explanation blue bibcodes open ADS page with paths to full text
Author name code: hammerschlag
ADS astronomy entries on 2022-09-14
author:"Hammerschlag, Robert H."
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Title: Micro-meteorological contribution to the SHABAR seeing
retrieval
Authors: Hartogensis, Oscar; Hammerschlag, Robert; Sliepen, Guus;
Sprung, Detlev; von der Lühe, Oskar; Collados, Manuel
2017psio.confE.102H Altcode:
No abstract at ADS
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Title: SOLARNET WP70: Fully open-foldable dome cool in Sinshine:
Fast temperature equilibrium and no heat production
Authors: Hammerschlag, R.
2017psio.confE..97H Altcode:
No abstract at ADS
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Title: Completely open-foldable domes remaining cool in sunshine
Authors: Hammerschlag, Robert H.; Deelen, Sander; Hoogendoorn, Pieter
W.; Kommers, Johannes N. M.; Sonner, Thomas; Simoes, Roberto; Grassin,
Olivier; Fischer, Andreas; Visser, Simon; Thewissen, Kristof
2016SPIE.9912E..1EH Altcode:
These open-foldable very light-weight domes, based on very strong
textile membranes highly tensioned between steel bows, are designed for
bad-weather protection and maintenance of instruments for astronomical,
meteorological and civil-engineering measurements and have extremely
high wind stability. The domes of the GREGOR telescope and the
Dutch Open Telescope are the two existing prototypes. Improvements
were developed with all parts light-colored to remain cool in solar
light. The new specially made connection parts (eyes) between the
textile parts are made from white-colored PETP, a very strong and
UV-stable synthetic, and have a better geometrical shape giving
higher stability. The rubber seal tubes on top of the dome were of
black-colored chloride rubber CR (neoprene), strong and UV stable,
but very warm in sunlight. New UV-stable EPDM rubber tubes were
produced in natural light color. To get this rubber stiff enough to
give good sealing, a black-colored stiff EPDM rubber is put inside the
light-colored one. Tests were performed and the forces necessary for
compression of the rubber tubes were measured. An inside black tube with
a circa 1.3 times larger compression force than the original black tubes
was applied. The assembling of the black tubes into the light-colored
tubes was successfully applied at the DOT and GREGOR domes.
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Title: Transmission profile of the Dutch Open Telescope Hα Lyot
filter
Authors: Koza, J.; Hammerschlag, R. H.; Rybák, J.; Gömöry, P.;
Kučera, A.; Schwartz, P.
2014AN....335..409K Altcode: 2017arXiv171209253K
Context Accurate knowledge of the spectral transmission profile of
a Lyot filter is important, in particular in comparing observations
with simulated data. The paper summarizes available facts about the
transmission profile of the Dutch Open Telescope (DOT) Hα Lyot filter
pointing to a discrepancy between sidelobe-free Gaussian-like profile
measured spectroscopically and signatures of possible leakage of
parasitic continuum light in DOT Hα images. We compute wing-to-center
intensity ratios resulting from convolutions of Gaussian and square
of the sinc function with the Hα atlas profile and compare them with
the ratios derived from observations of the quiet Sun chromosphere at
disk center. We interpret discrepancies between the anticipated and
observed ratios and the sharp limb visible in the DOT Hα image as an
indication of possible leakage of parasitic continuum light. A method
suggested here can be applied also to indirect testing of transmission
profiles of other Lyot filters. We suggest two theoretical transmission
profiles of the DOT Hα Lyot filter which should be considered as the
best available approximations. Conclusive answer can only be given by
spectroscopic re-measurement of the filter.
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Title: Kees Zwaan, open principle, future of high-resolution solar
telescopes
Authors: Hammerschlag, R. H.; Bettonvil, F. C. M.
