide Stars (LGSs). For 1 arcsec seeing at 500 nm wavelength deformable mirrors (DMs) with about 150000 actuators will be needed and LGSs of a brightness of V = 8 to 9. That exceeds our present capabilities by a factor of about 100 and 2 magnitudes respectively. One might expect both to improve with time. We propose to combine the techniques of "pupil slicing" and AO to sharpen the telescope images at short wavelengths to the size of Airy disk of the pupil slices. I refer to this technique as "Pupil Slicing Adaptive Optics" or PSAO. At 500 nm wavelength that would correspond to the Airy disk of an approximately 5 meter diameter aperture, or a FWHM of 0.02 arcsec. As DMs increase in their number of actuators, the size of the pupil slices increases thus improving the angular resolution. Ultimately the full angular resolution of, for example, a 42 meter aperture would be reached (0.0024 arcsec at 500 nm). Of course, this does not resolve the issue of the limited brightness of LGSs. For it one has to wait for more powerful lasers and the development of perspective elongation correction techniques. Alternatively one would accept limited sky coverage (0.1%) when using natural guide stars (NGSs). Particularly interesting is the PSAO technique for high resolution spectroscopy where the smaller image sizes even for many slices results in a significant decrease in spectrograph dimensions.

Note from Publisher: This article contains the abstract only. Title: Using the Scintillation of Extended Objects to Probe the Lower Atmosphere Authors: Beckers, Jacques M. Bibcode: 2009otam.conf...23B Altcode: The scintillation of point-like objects is primarily caused by thermal fluctuations in the upper atmosphere. For it the scintillation index (σI2) is proportional to the height integral of Cn2(h) weighted by a height dependent function F(h) = hα where α = +5/3. For extended objects like the Sun or the Moon the height contribution to the (much smaller) scintillation is quite different. Because of their size the effects of the optical turbulence is averaged over an ever increasing area as the distance to the detector increases. Assuming vertical viewing, the area diameter increases like h*Ω where Ω is the angular diameter of the Sun or Moon. For Kolmogorov turbulence the function F(h) then still has the same shape, but with α = -1/3 so that the lower layers contribute more to scintillation. This makes it a good tool for the probing of the lower atmospheric layers. Unlike the σI2 for stellar scintillation, the σI2 for the Sun and the Moon is wavelength independent. Using an array of scintillometers one can probe the Cn2(h) distribution of those lower layers in a technique called SHABAR. SHABARs have been used in site testing for lower atmosphere probing for solar and nighttime telescopes. The aim is to establish the height to place telescopes, like the Advanced Technology Solar Telescope (ATST), to minimize boundary layer seeing effects. SHABAR site tests using the Moon are planned both for Arctic sites (Hickson's contribution to this meeting) and Antarctic sites (Storey's contribution to this meeting) where boundary layer heights are very site dependant reaching sometimes very small values. In my contribution I described some of the solar results related to the ATST site testing. The scintillation of planets have an F(h) function different in shape from that of the Sun or Moon. For low heights, where their beams still are narrow, F(h) has an α of +5/3 (as for stars); for large heights it is -1/3 (as for the Sun & Moon). For Mars the height contributions F(h) for seeing and scintillation are similar. Title: Laser guide stars for daytime thermal IR observations Authors: Beckers, Jacques M. Bibcode: 2008SPIE.6986E..0GB Altcode: 2008SPIE.6986E..16B In connection with the planning for Extremely Large Telescopes, I revisit a 2001 paper in which Cacciani and I describe the use of Sodium Laser Guide Stars (LGSs) for diffraction limited daytime astronomical observations. The enabling technology for seeing LGSs in broad daylight is the availability of very narrow band magneto-optical filters. Considering the dominance of the atmospheric scattering of sunlight at wavelengths below 3.5 μm, daytime use is only indicated for mid- and thermal IR observations. The launch of the 6.5 meter aperture James Web Space Telescope (JWST) appears to be assured and planned for 2013, preceding the most optimistic projections for the completion date of the first ELT. The projected thermal background of the JWST is very much less than that of ground-based telescopes so that any competing ground-based observations are limited to those parameters not covered by the JWST: angular resolution (requiring apertures > 6.5 meter) and spectral resolution (R>3000). I compare the benefits of daytime observations with Na-LGS equipped telescopes and interferometers at moderate latitudes and in the Antarctic (specifically Dome C). In both cases daytime observations extend the amount of observing time available for TIR observations. Antarctic observations have the advantage of having very good seeing during the daytime, significantly better than nighttime seeing. In contrast the seeing at moderate latitude sites significantly deteriorates during daytime resulting in lower quality observations than during nighttime. In addition Antarctic sites are less hostile to maintenance and operations during daytime (summer) observations as compared to nighttime (winter) observations. Title: Introduction to the Discussion on: How to Mitigate the Ground-Layer Seeing Effects at Dome C? Authors: Beckers, J.; Travouillon, T. Bibcode: 2008EAS....33..221B Altcode: At Dome C most of the seeing is located in the lower atmosphere, below 50 meters height. In this introduction we describe ways in which one might mitigate those ground layer seeing effects and thus be limited solely by the ~0.25 arcsec seeing of the so-called “free atmosphere”. Title: On the Daytime Use of Dome C for Astronomy Authors: Beckers, J. M. Bibcode: 2008EAS....33..307B Altcode: I describe aspects of the non-solar astronomy use of Dome C telescopes under daytime/summer conditions. In the thermal IR (TIR) wavelength region, where scattered sunlight is dwarfed by sky and facility radiation, astronomy benefits from the better seeing, continuous sky coverage, a more than doubling of the observing time and the improved site accessibility and logistics. Na-Laser Guide Stars (LGSs) can be used for wavefront sensing in daytime using very narrow band filters to suppress the sky background at visible wavelengths. It enables the use of Adaptive Optics for diffraction limited imaging in the TIR during daytime at Dome C. Title: Towards the Interferometric Imaging of Red Supergiants Authors: Ludwig, Hans-Günter; Beckers, Jacques Bibcode: 2008poii.conf..485L Altcode: 2008poio.conf..485L No abstract at ADS Title: 1988 1993: The Final Definition of the Very Large Telescope Interferometer, its Site and Configuration Authors: Beckers, Jacques M. Bibcode: 2008poii.conf...23B Altcode: 2008poio.conf...23B This paper focuses on the period during which the VLTI evolved from its conceptual phase to the way it is largely implemented now. That phase did not include the VLTI instrumentation, which was defined later and which did not make use of the homothetic beamcombining system that was part of the 1988 - 199 design. Title: Can variable meridional flows lead to false exoplanet detections? Authors: Beckers, J. M. Bibcode: 2007AN....328.1084B Altcode: The search for habitable exoplanets centers on planets with Earth-like conditions around late type stars. Radial velocity searches for these planets require precisions of 1 m/s and better. That is now being achieved. At these precisions stellar surface motions might lead to false detections. Of particular interest are variable meridional flows on stellar surfaces. I review the available observations of solar surface meridional flows using both Doppler shift and local helioseismology techniques. Interpretation in terms of Doppler shifts in integrated starlight leads to estimates of the likelihood of false detections. It is unlikely that these false detections occur in the habitability zones of exoplanets. Title: Very high-resolution spectroscopy for extremely large telescopes using pupil slicing and adaptive optics Authors: Beckers, Jacques M.; Andersen, Torben E.; Owner-Petersen, Mette Bibcode: 2007OExpr..15.1983B Altcode: Under seeing limited conditions very high resolution spectroscopy becomes very difficult for extremely large telescopes (ELTs). Using adaptive optics (AO) the stellar image size decreases proportional with the telescope diameter. This makes the spectrograph optics and hence its resolution independent of the telescope diameter. However AO for use with ELTs at visible wavelengths require deformable mirrors with many elements. Those are not likely to be available for quite some time. We propose to use the pupil slicing technique to create a number of sub-pupils each of which having its own deformable mirror. The images from all sub-pupils are combined incoherently with a diameter corresponding to the diffraction limit of the sub-pupil. The technique is referred to as “Pupil Slicing Adaptive Optics” or PSAO. Title: Effects of Foreshortening on Shallow Sub-surface Flows Observed with Local Helioseismology Authors: Beckers, Jacques M. Bibcode: 2007SoPh..240....3B Altcode: From the results given in a recent paper by Zaatri et al. (2006, Solar Phys.236, 227) it is clear that foreshortening effects play a major role in estimating the magnitude and direction of meridional and other flows in the shallow solar sub-surface layers using local helioseismology. Using a different algorithm to account for these effects I arrive at a significantly different estimate for the meridional flows. Title: From Euro50 toward a European ELT Authors: Ardeberg, Arne; Andersen, Torben; Beckers, Jacques; Browne, Michael; Enmark, Anita; Knutsson, Per; Owner-Petersen, Mette Bibcode: 2006SPIE.6267E..25A Altcode: 2006SPIE.6267E..68A With Euro50 as a convenient telescope laboratory, the Euro50 team has continued development aiming at a European extremely large telescope (ELT). Here, we give a progress report. The needs of science and instrumentation are briefly discussed as is the importance of photometric stability and precision. Results are reported from work on integrated modelling. Details are given concerning point-spread functions (PSFs) obtained with and without adaptive optics (AO). Our results are rather encouraging concerning AO photometry and compensation of edge sensor noise as well as regarding seeing-limited ELT operation. The current status of our development of large deformable mirrors is shown. Low-cost actuators and deflection sensors have been developed as have hierarchic control algorithms. Fabrication of large thin mirror blanks as well as polishing and handling of thin mirrors has been studied experimentally. Regarding adaptive optics, we discuss differential refraction and the limitations imposed by dispersive optical path differences (OPDs) and dispersive anisoplanatism. We report on progress in laser guide star (LGS) performance and a real-time online experiment in multi-conjugate AO (MCAO). We discuss ELTs, high-resolution spectroscopy and pupil slicing with and without use of AO. Finally, we present some recent studies of ELT enclosure options. Title: High Resolution Spectroscopy with Extremely Large Telescopes Using Pupil Slicing Adaptive Optics Authors: Beckers, Jacques M.; Andersen, T.; Owner-Petersen, M. Bibcode: 2006AAS...208.5504B Altcode: 2006BAAS...38R.135B Under seeing limited imaging conditions, high resolution spectroscopy (R ≥ 100,000 at visible wavelengths) on large aperture telescopes requires huge instruments. This will cause major problems in future Extremely Large Telescopes (ELTs; diameters D = 20 - 60 meters). With diffraction limited imaging using adaptive optics the size of the spectrograph will become independent of the telescope diameter since the image size shrinks at the same rate as the telescope diameter increases. However the complexity of adaptive optics at visible wavelengths will be very high, requiring a large number of deformable mirrors elements (50000 to 100000 for D = 50 meters). It is not likely that devices of that complexity will be available soon.In this paper we propose an intermediate step in that direction using so-called Pupil-Slicing Adaptive Optics (PSAO). In it the telescope aperture (its "pupil") will be divided into N equal sub-pupils. Each sub-pupil will have its own adaptive optics to give a diffraction limited image size corresponding to its diameter. The N resulting images are then combined on the entrance of a multi-mode fiber which feeds the high resolution spectrograph. The fiber scrambles the light and avoids variations of the position of the spectrum due to variations of the spectrograph slit illumination.As an example, we present a strawman design for a PSAO spectrograph for the Euro50, D = 50 meter telescope. It uses N = 18 and 4000 element MEMS deformable mirrors. Such mirrors are currently under development and are likely to be available at the time of the commissioning of the first ELT. A spectral resolution of around R = 200000 seems feasible for spectrographs less than 2 meters in size. Title: Site testing for the Advanced Technology Solar Telescope Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K. Bibcode: 2006SPIE.6267E..1TH Altcode: 2006SPIE.6267E..59H The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope being designed for high spatial, spectral and temporal resolution, as well as IR and low-scattered light observations. The overall limit of performance of the telescope is strongly influenced by the qualities of the site at which it is located. Six sites were tested with a seeing monitor and a sky brightness instrument for 1.5 to 2 years. The sites were Big Bear (California), Haleakala (Hawaii), La Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico), and San Pedro Martir (Baja California, Mexico). In this paper we will describe the methods and results of the site survey, which chose Haleakala as the location of the ATST. Title: Solar Site Survey for the Advanced Technology Solar Telescope. I. Analysis of the Seeing Data Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Streander, K. Bibcode: 2005PASP..117.1296S Altcode: 2005astro.ph..8690S The site survey for the Advanced Technology Solar Telescope concluded recently after more than 2 years of data gathering and analysis. Six locations, including lake, island, and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial, because daytime seeing is often very different between the actual telescope aperture (~30 m) and the ground. Two independent inversion codes have been developed to simultaneously analyze data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from 2003 May that was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high-altitude seeing) and the rest (dominated by near-ground turbulence). Title: The Western Mediterranean Deep Water: A proxy for climate change Authors: Rixen, M.; Beckers, J. -M.; Levitus, S.; Antonov, J.; Boyer, T.; Maillard, C.; Fichaut, M.; Balopoulos, E.; Iona, S.; Dooley, H.; Garcia, M. -J.; Manca, B.; Giorgetti, A.; Manzella, G.; Mikhailov, N.; Pinardi, N.; Zavatarelli, M. Bibcode: 2005GeoRL..3212608R Altcode: Reconstructions of Mediterranean ocean temperature fields back to 1950 show a proxy relationship between heat content changes in the North Atlantic and the Western Mediterranean Deep Water (WMDW) formed in the Gulf of Lions in winter, because of consistent air-sea heat fluxes over these areas, strongly correlated to the North Atlantic Oscillation (NAO). Title: The ATST Site Survey Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K. Bibcode: 2005AGUSMSP34A..04H Altcode: The Advanced Technology Solar Telescope (ATST) will be the world's largest aperture solar telescope, and is being designed for high resolution, IR, and coronal research. It must be located at a site that maximizes the scientific return of this substantial investment. We present the instrumentation, analysis and results of the ATST site survey. Two instrumentation sets were deployed at each of six sites to measure seeing as a function of height, and sky brightness as a function of wavelength and off-limb position. Analysis software was developed to estimate the structure function Cn2 as a function of height near the ground, and the results were verified by comparison with in-situ measurements. Additional software was developed to estimate the sky brightness. The statistics of the conditions at the sites were corrected for observing habits and the annualized hours of specific observing conditions were estimated. These results were used to identify three excellent sites suitable to host the ATST: Haleakala, Big Bear and La Palma. Among them, Haleakala is proposed as the optimal location of the ATST, La Palma and Big Bear being viable alternative sites. Title: The Effect of Stellar Meridional Motions on Extrasolar Planet Detection Authors: Beckers, J. M. Bibcode: 2005AAS...206.2306B Altcode: 2005BAAS...37..464B Most Extrasolar Planet detections use periodic Doppler velocity variations of the parent star to infer the presence of a planet. Refinements of this technique have reached precisions of 1 m/sec and better. At these precisions periodic flows on the stellar surface may well lead to false detections. The most likely flows of concern are meridional motions.

Solar surface meridional motions have unambiguously been observed. They move towards the pole and have an approximate shape of the second Legendre Polynomial of order m=1 reaching a maximum surface velocity of about 30 m/sec. Depending on the inclination of the rotation axis to the line of sight this would cause a red shift in the spectrum of integrated sunlight of 8 m/sec when viewed perpendicular to this axis [sin(i)=1] and a blue shift of 15 m/sec when viewed along this axis [sin(i)=0]. The Sun is a relatively slow rotator among G and earlier type stars, so that many of the stellar effects are likely to be larger.

