beckers

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Author name code: beckers
ADS astronomy entries on 2022-09-14
author:"Beckers, Jacques Maurice"

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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.
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.

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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.
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.

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Title: Tropospheric seeing effects on site selection and the use of
adaptive optics for solar telescopes
Authors: Beckers, Jacques M.
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.

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Title: The Effect of Tropopause Seeing on Solar Telescope Site Testing
Authors: Beckers, Jacques M.
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.

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Title: Isoplanatic patch considerations for solar telescope
multi-conjugate adaptive optics
Authors: Beckers, Jacques M.
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.

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Title: Adaptive Optics for the 8 meter Chinese Giant Solar Telescope
Authors: Beckers, Jacques; Liu, Zhong; Deng, Yuanyong; Ji, Haisheng
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 &amp; Technology and the
Beijing Normal University.

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Title: The History of the Fourier Tachometer
Authors: Beckers, J. M.; Brown, T. M.
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 &amp; 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.

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Title: Planning the 8-meter Chinese Giant Solar Telescope
Authors: Beckers, Jacques M.; Liu, Z.; Deng, Y.; Ji, H.
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.

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Title: Daytime Observations with ELTs in the Thermal Infrared Using
Laser Guide Star Adaptive Optics
Authors: Beckers, J. M.
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.

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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.
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.

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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.
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.

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Title: Optical Turbulence in High Angular Resolution Techniques
in Astronomy
Authors: Beckers, Jacques M.
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.

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Title: Pupil Slicing Adaptive Optics:. Making Extremely Large
Telescopes Diffraction Limited at Short Wavelengths
Authors: Beckers, Jacques M.
2009otam.conf..307B Altcode:
Extremely Large Telescopes (ELTs) will have aperture diameters up to
42 meters. Adaptive Optics (AO) at short wavelengths (&lt; 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.

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Title: Using the Scintillation of Extended Objects to Probe the
Lower Atmosphere
Authors: Beckers, Jacques M.
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 &amp; Moon). For Mars the height contributions F(h)
for seeing and scintillation are similar.

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Title: Laser guide stars for daytime thermal IR observations
Authors: Beckers, Jacques M.
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 &gt; 6.5 meter)
and spectral resolution (R&gt;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.

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Title: Introduction to the Discussion on: How to Mitigate the
Ground-Layer Seeing Effects at Dome C?
Authors: Beckers, J.; Travouillon, T.
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”.

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Title: On the Daytime Use of Dome C for Astronomy
Authors: Beckers, J. M.
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.

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Title: Towards the Interferometric Imaging of Red Supergiants
Authors: Ludwig, Hans-Günter; Beckers, Jacques
2008poii.conf..485L Altcode: 2008poio.conf..485L
No abstract at ADS

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Title: 1988 1993: The Final Definition of the Very Large Telescope
Interferometer, its Site and Configuration
Authors: Beckers, Jacques M.
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.

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Title: Can variable meridional flows lead to false exoplanet
detections?
Authors: Beckers, J. M.
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.

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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
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.

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Title: Effects of Foreshortening on Shallow Sub-surface Flows Observed
with Local Helioseismology
Authors: Beckers, Jacques M.
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.

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Title: From Euro50 toward a European ELT
Authors: Ardeberg, Arne; Andersen, Torben; Beckers, Jacques; Browne,
Michael; Enmark, Anita; Knutsson, Per; Owner-Petersen, Mette
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.
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.
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.
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.
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.
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.
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.
2005dsr..conf..285B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Sunspots, gravitational redshift and exo-solar planet detection
Authors: Beckers, Jacques M.
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
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
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
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
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.
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.
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.
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.
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
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 (&lt;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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
2000ESOC...57...72A Altcode: 2000elt..conf...72A
No abstract at ADS

---------------------------------------------------------
Title: Extremely large multiple mirror telescopes
Authors: Beckers, J. M.
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.
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.
1999ASPC..183..177B Altcode: 1999hrsp.conf..177B
No abstract at ADS

---------------------------------------------------------
Title: Adaptive optics in solar astronomy
Authors: Beckers, J.
1999aoa..book..235B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Site tests for CLEAR by solar scintillometry
Authors: Beckers, Jacques M.; Rutten, Robert J.
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
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.
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 (&gt; 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 (&lt; 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.
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.
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.
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
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.
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
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.
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
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.
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.
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.
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
&amp; 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.
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.
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.
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.
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.
1995itsa.conf..145B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prospects for high spatial resolution astronomy.
Authors: Beckers, J. M.
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.
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.
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
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.
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.
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.
1994IAUS..158..143B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar surface magnetism: quests for observations
Authors: Beckers, J. M.
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.
1993SPIE.1983..186B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Relation Between Scintillation and Seeing Observations
of Extended Objects
Authors: Beckers, Jacques M.
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.
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.
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.
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.
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.
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.
1992ESOC...40....1B Altcode: 1992hrsw.conf....1B
No abstract at ADS

---------------------------------------------------------
Title: Introducing the First VLT Instrument Science Teams
Authors: Beckers, J. M.
1992Msngr..68....8B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: ESO-VLT Program Status Report
Authors: Beckers, J. M.; Tarenghi, M.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1992ESOC...39..939P Altcode: 1992hrii.conf..939P
No abstract at ADS