2013ASPC..470..381H Altcode:
It was around the 1970s that during site-test campaigns masts were
erected up till 30 m height with sensors at several heights for the
measurement of temperature fluctuations. Kees Zwaan discovered that
the fluctuations decrease drastically at heights from about 15 m and
upward when there is some wind. The conclusion from this experience
was the open telescope principle: a telescope completely free in the
air 15 m or more above the ground. The Dutch Open Telescope (DOT)
was the pioneering demonstrator of the open-telescope technology. Now
that larger high-resolution telescopes come in view, it is time to
analyze again the principle: the essentials for proper working of the
open principle and the design consequences for the new generation of
high-resolution solar telescopes.
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Title: Open-foldable domes with high-tension textile membranes:
The GREGOR dome
Authors: Hammerschlag, R. H.; Kommers, J. N.; Visser, S.; Bettonvil,
F. C. M.; van Schie, A. G. M.; van Leverink, S. J.; Sliepen, G.;
Jägers, A. P. L.; Schmidt, W.; Volkmer, R.
2012AN....333..830H Altcode:
Double layers of high-tensioned textile membranes were applied to the
completely open-foldable dome for the GREGOR telescope for the first
time. Simultaneous climate measurements inside and outside the dome
have proven the thermal-insulating capability of this double-layer
construction. The GREGOR dome is the result of the continuation of the
ESO research on open-foldable domes with textile structures, followed by
the research for the DOT dome with high-tensioned textile membranes. It
cleared the way to extreme stability required for astronomical practice
on high mountain sites with heavy storms and ice formation. The storm
Delta with 245 km/h 1-minute mean maximum at the location of the GREGOR
caused no problems, nor did other storms afterwards. Opening and closing
experiences up to wind speeds of 90 km/h were without problems. New
technical developments were implemented and tested at the GREGOR dome,
opening the way for application to much larger domes up to the 30 m
diameter-class range.
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Title: The GREGOR dome, pathfinder for the EST dome
Authors: Hammerschlag, Robert H.; Kommers, Johannes N.; Visser,
Simon; Bettonvil, Felix C. M.; van Schie, Anton G. M.; van Leverink,
Simon J.; Sliepen, Guus; Jägers, Aswin P. L.
2012SPIE.8450E..07H Altcode:
The completely open-foldable dome of the GREGOR telescope is a further
development of the DOT dome, respectively 9 and 7 meter in diameter. New
technical developments are implemented and tested at the GREGOR dome,
that are important for the design of the much larger dome for the
EST, which will be 28 meter in diameter. The GREGOR dome is the first
with more than one clamp working simultaneously for closing the dome
and bringing the membranes on the required high tension for storm
resistance. The storm Delta with 245 km/h 1-minute mean maximum
at the location of the GREGOR gave no problems nor did the storms
afterwards. Opening and closing experiences are up to wind speeds of
90 km/h without problems. Good observing circumstances never occur
with higher wind speeds. A double layer of membranes is applied in
the GREGOR construction whereas the DOT dome is equipped with a single
layer. Simultaneous climate measurements inside and outside the dome
have proven the thermal-insulation capability of this double-layer
construction. The experiences with the GREGOR showed that the elongation
by tensioning of the prestrained membrane material is much lower than
originally expected. In the meantime, more strong and stiff membrane
material is available and applied in the EST design. As a consequence,
the clamps of the EST can have a relatively much shorter length and
there is no need anymore for simultaneous operation of the clamps and
the main actuators in low speed with help of a frequency inverter. The
clamps can close after the main bow operation is finished, which
simplifies the electrical control.