Of interest is, of course, the temporal variation of this motion. Observations of solar surface meridional flows go back to 1967. They appear to show variations but my search for periodic meridional motion changes is so far inconclusive. This search is complicated by possible changing instrumental effects and latitudinal change in convective blue shift ("limb effect"). The latter is also of interest for false Extrasolar Planet detection techniques. It can be evaluated by observing the Doppler shifts for different line strengths and excitation potential. The former requires a long time sequence of solar observations of surface meridional flows using the same, unchanging instrument. The GONG and SOHO/MDI helioseismology observatories, now in operation for about one solar cycle, might provide the necessary data. Title: Sunspots, gravitational redshift and exo-solar planet detection Authors: Beckers, Jacques M. Bibcode: 2005dsr..conf..285B Altcode: No abstract at ADS Title: Sunspots, gravitational redshift and exo-solar planet detection Authors: Beckers, Jacques M. Bibcode: 2005AcHA...25..285B Altcode: I revisit a paper that I published over 25 years ago (Beckers 1977) which has recently attracted renewed attention in connection with searches for exo-solar planets using the periodic Doppler motions of the star resulting from the center of gravity in these planetary systems being offset from the center of that star. The original goal of the research reported in the paper was concerned with the accurate determination of absolute motions of and in sunspots. I used the wavelengths of Iodine absorption lines introduced by an Iodine absorption tube as the wavelength reference. The experiment resulted in addition to the intended measurement of sunspot motions in the affirmation of the interpretation of the solar limb effect and in the measurement of the gravitational redshift of the solar disk radiation. Only recently did I become aware that it was this use of the Iodine absorption spectrum as a stable and precise wavelength reference that led to many of the current programs aimed at the detection of exo-solar planets. Title: Solar site testing for the Advanced Technology Solar Telescope Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John; Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher, Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski, Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas R.; Socas-Navarro, Hector; Streander, Kim Bibcode: 2004SPIE.5489..122H Altcode: The location of the Advanced Technology Solar Telescope (ATST) is a critical factor in the overall performance of the telescope. We have developed a set of instrumentation to measure daytime seeing, sky brightness, cloud cover, water vapor, dust levels, and weather. The instruments have been located at six sites for periods of one to two years. Here we describe the sites and instrumentation, discuss the data reduction, and present some preliminary results. We demonstrate that it is possible to estimate seeing as a function of height near the ground with an array of scintillometers, and that there is a distinct qualitative difference in daytime seeing between sites with or without a nearby lake. Title: Euro50 Authors: Andersen, Torben E.; Ardeberg, Arne L.; Beckers, Jacques M.; Goncharov, Alexander V.; Owner-Petersen, Mette; Riewaldt, Holger Bibcode: 2004SPIE.5382..169A Altcode: The Euro50 is a telescope for optical and infrared wavelengths. It has an aspherical primary mirror with a size of 50 meters and 618 segments. The optical configuration is of Gregorian type and the secondary mirror is deformable for adaptive optics. Observations can take place in prime focus, Gregorian foci, and Nasmyth foci using additional relay mirrors. The telescope provides seeing limited observations, partial adaptive optics with ground layer correction, single conjugate adaptive optics and dual-conjugate adaptive optics. For prime focus observations, a clam-shell corrector with a doublet lens is used. The primary mirror segments can be polished using the precessions polishing technique. "Live Optics" denotes the joint segment alignment system, secondary mirror control system, adaptive optics and main axes servos. An overview is given of the live optics architecture, including feedback from wavefront sensors for natural and laser guide stars, and from primary mirror segment edge sensors. A straw man concept of the laser guide star system using sum-frequency YAG lasers is presented together with a solution to the laser guide star perspective elongation problem. The structural design involves a large steel structure and a tripod of carbon fiber reinforced polymer to support the secondary mirror. Integrated models have been set up to simulate telescope performance. Results show that an enclosure is needed to protect the telescope against wind during observations. The enclosure is very large box-shaped steel structure. Title: Sodium beacon wavefront sensing for the Euro50 telescope in the presence of perspective elongation Authors: Beckers, Jacques M.; Owner-Petersen, Mette; Andersen, Torben E. Bibcode: 2004SPIE.5382..510B Altcode: To obtain full sky coverage, astronomical adaptive optics systems require Na Sodium Beacons (SBs) (also referred to as Laser Guide Stars or LGSs) located at heights extending from 85 to 100 km. When viewed at the edge of large telescopes these SBs appear elongated. For the Euro50 50 meter aperture telecopes this elongation amounts to 6 to 9 arcseconds when the laser is launched from a point on the telescope axis. This is substantially larger than the -0.6 arcsec FWHM SB when viewed near the telescope center. This so-called "perspective elongation" substantially decreases the sensitivity of SB aided adaptive optics. We describe a way of removing this elongation when using pulsed lasers. It uses rapid (microsecond) refocusing of the telescope with the aid of birefringent lenses and polarization modulators. We present an outline of the SB wavefront sensor for the Euro50. Title: Latest Results from the ATST Site Survey Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau, D.; Streander, K. Bibcode: 2004AAS...204.6909H Altcode: 2004BAAS...36..795H We present the latest results and current status of the site survey portion of the Advanced Technology Solar Telescope (ATST) project. The ATST will provide high resolution solar data in the visible and IR. The site is a major factor determining the performance of the telescope. The most critical site characteristics are the statistics of daytime seeing quality and sky clarity. These conditions are being measured by a suite of instruments at three sites (Big Bear, Haleakala, La Palma). These sites were chosen from a set of six that have been tested starting in November 2001. The instrumentation includes a solar differential image motion monitor, an array of scintillometers, a miniature coronagraph, a dust monitor, and a weather station. The analysis of the data provides an estimate of the seeing as a function of height near the ground. We will present the latest results of the analysis of the survey data set. Title: Development of SCIDAR for solar observations Authors: Beckers, Jacques M.; Rimmele, Thomas R. Bibcode: 2004SPIE.5171..195B Altcode: In nighttime astronomy Vernin and co-workers have proposed and subsequently developed the so-called SCIDAR (SCIntillation Detection And Ranging) technique to probe Cn2(h). It makes use of the double shadow band (or scintillation) pattern formed on a telescope aperture by the two components of a binary star. We are developing a variant of this technique for solar astronomy. It uses pairs of small apertures on the solar image with diameters smaller than the isoplanatic patch ("artificial double stars"). Within the isoplanatic patch the complex amplitude (intensity and phase) of the atmospheric wavefront disturbances is constant. Solar SCIDAR (or S-SCIDAR) makes use of this. We will present the results of the first (inconclusive) experiments of this S-SCIDAR technique as used on the 76 cm aperture Dunn Solar Telescope (DST) and the 152 cm aperture McMath-Pierce facility (McM-P) of the US National Solar Observatory. It uses a 45 x 45 lenslet array placed in the solar image. The size of the lenslets corresponds to 2.25 x 2.25 arcsec at the DST and 1.67 x 1.67 arcsec at the McM-P; the separation of lenslet pairs on the DST (and hence of the separations of the artificial double stars) ranges from 2.25 arcsec to 140 arcsec. The lenslet array forms an array of pupil images on a CCD detector. Title: Interferometric Imaging in Astronomy: A Personal Retrospective (With 17 Figures) Authors: Beckers, Jacques M. Bibcode: 2004RvMA...17..239B Altcode: No abstract at ADS Title: Study of the impact of satellite data assimilation into a hydrodynamic model of the Ligurian Sea. Comparison between SST fields and SST satellite-based predicted fields Authors: Alvera-Azcarate, A.; Barth, A.; Rixen, M.; Beckers, J. -M. Bibcode: 2004cosp...35.2968A Altcode: 2004cosp.meet.2968A The verification of a 3D hydrodynamic model of the Ligurian Sea is presented. Two assimilation experiments have been carried out with this model: the assimilation of real SST, and the assimilation of SST forecasted by a statistical predictor. The aim of the study is to establish the skill of the model in these two configurations. The assimilation of predicted SST can help to increase the model skill when observations are not available, and preliminary results show that both approaches obtained similar results. The verification is done in a multi-scale approach, by decomposing the model results and the observations into several spatial scales, using 2D discrete wavelet transforms. At each scale the error between the model and the observations is calculated, and the scales where the biggest errors occur can be identified. The variability distribution of the model and the observations is also examined at each scale, to study the impact of the assimilation on the model variability. This methodology provides a scale-dependent insight in the study of the assimilation of SST and predicted SST. The differences between both assimilated data and how these differences affect the model results are examined. Title: Recovering missing data in satellite images. An application to Adriatic SST and comparison with in situ data Authors: Alvera-Azcarate, A.; Barth, A.; Rixen, M.; Beckers, J. -M. Bibcode: 2004cosp...35.2980A Altcode: 2004cosp.meet.2980A Satellite images are very useful for many applications in oceanography and other environmental sciences. They offer a great coverage both in time and space, not attained by in situ measurements. Clouds are responsible for missing data on images provided by receptors working in the visible and IR range receptors. In some seasons the cloud coverage can reach an important percentage. Many data analysis techniques do not need a total coverage, although it is always desirable. Some applications, such as Empirical Orthogonal Function (EOF) analysis, or wavelet decomposition need a complete set of data, and a technique for recovering these missing data is indispensable. In this work we present DINEOF (Data INterpolating Empirical Orthogonal Functions), a method for the reconstruction of satellite data, based on an EOF decomposition. DINEOF reconstructs the missing data from an optimal set of EOFs. The optimal number of EOFs is determined by cross-validation. This method has shown to obtain robust results. DINEOF has been applied to a series of 105 AVHRR SST images of the Adriatic Sea, in a period ranging from May to October 1995. The mean cloud coverage of this data set is 52%. The error obtained by the cross-validation is of 0.6°C, and a total of 10 EOFs were necessary to reconstruct the data. A comparison with in situ data obtained form the MEDAR/Medatlas database is made. A total of 452 stations are examined. The RMS error between MEDAR/Medatlas and the reconstructed data is of 0.95°C. The error between MEDAR/Medatlas data and the points that are not missing in the Adriatic data set is of 0.67°C, which can be considered as the inherent error between the in situ and remote sensed data sets. Title: Assimilation of Sea Surface Temperature predicted by a satellite-based forecasting system in a doubly nested primitive equation model of the Ligurian Sea Authors: Barth, A.; Alvera-Azcárate, A.; Alvarez, A.; Beckers, J. -M. Bibcode: 2004cosp...35.2744B Altcode: 2004cosp.meet.2744B Data assimilation is traditionally used to combine model dynamics and observations in a statistical optimal way. Assimilation of observations improves therefore hindcasts and nowcasts of the ocean state than otherwise obtained by the model alone. The observational constraints are necessary to reduce uncertainties and imperfections of the ocean model. Due to the obvious lack of future observations, the model forecast cannot be controlled by observations and the predictive skill degrades as the forecast time lag increases. The error grow is not only caused by the chaotic nature of the system but also by the biases and drifts of the model. The later part can be reduced by considering different models with different imperfections. Data assimilation provides the statistical frame for merging the different model results. A primitive equation model of the Mediterranean Sea (1/4° resolution) has been implemented with two successive grid refinements of the Liguro-Provençal Basin (1/20°) and the Ligurian Sea (1/60°) respectively (Barth et al, 2003). The dependence of the ``parent'' model and the embedded ``child'' model is bi-directional; it involves the exchange of boundary conditions and feedback between the models. Alvarez el al. (2004) developed a statistical predictor for forecasting the SST of the Ligurian Sea with a time lag of 7 days based on the previous remote sensed SST. The degrees of freedom of the SST are reduced by an Empirical Orthogonal Function (EOF) analysis. A genetic algorithm trained by the historical SST evolution in the Ligurian Sea is used to predict the EOF amplitudes. Observed and forecasted SST are assimilated in the hydrodynamic model and the results of this two experiments are compared to the model run without assimilation. The assimilation of the forecasted SST reduces the error of the model by an amount comparable to the assimilation of real SST, showing the potential of skill improvement of combining statistical and hydrodynamic models. Title: Rapid refocusing system for the Euro50 telescope aimed at removing the perspective elongation of laser beacons Authors: Beckers, Jacques M.; Owner-Petersen, Mette; Andersen, Torben Bibcode: 2003SPIE.5169..123B Altcode: To obtain full sky coverage, astronomical adaptive optics systems require Na Sodium Beacons (SBs) (also referred to as Laser Guide Stars or LGSs) located at heights extending from 85 to 100 km. When viewed at the edge of large telescopes these SBs appear elongated. For the Euro50 50 meter aperture telescopes this elongation amounts to 6 to 9 arcseconds when the laser is launched from a point on the telescope axis. This is substantially larger than the ~0.6 arcsec FWHM SB when viewed near the telescope center. This so-called "perspective elongation" substantially decreases the sensitivity of SB aided adaptive optics. We describe a way of removing this elongation when using pulsed lasers. It uses rapid (microsecond) refocusing of the telescope with the aid of birefringent lenses and polarization modulators. We present an outline of the SB wavefront sensor for the Euro50. Title: Sunspots, Gravitational Redshift and Exo-solar Planet Detection Authors: Beckers, Jacques M. Bibcode: 2003ANS...324Q..95B Altcode: 2003ANS...324..K10B No abstract at ADS Title: Along or across front ocean survey strategy? The estimation of quasi-geostrophic vertical velocities and temperature fluxes Authors: Rixen, M.; Allen, J. T.; Pollard, R. T.; Beckers, J. -M. Bibcode: 2003GeoRL..30.1264R Altcode: 2003GeoRL..30e..68R In a companion paper we have shown that at the mesoscale, the unusual across front sampling strategy (AL) is more accurate than the usual across front sampling strategy (AC) on hydrographic and bio-chemical properties when the front is sufficiently developed. The cruise design based on the optimal reconstruction of the density fields does however not imply that derived variables like quasi-geostrophic (QG) vertical velocities and temperature fluxes also exhibit minimal associated errors. Here we present results of optimized sampling strategies for diagnostic QG vertical velocities (wQG) and temperature fluxes (θQG) derived from the omega equation. Results are illustrated in the same framework, for the Iceland-Faroes oceanic frontal area and for a control model and reveal that at these spatio-temporal scales, the unusual AL may also provide better estimations of vertical velocities and temperature fluxes compared to the classic AC, especially when the front is sufficiently developed. Title: ATST seeing monitor: February 2002 observations at Fuxian Lake Authors: Beckers, Jacques M.; Liu, Zhong; Jin, Zhenyu Bibcode: 2003SPIE.4853..273B Altcode: We describe a solar seeing monitor used for the site testing for the 4 meter US Advanced Technology Solar Telescope and the 1 meter Yunnan Observatory Solar Telescope. It has two parts: a solar Differential Image Motion Monitor (S-DIMM) and a linear array of 6 solar scintillometers (SHABAR= SHAdow BAnd Ranger). The results obtained by both methods are compared on the basis of observations obtained in February 2002 at the Yunnan Observatory Fuxian Lake solar station. Analysis showed that these two ways of measuring the Fried parameter give consistent results. We confirm earlier observations that showed that the boundary layer seeing over lakes is strongly suppressed. The amount of this boundary layer seeing depends on the temperature difference between lake and air and on the wind velocity. We have also carried out seeing observation along a 9.15 km horizontal path across the lake. The Cn2 values derived from these is consistent with the solar observations. They confirm the dependence of Cn2 on the lake-to-air temperature difference. From the SHABAR we find a typical scale height for the boundary layer seeing of 20 meters and from inter-comparison of the S-DIMM and SHABAR observations we derive an outer scale of turbulence of about 50 meters. Title: Adaptive optics for the Euro50: design and performance Authors: Goncharov, Alexander V.; Owner-Petersen, Mette; Andersen, Torben; Beckers, Jacques M.; Devaney, Nicholas Bibcode: 2003SPIE.4840...36G Altcode: The optical design for the proposed Euro50 extremely large telescope with integrated adaptive optics (AO) is presented. For atmospheric turbulence correction, we propose using single and dual-conjugate AO systems working with natural and laser guide stars. The corrective shape of the deformable mirrors (DMs) is derived from an analytical algorithm based on minimization of the sum of the residual power spectra of the phase fluctuations seen by guide stars after correction. Predictions for performance of the Euro50 ELT with Dual-conjugate AO are given for the K band using a seven layer atmospheric model for the atmosphere at the Observatorio del Roque de los Muchachos (ORM) on La Palma. The average Strehl ratio is used to quantify the system performance for different values of actuator pitch and DM conjugation altitudes. The influence of the outer scale and telescope pointing on the RMS stroke of the DMs is presented. It is concluded that construction of such a system is feasible and that there is a need for development of a simulation tool to verify the analytical calculations. Precise knowledge of the outer scale of the atmosphere at the ORM is needed to establish the dynamical range of the mirrors. Title: The Euro50 Extremely Large Telescope Authors: Andersen, Torben; Ardeberg, Arne L.; Beckers, Jacques; Goncharov, Alexander; Owner-Petersen, Mette; Riewaldt, Holger; Snel, Ralph; Walker, David Bibcode: 2003SPIE.4840..214A Altcode: Euro50 is a proposed optical telescope with an equivalent primary mirror diameter of 50 m. Partners of the collaboration are institutes in Sweden, Spain, Ireland, Finland, and the UK. The telescope will have a segmented primary mirror and an aplanatic Gregorian configuration with two elliptical mirrors. For a 50 m telescope there would be no economical advantage in going to a spherical primary. The size of the primary mirror segments (2 m) has been selected on the basis of a minimization of cost. An adaptive optics system will be integrated into the telescope. The telescope will have three operational modes: Seeing limited observations, single conjugate adaptive observations in the K-band, and dual conjugate observations also in the K-band. An upgrade to adaptive optics also in the visible down to 500 nm is foreseen. There will be an enclosure to protect the telescope against adverse weather and wind disturbances. Integrated simulation models are under development. The project time will be 10 years and the cost some 591 MEuros. Title: Future giant telescopes: astronomy's Holy Grail or Pandora's Box? Authors: Beckers, Jacques M. Bibcode: 2003SPIE.4840..378B Altcode: In this paper I review and reflect on the contributions given at this conference and place them in a broader context. Emboldened by the recent successes of 8 to 10-meter class telescopes and by the success of adaptive optics in making these telescopes diffraction limited, astronomers and engineers are now embarking on the quest for giant telescopes. Are these plans realistic? Are we overreaching ourselves? Title: Along or across front survey strategy? An operational example at an unstable front Authors: Rixen, M.; Allen, J. T.; Alderson, S.; Cornell, V.; Crisp, N.; Fielding, S.; Mustard, A. T.; Pollard, R. T.; Popova, E. E.; Smeed, D. A.; Srokosz, M. A.; Barth, A.; Beckers, J. -M. Bibcode: 2003GeoRL..30.1017R Altcode: 2003GeoRL..30a..17R We present results of the optimization of near-real time on-board sampling strategy in the Iceland-Faroes oceanic frontal area, based on the outputs of a mesoscale 3D operational data assimilation forecasting experiment. By minimizing a root mean square error cost function, we show that in this example an along-front sampling strategy, i.e. with transects parallel to the front, produces smaller errors in temperature, salinity, nitrate, phytoplankton, and zooplankton fields, as a result of a combination of the direction of the sampling of the front and errors associated with the asynopticy of observations (Doppler effect). This is contrary to the classic across-front sampling strategies that are used in most field experiments reported in the literature, i.e. where transects are perpendicular to the front. A control model shows that at these spatio-temporal scales, the along front sampling strategy is optimal when the frontal instability has sufficiently developed. Title: Control strategy for the adaptive optics of the Euro50 Authors: Owner-Petersen, Mette; Andersen, Torben; Goncharov, Alexander V.; Beckers, Jacques M. Bibcode: 2003SPIE.4840..427O Altcode: The scheme presently envisaged for the EURO50 adaptive optics is presented. The Euro50 adaptive optics will primarily work with laser guide stars (LGSs) and control of either one or two deformable mirrors (SCAO and DCAO respectively), but operation using a natural guide star (NGS) is also foreseen. The point spread function (PSF) for SCAO operation using a single NGS is evaluated. An algorithm for optimal control of the deformable mirrors (DMs) using LGSs and Shack-Hartman wavefront sensors is presented and commented upon. It is an extension of a recently developed algorithm for optimal control using NGSs and working in the spatial Fourier domain. In addition the concept of a virtual wavefront sensor is introduced to overcome the difficulty in transmitting a large number (37) of LGSs to the final DCAO focus with both adequate field and adequate aberrations. The expected performance is estimated in form of maps of the Strehl ratio versus field angle using a standard seven layer atmospheric model for the Observatorio del Roque de los Muchachos (ORM) site on la Palma for the case of the outer scale being either 20 m (nominal for ORM) or infinity (Kolmogorov - most pessimistic case). Title: Adaptive optics schemes for future extremely large telescopes Authors: Goncharov, Alexander V.; Owner-Petersen, Mette; Andersen, Torben; Beckers, Jacques M. Bibcode: 2002OptEn..41.1065G Altcode: The adaptive optics for any telescope in the 25- to 100-m class will be complex. It is believed that adaptive optics should, to the maximum extent, be designed as an integrated part of a telescope. The proposed Swedish 50-m Extremely Large Telescope is considered here to illustrate the principle of integrated adaptive optics. Two alternative designs both using the Ritchey-Chretien telescope system and laser guide star (LGS) reference sources are presented. The first design employs trombone optics, which bring the laser guide star images back to the normal Ritchey-Chretien focal surface (referred to as the RC-focus) from the LGS focal surface (referred to as the LRC-focus), and a layer-oriented wavefront sensor system optically performing the averaging `shift and add' in the final focus. According to this procedure, sensed wavefronts are overlapped with a certain mutual shift and added for estimation of wavefront average slope values, resulting in actuator commands for driving the shape of the deformable mirrors. The second design employs a numerical `shift and add' procedure and has two wavefront sensors. The first one performs LGS sensing in an intermediate focus (LRC-focus), giving the input data for an analytical algorithm for deriving the mirror deformations to correct for atmospheric turbulence. By using an artificial laser source at the intermediate focus, the shape of the second deformable mirror is controlled by a second wavefront sensor in the final focus. The capability of the analytical algorithm to derive the mirror corrections from the measured wavefronts ensures proper functioning of the adaptive optics system. This system has a simpler optical design compared to the first design. Title: Solar Seeing Measurements at the Fuxian Lake Observatory Authors: Beckers, J. M.; Liu, Zhong Bibcode: 2002AAS...200.5603B Altcode: 2002BAAS...34Q.735B A collaborative effort between the Yunnan Observatory (YO) of the Chinese Academy of Science and the National Solar Observatory (NSO) has led to the development of the seeing monitor now being used by the NSO for the site testing for the 4 meter Advanced Technology Solar Telescope (ATST). The ATST seeing monitor contains a solar differential image motion monitor (S-DIMM) modeled after the one used by the YO for the site testing at Fuxian Lake. The S-DIMM results in a determination of the Fried Parameter r0. NSO added a linear array of 6 scintillometers which measure cloud cover, the scintillation index and the spatial co-variance of the solar shadow bands. This array is called the SHABAR = SHAdow BAnd Ranger because of its ability to give the height structure of the atmospheric seeing (see the attached web page). In February this year we combined the ATST SHABAR with the S-DIMM at the Fuxian Lake site. We describe the results of 5 days of observations in the February 9 to 14 period. In summary they are: (a) the average seeing was 1.6 arcsec in the solar direction, 1.2 arcsec for zenith direction, (b) for half of the time the boundary layer seeing contribution was negligible (<10%), (c) at the times when it was significant the scale height of the refractive index structure constant Cn2 was determined to be 20 meters, (d) at those times the r0 derived from the SHABAR agreed well with that observed with the S-DIMM, and (e) the r0 derived from the SHABAR at times when it is small exceeds that of the S-DIMM. This is almost certainly due to the outer scale of turbulence being around 10 - 30 meters in the free atmosphere at heights 1 km and above. Title: Correlation tracking algorithms for low-contrast extended object Authors: Rao, Changhui; Jiang, Wenhan; Ning, Ling; Beckers, Jacques M. Bibcode: 2002SPIE.4494..245R Altcode: Based on the principle of correlation tracking algorithm, the effectiveness of Cross Correlation coefficient and Absolute Difference algorithms for the low contrast extended objects such as solar granulation and the sunspot is studied. The tilt signals computed by computer post- processing are presented for the successively acquired solar granulation images. Moreover, the contrasts of the long exposure images of the solar granulation and sunspot without and with tilt removal are compared. Title: Multi-conjugate Adaptive Optics: Experiment in Atmospheric Tomography Authors: Beckers, J. Bibcode: 2002ASPC..266..562B Altcode: 2002asev.conf..562B No abstract at ADS Title: Tracking algorithms for low-contrast extended objects Authors: Rao, Chang-hui; Jiang, Wen-han; Ling, Ning; Beckers, Jacques M. Bibcode: 2002ChA&A..26..115R Altcode: We studied the effectiveness of two algorithms, of cross-correlation coefficient and of absolute difference in the case of extended, low-contrast objects, such as solar granulation and sunspots. Wave-front overall tilt signals, acquired via post-processing of sampled solar granulation and sunspot images, are presented. Furthermore, long-exposure images of solar granulation before and after the tilt elimination are compared as regards rms contrast. Title: Daytime seeing measurements for the advanced technology Sslar telescope Authors: Beckers, J. Bibcode: 2002ASPC..266..350B Altcode: 2002asev.conf..350B No abstract at ADS Title: The daytime use of Adaptive Optics for solar and stellar Extremely Large Telescopes Authors: Beckers, Jacques Bibcode: 2002ESOC...58...83B Altcode: 2002bcao.conf...83B Now Single Conjugate Adaptive Optics (SCAO) has been successfully implemented on both nighttime and solar telescopes, there is a rapidly growing interest in developing, what will be the next step in astronomical adaptive optics, Multi-Conjugate Adaptive Optics (MCAO). MCAO aims at breaking the small