---------------------------------------------------------
Title: Optimization of partial adaptive optics
Authors: Beckers, Jacques M.
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.
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.
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.
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.
1991Msngr..66....5B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Differential adaptive optics for astronomical interferometry
Authors: Beckers, Jacques M.
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.
1991Msngr..65...10D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interferometric imaging with the Very Large Telescope.
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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
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.
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.
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.
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
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.
1989ASIC..263..607B Altcode: 1989ssg..conf..607B
No abstract at ADS

---------------------------------------------------------
Title: Plans for high resolution imaging with the VLT.
Authors: Beckers, J. M.
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.
1989ASIC..263...43B Altcode: 1989ssg..conf...43B
No abstract at ADS

---------------------------------------------------------
Title: Cophasing Telescope Arrays
Authors: Beckers, J. M.
1989ASIC..274..355B Altcode: 1989dli..conf..355B
No abstract at ADS

---------------------------------------------------------
Title: Improving Solar Image Quality by Image Selection
Authors: Beckers, J. M.
1989ASIC..263...55B Altcode: 1989ssg..conf...55B
No abstract at ADS

---------------------------------------------------------
Title: Plan for High Resolution Imaging with the VLT.
Authors: Beckers, J. M.
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.
1989ASIC..274..365B Altcode: 1989dli..conf..365B
No abstract at ADS

---------------------------------------------------------
Title: Christian Perrier Recieves Award
Authors: Beckers, J.
1988Msngr..54...63B Altcode:
Christian Perrier Receives Award

---------------------------------------------------------
Title: Increasing the Size of the Isoplanatic Patch with
Multiconjugate Adaptive Optics
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
1988BAAS...20.1053C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interferometry with the MMT and NNTT.
Authors: Beckers, J. M.
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.
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.
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.
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: Cophasing Telescope Arrays
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
1987iia..conf..171B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Economy figure of merit for large telescope sites.
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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
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
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.
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.
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.
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.
1985BAAS...17R.571B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Contributions by R.G. Giovanelli to Solar Instrumentation
Authors: Beckers, J. M.
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.
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.
1985spit.conf..758H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Future techniques and instrumentation in solar-stellar physics
Authors: Beckers, J. M.
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.
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.
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.
1984BAAS...16Q.517S Altcode: 1984BAAS...16..517S
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Imaging of Spectroscopic Binaries
Authors: Beckers, J. M.
1984BAAS...16..498B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A solar Lyman alpha coronagraph.
Authors: Beckers, J. M.; Argo, H. V.
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.
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.
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.
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.
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.
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.
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, &lt;VR2
sin i&gt;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.
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.
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.
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.
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: 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.
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.
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.
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.
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.
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.
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.
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.
1982BAAS...14R.918B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The solar beacon, an experiment in solar astrometry.
Authors: Beckers, J. M.
1982AcOpt..29..913B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Differential speckle interferometry.
Authors: Beckers, J. M.
1982AcOpt..29..361B Altcode: 1982JMOp...29..361B
No abstract at ADS

---------------------------------------------------------
Title: Experiments with the Multiple Mirror Telescope.
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
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.
1982tsef.conf...11A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of the solar photosphere.
Authors: Beckers, J. M.
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.
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.
1981BAAS...13..890B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Multiple Mirror Telescope Observatory, Tucson, Arizona
85721. Report.
Authors: Beckers, J. M.
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.
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.
1981BAAS...13..490B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermography of the MMT.
Authors: Beckers, J. M.; Ulich, B. L.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1980fsoo.conf..279B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar circulation measurements: consideration and plans
Authors: Beckers, J. M.; Brown, T. M.
1980fsoo.conf..189B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The MMT as it Exists Today
Authors: Beckers, J.; Williams, J.
1980oits.conf..108B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Examples of non-thermal motions as seen on the sun
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
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.
1979JOSA...69.1436B Altcode: 1979OSAJ...69.1436B
No abstract at ADS

---------------------------------------------------------
Title: Some thoughts on the Large European Solar Telescope.
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
1979MmArc.106..245D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Is there a solar polar vortex?
Authors: Beckers, J. M.
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.
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.
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.
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.
1978BAAS...10..430B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Some thoughts on the large european solar telescope
Authors: Beckers, J. M.
1978fsoo.conf..279B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar circulation measurements: consideration and plans
Authors: Beckers, J. M.; Brown, T. M.
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.
1977ApJ...217L..69B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Limb Effect.
Authors: Beckers, J. M.
1977BAAS....9..616B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Alfvén waves in the corona above sunspots.
Authors: Beckers, J. M.; Schneeberger, T. J.
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.
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.
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.
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.
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.
1976BAAS....8..501P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic fields in the solar atmosphere
Authors: Beckers, J. M.
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.
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.
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.
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.
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.
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.
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.
1976pmas.conf..291C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spatially resolved motions in stellar atmospheres
Authors: Beckers, J. M.; Canfield, R. C.
1976pmas.conf..207B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic fields in the solar atmosphere.
Authors: Beckers, J. M.
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.
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.
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.
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.
1975BAAS....7Q.459B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The compression of data resulting from photon counters.
Authors: Beckers, J. M.
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.
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.
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.
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
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
1975SoPh...40...65M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A search for deuterium on the sun.
Authors: Beckers, J. M.
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.
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.
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.
1974IAUS...56...45D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Profile and Polarization of the Coronal Lα Line
Authors: Beckers, Jacques M.; Chipman, Eric
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 (&gt;
70 G).