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Title: Large-field high-resolution mosaic movies
Authors: Hammerschlag, Robert H.; Sliepen, Guus; Bettonvil, Felix
C. M.; Jägers, Aswin P. L.; Sütterlin, Peter; Martin, Sara F.
2012SPIE.8444E..06H Altcode:
Movies with fields-of-view larger than normal for high-resolution
telescopes will give a better understanding of processes on the
Sun, such as filament and active region developments and their
possible interactions. New active regions can influence, by their
emergence, their environment to the extent of possibly serving
as an igniter of the eruption of a nearby filament. A method to
create a large field-of-view is to join several fields-of-view into
a mosaic. Fields are imaged quickly one after another using fast
telescope-pointing. Such a pointing cycle has been automated at the
Dutch Open Telescope (DOT), a high-resolution solar telescope located
on the Canary Island La Palma. The observer can draw with the computer
mouse the desired total field in the guider-telescope image of the
whole Sun. The guider telescope is equipped with an H-alpha filter and
electronic enhancement of contrast in the image for good visibility of
filaments and prominences. The number and positions of the subfields
are calculated automatically and represented by an array of bright
points indicating the subfield centers inside the drawn rectangle of
the total field on the computer screen with the whole-sun image. When
the exposures start the telescope repeats automatically the sequence of
subfields. Automatic production of flats is also programmed including
defocusing and fast motion over the solar disk of the image field. For
the first time mosaic movies were programmed from stored information
on automated telescope motions from one field to the next. The mosaic
movies fill the gap between whole-sun images with limited resolution
of synoptic telescopes including space instruments and small-field
high-cadence movies of high-resolution solar telescopes.
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Title: The Irkutsk Barium filter for narrow-band wide-field
high-resolution solar images at the Dutch Open Telescope
Authors: Hammerschlag, Robert H.; Skomorovsky, Valery I.; Bettonvil,
Felix C. M.; Kushtal, Galina I.; Olshevsky, Vyacheslav L.; Rutten,
Robert J.; Jägers, Aswin P. L.; Sliepen, Guus; Snik, Frans
2010SPIE.7735E..85H Altcode: 2010SPIE.7735E.265H
A wide-field birefringent filter for the barium II line at 455.4nm is
developed in Irkutsk. The Barium line is excellent for Doppler-shift
measurements because of low thermal line-broadening and steep
flanks of the line profile. The filter width is 0.008nm and the
filter is tunable over 0.4nm through the whole line and far enough
in the neighboring regions. A fast tuning system with servomotor is
developed at the Dutch Open Telescope (DOT). Observations are done
in speckle mode with 10 images per second and Keller-VonDerLühe
reconstruction using synchronous images of a nearby bluecontinuum
channel at 450.5nm. Simultaneous observation of several line positions,
typically 3 or 5, are made with this combination of fast tuning and
speckle. All polarizers are birefringent prisms which largely reduced
the light loss compared to polarizing sheets. The advantage of this
filter over Fabry-Perot filters is its wide field due to a large
permitted entrance angle and no need of polishing extremely precise
surfaces. The BaII observations at the DOT occur simultaneously with
those of a fast-tunable birefringent H-alpha filter. This gives the
unique possibility of simultaneous speckle-reconstructed observations
of velocities in photosphere (BaII) and chromosphere (H-alpha).
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Title: Mechanical design of a completely open-foldable dome for EST
Authors: Hammerschlag, Robert H.; Kommers, Johannes N. M.; van
Leverink, Simon J.; Bettonvil, Felix C. M.; Visser, Simon; Jägers,
Aswin P. L.; Sliepen, Guus
2010SPIE.7733E..0JH Altcode:
In the context of the EST design study for a 4m-class solar
telescope and a study for large open-foldable domes of the Dutch
Technology Foundation STW, a design is made for the 20 to 30m diameter
range. Detailed designs are made for three specific diameter sizes:
23, 28 and 33m. Smaller-size open-foldable domes based on tensioned
cloth and in use at the Dutch Open Telescope (7m) and the GREGOR (9m)
have proven to be all-weather stable and very effective for good seeing
conditions for solar telescopes. The cloth has shown no degradation
over the past 14 (DOT) resp. 6 (GREGOR) years of experience and no
permanent elongation with the frequent de-tensioning and tensioning
during opening and closing. The application of cloth permits a dome
design leaving, when opened, the telescope completely free without
any structure over the telescope and no massive structures besides
or under it. Basis for the new design is the available prestretched
stable cloth, which is nowadays produced in much stronger qualities than
used for DOT and GREGOR. The larger curvature radius requires larger
tension in the cloth, but combination with stronger cloth fits for the
upscaling. Calculations show that the steel construction geometries
of the GREGOR dome can be upscaled with a few adjustments. Bearings
and drives remain within normal sizes. Cost calculations show that
open-foldable domes of this size are remarkably lower in price than
closed domes. In addition, an interesting option is presented for a
semi-transparent windshield of which the position can be adapted to the
wind direction. This shield gives an effective wind protection of the
region around the primary mirror without disturbing the wind flows above
the shield and without stagnant air or big eddies behind it. It is storm
safe and the costs are only a fraction of the open-foldable dome costs.