field-of-view barrier inherent in SCAO. MCAO is considered an essential component for both future solar and nighttime extremely large telescopes (4m and 30m telescope apertures respectively). I will compare the application of MCAO to both types of telescope. Specifically my talk will focus on the following topics: (i) the advantages and disadvantages in of MCAO for solar telescopes, (ii) the status of a program for developing Atmospheric Wavefront Tomography using a large area solar Shack-Hartmann wavefront sensors, (iii) the daytime use of Sodium Laser Guide Stars in solar ELTs for observing the solar corona and prominences, (iv) the opportunities that this daytime use of Na LGS open up for nighttime ELTs. The latter of course requires the engineering of the nighttime ELTs to take into account their exposure to the daytime thermal and radiation environment. The resulting pay-off in extending the observing time beyond the common nighttime interval is scientifically significant especially when observations of objects in the thermal infrared and of time variable objects at all wavelengths are considered, and (v) the development of the solar SHAdow BAnd Ranging (SHABAR) device which is the solar equivalent of SCIDAR both of which aim at measuring in real time the height distribution of Cn2, information important for the implementation of MCAO systems. Title: An analysis of the observed contrast of solar surface granulation Authors: Rao, Chang-hui; Jiang, Wen-han; Ling, Ning; Beckers, Jacques M. Bibcode: 2001ChA&A..25..439R Altcode: The contrast of the solar surface granulation detected in the focal plane of the observing system as well as its relations with the aperture of the observing system, the coherent length of atmospheric turbulence and the sensitivity of the detecting system are analyzed. The results of numerical calculation of the granulation contrast as functions of aperture, coherent length of atmospheric turbulence and sensitivity of the detecting system are presented. Results of a related observation are also given. Title: Tracking algorithm for low contrast extended object Authors: Rao, C. H.; Jiang, W. H.; Ling, N.; Beckers, Jacques M. Bibcode: 2001AcASn..42..329R Altcode: No abstract at ADS Title: Analysis of the observed r.m.s contrast in solar granulation Authors: Rao, C. H.; Jiang, W. H.; Ling, N.; Beckers, J. M. Bibcode: 2001AcASn..42..134R Altcode: On the focal plane of the telescope and the detector, the relationships between the r.m.s. contrast in the solar granulation and the diameter of the telescope, the atmospheric coherent length and the detecting sensitivity of the system are analyzed respectively. The numerical results of the r.m.s. contrast in the solar granulation as functions of the diameter, the atmospheric coherent length and the detecting sensitivity of the system are presented. Furthermore, the related experimental results are given. Title: Solar Seeing Seven Ways From Sunday Authors: Hill, F.; Balasubramaniam, K. S.; Beckers, J. M.; Briggs, J. W.; Hegwer, S.; Radick, R. R.; Rimmele, T. R.; Richards, K.; Denker, C. Bibcode: 2001AGUSM..SP21B03H Altcode: The Advanced Technology Solar Telescope (ATST) site survey will be carried out with a Solar Differential Image Motion Monitor (S-DIMM) and a six-scintillometer SHAdow BAnd Ranging (SHABAR) array. This device will provide estimates of the Fried parameter, R0, derived from the differential motion measurements of two images of the same cut across the solar limb formed by two 45 mm diameter telescope apertures 225 mm apart, and an estimate of the height dependence of the index of refraction structure parameter, Cn2, from the co-variance of the signals from an array of 6 scintillometers with 15 baseline separations. It will also provide a cloud cover measurement and RMS scintillation signal. In preparation for the survey, we compare estimates of daytime solar seeing obtained simultaneously from seven different instruments. The observations were made at NSO/Sacramento Peak during the period January 26 - February 5, 2001 under a variety of seeing and transparency conditions ranging from poor to excellent. The seven instruments were: 1. a S-DIMM/SHABAR mounted at the top of the Dunn Solar Tower (DST) 2. an identical S-DIMM/SHABAR mounted at ground level 3. the NSO/SP Adaptive Optics wavefront sensor providing subaperature image motion measurements 4. a Dalsa camera providing bursts of high-speed images for spectral ratio seeing estimates 5. a Xedar camera obtaining granulation images for contrast and differential stretching measurements 6. a Seykora scintillometer mounted in the DST 7. a video camera recording a movie of the visual quality of the image The analysis of this data set will provide the first direct comparison of this many simultaneous solar seeing measurements, test the ATST site survey system, and verify the SHABAR measurement of the seeing height profile. Title: Using Laser Beacons for Daytime Adaptive Optics Authors: Beckers, Jacques M.; Cacciani, Alessandro Bibcode: 2001ExA....11..133B Altcode: This article examines the use of Laser Beacons for daytime astronomical observations. There are two potential applications: the diffraction limited observation of (1) the structure in the solar corona at all wavelengths, and (2) non-solar astronomical objects in the thermal infrared part of the spectrum. We examine the brightness of the Laser Beacon required as well as the limitations imposed by the daytime sky brightness and sky/telescope thermal emission on the observable magnitude limits. For both applications the use of Laser Beacon adaptive optics in daytime results in important research opportunities. Title: A Seeing Monitor for Solar and Other Extended Object Observations Authors: Beckers, Jacques M. Bibcode: 2001ExA....12....1B Altcode: In this article I describe a site survey facility, which measures the signals of the solar equivalent of a Differential Image Motion Monitor (S-DIMM) and of a six element linear array of solar scintillometers. Combining the S-DIMM r_o and scintillometer σ_I observations allows the determination of the fractions of the seeing in the free atmosphere and in the ground/lake layer. From the scintillometer array observations C_n^2(h) is determined for heights corresponding to the first ~500 m along the line-of-sight. With minor changes this seeing monitor can also be used for other extended objects like the Moon and planets. Title: Comparative Solar Seeing and Scintillation Studies at the Fuxian Lake Solar Station Authors: Liu, Zhong; Beckers, Jacques M. Bibcode: 2001SoPh..198..197L Altcode: 2001SoPh..198..197Z Starting November 1999 we are carrying out simultaneous seeing observations with the Solar Differential Image Motion Monitor (S-DIMM) at the Fuxian Lake station of the Yunnan Observatory and a solar scintillometer of the type used in the recent site survey by one of us (Beckers et al., 1997). The purpose was to compare the two methods of assessing the daytime atmospheric seeing for a lake site. We report here the first results of this comparison. We find that the relation between the seeing as measured by the S-DIMM (the Fried parameter r_0) and the scintillation in the solar irradiance (σ_I) differs greatly from the relation found by Seykora (1993) for NSO/Sac Peak. We conclude that the σ_I measurements give a good indication for the amount of near-Earth seeing but that they are a poor proxy for the total atmospheric seeing. We interpret the simultaneous (r_0, σ_I) observations in terms of an atmospheric seeing model and find good quantitative agreement with a model in which a fraction (α) of the seeing originated near the Earth (ground or water) and the rest (1-α) originates at higher layers. For lake sites α is small all day and the seeing is determined primarily by the refractive index variations at higher atmospheric layers. For land sites α is small in the early morning but rapidly increases as the day progresses, near-Earth seeing dominating there most of the time. Title: Chromosphere: Spicules Authors: Beckers, J. Bibcode: 2000eaa..bookE2019B Altcode: As early as 1877 Father Secchi described the jet like, elongated structures in the solar chromospheres which were named spicules by Walter Orr Roberts in 1945. They are observed in the optical chromospheric emission lines of hydrogen (especially the 656 nm Hα line), ionized calcium (especially the 393 nm and 397 nm H and K lines) and helium lines (especially the 588 nm and 1083 nm neutral helium ... Title: Multiconjugate adaptive optics: experiments in atmospheric tomography Authors: Beckers, Jacques M. Bibcode: 2000SPIE.4007.1056B Altcode: In 1987 I described a technique call Multi-Conjugate Adaptive Optics (MCAO) as a way of increasing the size of the area on the sky over which Adaptive Optics corrects for atmospheric wavefront distortions. An essential component of MCAO is the estimation of this wavefront distortion at different heights in the atmosphere. The technique proposed to do so was called 'Atmospheric Tomography,' or AT, since it uses tomographic techniques using the wavefront distortions at the telescope entrance pupil of objects observed in a number of different directions in the sky to infer the 3-D wavefront behavior. This paper describes a program to do so using the small scale structure on the solar surface (sunspots, pores and granulation). The Sun has the advantage of being an extended object on which the wavefront can be observed in a large number of directions using correlation Hartmann-Shack wavefront sensing. The AT experiment described in this paper uses the 76 cm Dunn Solar Telescope at NSO, 69 sub-apertures, a 2 X 2 arcmin2 field-of-view and a wavelength of 411 nm. The MCAO-AT system is being developed for the future 4 meter aperture Advanced Solar Telescope. Title: The proposed 50 m Swedish Extremely Large Telescope Authors: Andersen, T.; Ardeberg, A.; Beckers, J. M.; Flicker, R.; Jessen, N. C.; Gontcharov, A.; Mannery, E.; Owner-Petersen, M.; Riewaldt, H. Bibcode: 2000ESOC...57...72A Altcode: 2000elt..conf...72A No abstract at ADS Title: Extremely large multiple mirror telescopes Authors: Beckers, J. M. Bibcode: 2000ESOC...57...83B Altcode: 2000elt..conf...83B No abstract at ADS Title: The Determination of Seeing, Isoplanatic Patch Size and Coherence Time by Solar Shadow Band Ranging Authors: Beckers, J. M. Bibcode: 1999ASPC..184..309B Altcode: Using an array of solar scintillometers (Seykora 1993; Beckers and Mason 1998), I characterize the shadow band patterns as seen from the un-eclipsed sun. The spatial and temporal structure of these patterns provide a measure of the optical turbulence in the earth' atmosphere from which the r_0 (Fried Parameter), Θ_0 (isoplanatic patch diameter) and τ_0 (coherence time) can be estimated. Title: The Advanced Solar Telescope: II. Technical Aspects Authors: Beckers, J. Bibcode: 1999ASPC..183..177B Altcode: 1999hrsp.conf..177B No abstract at ADS Title: Adaptive optics in solar astronomy Authors: Beckers, J. Bibcode: 1999aoa..book..235B Altcode: No abstract at ADS Title: Site tests for CLEAR by solar scintillometry Authors: Beckers, Jacques M.; Rutten, Robert J. Bibcode: 1998NewAR..42..489B Altcode: We briefly describe the ongoing site survey for the NSO CLEAR project which aims to put a large-aperture solar telescope at a superior location. The initial results indicate that lake sites are far better than mountain sites, at least in the US. Title: Site survey for a large solar telescope Authors: Beckers, Jacques M.; Mason, James Bibcode: 1998SPIE.3352..858B Altcode: In 1996 we started a seeing survey of a number of existing and potential solar observing sites using solar scintillometry. This paper reports the result of the first year of that survey. It confirms earlier reports about the superior observing conditions of lake sites. I also describe the first results of atmospheric structure constant (C(subscript n)(superscript 2)) probing using a solar scintillometer array. Title: Design of a large low-scattered light telescope for solar observations Authors: Beckers, Jacques M. Bibcode: 1998SPIE.3352..588B Altcode: This paper is an interim report of a feasibility study which is in progress for a large 400 cm aperture solar telescope (`CLEAR'). Unlike other large solar telescopes constructed in the last three decades, CLEAR does not use the concept of evacuated telescopes to eliminate internal seeing. The requirement for full access to the far infrared spectral region (> 2.5 micrometers ), and for low scattered light, eliminates the use of the entrance window which evacuated telescopes require. Instead, CLEAR avoids internal seeing by carefully controlling the internal thermal environment of the telescope by a number of means: (1) thermal control of the primary mirror; (2) flow of ambient air over the primary mirror surface and in the telescope; (3) locating the primary focus outside the telescope beam and enclosure where the heating resulting in concentrated sunlight can be managed better (this requires the use of an off-axis primary mirror); and (4) the use of a prime focus heat stop/absorber. In addition to controlling the internal seeing, such a configuration produces a telescope with very low scattered light characteristics, allowing quality observation of regions outside the solar limb and of sunspots. By eliminating the need for a large entrance window, the CLEAR concept therefore opens up the possibility of larger aperture solar telescopes. Notwithstanding its off-axis configuration, the Gregorian telescope produces excellent images (< 0.1 arcsec) over a 5 arcminute diameter field-of-view at the f/130 Gregorian focus. In addition to the four instrumentation stations near the Gregorian focus (i.e., direct Gregorian, Nasmyth, two `folded Gregorian'), the design provides for extensive instrumentation locations in a coude area. By means of a 3- level rotating coude platform, large instruments can be located at respectively f/30, f/45 and f/60 foci. Title: Effect of telecentric use of narrow-band filters on diffraction-limited imaging Authors: Beckers, Jacques M. Bibcode: 1998SPIE.3355..955B Altcode: Sometimes Fabry-Perot, and other narrow-band filters, are used for astronomical imaging in the so-called telecentric mode. In it the pupil is collimated through the filter, resulting in different incidence angles on the filter for rays coming from different parts of the objective. This results in variations of the central transmission wavelength, which broaden the effective filter bandpath. In addition each wavelength within this filter bandpath sees a different illumiatnon of the pupil when viewed from behind the fitler. This causes the diffraction limited point-spread-function to vary with wavelength. With the advent of diffraction limited imaging using adaptive optics, this can cause complications. In this paper, which elaborates further on research published elsewhere, I examine the magnitude of this effect. Title: On the effect of narrow-band filters on the diffraction limited resolution of astronomical telescopes Authors: Beckers, J. M. Bibcode: 1998A&AS..129..191B Altcode: Sometimes Fabry-Perot and other narrow-band filters are used for astronomical imaging in the so-called telecentric mode. In it the pupil is collimated through the filter, resulting in different incidence angles on the filter for rays coming from different parts of the objective. This results in variations of the central transmission wavelength, which broaden the effective filter band path. In addition each wavelength within this filter band path sees a different illumination of the pupil when viewed from behind the filter. This causes the diffraction limited point-spread-function to vary with wavelength. With the advent of diffraction limited imaging using adaptive optics, this can cause complications. In this note I examine the magnitude of this effect. Title: Results of Site Testing for a Large Visible/Infrared Telescope Authors: Beckers, Jacques M. Bibcode: 1998ASPC..155..255B Altcode: 1998sasp.conf..255B No abstract at ADS Title: Solar Scintillometry: Calibration of Signals and its Use for Seeing Measurements Authors: Beckers, Jacques M.; Leon, Ed; Mason, Jim; Wilkins, Larry Bibcode: 1997SoPh..176...23B Altcode: Since 1993 it is known that there is a good correlation between the scintillation in the solar irradiance and solar image quality (Seykora, 1993). This effect is now being used in a number of experiments to evaluate solar image quality and to measure site seeing. In this paper we explore further the calibration of this scintillation (σI) in terms of the Fried parameter (r0) taking into account variations in the refractive index structure constant CN2 with height (h), zenith distance (ζ) dependence and the effects of wind velocities. A variant in the scintillometer setup is proposed which decreases sharply the dependance on CN2 , ζ, and the wind velocities. It uses an array of scintillometers. The same array can be used to measure theCN2 profile with height. Some preliminary results of the calibration of current NSO site survey measurements are presented. Title: High Resolution Solar Observations from the Ground Authors: Rimmele, T.; Beckers, J.; Dunn, R.; Radick, R.; Roeser, M. Bibcode: 1997hrsa.rept.....R Altcode: We describe an ongoing effort to improve the capabilities for achieving spectroscopic and imaging observations at the highest spatial resolution at the Sacramento Peak Vacuum Tower Telescope of the National Solar Observatory. We report on improvements of the optical performance of the VTT/SP and describe results from the first solar active optics system, which was recently successfully tested at the VTT/SP. Our final goal is the implementation of solar adaptive optics at the VTT/SP. We describe progress and future plans of the adaptive optics program. Title: First Results of the Site Survey for a Large Solar Optical/Infrared Telescope Authors: Beckers, Jacques M.; Mason, Jim Bibcode: 1997SPD....28.0223B Altcode: 1997BAAS...29..897B We will present the first results of a seeing survey of four existing solar observatories : the HAO Mauna Loa Observatory, the Big Bear Solar Observatory, the Sacramento Peak Observatory and the solar observatory site on La Palma. The measurements started in September 1996. The survey uses observations of the scintillation of the solar irradiance (Seykora meters, see Solar Physics Volume 145, p.389) as a proxy for the atmospheric seeing. In addition to presenting the results, issues relating to the calibration of the measurements in terms of the Fried Parameter will be discussed. A modification of the Seykora meter will be described which is capable of measuring the atmospheric refractive index structure constant as a function of height. Title: Atmospheric dispersion correction for the FORS Focal Reducers at the ESO VLT Authors: Avila, Gerardo; Rupprecht, Gero; Beckers, J. M. Bibcode: 1997SPIE.2871.1135A Altcode: The need for atmospheric dispersion correction on large telescopes is well known. Therefore it was decided to implement atmospheric dispersion correctors for FORS, the focal reducer/spectrographs of the ESO very large telescope. The boundary conditions at the VLT Cassegrain foci excluded however all previously known ADC concepts and therefore we were forced to design a new one, the longitudinal atmospheric dispersion corrector (LADC) consisting of two thin prisms with variable distance. This design has several advantages compared to the 'classical concepts:' among others it avoids tilting the pupil axis and uses only one material (silica) which has a very high transmission over the operating wavelength range of FORS (330 - 1000 nm). Title: Progress Report on a Feasibility Study of a Large Optical/Infrared Solar Telescope (CLEAR) Authors: Beckers, Jacques M.; NSO Staff Bibcode: 1997ASPC..118..340B Altcode: 1997fasp.conf..340B With the end of the US participation in LEST, the question of the development of modern, large, ground-based facilities to satisfy the research needs of solar physics in the USA is open. Large telescopes are needed to answer many important science issues. Among these are (i) high angular resolution needed to resolve the scales at which most of the action is in solar magneto-hydrodynamics (ii) access to the infrared part of the solar spectrum wanted to extend the range over physical conditions over which the solar atmosphere is studied (iii) accurate polarization observations needed to measure solar magnetic fields, (iv) high sensitivities, essential to study variations in these and other solar conditions, and (v) coronagraphic capability to observe magnetic fields and small scale structures in the solar corona. CLEAR (Coronagraph and Low Emissivity Astronomical Reflector) is a concept that attempts to combine these qualities in one telescope, 2 to 4 meter in aperture, without compromising the solar science goals. This is a status report on the on-going feasibility study of CLEAR that addresses both technical and budgetary issues. A site survey is being conducted among existing solar sites to identify the optimum location. Title: Techniques for high angular resolution astronomical imaging. Authors: Beckers, J. M. Bibcode: 1997ilt..book....1B Altcode: After introducing the basics of atmospheric wavefront distortions, the author describes the principles of adaptive optics for large optical telescopes and gives an overview of the present status of its application. Then, he discusses the principles and the development of interferometric arrays of optical telescopes. As specific example, the author describes in some detail ESO's Very Large Telescope Interferometer project. Title: Comments on the Next Generation of Ground-based Solar Telescopes Authors: Beckers, Jacques M. Bibcode: 1996SoPh..169..431B Altcode: The development of telescope capabilities tends to go in spurts. These are triggered by the availability of new techniques in optics, mechanics and/or instrumentation. So has nighttime telescope technology developed since the construction in the nineteen-forties of the 5-m Hale telescope, first by the introduction in the sixties of high efficiency electronic detectors, followed recently by the production of large 8- to 10-m mirrors and now by the implementation of adaptive optics. In solar astronomy, major steps were the introduction of the coronagraph by Lyot in the nineteen-thirties and the vacuum telescope concept by Dunn in the sixties. In the last thirty years, telescope developments in solar astronomy have relied primarily on improved instrumental capabilities. As in nighttime astronomy, these instruments and their detectors are reaching their limits set by the quantum nature of light and the telescope diffraction. Larger telescopes are needed to increase sensitivity and angular resolution of the observations. In this paper, I will review recent efforts to increase substantially the telescope capabilities themselves. I will emphasize the concept of a large all-wavelength, coronagraphic telescope (CLEAR) which is presently being developed. Title: Limitations Placed on the Time Coverage, Isoplanatic Patch Size and Exposure Time for Solar Observations Using Image Selection Procedures in the Presence of Telescope Aberrations Authors: Beckers, J. M.; Rimmele, T. R. Bibcode: 1996AAS...189.4209B Altcode: 1996BAAS...28.1325B Image selection, adaptive optics and post-facto image restoration methods are all techniques being used for diffraction limited imaging with ground-based solar and stellar telescopes. Often these techniques are used in a hybrid form like e.g. the application of adaptive optics and/or post-facto image restoration in combination with already good images obtained by image selection in periods of good seeing. Fried (JOSA 56, 1372, 1966), Hecquet and Coupinot (J. Optics/Paris 16, 21, 1985) and Beckers ("Solar and Stellar Granulation", Kluwer, Rutten & Severino Eds, 55, 1988) already discussed the usefulness of image selection, or the "Lucky Observer" mode, for high resolution imaging. All assumed perfect telescope optics. In case of moderate telescope aberrations image selection can still lead to diffraction limited imaging but only when the atmospheric wavefront aberration happens to compensate that of the telescope. In this "Very Lucky Observer" mode the probability of obtaining a good image is reduced over the un-aberrated case, as are the size of the isoplanatic patch and the exposure time. We describe an analysis of these effects for varying telescope aberrations. These result in a strong case for the removal of telescope aberrations either by initial implementation or by the use of slow active optics. Title: Progress Report on a Feasibility Study for a Ground-Based Large Solar Telescope Authors: Beckers, J. M. Bibcode: 1996AAS...188.6701B Altcode: 1996BAAS...28R.933B Whereas optical nighttime is undergoing a revolution with the deployment of very large ground-based telescopes in the 6.5 to 10 meter class, solar telescope technology has stagnated at the meter class aperture level. Space and balloon borne solar telescopes are now being built and planned in this aperture range. Are they likely to take over most of the roles of these ground-based facilities? There is undoubtedly a need for solar telescopes with larger apertures to explore important solar physics issues which require the highest possible angular resolution, high sensitivity, full visible and infrared wavelength coverage and low scattered light. Using advances in astronomical telescope technologies at optical and X-ray wavelengths, we (NSO staff together with engineering and scientific working group) are undertaking a feasibility study of a 4-meter class solar telescope with these qualities. Such a powerful, special purpose telescope will find many applications in other areas of astronomy in which low scattered light coronagraphic properties are at a premium. Since the telescope technologies needed to achieve these are similar to those needed for low emissivity telescopes, the telescope concept has been labelled CLEAR = Coronagraphic and Low Emissivity Astronomical Reflector. CLEAR will have a 5 arcmin diameter field-of-view (the size of a solar active region), wavelength coverage of at least 0.38 to 15 microns (including all of the visible and infrared solar spectral lines and regions of interest), low and constant polarization (enabling accurate and precise magnetic field observations), and scattered light low enough to enable studies of the coronal magnetic fields and coronal fine structure. It will include coud, Nasmyth and Gregorian focal stations for a variety of instruments. Its unobstructed aperture will allow optimum imaging, which will be enhanced by the incorporation of adaptive optics. In my lecture I will review the science drivers for CLEAR, and give a progress report on a feasibility study now underway. The scientific and technical goals set for CLEAR require a number new innovative technological solutions. These will be described and discussed. The siting of CLEAR is an important aspect of the study. I will review our present knowledge of possible solar observatory sites for CLEAR. Title: The Origin of Solar and Stellar Image Aureole Authors: Beckers, J. M.; Ftaclas, C. Bibcode: 1996AAS...188.5402B Altcode: 1996BAAS...28..904B The extended wings of the telescope point-spread-function affect the performance of solar and stellar reflecting coronagraphs used to study the faint envelopes of bright objects like the sun, planets, and stars. We are expanding an initial examination of the origin of these wings (Beckers, ``Scientific and Engineering Frontiers for 8 - 10 m Telescopes", Eds. M. Iye and T. Nishimura, 1995, 303 - 312) in order to obtain a quantitative evaluation of the observed point-spread-function and to derive the technical specifications for solar and stellar coronagraphs. We include the following factors contributing to the point-spread-function wings : (i) the atmospheric seeing, including the effects of the finite inner scale of turbulence, (ii) the scattering by atmospheric aerosol particles, (iii) the atmospheric Rayleigh scattering, (iv) the scattering by small scale surface irregularities in the telescope optics (micro-ripple), (v) the scattering by dust in the telescope, (vi) the diffraction on the telescope aperture, and (vii) diffraction on objects partially obscuring the aperture (e.g. spiders). It is assumed that care is taken not to increase the point-spread-function wings by ghosting and scattering in the astronomical instrument and in its detector(s). Using the resulting algorithms, we interpret observed stellar and solar image aureolae. The wavelength dependence of the point-spread-function wings is evaluated and applied to the performance estimates and technical specification definition of the CLEAR facility (CLEAR = ``Coronagraphic and Low Emissivity Astronomical Reflector"), a 4 meter class solar/stellar coronagraph presently under study. Title: CLEAR : A Concept for a "Coronagraph and Low Emissivity Astronomical Reflector" for Solar and Nighttime Observations Authors: Beckers, J. M.; Kuhn, J.; Neidig, D.; Rabin, R.; Rimmele, T.; Smartt, R. N. Bibcode: 1995SPD....26..722B Altcode: 1995BAAS...27..971B No abstract at ADS Title: Using Eclipse Observations to Test Scintillation Models Authors: Georgobiani, D.; Kuhn, J. R.; Beckers, J. M. Bibcode: 1995SoPh..156....1G Altcode: Near second and third contact during a solar eclipse the spatial spectrum of the solar illumination changes as the relative power at high spatial frequencies increases strongly. Since groundlevel atmospheric scintillation depends on a weighted integral of the image power spectrum, we can expect to see a measureable time dependence to solar scintillation during an eclipse. This effect was observed during an annular solar eclipse and quantitatively compared with a scintillation model. Title: CLEAR: A Concept for a Coronagraph and Low Emissivity Astronomical Reflector Authors: Beckers, J. M. Bibcode: 1995itsa.conf..145B Altcode: No abstract at ADS Title: Prospects for high spatial resolution astronomy. Authors: Beckers, J. M. Bibcode: 1995seft.conf..303B Altcode: The author summarizes