---------------------------------------------------------
Title: Spatial and Spectral Structure of Chromospheric Lines
Authors: Pasachoff, J. M.; Harris, F. S.; Beckers, J. M.
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.
1974sppp.book.....B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The next decade in observational solar research.
Authors: Beckers, J. M.
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.
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.
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.
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.
1973BAAS....5T.275L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sacramento Peak Observatory Universal Birefringent Filter
Authors: Beckers, J. M.
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.
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.
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.
1973IAUTA..15...75J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oscillatory Motions in Sunspots
Authors: Beckers, J. M.; Schultz, R. B.
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.
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.
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.
1972BAAS....4T.377B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oscillatory Phenomena in Sunspots
Authors: Beckers, J. M.; Schultz, R. B.
1972BAAS....4S.377B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Spicules
Authors: Beckers, Jacques M.
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.
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 (&gt;5%) polarization.

---------------------------------------------------------
Title: The Measurement of Solar Magnetic Fields
Authors: Beckers, J. M.
1971IAUS...43....3B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Achromatic linear retarders.
Authors: Beckers, J. M.
1971ApOpt..10..973B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The use of colored photographic images in photographic
subtraction.
Authors: Beckers, J. M.
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.
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.
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.
1970BAAS....2R.182B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Narrow band filters based on magnetooptical effects
Authors: Beckers, Jacques M.
1970ApOpt...9..595B Altcode:
Available from <A
href="http://www.opticsInfoBase.org/abstract.cfm?id=16268;">http://www.opticsInfoBase.org/abstract.cfm?id=16268;</A>

---------------------------------------------------------
Title: A photographic polarimeter for solar observations.
Authors: Beckers, J. M.; Wagner, W. J.
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.
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.
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.
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.
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 (&gt;5000 km) are eliminated.

---------------------------------------------------------
Title: The Interpretation of Velocity Filtergrams. I: The Effective
Depth of Line Formation
Authors: Parnell, R. L.; Beckers, J. M.
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.
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.
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.
1969SoPh....7...22B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Magnetic-Field Measurements using Babinet Compensators
Authors: Beckers, J. M.; Stenflo, J. O.
1969SoPh....6..480B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The microstructure of sunspots
Authors: Beckers, J. M.
1969pia..conf..139B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The microstructure of sunspots.
Authors: Beckers, J. M.
1969misu.book.....B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Photospheric Brightness Differences Associated with the
Solar Supergranulation
Authors: Beckers, Jacques M.
1968SoPh....5..309B Altcode:
The large scale (&gt; 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.
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.
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.
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.
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&gt;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.
1968SoPh....4..165B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Spicules (Invited Review Paper)
Authors: Beckers, J. M.
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.
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.
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.
1968IAUS...35..178B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Cinematography of Solar Oscillations.
Authors: Beckers, J. M.
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.
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.
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.
1966AJ.....71..866N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A photoelectric focus and seeing monitor for solar telescopes
Authors: Beckers, J. M.
1966ApOpt...5..301B Altcode:
Available from <A
href="http://www.opticsInfoBase.org/abstract.cfm?id=14096;">http://www.opticsInfoBase.org/abstract.cfm?id=14096;</A>

---------------------------------------------------------
Title: On the Relation Between Solar Granules and Spicules.
Authors: Beckers, J. M.
1964ApJ...140.1339B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Study of the Fine Structures in the Solar Chromosphere
Authors: Beckers, J. M.
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.

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Title: Inhomogeneities in the Evershed flow
Authors: Beckers, J. M.
1964susp.conf..186B Altcode:
No abstract at ADS

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Title: A study of the fine structure in the solar chromosphere
Authors: Beckers, Jacques Maurice
1964PhDT.......100B Altcode:
No abstract at ADS

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Title: Study of the Undisturbed Chromosphere from Ha-DISK Filtergrams,
with Particular Reference to the Indentification of Spicules.
Authors: Beckers, Jacques M.
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.

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Title: Appearance of Spicules on the Solar Disk.
Authors: Beckers, Jacques M.
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.

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Title: Motions in the Chromosphere near Sunspots
Authors: Beckers, J. M.
1962AuJPh..15..327B Altcode:
No abstract at ADS

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Title: A search for white light flares
Authors: Beckers, J. M.
1962Obs....82...66B Altcode:
No abstract at ADS

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Title: The variation of the wings of the calcium K line across the
solar disk
Authors: Beckers, J. M.
1962BAN....16..133B Altcode:
No abstract at ADS

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Title: Temperature variation on the Sun with heliographic latitude
Authors: Beckers, J. M.
1960BAN....15...85B Altcode:
No abstract at ADS