the present status in the development of large, 8 meter class telescopes, of adaptive optics and of imaging interferometers. Then he elaborates on the limitations of the astronomical use of adaptive optics, on stellar coronagraphy and on the limitations of interferometric imaging of faint astronomical sources. Title: Estimating the effects of nitrate mining activities on the astronomical site quality of the Cerro Paranal Observatory Authors: Beckers, Jacques M. Bibcode: 1994SPIE.2199..817B Altcode: The European Southern Observatory is planning to construct its Very Large Telescope on Cerro Paranal, a site with superb astronomical observing conditions located in the Atacama Desert of Northern Chile some 100 km south of the town of Antofagasta and 16 km from the Pacific Ocean. This region of Chile is know for its rich mineral resources. One of these, Nitrates, are mined by surface, strip mining causing extensive area air pollution. To estimate the effects of a Nitrate mine which may be started 25 km SSE from Cerro Paranal a model for this pollution, based on estimates of aerosols resulting from similar mines north of Antofagasta, was developed. These estimates are based on measurements of the solar aureole brightness. The expected deteriorating effects on atmospheric extinction, sky thermal emissivity and night-time sky brightness appear acceptable. Title: Imaging with array detectors using chopping and other forms of differential detection Authors: Beckers, Jacques M. Bibcode: 1994SPIE.2198.1432B Altcode: To detect faint signals in the presence of a high background, differential techniques are often used. In IR astronomy this has led to the so-called chopping and nodding techniques. The introduction of array detectors especially for imaging in the thermal IR region of the astronomical spectrum requires an adaptations of these techniques which also takes into account the pixel nonuniformity of the array detector. I describe one possible imaging algorithm and the associated requirements for the chopping mechanisms of an 8-m telescope. Title: Effects of heat sources in the telescope beam on astronomical image quality Authors: Beckers, Jacques M.; Melnick, Jorge Bibcode: 1994SPIE.2199..478B Altcode: Heating of the air in astronomical telescopes is known to have a deteriorating effect on the image quality. Main heat sources are the primary mirror and localized electrical components in or near the light beam. To evaluate the effects of these localized heat sources we measured the image quality deterioration at the focus of the ESO-La Silla 2.2 meter telescopes with variable amounts of heating of a dummy electronics box and of a bar simulating one of the secondary mirror spiders. The effects on the FWHM of the image profile turned out to be remarkably small. Most of the effect of the heating showed up in the removal of energy of the core into the far wings of the image profile. For a heat input of 560 Watts (resulting in an excess temperature of 60 K) the amount of energy removed amounted to 13%. This behavior can be explained by a model in which the heating destroys the wave-front over only a part of the aperture while leaving it unaffected over most of the aperture. With such a model we predict the amount of energy removed by a 500 Watt heat source in an 8 meter telescope to be only 1%. Title: First Images with the MPE Imaging Beam Combiner Simulator COSI Authors: Böker, T.; Cruzalèbes, P.; Hofmann, R.; Katterloher, R.; Eckart, A.; Genzel, R.; Drapatz, S.; Beckers, J.; von der Lühe, O.; Merkle, F. Bibcode: 1994ESOC...48..161B Altcode: 1994aao..conf..161B No abstract at ADS Title: Interpretation of out-of-focus star images in terms of wave-front curvature. Authors: Beckers, J. M. Bibcode: 1994JOSAA..11..425B Altcode: 1994JOSA...11..425B; 1994OSAJ...11..425B The wave-front-curvature-sensing method used by F. Roddier for the University of Hawaii's curvature-adaptive-optics system is derived from the interpretation in 1979 of the out-of-focus images obtained by use of the Multiple Mirror Telescope. The author summarizes those original Multiple Mirror Telescope observations and the simple interpretation given in terms of wave-front curvature by use of geometrical optics at that time. Title: The VLT Interferometer [invited] Authors: Bedding, T. R.; Beckers, J. M.; Faucherre, M.; Hubin, N.; Koehler, B.; von der Lühe, O.; Merkle, F.; Zhu, N. Bibcode: 1994IAUS..158..143B Altcode: No abstract at ADS Title: Solar surface magnetism: quests for observations Authors: Beckers, J. M. Bibcode: 1994ASIC..433..501B Altcode: No abstract at ADS Title: Progress in High-Resolution Astronomical Imaging Including Active and Adaptive Optics (Invited Lecture) Authors: Beckers, J. M. Bibcode: 1993SPIE.1983..186B Altcode: No abstract at ADS Title: On the Relation Between Scintillation and Seeing Observations of Extended Objects Authors: Beckers, Jacques M. Bibcode: 1993SoPh..145..399B Altcode: In a recent article Seykora (1993) compares measurements of scintillation in the solar irradiance with solar seeing measurements. In this article I interpret the close linear relation which he found in terms of the common theory of atmospheric optics in the presence of turbulence. Title: Adaptive Optics for Astronomy: Principles, Performance, and Applications Authors: Beckers, Jacques M. Bibcode: 1993ARA&A..31...13B Altcode: An overview of the principles, performance, and application (solar and nighttime) of adaptive optics for astronomical telescopes is presented. Attention is given to a historical background of the use of adaptive optics for compensating atmospheric seeing, wavefront distortion by the atmosphere, and assessment and correction of the wavefront distortion. Predicted and achieved performance, the first astronomical results, and limitations to the astronomical applications of adaptive optics systems and ways of removing them are also discussed. Title: Summary of the splinter session on optical and UV science Authors: Beckers, Jacques M. Bibcode: 1992ESASP.354..157B Altcode: 1992tsbi.rept..157B The goal of the splinter group was to discuss the most prominent astrophysical objectives for a space based interferometer in the optical (UV, visible, near IR) domain. The discussion was organized around three main themes: solar system, stellar and galactic astrophysics, extragalactic astrophysics and cosmology. The scientific objectives and specifications for a space based solar interferometer, for an astrometric interferometer, and for a stellar interferometer, are given. Tentative conclusions for the splinter session are given. Title: Overcoming perspective elongation effects in laser-guide-star-aided adaptive optics Authors: Beckers, Jacques M. Bibcode: 1992ApOpt..31.6592B Altcode: A method of compensating for the perspective elongation effect, and thus of separating the laser transmitter(s) from the four Very Large Telescope (VLT) 8-m telescopes, is presented. The method involves tracking the instantaneous position of the laser guide star. For the initial N of about 200 VLT adaptive optics system, a single laser transmitting station is to place all four 8-m telescopes, and a substantial number of auxiliary telescope stations, within the 71-m range of a single laser transmission system. Title: A Fourth VLT Instrument Science Team Authors: Beckers, J. M. Bibcode: 1992Msngr..69....5B Altcode: No abstract at ADS Title: A Report on the Second ESO Conference on High Resolution Imaging by Interferometry Authors: Beckers, J. M.; Merkle, F. Bibcode: 1992ESOC...42..387B Altcode: 1992ptit.conf..387B No abstract at ADS Title: High Resolution Spectroscopy with the VLT - Summary of Experimental Aspects Authors: Beckers, J. M. Bibcode: 1992ESOC...40....1B Altcode: 1992hrsw.conf....1B No abstract at ADS Title: Introducing the First VLT Instrument Science Teams Authors: Beckers, J. M. Bibcode: 1992Msngr..68....8B Altcode: No abstract at ADS Title: ESO-VLT Program Status Report Authors: Beckers, J. M.; Tarenghi, M. Bibcode: 1992ESOC...42...13B Altcode: 1992ptit.conf...13B No abstract at ADS Title: Report on the Lunar Interferometry Study Team (LIST) activities. Authors: Dainty, J. C.; Faucherre, M.; Greenaway, A. H.; Harris, A. I.; Labeyrie, A.; Noordam, J. E.; Weigelt, G. P.; Beckers, J.; Lequeux, J.; Fridlund, C. M.; Hawkyard, A.; Roussel, P. H.; Volonté, S. Bibcode: 1992ESASP.344..259D Altcode: 1992spai.rept..259D During the first half of 1991, the Lunar Interferometry Study Team (LIST) produced an Interim Report outlining a possible strategy for the development of a lunar interferometry programme. The formulation of an overall strategy for ESA towards lunar interferometry requires further consideration before firm recommendations can be made. However, it is clear at this early stage that there are three principal elements in that strategy. (1) ESA should commence conceptual studies for interferometers in readiness for their location on the Moon in (a) the UV/visible/IR and (b) the sub-millimetre region. (2) Considering the scientific benefit, technical readiness and realistic timescale of a lunar interferometer, ESA should plan for at least one "precursor" interferometer missions in space. (3) ESA should identify key technologies of crucial importance to space-based interferometry in general and lunar interferometry in particular, and support their development by a variety of routes. Title: Interferometry with the Very Large Telescope. Authors: Vonderluehe, O.; Beckers, J. M.; Faucherre, M.; Koehler, B.; Merkle, F.; Zhu, N. Bibcode: 1992ESASP.344..247V Altcode: 1992spai.rept..247V One of the observing modes available with the ESO Very Large Telescope (VLT) will be coherent combination of the light received by up to four 8 m diameter unit telescopes and several 1.8 m diameter auxiliary telescopes. While the location of the main telescopes is fixed, auxiliary telescopes can be moved among some 30 observing stations designed to efficiently complement the unit telescopes as well as to function as an independent interferometric array. A distinct feature of the VLT interferometer will be its sensitivity due to the large diameter of the unit telescopes, and due to the adaptive optics which will remove instrumental and atmospheric wavefront disturbances in the near-infrared spectral regime. This paper presents an overview of the VLT interferometer, highlights some of its characteristics, and gives a status update. Title: The Design of Delay Lines for the VLT Interferometer Authors: Jorck, H.; Maurer, R.; Kase, J.; Faucherre, M.; Beckers, J. M.; Kuhn, G.; Hupe, H. Bibcode: 1992ESOC...39.1157J Altcode: 1992hrii.conf.1157J No abstract at ADS Title: The Use of Differential Adaptive Optics for Astronomical Interferometry Authors: Beckers, J. M. Bibcode: 1992ESOC...39.1079B Altcode: 1992hrii.conf.1079B No abstract at ADS Title: High resolution imaging by interferometry II. Ground-based interferometry at visible and infrared wavelengths. Proceedings. Authors: Beckers, J. M.; Merkle, F. Bibcode: 1992ESOC...39.....B Altcode: 1992hrii.conf.....B Contents: Part I. Title: The Configuration of the VLT Interferometer on the Paranal Site Authors: von der Luhe, O.; Beckers, J. M.; Braun, R. Bibcode: 1992ESOC...39..959V Altcode: 1992hrii.conf..959V No abstract at ADS Title: A Progress Report on the Implementation of the VLT Interferometer Authors: Beckers, J. M.; Faucherre, M.; Koehler, B.; von der Luhe, O. Bibcode: 1992ESOC...39..775B Altcode: 1992hrii.conf..775B No abstract at ADS Title: Performance Comparison of VLT Using Partial Adaptive Optics with a Lunar Interferometer Authors: Greenaway, A. H.; Beckers, J. M. Bibcode: 1992ESOC...39..985G Altcode: 1992hrii.conf..985G No abstract at ADS Title: The Design of the Auxiliary Telescopes for the VLT Interferometer Authors: Plathner, D.; Beckers, J. M. Bibcode: 1992ESOC...39..939P Altcode: 1992hrii.conf..939P No abstract at ADS Title: Optimization of partial adaptive optics Authors: Beckers, Jacques M. Bibcode: 1992ApOpt..31..424B Altcode: Partial adaptive optics employed in astronomical settings are examined to develop suitable wavefront control algorithms that maximize the fractional area of the pupil. Attention is given to the previous models and profiles, and the maximum-fraction and other algorithms are used to fit wavefront distortion profiles and develop corresponding point-spread functions. The algorithms are shown to maximize the fractional area of the pupil over which the wavefront distortion is smaller than an eighth of a wave. Title: Requirements for adaptive optics in large astronomical telescopes. Authors: Beckers, J. M. Bibcode: 1992aolt.meet...56B Altcode: Some of the astronomical uses of adaptive optics for large telescope are reviewed, and the resulting requirements discussed. Title: On the Optimization of Partial Adaptive Optics Authors: Beckers, J. M. Bibcode: 1992ESOC...42..497B Altcode: 1992ptit.conf..497B No abstract at ADS Title: Removing Perspective Elongation Effects in Laser Guide Stars and Their Use in the ESO Very Large Telescope Authors: Beckers, J. M. Bibcode: 1992ESOC...42..505B Altcode: 1992ptit.conf..505B No abstract at ADS Title: A report on the second ESO Conference on High Resolution Imaging by Interferometry. Authors: Beckers, J. M.; Merkle, F. Bibcode: 1991Msngr..66....5B Altcode: No abstract at ADS Title: Differential adaptive optics for astronomical interferometry Authors: Beckers, Jacques M. Bibcode: 1991ApOpt..30.5010B Altcode: In astronomical interferometer the interference signal is often detected on the pupil plane. To achieve good signal strength it is necessary to keep the wavefront distortions caused by the optics and the atmosphere small. This paper indicates that it often suffices to make the wavefront distortions in the pupils equal rather than zero to achieve good signal strength. A way to achieve this is by using a differential adaptive optics approach is proposed. Title: A progress report on the VLT instrumentation plan. Authors: D'Odorico, S.; Beckers, J.; Moorwood, A. Bibcode: 1991Msngr..65...10D Altcode: No abstract at ADS Title: Interferometric imaging with the Very Large Telescope. Authors: Beckers, J. M. Bibcode: 1991JOpt...22...73B Altcode: 1991JOp....22...73B The Very Large Telescope Interferometer (VLTI) is one of the operating modes of the VLT. In addition to consisting of an array of four stationary 8 m diameter telescopes, the VLTI includes a number of movable Auxiliary Telescopes which both complement the (u, v) plane coverage of the large telescopes and provide a powerful interferometric facility by itself (available 100% of the time). The author describes the current plans for the implementation of the VLTI. These plans will be finalized in 1991 after the choice of the VLT site. Title: Instrumentation for the ESO Very Large Telescope. Authors: D'Odorico, S.; Moorwood, F. M.; Beckers, J. Bibcode: 1991JOpt...22...85D Altcode: 1991JOp....22...85D The instrumentation plan for the ESO VLT has been approved in March 1990: it includes 10 instruments, two of which are to be replicated, distributed among the Nasmyth, Cassegrain and coude focii of the four unit telescopes of the VLT and the incoherently combined focus. The instruments will be used for a variety of observations in the wavelength range from the UV atmospheric cutoff to around 20 μm. Conceptual designs are presented for a Medium Resolution IR Spectrometer/Imager, a Focal Reducer/Low Dispersion Spectrograph, an Echelle Spectrograph, a Multi-fibre spectrograph and an 8 - 14 μm Imager/Spectrometer. Design requirements and expected capabilities are given for an High Resolution Infrared Camera and for a Speckle Camera, planned to operate in combination with the telescope adaptive optics systems. The current design options for the high spectral resolution spectrometers for the UV-visual and the infrared region are also presented. Title: Blind operation of optical astronomical interferometers options and predicted performance Authors: Beckers, Jacques M. Bibcode: 1991ExA.....2...57B Altcode: Maximum sensitivity for optical interferometers is achieved only when the optical pathlengths between the different arms can be equalized without using interference fringes on the research object itself. This is called “blind operation” of the interferometer. In this paper I examine different options to achieve this, focussing on the application to the Very Large Telescope Interferometer (VLTI). It is proposed that blind operation should be done using a so-called “coherence autoguider”, working on an unresolved star of magnitude V=11 to 13 within the “isoplanatic patch for coherencing”, which has a diameter of about 1 degree. Estimates of limiting magnitudes for the VLTI are also derived. Title: Instrumental factors affecting the fringe contrast in optical interferometers Authors: Beckers, Jacques M. Bibcode: 1990Ap&SS.171..333B Altcode: Interference fringes are the prime observable quantity in astronomical optical and radio interferometers. To maximize the signal-to-noise ratio it is important to keep instrumental causes of fringe contrast decrease to a minimum. I discuss these and derive the tolerances to be, placed on them. Title: VLT Interferometer: II. Factors affecting on-axis operation Authors: Beckers, Jacques M. Bibcode: 1990SPIE.1236..364B Altcode: The factors contributing to fringe contrast decrease for telescopes working near their diffraction limits are summarized. These factors include variations with time, such as atmospheric variations, vibrations, pathlength drift, and fringe tracking noise; and variations accross the pupil; variation with wavelength and factors relating to polarization effects; unequal beam intensities; detector resolution; and pupil transfer geometry. The effects on multispeckle images are also considered. The resulting error budget for the Very Large Telescope Interferometer (VLTI) is derived. It is concluded that the total random error in the fringe contrast is 4.2. The total calibratable systematic error amounts to 34 percent (27 percent due to the instrument, 9 percent due to the atmosphere). Title: VLT interferometer: IV. The utility of partial adaptive optics Authors: Beckers, Jacques M. Bibcode: 1990SPIE.1236..154B Altcode: The application of full adaptive optics to astronomical telescopes in the foreseeable future is likely to be limited to infrared wavelengths greater than 1 micron both because of the limited number of bright enough wavefront sensing objects at visible wavelengths and because of the complexity and expense of making an adaptive optics system for large telescopes with the large number of elements required at visible wavelengths. Adaptive optics designed for infrared wavelengths do, however, improve the image quality at wavelengths shorter than the design wavelength, thus improving the sensitivity of interferometric imaging at those wavelengths. Title: VLT Interferometer: III. Factors affecting wide field-of-view operation Authors: Beckers, Jacques M. Bibcode: 1990SPIE.1236..379B Altcode: This paper discusses the requirements posed on the ESO Very Large Telescope (VLT) Interferometer by the applications that require a field-of-view larger than the Airy disk of the individual telescopes. The most essential requirement for such wide field-of-view use of interferometric arrays is the maintenance of the pupil configuration, which applies to all the details of this configuration. Not meeting this requirement leads to path-length differences among the rays of each of the telescopes composing the array. An error budget for the optical design parameters of the VLT Interferometer is derived. Title: VLT interferometer: proposed implementation Authors: Beckers, Jacques M.; Enard, Daniel; Faucherre, Michel; Merkle, Fritz; di Benedetto, G. P.; Braun, R.; Foy, R.; Genzel, R.; Koechlin, Laurent; Weigelt, Gerd Bibcode: 1990SPIE.1236..108B Altcode: The Very Large Telescope Interferometer (VLTI) is one of the operating modes of the VLT. In addition to consisting of the four stationary 8 m diameter telescopes, it includes a number of movable Auxiliary Telescopes which both complement the (u, v) plane coverage of the large telescopes and provide a powerful interferometric facility by itself (available 100% of the time). The authors describe the current plans for the implementation of the VLTI. These plans will be finalized after the choice of the VLT site in 1990. Title: Planning the VLT interferometer. Authors: Beckers, J. M. Bibcode: 1990Msngr..60....1B Altcode: The paper deals with the implementation plan for the Very Large Telescope (VLT) interferometer as proposed by the European Southern Observatory. The philosophy followed in the plan is based on the opportunity provided by the presence on one site of four identical 8-meter telescopes to do interferometric imaging. The properties of existing optical interferometers as well as those in the construction and planning stages are outlined, and the similarities and differences of optical and radio types of interferometry are discussed, with focus placed on adaptive optics. A proposed configuration of the VLT telescopes and the resulting plane coverage for different declinations and for zenith distance angles up to 60 deg are presented, along with some characteristics of auxiliary telescopes. Site aspects are covered, and attention is given to special tools developed for handling mirrors. Title: Polarization effects in astronomical spatial interferometry. Authors: Beckers, Jacques M. Bibcode: 1990SPIE.1166..380B Altcode: One of the operational modes of the European Very Large Telescope (VLT) will be the one in which the four 8.2 m diameter telescopes will be used together with two or more smaller telescopes with about 2 m aperture as a spatial amplitude interferometer. One of the main factors affecting the performance of this interferometric array relates to the polarization characteristics of the optics composing the legs of the array. Retardation effects and reorientation of the polarization coordinate frame of reference by reflections are a major cause of fringe contrast decrease (and even disappearance). The author has analyzed these effects and developed a raytracing algorithm to calculate the polarization transfer and the resulting fringe contrast decrease. Title: Interferometry with ESO's very large telescope. Authors: Beckers, J. M. Bibcode: 1990SPIE.1319..434B Altcode: The Very Large Telescope, being build by the European Southern Observatory, has an interferoetric node in which the light of the four 8 eter aperture telescopes, and of a number of smaller telescopes, will be combined coherently to give iilliarcsecond level angular resolution at optical wavelengths on very faint objects. This paper describes current plans to impleMent this mode. Title: Adaptive Optics for Large Telescopes Authors: Beckers, Jacques M.; Merkle, Fritz Bibcode: 1989Ap&SS.160..345B Altcode: The performance of large telescopes is determined both by their angular resolution and by their collection area. It is, therefore, important to achieve as high an angular resolution as possible by site selection, by avoiding image deterioration by the telescope and its environment, and by real time image restoration by adaptive optics. We summarize the principles of adaptive optics, their predicted performance and the current programs underway to implement adaptive optics for astronomical purposes. Title: Detailed compensation of atmospheric seeing using multiconjugate adaptive optics. Authors: Beckers, J. M. Bibcode: 1989SPIE.1114..215B Altcode: By the simultaneous observation of the atmospheric wavefront of a number of adjacent objects in the sky it appears possible to determine the atmospheric wavefront distortion in 3 dimensions using tomography techniques. Once obtained it becomes then possible to correct the atmospheric wavefront distortions in detail using adaptive optics at the conjugates of a number of atmospheric layers. Title: Application of adaptive optics to astronomy. Authors: Merkle, Fritz; Beckers, Jacques M. Bibcode: 1989SPIE.1114...36M Altcode: Adaptive optical systems and their applications in astronomy have been discussed for over a decade. Meanwhile the main components like deformable mirrors, wavefront sensors etc. for these real time correction systems of atmospheric turbulence effects, are commercially available. The principles of of this technology, its predicted performance and the current programs underway to implement adaptive optics for astronomical purposes are summarized. Title: A near infrared astronomical adaptive optics system. Authors: Goad, L.; Beckers, J. Bibcode: 1989SPIE.1114...73G Altcode: The authors describe an adaptive optics system designed to obtain diffraction limited imaging in the near infrared (≡2 microns) with the Mayall 4-meter telescope at Kitt Peak National Observatory. The basic system consists of a 55 element adaptive mirror, a 37 element Hartmann-Shack wavefront sensor, and a dedicated microprocessor for analysis of sensor data and active mirror control. This polychromatic adaptive optics system utilizes the visible radiation from a semi-stellar source, or nearby star, for wavefront sensing while imaging the near-infrared radiation on an InSb array detector. Recent laboratory tests of the working system are summarized. Title: Survey of present efforts in astronomical adaptive optics Authors: Beckers, Jacques M.; Merkle, Fritz Bibcode: 1989SPIE.1130...10B Altcode: In addition to improving the angular resolution of solar and stellar observations, the application of adaptive optics to astronomical telescopes will improve the contrast of pointlike sources against both sky and telescopic apparatus thermal backgrounds, enhance spectroscopic resolution, and increase the sensitivity of optical interferometry. Performance projections are made for a prospective 8 m aperture telescope incorporating wavefront sensor-based adaptive mirror and digital servocontrol systems; results comparable to those of space-based telescopes appear obtainable, albeit at atmospherically transmissible wavelengths. The development status and focus of the various current programs in astronomical adaptive optics are noted. Title: Workshop Impressions Authors: Beckers, J. M. Bibcode: 1989ASIC..263..607B Altcode: 1989ssg..conf..607B No abstract at ADS Title: Plans for high resolution imaging with the VLT. Authors: Beckers, J. M. Bibcode: 1989amts.conf...90B Altcode: The author reviews the methods used to improve the angular resolution of large telescopes. He describes plans to use the VLT with adaptive optics and interferometric imaging techniques to improve image quality, and places the VLT plans in broader (past and future) perspective. Title: Solar Image Restoration by Adaptive Optics Authors: Beckers, J. M. Bibcode: 1989ASIC..263...43B Altcode: 1989ssg..conf...43B No abstract at ADS Title: Cophasing Telescope Arrays Authors: Beckers, J. M. Bibcode: 1989ASIC..274..355B Altcode: 1989dli..conf..355B No abstract at ADS Title: Improving Solar Image Quality by Image Selection Authors: Beckers, J. M. Bibcode: 1989ASIC..263...55B Altcode: 1989ssg..conf...55B No abstract at ADS Title: Plan for High Resolution Imaging with the VLT. Authors: Beckers, J. M. Bibcode: 1989RvMA....2...90B Altcode: No abstract at ADS Title: Some Thoughts on the Combination of Beams in Interferometers Using Telescopes of Unequal Size Authors: Beckers, J. M. Bibcode: 1989ASIC..274..365B Altcode: 1989dli..conf..365B No abstract at ADS Title: Christian Perrier Recieves Award Authors: Beckers, J. Bibcode: 1988Msngr..54...63B Altcode: Christian Perrier Receives Award Title: Increasing the Size of the Isoplanatic Patch with Multiconjugate Adaptive Optics Authors: Beckers, J. M. Bibcode: 1988ESOC...30..693B Altcode: 1988vlti....2..693B; 1988vltt.conf..693B No abstract at ADS Title: Reducing Mirror Seeing Problems in Meniscus Mirrors Authors: Barr, L. D.; Beckers, J. M.; Pearson, E. T.; Hobbs, T. W.; Spangenberg-Jolley, J. Bibcode: 1988ESOC...30..595B Altcode: 1988vlti....1..595B; 1988vltt.conf..595B It is well known that telescope seeing is worsened when temperature differences exist between the primary mirror and the air above the surface. The author describe a new mirror blank configuration that enables mirror blank temperature control sufficient to substantially eliminate mirror seeing through liquid cooling. Thermal properties and manufacturing feasibility have been studied. Title: Grisms for Infrared Observations Authors: Beckers, J. M.; Gatley, I. Bibcode: 1988ESOC...30.1093B Altcode: 1988vltt.conf.1093B; 1988vlti....2.1093B The recent availability of 2-D infrared array detectors suggests the application of visible light techniques to infrared astronomy. This paper examines grism spectroscopy and reports the first results of an IR grism spectrograph. Title: Adaptive Optics Development at NOAO Authors: Beckers, J. M. Bibcode: 1988ESOC...30..627B Altcode: 1988vlti....2..627B; 1988vltt.conf..627B The Advanced Development Program and the National Solar Observatory within NOAO are engaged in the development of adaptive optics for both solar and stellar observations and for visible and infrared telescopes. These different applications require different techniques but also share many common aspects. The author reviews these programs, discusses results of their analysis, discusses some of their hardware and project towards future plans. Title: Diffraction-limited astronomical infrared imaging through the turbulent atmosphere Authors: Christou, J. C.; Freeman, J. D.; McCarthy, D. W., Jr.; Roddier, F.; Beckers, J. M. Bibcode: 1988JPhD...21S..49C Altcode: No abstract at ADS Title: Two-dimensional Infrared Diffraction-limited Imaging of Circumstellar Envelopes Authors: Christou, J. C.; Ridgway, S. T.; Beckers, J. M.; Probst, R. G. Bibcode: 1988BAAS...20.1053C Altcode: No abstract at ADS Title: Interferometry with the MMT and NNTT. Authors: Beckers, J. M. Bibcode: 1988ESOC...29..879B Altcode: 1988hrii.conf..879B The author summarizes the experiments in interferometry done on the MMT and planned for the NNTT. He refers to the numerous other publications on this topic which are given in the references for detailed information. Title: Application of the NOAO Infrared Imaging Array for 2-D Infrared Speckle Interferometry Authors: Beckers, J. M.; Ridgway, S.; Christou, J. C.; Probst, R. Bibcode: 1988BAAS...20..649B Altcode: No abstract at ADS Title: High Resolution Imaging in the Infrared Using Adaptive Optics Authors: Beckers, Jacques M.; Goad, Larry E. Bibcode: 1988ASSL..141..319B Altcode: 1988uglr.work..319B The authors describe the principles behind the prototype of a so-called polychromatic adaptive optics system now being assembled at NOAO to be used at the 150 cm McMath and 380 cm Mayall telescopes on Kitt Peak. In it, the wavefront errors due to seeing and the telescope itself are being corrected for IR wavelengths, while the wavefront disturbances are being sensed at visible and near IR wavelengths. Title: First results with the NOAO 2-D speckle camera for infrared wavelengths. Authors: Beckers, J. M.; Christou, J. C.; Probst, R. G.; Ridgway, S. T.; von der Lühe, O. Bibcode: 1988ESOC...29..393B Altcode: 1988hrii.conf..393B The authors have constructed an infrared speckle camera using the NOAO SBRC 58×62 InSb array detector. The camera and detector can be used anywhere in the 1 to 5 μm wavelength region. The authors describe the first observations. These observations illustrate the performance of the camera for an unresolved object, for a double star (ζ Aqr) and for a resolved object (the "Red Rectangle"). The authors have analyzed the observations using shift-and-add, power spectrum/autocorrelation function, and Knox-Thompson methods. Title: Some Thoughts on the Combination of Beams in Interferometers Using Telescopes of Unequal Size Authors: Beckers, J. M. Bibcode: 1988dli..conf..365B Altcode: No abstract at ADS Title: Cophasing Telescope Arrays Authors: Beckers, J. M. Bibcode: 1988dli..conf..355B Altcode: No abstract at ADS Title: Two-dimensional infrared astronomical speckle interferometry Authors: Christou, Julian C.; Ridgway, Stephen T.; Probst, Ronald G.; Beckers, Jacques M.; Freeman, Jonathan D. Bibcode: 1988SPIE..976..193C Altcode: The infrared imager currently in use at the National Optical Astronomy Observatories (NOAO) has been adapted for use as a two-dinmensional infrared speckle camera operating at wavelengths of 1 - 5 microns. Data have been obtained at the Kitt Peak National Observatory (KPNO) Mayall telescope (effective aperture of about 3.8 m) for a number of different sources. Diffraction-limited images are presented for two objects, the 'Red Rectangle' and NML Cygnus, using the Knox-Thompson algorithm to recover the Fourier phases. A comparison of phase-relaxation techniques applied to the integrated phase differences is presented using both the Hudgin method and successive over-relaxation. Title: Image Reconstruction Using Adaptive Optics Authors: Beckers, J. M.; Goad, L. E. Bibcode: 1988igbo.conf..315B Altcode: Adaptive optics is an especially powerful tool for high resolution imaging in the infrared beyond 2 μm, where it can cover all or a large fraction of the sky and where the complexity and cost is modest as compared with the telescope itself. The authors describe the principles behind the prototype of a so-called polychromatic adaptive optics system now being assembled at NOAO to be used at the 150 cm McMath and 380 cm Mayall telescopes on Kitt Peak. In it, the wavefront errors due to seeing and the telescope itself are being corrected for IR wavelengths, while the wavefront disturbances are being sensed at visible and near IR wavelengths. Title: Optical concepts for the Binary Star Explorer. Authors: Traub, W. A.; Massa, D. L.; Endal, A. S.; Beckers, J. M.; Latham, D. W.; McAlister, H. A.; Parsons, S. B. Bibcode: 1987SPIE..751...72T Altcode: The conceptual design of a proposed first-generation optical interferometer in space, the Binary Star Explorer, is described. The scientific objectives for this interferometer are to determine the fundamental astrophysical quantities of distance and mass for stars in binary systems. In particular, the interferometer will be able to make accurate distance measurements to an estimated 40 Cepheid binary systems in the Galaxy, and 28 supergiant binary systems in the LMC. The interferometer comprises two fixed telescopes on a 5-m baseline, beam-combining optics, and a visible/ultraviolet fringe detecting system. The angular separation of binary systems made up of a cool giant star and hot dwarf companion are determined by measuring the shift between the optical and ultraviolet fringes. In combination with knowledge of the physical size of the orbit (which must be obtained separately from radial velocity measurements on both stars), the distance to the binary is obtained as the ratio of the physical to angular sizes. Title: The NOAO/ADP adaptive optics program and its application to solar physics. Authors: Beckers, J. M. Bibcode: 1987LFTR...28...55B Altcode: The NOAO Advanced Development Program is pursuing a program to develop adaptive optics for both nighttime and solar observations. Initially this program is directed towards image sharpening at infrared wavelengths (1 - 10 μm) at large stellar and solar telescopes. Although observing will be done in the infrared this "polychromatic" adaptive optics system will do the wavefront sensing at visible wavelengths. Title: Interferometric Capabilities of the Nntt Authors: Beckers, J. M. Bibcode: 1987iia..conf..171B Altcode: No abstract at ADS Title: Economy figure of merit for large telescope sites. Authors: Beckers, J. M. Bibcode: 1987iopo.conf..138B Altcode: The author attempts to combine the factors determining the quality of an astronomical site into a single quantity called the "Economy Figure of Merit," which describes a site in terms of the cost of constructing a facility to achieve a given performance. Title: High angular resolution infrared imaging at NOAO (Poster) Authors: Christou, J. C.; Beckers, J. M.; Roddier, F.; Ridgway, S.; Probst, R.; Freeman, J. D.; McCarthy, D. W., Jr.; Cobb, M. L. Bibcode: 1987iawa.conf..464C Altcode: The authors discuss how the SBRC 58×62 InSb infrared imaging array will be used for 2-D infrared speckle interferometry (IRSI) at NOAO. The 2-D IRSI is a logical extension of the 1-D slit-scanning technique currently employed by a number of groups. Title: A deep polar spectroscopic telescope "DEEPS". Authors: Davies, R.; Seitzer, P.; Beckers, J.; Simmons, J. Bibcode: 1987inco.conf...45D Altcode: DEEPS is a concept for a fixed telescope pointing at a celestial pole which would perform multiple object spectroscopy on galaxies ten to twenty times fainter than those at the current limit of observation using large ground based telescopes. Title: Telescope sites: summary and conclusions. Authors: Beckers, J. M. Bibcode: 1987iopo.conf..212B Altcode: No abstract at ADS Title: Two-dimensional Images of Alpha Orionis Authors: Hebden, J. C.; Christou, J. C.; Cheng, A. Y. S.; Hege, E. K.; Strittmatter, P. A.; Beckers, J. M.; Murphy, H. P. Bibcode: 1986ApJ...309..745H Altcode: Between February 1981 and December 1983 a series of speckle interferometric observations were made of the M-type supergiant Alpha Orionis in an attempt to produce two-dimensional images of the star at the H-alpha line. Two types of data reduction techniques were used: (1) shift-and-add methods applied to conventional speckle interferometric observations, and (2) differential speckle interferometry. Data analysis included the application of the CLEAN algorithm to calibrate the images produced by the shift-and-add technique with data reduced similarly for a point source. The images produced are encouragingly consistent in suggesting asymmetric atmospheric structure; possible evolution of that structure over the three-year period of observations is noted. Title: Planning the National New Technology Telescope Authors: Beckers, J. M. Bibcode: 1986BAAS...18..955B Altcode: No abstract at ADS Title: Differential speckle imaging with the cophased Multiple Mirror Telescope. Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M. Bibcode: 1986OptEn..25..712H Altcode: Differential speckle interferometry has been applied to data obtained using the fully phased six-mirror aperture of te Multiple Mirror Telescope. Wavelength-dependent differences in the appearance of a stellar object are derived from simultaneous observations at two distinct wavebands. The supergiaint star Alpha Orionis was observed this way to investigate its appearance in hydrogen-alpha emission. Data reduction consists of a frame-by-frame weighted deconvolution. An inherent Wiener-type filtering must be removed in order to preserve high spatial frequency information. Results for Alpha Orionis are compared to similar results for the unresolved source Gamma Orionis. Title: The Magnetic Field of the BY Draconis Flare Star EQ Virginis Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M. Bibcode: 1986ApJ...302..777S Altcode: High resolution, high S/N-ratio line profiles of the BY Draconis-type flare star EQ Vir obtained with the MMT are presently subjected to a novel Zeeman analysis procedure which includes radiative transfer effects and compensation for blends. A mean field of 2500 + or - 300 G covering 80 + or 15 percent of EQ Vir is determined. This constitutes the first positive detection of a magnetic field in a BY Draconis-type flare star, confirming that magnetic fields are present on these stars. The value of 2500 G obtained for the photospheric field strength is similar to the value derived by assuming equipartition of magnetic and thermal energy densities in the photosphere and scaling from the solar network fields, suggesting that equipartition may determine the mean field strength in the nonspotted portion of the flare star photosphere. Title: IR thermography and observatory thermal pollution Authors: Williams, J. T.; Beckers, J. M.; Salmon, D.; Kern, P. Bibcode: 1986SPIE..628...30W Altcode: A 10 micron imaging camera has been used to identify subtle and not-so-subtle thermal pollution of the near telescope environment at several large telescopes, and can also be used to monitor progress in eliminating such pollution. This paper reports some highlights of data taken at the Multiple Mirror Telescope (MMT), the Kitt Peak National Observatory (KPNO), and Cerro Tololo Inter-American Observatory (CTIO) 4 meter telescopes, and Canada-France-Hawaii (CFHT) 3.6 meter telescope on Mauna Kea, the McDonald Observatory 2.7 and 2.1 meter telescopes and the 5 meter telescope at Mt. Palomar. Title: Planning the National New Technology Telescope (NNTT). IV - Coalignment/cophasing system Authors: Beckers, Jacques M.; Shu, Ker-Li; Shaklan, Stuart Bibcode: 1986SPIE..628..102B Altcode: The NNTT will be a multiple mirror telescope consisting of an array of four 7.5-meter telescopes to be coaligned and cophased by means of an internal optical metering device. As a result, the NNTT acts like a single telescope with a 15-meter collecting diameter and a 21-meter resolution diameter. This paper describes the coalignment/cophasing system. Title: Field of view considerations for telescope arrays Authors: Beckers, Jacques M. Bibcode: 1986SPIE..628..255B Altcode: The limitation of the field of view for three different types of interferometric imaging telescope arrays is examined, and means for its optimization are identified. The array types are the compact monolithic, thin monolithic, and nonmonolithic (individual telescopes). Attention is given to the optical path of two elements of the nonmonolithic array type for the case of an on-axis star. Title: Use of the coherent MMT for diffraction limited imaging Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M. Bibcode: 1986SPIE..628...42H Altcode: All six MMT telescopes can now be optically cophased simultaneously over a wide field of view yielding coherent coverage of the complete Fourier transform plane corresponding to that of a pupil-masked telescope of 6.86-m aperture. Open-loop phasing control compensates for flexure-induced path-length changes due to variable gravitational loading as a function of elevation. The system has been used to produce diffraction limited images and differential images of Alpha Orionis using narrow-band (1.2 A) filters centered both on Hydrogen-alpha and on a similar bandpass out of the absorption line. Corresponding wide (100 A) and narrow-band images of Gamma and Epsilon Orionis show the expected result for unresolved sources at the diffraction limited resolution of the fully-phased MMT. Title: National Optical Astronomy Observatories (NOAO) IR adaptive optics program. III - Criteria for the wavefront sensor selection Authors: Goad, L.; Roddier, F.; Beckers, J.; Eisenhardt, P. Bibcode: 1986SPIE..628..305G Altcode: The NOAO IR Adaptive Optics Program has elected to develop a system using the visual light from an object to sense the wavefront errors and generate the corrections required to give diffraction-limited imaging in the near-IR (2-10 microns). The performance of a variety of possible sensors systems has been evaluated, computing both their ideal performance and their expected performance with available detectors. A major consideration in this evaluation is the ability of the sensor to measure mean wavefront tilts of the visual wavefront over subapertures corresponding to the (larger) IR wavefront scale lengths. A Hartmann-Shack sensor with red-sensitive image intensifiers and a Reticon detector are used. Title: The National New Technology Telescope as a phased array. Authors: Beckers, J. M. Bibcode: 1986JOSAA...3R...5B Altcode: 1986OSAJ....3R...5B No abstract at ADS Title: Proposal for a deep polar spectroscopic survey. Authors: Beckers, J. M.; Davies, R. L.; Phillips, M. M.; Seitzer, P. O. Bibcode: 1986BAAS...18Q.848B Altcode: No abstract at ADS Title: Plans for coalignment and cophasing of the optics in the 15-m National New Technology Telescope (NNTT). Authors: Beckers, Jacques M.; Shu, Ker-Li; Shaklan, Stuart Bibcode: 1986SPIE..608...18B Altcode: The NNTT concept is a multiple mirror type telescope consisting of an array of four 7.5-meter diameter telescopes which are coaligned and cophased by means of an internal optical metering device. As a result, the NNTT acts like a single telescope with a 15-meter collecting diameter and a 21-meter resolution diameter. This paper describes this coalignment/cophasing system. Title: National Optical Astronomy Observatories (NOAO) infrared adaptive optics program. I - General description Authors: Beckers, Jacques M.; Roddier, Francois J.; Eisenhardt, Peter R.; Goad, Larry E.; Shu, Ker-Li Bibcode: 1986SPIE..628..290B Altcode: The authors describe the general principles behind a polychromatic adaptive optics program for astronomy. In this program the atmospheric wavefront distortions are measured at visible wavelengths (700 nm) using an astronomical object in the vicinity of the infrared object of interest. The resulting wavefront corrections are applied to an infrared imaging system which utilizes a two-dimensional detector array. The authors describe the principles of this adaptive optics system. Title: The Coalignment and Cophasing of the National New Technology Telescope Authors: Beckers, J. M.; Shu, K. L.; Shaklan, S. Bibcode: 1985BAAS...17..900B Altcode: No abstract at ADS Title: Multiple mirror telescope as a phased array telescope Authors: Hege, E. Keith; Beckers, Jacques Maurice; Strittmatter, Peter A.; McCarthy, Donald W., Jr. Bibcode: 1985ApOpt..24.2565H Altcode: Experiments are summarized which have used the multiple mirror telescope (MMT) subapertures as a phased array and as a coherent phased telescope. A simple analysis is presented of the tilted focal plane geometry for coherent observation. The phased operation of the MMT is important not only for obtaining high angular resolution but also for obtaining the higher detection sensitivity which results from the better discrimination against the sky emission background for IR diffraction-limited images. Full-aperture (six-beam) diffraction-limited results for the unresolved source Gama Orionis, the well-known close binary Capella, and the resolved red supergiant Betelgeuse (including a diffraction-limited differential speckle image of the latter) are presented as a preliminary demonstration of the potential capabilities of this configuration. Title: Results from Optical Interferometry (Review) Authors: Beckers, J. M. Bibcode: 1985ASSL..117...57B Altcode: 1985mlrg.proc...57B The techniques of optical speckle and Michelson interferometry have both contributed significant information on the diameter, the atmospheres, and the envelopes of red supergiant stars. In this paper, the author summarizes the observations obtained to date and previews future plans. Title: Polychromatic Adaptive Optics for Infrared Telescopes Authors: Beckers, J. M.; Eisenhardt, P.; Goad, L.; Roddier, F. Bibcode: 1985BAAS...17R.571B Altcode: No abstract at ADS Title: Contributions by R.G. Giovanelli to Solar Instrumentation Authors: Beckers, J. M. Bibcode: 1985AuJPh..38..769B Altcode: No abstract at ADS Title: Differential speckle imaging with the cophased Multiple Mirror Telescope. Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M. Bibcode: 1985SPIE..556..284H Altcode: A new technique known as differential speckle interferometry has been applied to data obtained using the fully-phased six-mirror aperture of the Multiple Mirror Telescope. By observing stellar objects at two distinct wavebands simultaneously, differences in the object resulting from the different wavelengths can be derived. Observations were made of the supergiant star Alpha Orionis in order to investigate the hydrogen-alpha emission from the surrounding envelope. The data reduction process consists of a frame-by-frame weighted deconvolution procedure. This process involves an inherent Wiener-type filtering which must be removed in order to preserve high spatial frequency information. Results for Alpha Orionis and for the unresolved source Gamma Orionis are presented. Title: Energy Release and Energy Transport Below the Transition Zone in Solar Flares Authors: Hénoux, J. C.; Chambe, G.; Heristchi, D.; Semel, M.; Woodgate, B.; Shine, R.; Beckers, J. Bibcode: 1985spit.conf..758H Altcode: No abstract at ADS Title: Future techniques and instrumentation in solar-stellar physics Authors: Beckers, J. M. Bibcode: 1985AuJPh..38..791B Altcode: A projection is made of instrumentation developments in future solar-stellar physics research, encompassing stellar activity and its cycles, stellar rotation, stellar surface motions and magnetic fields, stellar pulsations and oscillations, and stellar chromospheres, coronae, and winds. In treating each of these fields, current techniques are characterized and the observations integrates sunlight that couple the properties of the sun to those of the stars are noted. Solar-stellar research may be the primary driver in stellar photometric and spectroscopic research in the foreseeable future. Title: Spectroscopy of 26 QSO candidates form the Jodrell Bank 966-MHz survey. Authors: Walsh, D.; Beckers, J. M.; Carswell, R. F.; Weymann, R. J. Bibcode: 1984MNRAS.211..105W Altcode: Twenty-six QSO candidates from the Jodrell Bank 966-MHz survey have been observed spectroscopically at the Multiple Mirror Telescope. Nineteen are emission-line QSOs and redshifts are given for these. Four have smooth, featureless spectra and are classified as BL Lacertae-type objects. The remaining three objects are galactic stars. Title: Differential Speckle Interferometry-Using the MMT Authors: Hebden, J.; Hege, E. K.; Beckers, J. Bibcode: 1984BAAS...16..886H Altcode: No abstract at ADS Title: First Measurement of Magnetic Fields on a BY Draconis Flare Star: EQ Virginis Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M. Bibcode: 1984BAAS...16Q.517S Altcode: 1984BAAS...16..517S No abstract at ADS Title: High Resolution Imaging of Spectroscopic Binaries Authors: Beckers, J. M. Bibcode: 1984BAAS...16..498B Altcode: No abstract at ADS Title: A solar Lyman alpha coronagraph. Authors: Beckers, J. M.; Argo, H. V. Bibcode: 1984SPIE..445..312B Altcode: An all reflecting externally and internally occulting solar coronagraph which can be used for observations of the sun in the hydrogen Lyman-alpha line is described. In the particular design considered and tested, a multiple occulting disk assembly is integrated with a Gregorian telescope in such a way that (1) scattered and diffracted light is minimized, and (2) a large effective collecting area (16 sq cm) as compared to the total telescope length (95 cm) is obtained. The telescope is sun-centered pointed and has a large field of view (2.3 degrees diameter). Its image can be used to feed a multiple slit spectrograph, a camera using a Lyman-alpha interference filter or other instrumentation which can make use of the availability of a full coronal image. Title: The differential speckle interferometer. Authors: Beckers, J. M.; Hege, E. K.; Murphy, H. P. Bibcode: 1984SPIE..445..462B Altcode: The authors describe a new technique called "Differential Speckle Interferometry" (DSI) which uses simultaneous narrow band images of astronomical objects to study their structure. Simultaneous specklegrams of red supergiant and giant stars taken in the hydrogen lines and in the nearby continuum allow to reconstruct the image of the extended chromospheres of these stars at resolutions of 100 nanoradians and better. The authors describe the instrumentation, analysis techniques, and results related to DSI. Title: The use of the MMT for interferometric imaging Authors: Beckers, J. M.; Hege, E. K. Bibcode: 1984vlti.conf..279B Altcode: 1984IAUCo..79..279B The progress made in interferometric imaging using the multiple-mirror telescope (MMT) as a fully phased array in visible wavelengths is discussed. It is shown that all six MMT telescopes can now be phased over a wide field of view simultaneously resulting in a (u,v) plane coverage corresponding in size to a 686-cm telescope aperture. The open-loop phasing control of the MMT for gravitational changes, as well as a concept of an internal cophasing/coalignment system for MMT-type telescopes are described. Title: The use of the Multiple Mirror Telescope as a phased array. Authors: Beckers, J. M.; Hege, E. K.; Low, F. J.; McCarthy, D. W.; Strittmatter, P. A. Bibcode: 1984SPIE..440..136B Altcode: A summary is provided of the experiments which have used the Multiple Mirror Telescope (MMT) subapertures as a phased array in the optical, infrared, and submillimeter spectum regions. Those experiments exploit the unique, very high angular resolution of the MMT being equivalent to that of a conventional telescope 686 cm in diameter. The operation of the MMT as a phased array is not only important for obtaining high angular resolution but also for obtaining the higher detection sensitivity which results from the better discrimination against the sky emission background for infrared diffraction limited images. A description is presented of future plans to make the MMT into a phased telescope. Title: Optical interferometry with the MMT. Authors: Beckers, J. M.; Hege, E. K.; Strittmatter, P. A. Bibcode: 1983SPIE..444...85B Altcode: 1984SPIE..444...85B A phased array with a 680-cm baseline can be devised by adjusting the optical path lengths of the University of Arizona's six Multiple Mirror Telescope (MMT) elements. Attention is presently given to the procedures and results of experiments in spectroscopy and speckle interferometry, which have been conducted using either two or three of the telescopic elements. Adjustments of the optical configuration of the MMT are planned which will lead to coherent operation over a large field of view, with all six telescopic elements phased simultaneously. Title: The Multiple Mirror Telescope: a progress report. Authors: Beckers, J. M.; Ulich, B. L.; Williams, J. T. Bibcode: 1983SPIE..444....2B Altcode: 1984SPIE..444....2B Attention is given to engineering design and operational aspects of the Multiple Mirror Telescope (MMT). A novel detector cooling system for the MMT's spectrographs permits echelle spectroscopy of extremely faint objects to be conducted, in order to obtain data bearing on such questions as the chemical abundances of the early universe, the velocity dispersions in globular clusters and dwarf spheroidal galaxies, and the rotation and magnetic fields of galactic stars. The MMT's IR photometer has identified many optically invisible radio sources, and is being used to devise an improved Cepheid period-luminosity relationship that is not affected by interstellar absorption. Title: Rotation among Orion IC G stars : Angular momentum loss considerations in pre-main-sequence stars. Authors: Smith, M. A.; Beckers, J. M.; Barden, S. C. Bibcode: 1983ApJ...271..237S Altcode: Echelle spectra of the Na D lines or weak subordinate lines have been observed and analyzed for rotational velocities for 51 G type stars in the Orion Ic cluster. The high resolution of these MMT spectra permit a detection threshold VR sin i = 7 km s-1 or better to be attained. The results indicate that the velocity distribution of these stars can be represented by two components, a quasi-Maxwellian with a low modal value, <VR2 sin i>1/2 = 12 km s-1, and a flat distribution extending out to 200 km s-1. The D line spectra of the rapid rotators exhibit narrow absorption or emission features which are attributed to circumstellar disks close to the star. These disks appear to be quasi-permanent features and almost certainly are not remnants of the protostellar accretion phase. Several of the rapid rotators exhibit X-ray emission which also appears to be correlated with rotation. The implications of these results for the angular momentum problem in star formation are discussed in detail. It is suggested that a typical star loses some of its spin angular momentum to orbital momentum in a binary. This could occur by rotational synchronism during a protostellar fragmentation process. Title: Conductive Heat Flux in the Chromosphere Derived from Line Linear Polarization Observation Authors: Henoux, J. -C.; Chambe, G.; Heristchi, D.; Semel, M.; Woodgate, B.; Shine, D.; Beckers, J. Bibcode: 1983SoPh...86..115H Altcode: Linear polarization in two chromospheric lines (Hα and SI 1437 A) was observed in the gradual phase of solar flares. The polarized electric vector is directed towards disk center. Title: Vertical Gradients of Sunspot Magnetic Fields Authors: Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen, E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate, B. E. Bibcode: 1983SoPh...84...13H Altcode: In this paper, we describe results of a Solar Maximum Mission (SMM) guest investigation to determine vertical gradients of sunspot magnetic fields for the first time from coordinated observations of photospheric and transition-region fields. Both the photospheric vector field of a sunspot, derived from observations using the NASA Marshall Space Flight Center vector magnetograph, and the line-of-sight component in the transition region, obtained from the SMM Ultraviolet Spectrometer and Polarimeter instrument, are described. From these data, vertical gradients of the line-of-sight magnetic field component are calculated using three methods. (1) The vertical gradient is derived directly from the observations assuming a height difference of 2000 km between the photosphere and transition region. (2) Using the observed transverse photospheric field, the initial gradient (ΔBz/Δz)z = 0, is calculated from the condition ▽ . B = 0. (3) Using the photospheric line-of-sight component as the boundary condition in a potential-field calculation, the extrapolated potential field at different heights is compared to the observed transition-region field; from these comparisons, an average height difference is derived and used to calculate the average vertical gradient (ΔBz/Δz). Comparisons of gradients derived from these three methods show consistent results for methods (2) and (3). Deviations of the calculated potential transverse field at z = 0 from the observed transverse component are investigated to assess the validity of gradient calculations using method (3). Since the field is shown to be very close to a potential distribution, we conclude that the vertical gradient of Bz is lower than values from previous studies and the transition-region field occurs at a height of ≈ 4000-6000 km above the photosphere. Title: Observing White-Light Flares Authors: Neidig, D. F.; Beckers, J. M. Bibcode: 1983S&T....65..226N Altcode: Observational techniques and instrumentation for tracking the occurrence of solar white light flares back to their origin are discussed. The rare events have been found to happen in the chromospheric and coronal regions over sunspots, and are thought to be the release of accumulated energy breaking free from the magnetic field lines and reforming into simpler structures. Use of an achromatic f/15 objective lens, together with a reimaging system for field magnification as a prelude to 35 mm photography, at the Sacramento Peak Observatory is described. A Wollaston prism is also used to split the image into two beams for detection of intensity variations due to polarization, which has thus far not been observed in the white light flares. Spectroscopic data indicate visual emission due to negatively-charged hydrogen ions in the upper photosphere, and shorter wavelength neutral hydrogen Balmer continuum features. A white light flare can be up to 300% as brilliant as the surrounding region, and involve several percent of the total spontaneous solar output. Title: Conductive flux in flaring solar chromospheres deduced from the linear polarization observations Authors: Henoux, J. C.; Heristchi, D.; Chambe, G.; Woodgate, B.; Shine, R.; Beckers, J.; Machado, M. Bibcode: 1983A&A...119..233H Altcode: The linear polarization of Hα and S I 1437 Å lines produced in impact excitation by energetic electrons with an anisotropic velocity distribution function during solar flares is calculated. Selecting a function which represents the velocity distribution of electrons carrying heat flux, the relationship between conductive heat flux and linear line polarization has been computed.

The application of the relationship between linear polarization and heat flux to the observed degree of polarization leads to the determination of the conductive heat flux at the top of flaring chromospheric layers. This conductive flux is of the order of magnitude of the total radiation loss in the chromosphere and below, which is also of the order of magnitude of the conductive flux in the transition zone. Title: Vertical Gradients of Sunspot Magnetic Fields Authors: Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen, E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate, B. E. Bibcode: 1983BAAS...15..702H Altcode: No abstract at ADS Title: Impact linear polarization observed in a UV chromospheric line during a solar flare Authors: Henoux, J. C.; Chambe, G.; Sahal, S.; Semel, M.; Woodgate, B.; Shine, D.; Beckers, J.; Machado, M. Bibcode: 1983ApJ...265.1066H Altcode: Linear polarization was observed in the S 11437 A line in bright flaring points during the soft X-ray emission from a flare on 1980 July 15. The degree of polarization is about 25% and is detected at a signal-to-noise ratio of 2.9. The polarized electric vector is directed toward disk center to within 3°.

This polarization could be due to collisional excitation of S I by energetic electrons beamed in the vertical direction. Direct excitation by a highly energetic beam of electrons of order 10-100 keV is doubtful. We suggest that the heat flux in the region connecting the transition zone to the high chromosphere during the gradual phase of a flare could lead to an anisotropic excitation. Then the observed polarization would be due to vertical motions of the transition zone sweeping the preexisting chromosphere. Title: Observations of Alfven waves simultaneously in H-alpha and K Authors: Giovanelli, R. G.; Beckers, J. Bibcode: 1983IAUS..102..407G Altcode: Simultaneous spectroheliograms of a quiet region at solar disk centre in Hα +0.29 Å, Hα -0.29 Å, K +0.18 Å and K -0.18 Å show much similarity in the asymmetries in the two lines. The fibrils are identical geometrically. Both lines show patterns of line-of-sight motions propagating along the fibrils. Close to the network, the velocity of propagation is of the order of 12 km s-1 towards or away from the network; further away the patterns propagate away from the network at velocities of the order of 75 km s-1. The latter are interpreted as Alfvén waves, the former as due most likely to variations in longitudinal velocities along the fibrils. Title: Recent developments at the multiple mirror telescope. Authors: Beckers, J. M. Bibcode: 1983SPIE..365....2B Altcode: Although the Multiple Mirror Telescope (MMT) is a major astronomical facility in virture of its large collecting area (equivalent to a 4.5-m diameter single mirror telescope), it serves an equally important function as a testbed for unconventional, potentially lower cost (despite superior performance) telescope designs. The unconventional features being refined by the MMT include the use of multiple primary mirrors, an altitude-over-azimuth (rather than equatorial) mount, a barn-like enclosure, hollow 'egg-crate' fused silica mirrors, and precision ball bearings. Attention is given to the coalignment hardware and procedures used for the six primary mirrors, the image quality and interferometer performance achieved, and the annual service profile of the MMT. Title: Observations of the Longitudinal Magnetic Field in the Transition Region and Photosphere of a Sunspot Authors: Henze, W., Jr.; Tandberg-Hanssen, E.; Hagyard, M. J.; West, E. A.; Woodgate, B. E.; Shine, R. A.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; West, E. A. Bibcode: 1982SoPh...81..231H Altcode: The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacecraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arc sec and 3 arc sec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. Title: Performance of the Multiple Mirror Telescope (MMT). VI - MMT telescope coalignment system Authors: Beckers, J. M.; Poland, C.; Ulich, B. L.; Angel, J. R. P.; Low, F. J.; Wyatt, W. Bibcode: 1982SPIE..332...42B Altcode: The alignment of the Multiple Mirror Telescope (MMT) objectives so that the different star images coincide to within a fraction of the image size is conducted by the Telescope Coalignment System (TCS). The TCS is an autoguider which simultaneously operates on six telescopes, automatically coaligning them and tracking a field star. When such a star is not present in the small 4-arcmin field of view, the TCS coaligns the MMT on a nearby star and then tracks and maintains alignment of the six telescopes under computerized control, using separate flexure corrections for each. Title: Performance of the Multiple Mirror Telescope (MMT). III Seeing experiments with the MMT Authors: Beckers, J. M.; Williams, J. T. Bibcode: 1982SPIE..332...16B Altcode: Because of the Multiple Mirror Telescope's (MMT) location on an excellent site, the exposed construction of the telescope chamber, and the operator's ability to control the telescope's thermal environment, MMT image quality compares favorably with that of the best ground-based telescopes. On the nights of best seeing, image quality is determined by the telescope optics rather than the atmosphere, so that substantial improvements in image quality may be gained with further refinement of the MMT's multiple image integration system. MMT performance may become comparable to that of the Space Telescope, if its diameter/image ratio is taken as the figure of merit. Title: Performance of the Multiple Mirror Telescope (MMT). I - MMT The first of the advanced technology telescopes Authors: Beckers, J. M.; Ulich, B. L.; Williams, J. T. Bibcode: 1982SPIE..332....2B Altcode: The Multiple Mirror Telescope (MMT) incorporates many novel technological features, thereby serving as a test bed or prototype for future telescopes. Features of particular importance in this respect are the MMT altitude-over-azimuth mount, the corotating MMT building, lightweight honeycomb primary mirrors, multiple mirror optics configuration, active optical coalignment of the mirrors, and the ability to do interferometry using two or more of the total six 180-cm f/2.7 Cassegrain telescopes comprising the system. Title: First Results of Imaging of Supergiant Envelopes with the Differential Speckle Interferometer Authors: Beckers, J. M.; Hege, E. K.; Murphy, H. P.; Burnette, F. Bibcode: 1982BAAS...14R.918B Altcode: No abstract at ADS Title: The solar beacon, an experiment in solar astrometry. Authors: Beckers, J. M. Bibcode: 1982AcOpt..29..913B Altcode: No abstract at ADS Title: Differential speckle interferometry. Authors: Beckers, J. M. Bibcode: 1982AcOpt..29..361B Altcode: 1982JMOp...29..361B No abstract at ADS Title: Experiments with the Multiple Mirror Telescope. Authors: Beckers, J. M. Bibcode: 1982JOSA...72.1759B Altcode: 1982OSAJ...72.1759B No abstract at ADS Title: Progress report on the performance of the Multiple Mirror Telescope. Authors: Beckers, J. M.; Ulich, B. L. Bibcode: 1982ASSL...92...11B Altcode: 1982IAUCo..67...11B; 1982ialo.coll...11B A discussion of the unusual features of the Multiple Mirror Telescope (MMT), located in Tucson, Arizona, which will probably be included in future advanced technology telescopes, is presented. The MMT uses alt-azimuth mounts, and has a special optical configuration that makes it possible to make the optics support structure exceedingly rigid. The six MMT telescopes are coaligned on field stars and the coalignment system relies on the extraordinary mechanical stability of the MMT to keep the telescopes coaligned for long periods when no field stars are available. Details of the image quality of the MMT and the use of the MMT both for IR Michelson interferometry and for optical speckle interferometry, as well as of the building housing the MMT, are provided. Title: A rocket borne solar eclipse experiment to measure the temperature structure of the solar corona via Lyman-α line profile observations. Authors: Argo, H. V.; Laros, J. G.; Feldman, W. C.; Beckers, J. M.; Bruner, E. C. Bibcode: 1982PINSA..48...11A Altcode: No abstract at ADS Title: Impact linear polarization observed in a UV chromospheric line during a solar flare Authors: Henoux, J. C.; Chambe, G.; Semel, M.; Woodgate, B.; Shine, R.; Beckers, J. Bibcode: 1982AdSpR...2k.155H Altcode: 1982AdSpR...2..155H Linear polarization was observed in the S I 1437Å line in bright flaring points during the soft X-ray emission. The degree of polarization is about 25% and is detected at a signal to noise ratio of 2.9. The polarized electric vector is directed towards disk center to within 3°.

This polarization could be due to collisional excitationm of S I by energetic electrons beamed in the vertical direction. We suggest that the heat flux in the region interconnecting the transition zone to the high chromosphere during the gradual phase of a flare could lead to an anisotropic excitation. Then the observed polarization would be due to vertical motions of the transition zone sweeping the preexisting chromosphere. Title: Innovative research in the design and operation of large telescopes for space: Aspects of giant telescopes in space Authors: Angel, J. R. P.; Beckers, J. M.; Hoffmann, W. F.; McGraw, J. T.; Parks, R. E.; Stockman, H. S.; Woolf, N. J. Bibcode: 1982irdo.rept.....A Altcode: Eight areas of research on large space telescopes are identified and discussed. Telescope mirror technology in particular is addressed. Among the research topics described are: mirror substrates, physical optics, geometrical optics, optical surfaces, imagers, spacecraft guidance, and fiber optics. Title: Experiments in differential speckle interferometry. Authors: Beckers, J. M.; Hege, E. K. Bibcode: 1982ASSL...92..199B Altcode: 1982IAUCo..67..199B; 1982ialo.coll..199B A technique is proposed for achieving submillisecond of arc resolution on stellar objects by using the fact that the spectrum of the light emitted by stellar objects often changes across its surface either because of Doppler shifts, Zeeman splitting, abundance anomalies or changes in the stellar atmosphere. Differences between the positions of speckles in the stellar image when viewed in slightly different wavelengths can be obtained by using narrow band (0.5-1 A) filters. The difference in the position of the speckles can be determined with an accuracy much higher than the speckle itself using techniques which have already been developed for binary-star research. It is proposed that the technique of differential speckle interferometery be used to study stellar rotation, evolution of stellar systems, spectroscopic binaries, the mass-luminosity relation, and peculiar A stars. Title: A Rocket Borne Solar Eclipse Experiment to measure the Temperature Structure of the Solar Corona via Lyman-α Line Profile Observations Authors: Argo, Harold V.; Laros, John G.; Feldman, William C.; Beckers, Jacques M.; Bruner, Elmo C. Bibcode: 1982tsef.conf...11A Altcode: No abstract at ADS Title: Dynamics of the solar photosphere. Authors: Beckers, J. M. Bibcode: 1981NASSP.450...11B Altcode: 1981suas.nasa...11B Current knowledge of photospheric velocity fields is summarized. A model of the solar atmosphere is described along with the methods used in solar velocity field observations. The inferences drawn from integrated Sun observations, the velocity fields of the quiet Sun, sunspots, and other magnetic structures are discussed. Title: Preliminary observations and results obtained with the ultraviolet spectrometer and polarimeter Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Athay, R. G.; Beckers, J. M.; Brandt, J. C.; Chapman, R. D.; Bruner, E. C.; Henze, W.; Hyder, C. L.; Gurman, J. B. Bibcode: 1981ApJ...244L.127T Altcode: New observation with the Ultraviolet Spectrometer and Polarimeter (UVSP) of a number of manifestations of solar activity obtained during the first three months of Solar Maximum Mission operations are presented. Attention is given to polarimetry in sunspots, oscillations above sunspots, density diagnostics of transition-zone plasmas in active regions, and the eruptive prominence - coronal transient link. Title: The Solar Beacon, An Experiment in Solar Astometry Authors: Beckers, J. M. Bibcode: 1981BAAS...13..890B Altcode: No abstract at ADS Title: Multiple Mirror Telescope Observatory, Tucson, Arizona 85721. Report. Authors: Beckers, J. M. Bibcode: 1981BAAS...13..269B Altcode: No abstract at ADS Title: Solar maximum mission experiment: Ultraviolet spectroscopy and polarimetry on the solar maximum mission Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Woodgate, B. E.; Brandt, J. C.; Chapman, R. D.; Kenney, P. J.; Michalitsianos, A. G.; Shine, R. A.; Athay, R. G.; Beckers, J. M.; Bruner, E. C.; Rehse, R. A.; Schoolman, S. A.; Gurman, J. B.; Hyder, C. L.; Henze, W. Bibcode: 1981AdSpR...1m.275T Altcode: 1981AdSpR...1..275T We describe the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission (SMM) spacecraft. The instrument, which operates in the wavelength range 1150 - 3600 Å, has a spatial resolution of 2-3 arc sec and a spectral resolution of 0.02 Å FWHM in second order. A Gregorian telescope, focal length 1.8 m, feeds a 1 m Ebert-Fastie spectrometer. A polarimeter comprising rotating Mg F2 waveplates can be inserted behind the spectrometer entrance slit and allows all four Stokes parameters to be determined. The observing modes include rasters, spectral scans, velocity measurements, and polarimetry. Finally, we present examples of initial observations made since launch. Title: Seeing experiments with the MMT. Authors: Beckers, J. M. Bibcode: 1981BAAS...13..490B Altcode: No abstract at ADS Title: Thermography of the MMT. Authors: Beckers, J. M.; Ulich, B. L. Bibcode: 1981BAAS...13..488B Altcode: No abstract at ADS Title: The Multiple Mirror Telescope. Authors: Beckers, J. M.; Ulich, B. L.; Shannon, R. R.; Carleton, N. P.; Geary, J. C.; Latham, D. W.; Roger, J.; Angel, P.; Hoffmann, W. F.; Low, F. J.; Weymann, R. J.; Woolf, N. J. Bibcode: 1981tesc.book...63B Altcode: The Multiple Mirror Telescope (MMT), located on top of Mount Hopkins (2600 m) in Arizona, consists of six main telescope systems, each of which is a classical Cassegrain with a 1.8 m diameter parabolic primary with focal ratio f/2.7, and a hyperbolic secondary producing a final f/31.6 for each of the individual telescopes. The most significant departures of the MMT from conventional optical telescope technology are (1) the use of light-weight 'egg-crate' mirrors, which reduced the telescope weight, (2) the use of an alt-azimuth mount, which simplifies the gravitational effects on the structure, (3) the use of a ball-bearing support rather than hydrostatic bearings, resulting in cost savings and less maintenance, (4) the use of spur gear drives rather than worm gears, and (5) the use of multiple coaligned light collectors rather than a single monolithic mirror. Early multiple objective telescopes are discussed, and the early history of the MMT project is given. The design and performance of the telescope are explained, and MMT instrumentation (spectrograph, optical design, detector, infrared photometer, SAO CCD camera) is given. Astronomical research with the telescope is discussed, along with plans for future multiple objective telescopes. Title: Solar Maximum Mission experiment: ultraviolet spectroscopy and polarimetry on the Solar Maximum Mission. Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Athay, R. G.; Beckers, J. M.; Brandt, J. C.; Bruner, E. C.; Chapman, R. D.; Cheng, C. -C.; Gurman, J. B.; Hyder, C. L.; Kenney, P. J.; Michalitsianos, A. G.; Rehse, R. A.; Schoolman, S. A.; Shine, R. A.; Henze, W. Bibcode: 1981hea..conf..275T Altcode: No abstract at ADS Title: The photospheric vector magnetic field of a sunspot and its vertical gradient Authors: Hagyard, M. J.; West, E. A.; Tandberg-Hanssen, E.; Smith, J. E.; Henze, W., Jr.; Beckers, J. M.; Bruner, E. C.; Hyder, C. L.; Gurman, J. B.; Shine, R. A. Bibcode: 1981phss.conf..213H Altcode: The results of direct comparisons of photospheric and transition region line-of-sight field observations of sunspots using the SMM UV spectrometer and polarimeter are reported. The analysis accompanying the data is concentrated on demonstrating that the sunspot concentrated magnetic field extends into the transition region. An observation of a sunspot on Oct. 23, 1980 at the S 18 E 03 location is used as an example. Maximum field strengths ranged from 2030-2240 gauss for large and small umbrae viewed and inclination of the field to the line-of-sight was determined for the photosphere and transition region. The distribution of the magnetic field over the sunspot and variation of the line-of-sight gradient are discussed, as are the magnitudes and gradients of the photospheric field across the penumbral-photospheric boundaries. Title: Observations of dynamical phenomena in sunspots Authors: Nye, A. H.; Cram, L. E.; Beckers, J. M.; Thomas, J. H. Bibcode: 1981phss.conf..313N Altcode: A preliminary report of the results of one observing run based on data from one spectral line, the photospheric magnetic line Fe 6303, is presented as part of a series of observations of dynamical phenomena in sunspots using photographic spectra with the SPO vacuum tower telescope and echelle spectrograph. The ejection of a magnetic feature from the outer edge of the penumbra was observed. The initial total field strength of the feature was about 1000 gauss, which appeared to decrease as the feature moved away from the sunspot. The proper motion was about 2 km/s, and the velocity field measured in the V profile showed a downflow of 400 m/s on the spot-ward side of the moving magnetic feature. Umbral oscillations at the photospheric level with a herringbone structure characteristic of horizontally propagating waves, suggesting some overtone mode of membrane oscillation in the umbra, were seen. The peak amplitude of the oscillation was about 200 m/s, and the mean power spectrum had several clear peaks. Title: "Differential speckle interferometry", a new tool for double star research. Authors: Beckers, J. M. Bibcode: 1983LowOB...9..165B Altcode: 1983IAUCo..62..165B; 1981LowOB...9..165B; 1983LowOB.167..165B Speckle interferometry is a powerful tool for close binary star research allowing angular resolutions as small as 20 milliarcsecond. A technique is proposed to resolve spectroscopic binaries with even smaller separations. It uses the fact that speckle images taken in one or the other of the Doppler shifted spectral lines give a different intensity weighting of the two components of the binary. The location of the speckles in the two speckle images is therefore different, the direction of the displacement being related to the position angle of the binary, the amount of the displacement being related to its separation. Since the location of speckles can be determined with a much higher precision than their diameter, this creates the possibility for submilliarcsecond observations. This paper describes an experiment being started now to use this so-called 'Differential Speckle Interferometry' technique for the study of binaries, stellar rotation, stellar chromospheres, Ap stars and other objects. Title: Some Comments on the Limb Shift of Solar Lines - Part Three - Variation of Limb Shift with Solar Latitude across Plages and across Supergranules Authors: Beckers, J. M.; Taylor, W. R. Bibcode: 1980SoPh...68...41B Altcode: We searched for a variation with heliographic latitude of the solar limb effect by comparing the relative wavelengths of weak and strong Fraunhofer lines. The blue shifts associated with the limb effect appear 9%±5% larger in the polar radius vector than in an equatorial radius vector at cos θ = 0.5. This should perhaps be interpreted as an increase with latitude of either solar convection or of convective overshoot. Recent observations of poleward meridional flows of 30m s−1 should be corrected for this limb effect variation. This correction increases this flow velocity to ∼70 m s−1. A search for a similar variation in plages and in network boundaries had negative results, the variation being +1%±5% and -1%±6% respectively. Title: SMM/UVSP Observations of Magnetic Fields in the Transition Region above Sunspots Authors: Henze, W.; Beckers, J. M.; Gurman, J. B.; Hyder, C. L.; Schoolman, S. A.; Shine, R. A.; Tandberghanssen, E.; Woodgate, B. E.; Hagyard, M. J. Bibcode: 1980BAAS...12R.896H Altcode: No abstract at ADS Title: Sunspot Observations with the Ultraviolet Spectrometer and Polarimeter Experiment on the Solar Maximum Mission Authors: Gurman, J. B.; Woodgate, B. E.; Shine, R. A.; Brandt, J. C.; Chapman, R. D.; Michalitsianos, A. G.; Kenny, P. J.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Henze, W.; Brown, Teledyne; Hyder, C. L. Bibcode: 1980BAAS...12..535G Altcode: No abstract at ADS Title: Density Diagnostic of Solar Active Region and Flare Plasmas from Si IV/O IV Line Ratio as Observed from SMM Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Woodgate, B. E.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L. Bibcode: 1980BAAS...12R.539B Altcode: No abstract at ADS Title: Density diagnostic of solar active region and flare plasmas from Si IV/O IV line ratio as observed from SMM (Solar Maximum Mission). Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Woodgate, B. E.; Cheng, C. -C.; Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J. B.; Henze, W.; Hyder, C. L. Bibcode: 1980BAAS...12..534B Altcode: No abstract at ADS Title: Solar Flare and Surge Image Sequences as Seen by the Ultraviolet Spectrometer and Polarimeter on SMM Authors: Henze, W.; Brown, Teledyne; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Woodgate, B. E.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.; Hyder, C. L. Bibcode: 1980BAAS...12..532H Altcode: No abstract at ADS Title: The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission and Initial Results in Polarimetry Authors: Tandberg-Hanssen, E.; Athay, R. G.; Bruner, E. C.; Beckers, J. M.; Brandt, J. C.; Chapman, R. D.; Cheng, C. C.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.; Michalitsianos, A. G.; Shine, R. A.; Schoolman, S. A.; Woodgate, B. E. Bibcode: 1980BAAS...12..534T Altcode: No abstract at ADS Title: The Dynamics of Solar Flares and Surges as Seen at the Solar Limb in the Transition Zone Authors: Woodgate, B. E.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandbert-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L. Bibcode: 1980BAAS...12Q.535W Altcode: No abstract at ADS Title: Active Region Morphology and Evolution Images from the Ultraviolet Spectrometer and Polarimeter Authors: Shine, R. A.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Woodgate, B. E.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L. Bibcode: 1980BAAS...12R.531S Altcode: No abstract at ADS Title: The ultraviolet spectrometer and polarimeter on the Solar Maximum Mission. Authors: Woodgate, B. E.; Tandberg-Hanssen, E. A.; Bruner, E. C.; Beckers, J. M.; Brandt, J. C.; Henze, W.; Hyder, C. L.; Kalet, M. W.; Kenny, P. J.; Knox, E. D.; Michalitsianos, A. G.; Rehse, R.; Shine, R. A.; Tinsley, H. D. Bibcode: 1980SoPh...65...73W Altcode: The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission spacecraft is described, including the experiment objectives, system design, performance, and modes of operation. The instrument operates in the wavelength range 1150-3600 Å with better than 2 arc sec spatial resolution, raster range 256 × 256 arc sec2, and 20 mÅ spectral resolution in second order. Observations can be made with specific sets of 4 lines simultaneously, or with both sides of 2 lines simultaneously for velocity and polarization. A rotatable retarder can be inserted into the spectrometer beam for measurement of Zeeman splitting and linear polarization in the transition region and chromosphere. Title: Some thoughts on the large european solar telescope Authors: Beckers, J. M. Bibcode: 1980fsoo.conf..279B Altcode: No abstract at ADS Title: Solar circulation measurements: consideration and plans Authors: Beckers, J. M.; Brown, T. M. Bibcode: 1980fsoo.conf..189B Altcode: No abstract at ADS Title: The MMT as it Exists Today Authors: Beckers, J.; Williams, J. Bibcode: 1980oits.conf..108B Altcode: No abstract at ADS Title: Examples of non-thermal motions as seen on the sun Authors: Beckers, J. M. Bibcode: 1980LNP...114...85B Altcode: 1980IAUCo..51...85B; 1980sttu.coll...85B On the sun it is possible to identify many of the motions derived from stellar spectral analysis. A summary is given of the observed solar velocity phenomena. Many of these (e.g. meridional flow, giant cells, solar differential rotation, supergranulation) are of great interest in astrophysics especially for interior structure and chromospheric and coronal structuring but contribute virtually nothing to the velocities derived from a solar irradiance spectrum analysis. Others (granulation, very small scale motions and to a lesser extent, oscillations) do contribute substantially to the integrated sun velocity analysis. Some of the properties of these motion fields are described Title: Spatial Variation of the Solar Limb Effect Authors: Beckers, J. M.; Taylor, W. R. Bibcode: 1979BAAS...11Q.658B Altcode: No abstract at ADS Title: The night sky conditions at the Sacramento Peak Observatory. II - Cloud cover, seeing, and precipitable water Authors: Beckers, J. M.; Breedlove, W. O.; Devegvar, P. G. N.; Johansen, E. E.; Gilliam, L. B.; Mann, G. R.; Mauter, H. A.; Phillis, G. L.; Demastus, H. L. Bibcode: 1979PASP...91..857B Altcode: A summary is given of the following atmospheric conditions at the Sacramento Peak Observatory: cloud cover, seeing, and precipitable water. Sky brightness observations have been reported in an earlier paper. Title: The night sky conditions at the Sacramento Peak Observatory. I. Sky brightness. Authors: Schneeberger, T. J.; Worden, S. P.; Beckers, J. M. Bibcode: 1979PASP...91..530S Altcode: The night sky brightness at Sacramento Peak Observatory has been monitored over a period of nine months. The average zenith sky is 21.9 ± 0.1 mυ arc sec-2. The night sky brightness shows fluctuations of up to 25% during this period. The long record of daytime sky-brightness observations shows a strong seasonal effect with brightest skies occurring in the early summer months. This seasonal effect is marginally present in the night sky brightness results. Light pollution from the closest urban areas is also detailed. Title: Use of the solar limb effect to test photon decay and cosmological redshift theories Authors: Beckers, Jacques M.; Cram, Lawrence E. Bibcode: 1979Natur.280..255B Altcode: No abstract at ADS Title: An ultraviolet polarimeter for the Solar Maximum Mission Authors: Calvert, J.; Griner, D.; Montenegro, J.; Nola, F.; Rutledge, F.; Tandberg-Hanssen, E.; Wyman, C. L.; Beckers, J. M. Bibcode: 1979OptEn..18..287C Altcode: The Solar Maximum Mission experiment contingency will include one instrument originally designed and built for OSO-8. The engineering model of the OSO-8 High Resolution Spectrometer has been rebuilt to make it lightworthy and to encompass several new functions, including solar ultraviolet polarimetry. The rebuilt package is designated as the High Resolution Ultraviolet Spectrometer/Polarimeter. The device that enables polarimetry is a dual channel rotating waveplate system. The waveplates are magnesium fluoride and will allow measurements to be made ranging from the Lyman alpha line to near visible ultraviolet. One wavelength channel will use the polarization characteristics of the spectrometer diffraction grating as the analyzer. The second channel has a built-in four-mirror polarizer. This paper describes the polarimeter design, operation, and calibration. Title: Experiences with the Multiple Mirror Telescope. Authors: Beckers, J. M.; Woolf, N. J. Bibcode: 1979JOSA...69.1436B Altcode: 1979OSAJ...69.1436B No abstract at ADS Title: Some thoughts on the Large European Solar Telescope. Authors: Beckers, J. M. Bibcode: 1979MmArc.106..279B Altcode: No abstract at ADS Title: A broad look at solar physics adapted from the solar physics study of August 1975 Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.; Kundu, M. R.; Leith, C. E.; Lin, R.; Linsky, J.; MacDonald, F. B.; Noyes, R. Bibcode: 1979sswp.book....3P Altcode: 1979sswp.book....3B The current status of our knowledge of the basic mechanisms involved in fundamental solar phenomena is reviewed. These include mechanisms responsible for heating the corona, the generation of the solar wind, the particle acceleration in flares, and the dissipation of magnetic energy in field reversal regions, known as current sheets. The discussion covers solar flares and high-energy phenomena, solar active regions; solar interior, convection, and activity; the structure and energetics of the quiet solar atmosphere; the structure of the corona; the solar composition; and solar terrestrial interactions. It also covers a program of solar research, including the special observational requirements for spectral and angular resolution, sensitivity, time resolution, and duration of the techniques employed. Title: Solar circulation measurements: considerations and plans. Authors: Beckers, J. M.; Brown, T. M. Bibcode: 1979MmArc.106..189B Altcode: No abstract at ADS Title: Solar optical telescope (SOT). Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey, R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H. Bibcode: 1979MmArc.106..135D Altcode: No abstract at ADS Title: Solar maximum ultraviolet spectrometer and polarimeter Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Brandt, J. C.; Chapman, R. D.; Hyder, C. L.; Michalitsianos, A. G.; Shine, R. A.; Athay, R. G.; Beckers, J. M.; Bruner, E. C. Bibcode: 1979SPIE..184..264T Altcode: The objectives of the UVSP experiment are to study solar ultraviolet radiations, particularly from flares and active regions, and to measure constituents in the terrestrial atmosphere by the extinction of sunlight at satellite dawn and dusk. The instrument is designed to observe the Sun at a variety of spectral and spatial resolutions in the range from 1150 to 3600 A. A Gregorian telescope with effective focal length of 1.8 m is used to feed a 1 m Ebert-Fastie spectrometer. A polarimeter containing rotatable magnesium fluoride waveplates is included behind the spectrometer entrance slit and will allow all four Stokes parameters to be determined. Velocities on the Sun can also be measured. The instrument is controlled by a computer which can interact with the data stream to modify the observing program. The observing modes, including rasters, spectral scans, velocity measurements, and polarimetry, are also described along with plans for mission operations, data handling, and analysis of the observations. Title: Science opportunities with the SOT. Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey, R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H. Bibcode: 1979MmArc.106..245D Altcode: No abstract at ADS Title: Is there a solar polar vortex? Authors: Beckers, J. M. Bibcode: 1978ApJ...224L.143B Altcode: Results are reported for a spectroscopic determination of Doppler velocities near the solar poles which was performed to confirm or refute the existence of the 'polar vortex' (an increase in angular rotation in the vicinity of the rotation poles) predicted by Gilman (1976). The measurements and the analysis are shown not to support the notion of a polar vortex, and it is concluded that the existence of such a vortex on the sun has to be definitely ruled out. The results are also found to provide little evidence for the existence of a supergranulation velocity pattern. It is noted that large-scale velocity patterns of an as yet unknown nature and with a scale of about 60,000 km were detected during this study. Title: Spatial structure in lines in the 3398 3526 å region at the extreme limb: Observation, identification and interpretation Authors: Canfield, R. C.; Pasachoff, J. M.; Stencel, R. E.; Beckers, J. M. Bibcode: 1978SoPh...58..263C Altcode: We have obtained spectrograms of high spatial and spectral resolution of the extreme solar limb, using the vacuum tower telescope of Sacramento Peak Observatory. We have identified emission lines in the range 3398-3526 Å, and classified them according to intensity, spatial structure (intensity variation), and profile. Some lines show spatial intensity variation; others do not. We show that this effect is related to the abundance of the element responsible for the line and the mean lower-level excitation potential of interlocked lines. We explain the effect in terms of radiative interlocking with other lines, as well as the characteristic size of the volume contributing to the mean intensity. Title: Some comments on the limb shift of solar lines. II: The effect of granular motions. Authors: Beckers, J. M.; Nelson, G. D. Bibcode: 1978SoPh...58..243B Altcode: The well-known correlation between granulation intensity and velocity fluctuations causes a shift of the average line position called the `convective blue shift'. It is argued that this convective blue shift is most likely reponsible for the limb effect of solar Fraunhofer lines. To explain the center-to-limb variation of this limb effect it is essential that both horizontal and vertical motions in the granulation are considered. The effects of a variation in the granulation properties across the Sun on large scale velocity pattern observations are discussed. Abnormal granulation patterns observed inactive regions and at the boundaries of supergranules could be responsible for part or all of the `downflow' observed there. Title: Some comments on the limb shift of solar lines. I: The effect of pressure shifts on iron lines in the solar atmosphere. Authors: Beckers, J. M.; de Vegvar, P. Bibcode: 1978SoPh...58....7B Altcode: It has been suggested that pressure shifts are the sole cause for the systematic blue shift of solar fraunhofer lines (Hart, 1974). To check this we evaluate the significance of pressure shifts for Fe I lines. The observed wavelength shifts of a large number of lines are compared with the shifts calculated for the Lennard-Jones potential following Hindmarsh et al. (1967). The Lennard-Jones potential for the interatomic forces yield pressure shifts caused by neutral hydrogen, which explain only a small fraction of the observed blue shift. It is also shown that the quadratic Stark effect contributes insignificantly to the position of Fe I lines. Table I summarizes the average line shifts for iron lines at the center of the solar disk after correction for pressure shifts. Title: Large Scale Flows Near the Solar Poles. Authors: Beckers, J. M. Bibcode: 1978BAAS...10..430B Altcode: No abstract at ADS Title: Some thoughts on the large european solar telescope Authors: Beckers, J. M. Bibcode: 1978fsoo.conf..279B Altcode: No abstract at ADS Title: Solar circulation measurements: consideration and plans Authors: Beckers, J. M.; Brown, T. M. Bibcode: 1978fsoo.conf..189B Altcode: No abstract at ADS Title: A Search for Solar Global Oscillations in the CA Ii K-Line Authors: Beckers, Jacques M.; Ayres, Thomas R. Bibcode: 1977ApJ...217L..69B Altcode: No abstract at ADS Title: The Solar Limb Effect. Authors: Beckers, J. M. Bibcode: 1977BAAS....9..616B Altcode: No abstract at ADS Title: Alfvén waves in the corona above sunspots. Authors: Beckers, J. M.; Schneeberger, T. J. Bibcode: 1977ApJ...215..356B Altcode: From the line width in coronal arches above sunspots it is possible to estimate the amount of Alfven wave flux escaping from the spot into the solar corona. It is found to be less than 4 x 10 to the 7th ergs/sq cm/s in the corona just above the spot, which is less than 0.08% of the missing spot flux. If the Alfven-wave cooling mechanism for spots is to be valid, these waves have therefore to escape downward into the solar interior. Title: Material motions in sunspot umbrae. Authors: Beckers, J. M. Bibcode: 1977ApJ...213..900B Altcode: Material motions in the umbrae of a number of sunspots have been measured on an absolute scale by means of the g = 0 line of Ti I at 5713 A. It is found that the rates of solar rotation as derived from sunspot proper motions and from spectra are identical to within 1% and that the vertical flow inside umbrae is small, being less than 25 m/s when the pressure shift is ignored. The so-called limb effect is absent in the umbrae leading to an upper limit to the convective energy flux of 0.5% of the radiative energy flux outside sunspots. The position of the line with respect to its laboratory wavelengths is shifted to the red by 613 m/s, in agreement with the predicted gravitational redshift of 636 m/s. Title: High resolution spectroscopy of the disk chromosphere. V. Space-time variations observed simultaneously in seven lines. Authors: Cram, L. E.; Brown, D. R.; Beckers, J. M. Bibcode: 1977A&A....57..211C Altcode: Time sequence spectroscopic observations of the quiet solar chromosphere along a 200 Mm strip near the center of the disk were reduced to obtain 30 min of data. Oscillations appear in most of the observations in selected photospheric and chromospheric lines, but rarely in continuum observations. At a given point, the oscillations may be prominent or weak, they are never regular in time, and there is no unique relationship between the amplitudes at different heights. There are several examples of granules which apparently excite a burst of short period oscillations. By considering the line shift and intensity variations of all the lines, a working model is derived for the velocity field and related temperature variation. Title: A search for auroral type motions in solar flares Authors: Beckers, J. M.; Gilliam, L. B.; Stern, D. P. Bibcode: 1977JGR....82.1915B Altcode: The Sacramento Peak Observatory flare records of 37 double-ribbon solar flares observed from 1968 to 1972 were examined for evidence of systematic motion of the brightness along the flare ribbons. Because of analogies between aurorae and solar flares and because of well-established motion along aurorae (e.g., the so-called westward traveling surge) one might expect such motions. Brightness motions along the flare ribbon are common; we have, however, not been able to detect systematic motions in relation to the active region magnetic fields. The separation of the flare ribbons with time is well known and probably corresponds to the poleward motion of the aurorae during the auroral expansion phase. We found no counterpart in flares, however, of the equatorward motion of the aurorae during the auroral growth phase. Title: Quiet Photosphere and Chromosphere Authors: Beckers, J. M. Bibcode: 1977ASSL...69...21B Altcode: 1977igss.conf...21B Quiet Sun Atmospheric Models Oscillations Short Period Oscillations Limb Redshift Granulation Photospheric Network Chromospheric Network Supergranulation Mottle Rosette and Chain Chromospheric Grain Spicule Interspicular Region Macrospicule Chromospheric Bubbles or `Bulles' Emission Shell Flash Spectrum Spectroheliograph Birefringent Filter Title: Fine Structure Variations in High-Spatial-Resolution Solar Spectra. Authors: Pasachoff, J. M.; Canfield, R. C.; Stencel, R. E.; Beckers, J. M. Bibcode: 1976BAAS....8..501P Altcode: No abstract at ADS Title: Magnetic fields in the solar atmosphere Authors: Beckers, J. M. Bibcode: 1976erpa.reptQ....B Altcode: This paper describes the magnetic field configurations observed in the solar atmosphere including the corona and the solar wind. The techniques for observing solar magnetic fields are briefly reviewed. The significance of Alfven waves in transporting energy is stressed. Title: Reliability of sunspots as tracers of solar surface rotation Authors: Beckers, J. M. Bibcode: 1976Natur.260..227B Altcode: NEW methods of measuring solar rotation have produced significantly different rotation speeds to those derived from sunspots1,2. Spectroscopic measurements of Doppler displacements give a so-called plasma rotation velocity of 13.76° d-1 (sidereal) at the solar equator3 as against 14.38 ° d-1 (sidereal) from sunspot proper motion velocity4,5. Other techniques of measuring solar rotation lead to differences in the differential rotation from a strong variation of the solar rotation with latitude for sunspots4 and photospheric plasma3 to hardly any variation at all for coronal holes6. Our understanding of these differences is very poor. It is therefore appropriate to obtain additional accurate solar rotation measurements with as many different techniques as possible and to check the validity of the assumption that the proper motion of tracers, like sunspots, correspond to the actual motion of matter on the solar surface. We report here the result of plasma rotation velocity measurements inside sunspot umbrae and their relation to the rotation velocities derived from spot proper motions. We find that plasmas inside and outside the spots rotate at similar rates, and conclude that sunspots make poor tracers. Title: Solar Rotation and Gravitational Red Shift as Determined from Sunspot Spectra Authors: Beckers, J. M. Bibcode: 1976BAAS....8..308B Altcode: No abstract at ADS Title: Report on the solar physics - plasma physics workshop. held at Stanford University, 17 - 20 September 1974. Authors: Sturrock, P. A.; Baum, P. J.; Beckers, J. M.; Newman, C. E.; Priest, E. R.; Rosenberg, H.; Smith, D. F.; Wentzel, D. G. Bibcode: 1976SoPh...46..411S Altcode: This report summarizes the proceedings of a meeting held on 17-20 September 1974, at Stanford University. The purpose was to explore plasma physics problems which arise in the study of solar physics. Sessions were concerned with specific questions including the following: Is the solar plasma thermal or non-thermal? What spectroscopic data are required? What types of magnetic field structures exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities occur? What mechanisms of particle acceleration have been proposed? What information do we have concerning shock waves? Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments. Title: The flux of Alfvén waves in sunspots. Authors: Beckers, J. M. Bibcode: 1976ApJ...203..739B Altcode: Spectrographic observations of a large sunspot are used to derive the flux of Alfven waves in the spot's photosphere under the assumption that the horizontal velocities observed in the photosphere of a sunspot are caused by Alfven waves. Profiles of the Ti I (5713.90 A) and Fe I (5691.50) absorption lines are analyzed to determine the amount of nonthermal motion in the spot, and it is concluded that the line widths are entirely consistent with the hypothesis of sunspot cooling by Alfven waves. The wave flux in the spot's photosphere is found to be equal to 20% to 50% of the missing sunspot energy flux, or two to three times the spot's flux of electromagnetic energy. Title: High resolution spectral atlas of the solar irradiance from 380 to 700 nanometers Authors: Beckers, J. M.; Bridges, C. A.; Gilliam, L. B. Bibcode: 1976hrsa.book.....B Altcode: This report presents in graphical form the spectrum of the solar irradiance with high spectral resolution. Title: A time evolution study of limb spicule spectra. Authors: Krall, K. R.; Bessey, R. J.; Beckers, J. M. Bibcode: 1976SoPh...46...93K Altcode: Time sequences of simultaneous spectra of limb spicules, obtained using the Sacramento Peak Observatory's tower telescope and echelle spectrograph are analyzed. Intensity determinations of Hα and K, H, λ 8498 and λ 8542 of calcium are tabulated for three observing heights. Electron densities averaged over the entire visible lifetimes of spicules are ∼-6 × 1010 cm−3 at observing heights of 6000km, while maximum and minimum values were ∼-1.1 × 1011 cm−3 at 6000km and ∼- 2 × 1010 cm−3 at 10000km. Electron temperatures range between 12 000 K and 16 000 K. Profile halfwidths indicate turbulent velocities of 12 to 22 km s−1, and spectral tilts are interpreted as caused by differential velocity fields of ∼-3 km s−1 per 1000 km. No large scale spicule expansions or contractions are observed, although possible expulsions or accretions of material are observed. Spicules may be wider in the calcium K and H lines than in Hα. Title: Observational evidence for unresolved motions in the solar atmosphere Authors: Canfield, R. C.; Beckers, J. M. Bibcode: 1976pmas.conf..291C Altcode: No abstract at ADS Title: Spatially resolved motions in stellar atmospheres Authors: Beckers, J. M.; Canfield, R. C. Bibcode: 1976pmas.conf..207B Altcode: No abstract at ADS Title: Magnetic fields in the solar atmosphere. Authors: Beckers, J. M. Bibcode: 1976pspe.proc...89B Altcode: 1976pspe.conf...89B Observed properties of magnetic field in the solar atmosphere are reviewed. Among the aspects of photospheric magnetic fields which are considered are sunspots, plages and faculae, the motion of magnetic elements near sunspots, large scale magnetic field configurations, supergranule magnetic fields, and ephemeral regions. Methods of measuring solar magnetic fields are examined. Other topics include solar magnetic fields near the earth, the magnetic field and the mass and energy transport, and the extension of the solar magnetic fields upwards into the chromosphere and corona. Title: Motions in the solar atmosphere Authors: Beckers, J. M.; Canfield, R. C. Bibcode: 1975STIN...7630135B Altcode: The report presents two papers on observational evidence for large and small scale motions in the solar atmosphere. Title: Observing the sun with a fully tunable Lyot-Öhman filter. Authors: Beckers, J. M.; Dickson, L.; Joyce, R. S. Bibcode: 1975ApOpt..14.2061B Altcode: We describe the properties of the Zeiss universal birefringent filter and its optical and electronic interface with the Sacramento Peak Observatory's vacuum telescope. The instrument permits observations of solar intensities, velocities, and/or magnetic fields in rapid succession in any Fraunhofer line in the 410-700-nm wavelength region with high spectral (0.004-0.013 nm) and high spatial (about 1/3 sec of arc) resolution. Title: The Line Response Function of Stellar Atmospheres and the Effective Depth of Line Formation Authors: Beckers, J. M.; Milkey, R. W. Bibcode: 1975SoPh...43..289B Altcode: The response function defines the response of line profiles to a depth variation of such atmospheric parameters as velocity, magnetic field and turbulence. The properties of this function are derived and compared with the so-called contribution function. Title: The Flux of Alfven Waves in Sunspots. Authors: Beckers, J. M. Bibcode: 1975BAAS....7Q.459B Altcode: No abstract at ADS Title: The compression of data resulting from photon counters. Authors: Beckers, J. M. Bibcode: 1975SSI.....1..153B Altcode: A square-root transformation method is proposed for low-cost optimal compression of the counts resulting from random event detectors such as photon counters. As compared to the so-called floating point and logarithmic compression techniques proposed by Diamond et al. (1974), the square-root compression method permits almost doubling of the transmission rate for a given type of data from spacecraft with no significant loss of information. Title: Is the Solar Filigree the Site of Strong Photospheric Magnetic Fields? Authors: Beckers, J. M. Bibcode: 1975BAAS....7..346B Altcode: No abstract at ADS Title: Cinematography of solar intensity, velocity, and magnetic fields. Authors: Beckers, J. M.; Dickson, L.; Woodman, D. Bibcode: 1975OptEn..14...64B Altcode: Using a very narrow band (0.004-0.013 nm) Universal Birefringent Filter, rapidly turnable between 410 and 700 nm, and the vacuum telescope at the observatory, we have developed photographic and video techniques to observe solar magnetic and velocity fields utilizing the Zeeman and Doppler effects respectively. This is in addition to direct filtergrams which can also be obtained at any wavelength in this wavelength region. The video technique permits virtually real time display. Both techniques are used for time lapse cinematography of solar activity. Title: A fully tunable Lyot-Ohman filter Authors: Beckers, J. M.; Dickson, L.; Joyce, R. S. Bibcode: 1975aifo.reptQ....B Altcode: Properties of the Zeiss universal birefringent filter and its optical and electronic interface with the Sacramento Peak Observatory's vacuum telescope are described. The instrument permits observations of solar intensities, velocities and/or magnetic fields in rapid succession in any Fraunhofer line in the 410 to 700 nm wavelength region with high spectral (0.004 to 9.013 nm) and high spatial (approximately 1/3 arc second) resolution. Title: A Comparison of Spicules in the Hα and He II (304 Å) Lines Authors: Kjeldseth Moe, O.; Engvold, Olav Oddbjorn; Beckers, Jacques Maurice Bibcode: 1975SoPh...40...65K Altcode: 1975SoPh...40...65M On 1974 January 29 and 31, simultaneous satellite observations of spicule-like features in the 304-A L-alpha line of He(+) and ground observations of H-alpha spicules were obtained. It was then attempted to find a correlation between features of these two observations. Direct visual comparison failed to show a significant correspondence between the spicules in the He II and H-alpha spicules. Then the location and orientation of spicules in both images were measured and a correlation criterion was defined. Again no significant correspondence was found. It is concluded that the spicule-like structures in the He II (304) line are quite different from the H-alpha spicules. The possibility remains, though, that spicules are the same structures in both lines but that some spicules emit more strongly in He II (304) whereas others are better visible in H-alpha. Title: A comparison of spicules in the Hα and HeII (304 Å) lines Authors: Moe, Olav Kjeldseth; Engvold, Oddbjorn; Beckers, Jacques Maurice Bibcode: 1975SoPh...40...65M Altcode: No abstract at ADS Title: A search for deuterium on the sun. Authors: Beckers, J. M. Bibcode: 1975ApJ...195L..43B Altcode: The investigation reported is concerned with the determination of the D/H ratio on the sun, taking into account a study of the deuterium H-alpha line 1.785 A to the blue of the hydrogen H-alpha line. The upper limit obtained for the solar D/H ratio confirms current concepts regarding the creation and destruction of deuterium in the sun. Title: The Maximum Polarization for Resonance Scattering Authors: Beckers, J. M. Bibcode: 1974SoPh...37..351B Altcode: No abstract at ADS Title: High Resolution Spectroscopy of the Disk Chromosphere. III: Upward Moving Disturbances as Observed in the Ca II K-Line Wings Authors: Beckers, J. M.; Artzner, G. Bibcode: 1974SoPh...37..309B Altcode: We describe the properties of dark structures which are seen in the K-line wings and which seem to propagate inward into the K-line core, or upward in the solar atmosphere. These so-called dark whiskers appear to be related to the bright disturbances (bright whiskers) described by Liu (1974). Both may be related to the shocks that heat the chromosphere and corona. Title: Properties of the Solar Filigree Structure Authors: Dunn, R. B.; Zirker, J. B.; Beckers, J. M. Bibcode: 1974IAUS...56...45D Altcode: No abstract at ADS Title: The Profile and Polarization of the Coronal Lα Line Authors: Beckers, Jacques M.; Chipman, Eric Bibcode: 1974SoPh...34..151B Altcode: We calculate the profile and polarization of the Lα line in the solar corona. Coronal temperature variation, solar wind and other non-thermal motions have been taken into account. Because of the relatively low atomic weight of hydrogen the profile of the Lα line is a sensitive indicator of the coronal temperature. The line polarization contains relatively little information except for strong magnetic fields (> 70 G). Title: Spatial and Spectral Structure of Chromospheric Lines Authors: Pasachoff, J. M.; Harris, F. S.; Beckers, J. M. Bibcode: 1974IAUS...56...31P Altcode: No abstract at ADS Title: Solar physics. Plasma physics workshop. Authors: Baum, P. J.; Beckers, J. M.; Newman, C. E.; Priest, E. R.; Rosenberg, H.; Smith, D. F.; Sturrock, P. A.; Wentzel, D. G. Bibcode: 1974sppp.book.....B Altcode: No abstract at ADS Title: The next decade in observational solar research. Authors: Beckers, J. M. Bibcode: 1974HiA.....3..149B Altcode: The present status of observational solar research is examined, taking into account the spatial and spectral resolution which can be achieved with today's instrumentation, observations with the Harvard ATM telescope, and some experiments conducted with the aid of Skylab. Future objectives of observational solar research are considered, giving attention to the need for improved spatial and spectral resolution, the need for improved temporal resolution, and the need for novel observations and ideas. It is predicted that significant progress can be made in line profile calculations of two- and three-dimensional solar model atmospheres in which various velocity and magnetic field distributions are assumed. Title: The Profile of the Coronal Lyman-α Line. Authors: Beckers, J. M.; Chipman, E. Bibcode: 1973BAAS....5..446B Altcode: No abstract at ADS Title: High Spatial and Temporal Resolution Observations of the Magnetic Field in a Sunspot. Authors: Schultz, R. B.; White, O. R.; Beckers, J. M. Bibcode: 1973BAAS....5..339S Altcode: No abstract at ADS Title: A Morphological Study of Solar Spicules Authors: Lynch, D. K.; Beckers, J. M.; Dunn, R. B. Bibcode: 1973SoPh...30...63L Altcode: From improved spicule filtergrams obtained with the Sacramento Peak vacuum telescope we measured some spicule properties. The spicule diameter of 950 km was well resolved. A small decrease of diameter with height was observed confirming older observations. The expansion of the spicule was found to be at least an order of magnitude less than reported by Mouradian. Spicule counts are very sensitive to the threshold intensity of the observations. Counts, and their dependence on threshold intensity, height and wavelength are reported. Title: Airborne Video Recorded Coronal Emission Line Profiles of λ 5303 at the 10 July 1972 Total Solar Eclipse.* Authors: Liebenberg, D. H.; Hoffman, M.; Sanders, W. M.; Beckers, J. M. Bibcode: 1973BAAS....5T.275L Altcode: No abstract at ADS Title: The Sacramento Peak Observatory Universal Birefringent Filter Authors: Beckers, J. M. Bibcode: 1973BAAS....5R.269B Altcode: No abstract at ADS Title: The He+ λ 4686 line in the low chromosphere Authors: Worden, S. P.; Beckers, J. M.; Hirayama, T. Bibcode: 1973SoPh...28...27W Altcode: We report an unsuccessful search for the He+ λ 4686 line in the low chromosphere. However, at the location of this line we detect a number of other chromospheric emission lines. This leads us to the conclusion that the He+ λ 4686 identification made in the past, as well as other identifications, are probably in error. Additionally the region of the neutral helium λ4713 line is also studied. Title: Fully tunable Lyot-Öhmann filter. Authors: Beckers, J. M. Bibcode: 1973JOSA...63Q.484B Altcode: No abstract at ADS Title: Solar activity (Activité solaire). Authors: Jefferies, J. T.; Simon, P.; Beckers, J. M.; McLean, D. J. Bibcode: 1973IAUTA..15...75J Altcode: No abstract at ADS Title: Oscillatory Motions in Sunspots Authors: Beckers, J. M.; Schultz, R. B. Bibcode: 1972SoPh...27...61B Altcode: We observe vertical velocity oscillations in some sunspot umbrae with periods of about 180 s and peak to peak amplitudes up to 1 km s−1. These oscillations are not visible in either the line depth, line width or the continuum intensity. No correlation seems to exist between the occurence of these oscillations and the presence of the chromospheric umbral flashes (Solar Phys.7, 351, 1069). In the spot penumbra there is an indication of a long period oscillation, the period increasing from about 300 s in the inner penumbra to nearly 1000 s at the penumbra-photosphere boundary. An attempt has been made to interpret these oscillations in terms of gravity or acoustic waves, travelling along the magnetic field lines, taking into account the variation of scale height and magnetic field direction across the sunspot. Title: High Resolution Spectroscopy of the Disk Chromosphere. II. Time Sequence Observations of Ca II H and K Emissions Authors: Wilson, P. R.; Rees, D. E.; Beckers, J. M.; Brown, D. R. Bibcode: 1972SoPh...25...86W Altcode: Two independent sets of high resolution time series spectra of the CaII H and K emission obtained at the Solar Tower and at the Big Dome of the Sacramento Peak Observatory on September 11th, 1971 are reported. The evolutionary behaviour of the emission first reported by Wilson and Evans is confirmed but the detail of the evolution is found to be more complex. In one case, a doubly peaked feature showing some K3 emission evolves into a single K2 (red) peak with no K3 emission. Coincidentally, a neighbouring doubly peaked feature evolves to a very strong blue peak. In an entirely independent sequence a doubly peaked feature evolves into a single red peak. The K2 emission then fades completely although the continuum threads are still strong. Finally a strong K2 blue peak appears. These developments are confirmed by intensity profiles obtained from the spectra. Title: High Resolution Spectroscopy of the Disk Chromosphere. I. Observing Procedures Authors: Beckers, J. M.; Mauter, H. A.; Mann, G. R.; Brown, D. R. Bibcode: 1972SoPh...25...81B Altcode: This paper describes the details of an extensive observing program which is aimed at the precise photometric observation of chromospheric fine structures in the λ3933, λ3968, λ8498, and λ8542 lines of ionized calcium, the λ6563 line of hydrogen, and the λ5890 and λ5896 lines of sodium. Title: The Response of the Helium Triplet Radiation in Prominences to an Increase in Ultraviolet Flux resulting from Solar Flares Authors: Beckers, J. M. Bibcode: 1972BAAS....4T.377B Altcode: No abstract at ADS Title: Oscillatory Phenomena in Sunspots Authors: Beckers, J. M.; Schultz, R. B. Bibcode: 1972BAAS....4S.377B Altcode: No abstract at ADS Title: Solar Spicules Authors: Beckers, Jacques M. Bibcode: 1972ARA&A..10...73B Altcode: No abstract at ADS Title: The Polarization of Coronal Emission Lines (Papers presented at the Proceedings of the International Symposium on the 1970 Solar Eclipse, held in Seattle, U. S. A. , 18-21 June, 1971.) Authors: Beckers, J. M.; Wagner, W. J. Bibcode: 1971SoPh...21..439B Altcode: By means of a photographic polarimeter, we attempted to measure both the amount and direction of linear polarization of all emission lines between 3400 and 9000 Å in the inner corona (1.034 ≤ r/r0 ≤ 1.085). Only the green and red coronal lines have been analyzed in detail. Neither of these lines shows polarization exceeding the probable error of 1.0% for λ 5303 and 1.8% for λ 6374. None of the other 17 coronal lines observed during the 7 March, 1970 solar eclipse show any obvious (>5%) polarization. Title: The Measurement of Solar Magnetic Fields Authors: Beckers, J. M. Bibcode: 1971IAUS...43....3B Altcode: No abstract at ADS Title: Achromatic linear retarders. Authors: Beckers, J. M. Bibcode: 1971ApOpt..10..973B Altcode: No abstract at ADS Title: The use of colored photographic images in photographic subtraction. Authors: Beckers, J. M. Bibcode: 1971AASPB...4...13B Altcode: No abstract at ADS Title: Erratum: "The profiles of Fraunhofer lines in the presence of Zeeman splitting" [Sol. Phys., Vol. 9, p. 372 - 386 (1969)]. Authors: Stenflo, J. O.; Beckers, J. M. Bibcode: 1970SoPh...15..507S Altcode: No abstract at ADS Title: The Interpretation of Velocity Filtergrams. III: Velocities Inside Solar Granules Authors: Beckers, J. M.; Morrison, R. A. Bibcode: 1970SoPh...14..280B Altcode: From simultaneous filtergrams taken in opposite wings of the λ6569.2 solar absorption line we derive the velocity profile of an average solar granule. We definitely established the existence of the horizontal outflow in a granule in addition to the vertical upflow at the granule center. The magnitude of this outflow is strongly dependent on the influence of instrumental and atmospheric smoothing and on the effective height in the solar atmosphere at which the velocity is measured. The maximum upflow (at the granule center) equals 0.4 km/sec, the maximum outflow (500 km from the granule center) equals 0.25 km/sec. Title: The Flow Pattern within Solar Granules Authors: Beckers, Jacques M.; Morrison, Roger A. Bibcode: 1970BAAS....2R.182B Altcode: No abstract at ADS Title: Narrow band filters based on magnetooptical effects Authors: Beckers, Jacques M. Bibcode: 1970ApOpt...9..595B Altcode: Available from http://www.opticsInfoBase.org/abstract.cfm?id=16268; Title: A photographic polarimeter for solar observations. Authors: Beckers, J. M.; Wagner, W. J. Bibcode: 1970ApOpt...9.1933B Altcode: No abstract at ADS Title: The Profiles of Fraunhofer Lines in the Presence of Zeeman Splitting. II: Zeeman Multiplets for Dipole and Quadrupole Radiation Authors: Beckers, J. M. Bibcode: 1969SoPh...10..262B Altcode: The radiative transfer equations (LTE) in the four Stokes parameters are derived for the general case of a Zeeman multiplet for both electric and magnetic dipole as well as for electric quadrupole radiation. Title: The Intensity, Velocity and Magnetic Structure of a Sunspot Region. IV: Properties of a Unipolar Sunspot Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1969SoPh...10..384B Altcode: From an investigation of spectra in a magnetically sensitive (λ 6173, g = 2.5) and insensitive line (λ 5576, g = 0), we derived the following properties for a symmetrical sunspot: The magnetic field strength varies with the distance ρ(ρ ⩽ 1) from the sunspot center like H(ρ) = H(0) (1 + ρ2)-1 Title: The Profiles of Fraunhofer Lines in the Presence of Zeeman Splitting. I: The Zeeman Triplet Authors: Beckers, J. M. Bibcode: 1969SoPh....9..372B Altcode: For the case of pure absorption lines (LTE) a method is described which enables the general computation of Zeeman-split line profiles. The magnetic field vector, the Doppler shift and the line absorption coefficient is permitted to vary arbitrarily with optical depth. Elliptical birefringence (e.g., Faraday rotation) of the solar atmosphere is taken into account. Some numerical examples are given and some interesting behaviors of the line profiles are discussed. Title: The Interpretation of Velocity Filtergrams. II: The Velocity and Intensity Field of the Central Solar Disk Authors: Beckers, J. M.; Parnell, R. L. Bibcode: 1969SoPh....9...39B Altcode: From simultaneous filtergrams obtained in the blue and red wings of a Fraunhofer line we analyzed the velocity and intensity field at the center of the solar disk. Results are as follows: Cross correlation between velocity and intensity is 0.6. It increases somewhat when long wavelengths (>5000 km) are eliminated. Title: The Interpretation of Velocity Filtergrams. I: The Effective Depth of Line Formation Authors: Parnell, R. L.; Beckers, J. M. Bibcode: 1969SoPh....9...35P Altcode: The paper describes a numerical experiment in which the effect of an assumed velocity distribution in the solar atmosphere on the intensity difference between a blue- and a red-wing filter-gram is derived. This results in the effective optical depth at which the velocity is measured. It is shown that this τeff strongly depends on the assumed velocity distribution. Title: Chromospheric Inhomogeneities in Sunspot Umbrae Authors: Beckers, Jacques M.; Tallant, Paul E. Bibcode: 1969BAAS....1R.272B Altcode: No abstract at ADS Title: Chromospheric Inhomogeneities in Sunspot Umbrae Authors: Beckers, Jacques M.; Tallant, Paul E. Bibcode: 1969SoPh....7..351B Altcode: The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these `Umbral Flashes': A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness. Title: Analysis of Velocity Filtergrams Authors: Parnell, R.; Beckers, J. M. Bibcode: 1969BAAS....1Q.289P Altcode: No abstract at ADS Title: The Intensity, Velocity and Magnetic Structure of a Sunspot Region. III: On the Origin of the Apparent π Component in Sunspot Umbrae Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1969SoPh....7...22B Altcode: No abstract at ADS Title: Solar Magnetic-Field Measurements using Babinet Compensators Authors: Beckers, J. M.; Stenflo, J. O. Bibcode: 1969SoPh....6..480B Altcode: No abstract at ADS Title: The microstructure of sunspots Authors: Beckers, J. M. Bibcode: 1969pia..conf..139B Altcode: No abstract at ADS Title: The microstructure of sunspots. Authors: Beckers, J. M. Bibcode: 1969misu.book.....B Altcode: No abstract at ADS Title: Photospheric Brightness Differences Associated with the Solar Supergranulation Authors: Beckers, Jacques M. Bibcode: 1968SoPh....5..309B Altcode: The large scale (> 5000 km) intensity structure of the photosphere has been examined. The power per frequency unit indicates a continuous increase towards smaller spatial frequency. No excess power exists at wavelengths near the size of the supergranulation (30000 km) or at any other wavelength between 5000 and 100000 km. However, direct measurement of the intensity distribution in 1652 supergranulation cells shows a very small increase of the intensity towards the cell boundary. The amount of this increase is larger near the solar limb. It is probably due to a weak continuum emission associated with the chromospheric network. Any temperature difference arising from the supergranulation convection is obscured by this emission and is probably less than 1 K. Title: Spectral Observations of Spicules at Two Heights in the Solar Chromosphere Authors: Pasachoff, Jay M.; Noyes, Robert W.; Beckers, Jacques M. Bibcode: 1968SoPh....5..131P Altcode: An observational program at the Sacramento Peak Observatory in 1965 provided high-dispersion spectra of the solar chromosphere in several spectral regions simultaneously. These regions included various combinations of the spectral lines Hα, Hβ and Hɛ, the D3-line of HeI, the infrared triplet of OI, and the H- and K-lines and the infrared triplet of CaII. With the use of an image slicer the observations were made simultaneously at two heights in the solar chromosphere separated by several thousand kilometers. From these data we draw the following conclusions: Emission of different lines arises in the same chromospheric features. The intensity ratio of lines of different elements varies significantly from spicule to spicule. For the H- and K-lines of ionized calcium, this ratio remains constant, independent of wavelength throughout the line, overall intensity, and height in the chromosphere. Two rare-earth lines in the wing of the H-line show no spicular structure at all. Title: Principles of operation of solar magnetographs Authors: Beckers, J. M. Bibcode: 1968SoPh....5...15B Altcode: The principles of operation of photoelectric solar magnetographs are described in terms of the Poincaré sphere. The performance of photographic methods for measuring solar magnetic fields is compared with that of photoelectric magnetographs. Title: The Intensity, Velocity and Magnetic Structure of a Sunspot Region. II: Some Properties of Umbral Dots Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1968SoPh....4..303B Altcode: A time sequence of high-resolution sunspot photographs, exposed almost simultaneously in two continuum wavelengths (4680 Å and 6400 Å), was used to study some properties of umbral fine structures (`umbral dots'). The lifetime of the umbral dots is found to be 1500 sec. Photometry of some bright dots leads to an observed intensity excess of 0.129 Iphot and 0.134 Iphot in the blue and red respectively. The observed mean diameter of the dots is found to be 420 km. These values still include the action of image blurring. From the color index the true intensity and diameter of the dots are estimated. It appears that the umbral dots are in reality of photospheric brightness having true diameters of 150-200 km. The spatial distribution of the dots in sunspot umbrae is discussed. Some peculiarities in recent sunspot magnetic-field observations may be explained by magnetic inhomogeneities associated with umbral dots. Title: The Intensity, Velocity and Magnetic Structure of a Sunspot Region. I: Observational Technique; Properties of Magnetic Knots Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1968SoPh....4..142B Altcode: The observational set-up for a detailed study of the velocity, intensity and magnetic-field fine structure in and around a sunspot is described. On highly resolved spectra we detected in the vicinity of a sunspot a large number of points with strong magnetic fields (magnetic knots). The magnetic field in these knots causes a striking decrease of the line depth (or a `line gap' after SHEELEY, 1967). The properties of the magnetic knots are: (1) magnetic fields up to 1400 gauss; (2) diameter ≈ 1100 km; (3) coincidence with dark intergranular spaces; (4) generally downward material motion; (5) lifetime>30min; (6) estimated total number around an unipolar spot ⩾ 2000; (7) combined magnetic flux comparable to the sunspot flux; (8) coincidence with Ca+ plages. Title: On the Relation between the Photospheric Intensity, Velocity and Magnetic Fields Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1968SoPh....4..165B Altcode: No abstract at ADS Title: Solar Spicules (Invited Review Paper) Authors: Beckers, J. M. Bibcode: 1968SoPh....3..367B Altcode: The author of a review article is undoubtedly the one who benefits most from it. Only by reviewing an entire subject does it become clear how much is known of it and in what areas more information is desired. In the past 10 years, spicules have probably been the best studied fine structures on the sun. A substantial amount of observational information on spicules is available as seen in Section 3. Some of the most important questions that remain to be answered in greater detail than available now are, in my opinion, the following:Do spicules indeed diffuse after they reach their maximum growth and brightness? If so, is this an expansion of the spicule magnetic field, a change of the properties of the gases surrounding the spicule, or an actual diffusion of spicular matter across the spicular magnetic fields?

Is the group behaviour of spicules as that described by Lippincott (1957)? If true, it would imply that the spicule mechanism extends over a large area of the sun (100000 km), which conflicts with the spicule theories as given in Section 4.

Is the `tilt' of spicule-emission lines real? If so, is it caused by spicule rotation and how does it differ between the various spicule-emission lines?

Is the spicule diameter different in the different spicule-emission lines?

Is it possible to measure the spicular magnetic field How large is it?

Do the physical conditions vary from spicule to spicule? How do they vary with height and time within one spicule? For this, one needs simultaneous spectra of spicules in many lines which have a different temperature behaviour.

Is it true that both the bright and dark elongated fine mottles seen in disk spectroheliograms are spicules? This requires renewed study of the solar disk.

After a definite identification of spicules with disk structure is made, what can one learn about spicule properties from the disk study? One can, for example, try to find a direct link with the solar granulation.

Are there spicules in active regions of the sun? How do they differ from spicules in quiescent regions?

Are chromospheric grains perhaps spicules which do not grow upwards because of a lack of magnetic fields? Are they perhaps related to granules?

What are the implications of a breakdown of the `statistically steady-state' assumption in the spicule-intensity calculations?The answers to many of these questions are of great importance in the precise understanding of a spicule, and in the derivation of a magnetohydrodynamic model for it. Title: High-Resolution Measurements of Photosphere and Sun-Spot Velocity and Magnetic Fields using a Narrow-Band Birefringent Filter Authors: Beckers, J. M. Bibcode: 1968SoPh....3..258B Altcode: Modifications to a Zeiss 1/4 Å filter are described which allow high spatial resolution observations of the line-of-sight velocities and magnetic fields in the photosphere and in sunspots. First results show: (1) the granular velocity field to be very strong; differences in upward motions in the granules and downward motions in between are as much as 6 km/sec; (2) the Evershed effect in sunspots to originate primarily in the dark regions between bright penumbral filaments. Title: Magnetfeld und Materieströmungen in symmetrischen Einzelflecken Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1968MitAG..25..197B Altcode: No abstract at ADS Title: The Intensity, Velocity and Magnetic Structure in and around a Sunspot Authors: Beckers, J. M.; Schröter, E. H. Bibcode: 1968IAUS...35..178B Altcode: No abstract at ADS Title: Cinematography of Solar Oscillations. Authors: Beckers, J. M. Bibcode: 1968AJS....73Q.166B Altcode: A narrow- band Lyot filter (0.25 A) can be used to study velocity and magnetic fields on the sun (Beckers, J. M., Solar Phys. 3, 258,1968). Using this technique I obtained simultaneous motion pictures of the velocity field in the photospheric 6439 A line of Ca and in the chromospheric calcium K line. These motion pictures clearly show the 300-sec photospheric and the faster chromospheric oscillations in both quiescent and active regions on the sun. The reduction of these observations concentrates on: (a) the relation between the oscillations and the solar granulation and supergranulation, (b) the horizontal propagation of the oscillations (if any), (c) the behavior of the waves near and in sunspots, and (d) the relation of the waves and solar flares. Title: Some Comments on the Paper, Ein neuer Magnetograph etc. by G. Brückner Authors: Beckers, J. M. Bibcode: 1968ZA.....68..406B Altcode: No abstract at ADS Title: Observational Studies of the Solar Intensity Profile in the Far Infrared and Millimeter Regions Authors: Noyes, R. W.; Beckers, J. M.; Low, F. J. Bibcode: 1968SoPh....3...36N Altcode: Observations of the intensity distribution near the solar limb at 2.43 and 22.5 μ, show the absence of limb brightening to within 1 or 2 arc sec of the limb. Observations at 1.2 mm indicate limb brightening at this wavelength. These results are compared with the Utrecht Reference Photosphere and with existing data on the solar flux in the millimeter range, and suggest that the temperature minimum is broad and extends above τ5000 = 2 × 10−3. A sharp rise of temperature is required above τ5000 = 10−5. Title: Center-to-limb variations of the solar continuum in the far infrared and millimeter wavelength regions Authors: Noyes, R. W.; Beckers, J. M.; Low, F. J.; Davidson, A. W. Bibcode: 1966AJ.....71..866N Altcode: No abstract at ADS Title: A photoelectric focus and seeing monitor for solar telescopes Authors: Beckers, J. M. Bibcode: 1966ApOpt...5..301B Altcode: Available from http://www.opticsInfoBase.org/abstract.cfm?id=14096; Title: On the Relation Between Solar Granules and Spicules. Authors: Beckers, J. M. Bibcode: 1964ApJ...140.1339B Altcode: No abstract at ADS Title: A Study of the Fine Structures in the Solar Chromosphere Authors: Beckers, J. M. Bibcode: 1964PhDT........83B Altcode: The study of high-resolution solar disk spectroheliograms, or filtergrams, gives one an insight into the horizontal distribution of chromospheric fine structures which is hard to obtain from limb observations. The main part of this paper is concerned with such a study in the light of the Hydrogen Hα line (6562.8A) and of the Calcium K line (3933.7A).

Section 2 gives a description of the instrumentation used to secure the observations as well as some notes on observational techniques and experiences. It especially gives in detail some of the properties of the Sydney 1/8 A Hα birefringent filter.

Section 3 gives a description of the high-resolution Hα filtergrams obtained with this instrument and compares this description with those given by other authors. Details are given especially on (a) the morphology of the elongated fine mottles, which are the components of coarse mottles, (b) the spatial autocorrelation function and power spectrum for Hα +/- 0.5A filtergrams, and (c) the sytematic inflow of chromospheric matter into a sunspot (Evershed effect).

In Section 4 the elongated fine mottles are studied in more detail. The resulting properties are compared with those for spicules as studied on the limb. The following properties are found for fine mottling: (a) The width is 1.2 sec of arc, and the average length is 4.1 sec of arc. (b) The average orientation in space is vertical to the solar surface. The average angle to the vertical is 21O. (c) The average lifetime is 15 minutes. (d) The mottles are at first most visible at Hα - 0.5A, later at Hα + 0.5A, indicating a rising and falling. (e) The total number on the sun is 4 x 10^5, (f) Within the coarse mottle, the birth rate is equal to that of the solar granulation. All these properties agree with those for spicules, as far as known, except for the one under (d). There can be little doubt however that the elongated fine mottles are spicules.

Section 5 describes an attempt to measure the spectrum of such a spicule on the disk. Disk observations have the advantage of giving the source function and optical depth separately. Typical values for the optical depth and Doppler width are 1.5 and 0.5A while the source function is always lower than the intensity at the Hα - line center.

In Section 6, I computed the hydrogen spectrum of spicules under non-local thermodynamic equilibrium conditions for the Lyman α, β and γ lines, the Balmer α and β lines and the Paschen α line. At electron temperatures between 7500OK and 30,000OK, the Balmer-line emissions for limb spicules are nearly independent of electron temperature. The intensity observations give therefore a direct determination of the electron density. The Lyman-line intensities of the solar disk indicate the spicule temperature to be less than 9000OK.

Section 7 describes the appearance of K spectroheliograms. Spicules in K, as in Hα, are dark when seen on the solar disk. The Hα3 flocculi, the Hα1 grains, and the Hα3 vortex are recognized on these calcium images.

In Section 8, attention is drawn to the equality in birth rates for granules and spicules within the K flocculi, which indicates a physical relationship. Table 23 and Figure 47 summarize the terms used by the author in describing the chromospheric structures. Title: Inhomogeneities in the Evershed flow Authors: Beckers, J. M. Bibcode: 1964susp.conf..186B Altcode: No abstract at ADS Title: A study of the fine structure in the solar chromosphere Authors: Beckers, Jacques Maurice Bibcode: 1964PhDT.......100B Altcode: No abstract at ADS Title: Study of the Undisturbed Chromosphere from Ha-DISK Filtergrams, with Particular Reference to the Indentification of Spicules. Authors: Beckers, Jacques M. Bibcode: 1963ApJ...138..648B Altcode: High-resolution Ha filtergrams, made with a -81-angstrom birefringent filter, are described. A detailed study is made of the dark, fine mottles which are visible in the line wings. At low solar latitudes these dark, fine mottles have the following properties: (a) They are frequently elongated; the average length is 4'S, and the width lies between 0"7 and 1'S. (b) The average lifetime is 15.5 minutes. During the first half of their lifetime, however, they are best visible only in the violent Ha wing and during the second hall in the red wing. (c) From orientations near the solar limb they are shown to be predominantly vertical to the solar surface. (d) The total number of these mottles on the sun is found to be 4 X 1 . (e) From the spectrum, the Doppler width is found as 0.50 A, the optical depth is of the order of 5, and the source function is about 3 X 1013 erg . Mi these properties appear to agree with those expected of spicules in projection on the solar disk. There is little doubt that the mottles actually are spicules. Title: Appearance of Spicules on the Solar Disk. Authors: Beckers, Jacques M. Bibcode: 1963AJ.....68R.273B Altcode: The study of the dark fine structures visible on high resolutioi~ IIoL spectroheliograms obtained with the Sydney 1/8 A birefringent filter led to the following properties: (a) They are often elongated, the average length is 4'S compared with a width somewhere between 0.7 and 1'.'8. (b) Lifetime averages 15.5 min. (c) They are first visible mainly in the violet H~ wing, later in the red wing. (d) Near the solar limb the direction of elongation is predomii~antly radial, indicating them to be mostly vertical to the solar surface. (e) The total number on the sun is found to be 3.5 X 10~. (f) The contrast is greatest 0.5 A from the H~-line center. From the variation of the contrast with wavelength the source function, optical depth and Doppler width are found to be, respectively, 3 X 10'~ erg sr~1 cm-3 sec-', 4 and 0.50 A. All these properties correspoi~d with those known for the spicules as observed outside the solar limb. From this their identity is concluded. Title: Motions in the Chromosphere near Sunspots Authors: Beckers, J. M. Bibcode: 1962AuJPh..15..327B Altcode: No abstract at ADS Title: A search for white light flares Authors: Beckers, J. M. Bibcode: 1962Obs....82...66B Altcode: No abstract at ADS Title: The variation of the wings of the calcium K line across the solar disk Authors: Beckers, J. M. Bibcode: 1962BAN....16..133B Altcode: No abstract at ADS Title: Temperature variation on the Sun with heliographic latitude Authors: Beckers, J. M. Bibcode: 1960BAN....15...85B Altcode: No abstract at ADS