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Title: The pier and building of the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Codina, R.; Gómez Merchán, A.;
Hammerschlag, R. H.; Hartman, J. J. M.; Hernández Suárez, E.;
Jägers, A. P. L.; Murga Llano, G.; Pelser, J. W.; Sliepen, G.
2010SPIE.7733E..34B Altcode: 2010SPIE.7733E..97B
EST (European Solar Telescope) is a 4-m class solar telescope, which
is currently in the conceptual design phase. EST will be located in
the Canary Islands and will aim at high spectral, spatial and temporal
resolution observations in the photosphere and chromosphere, using
a suite of instruments that can produce efficiently two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic
properties of the plasma over many scale heights. The pier is defined as
the construction that supports the telescope and the enclosure. It needs
a certain height to minimize daytime ground turbulence. At the bottom of
the pier a large instrument lab is located, 16 m in diameter and 10 m
high. To the pier is attached a service building that accommodates all
auxiliary services, possibly together with a separate building. Solid
concrete- and open framework piers are compared, in terms of stability,
thermal properties and flow characteristics and building structures
in terms of construction issues. FE and CFD analysis are used to give
qualitative insight in the differences between the alternatives. The
preferred alternative is a cone shaped pier surrounded by an open
framework.
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Title: Foldable dome climate measurements and thermal properties
Authors: Sliepen, Guus; Jägers, Aswin P. L.; Hammerschlag, Robert H.;
Bettonvil, Felix C. M.
2010SPIE.7733E..32S Altcode: 2010SPIE.7733E..95S
As part of a larger project for measuring various aspects of foldable
domes in the context of EST and with support of the Dutch Technology
Foundation STW, we have collected over a year of continuous temperature
and humidity measurements, both inside and outside the domes of the
Dutch Open Telescope (DOT) on La Palma<SUP>5</SUP> and the GREGOR
telescope on Tenerife.<SUP>6</SUP> In addition, we have measured the
wind field around each dome. Although the structure of both domes is
similar, the DOT dome has a single layer of cloth, and is situated on
top of an open tower. In contrast, the GREGOR dome has a double layer
of cloth, and is situated on top of a tower-shaped building. These
differences result in large differences in temperature and humidity
insulation when the dome is closed. We will present the changes in
temperature and humidity one can expect for each dome within one day,
and the statistics for the variations throughout a year. In addition,
we will show that the main advantage of a foldable dome is the near
instantaneous equilibration of the air inside the volume originally
enclosed by the dome and that of the environment outside the dome. This
property allows one to operate a telescope without needing expensive
air conditioning and dome skin temperature control in order to limit
dome and shell seeing effects. The measurements give also information
about the weather fluctuations at the sites of the domes. It was
observed that on small time scales the temperature fluctuations are
significantly greater during the day than during the night.
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Title: Seeing measurements with autonomous, short-baseline shadow
band rangers
Authors: Sliepen, Guus; Jägers, Aswin P. L.; Bettonvil, Felix C. M.;
Hammerschlag, Robert H.
2010SPIE.7733E..4LS Altcode: 2010SPIE.7733E.144S
There is growing interest in measuring seeing at existing and
prospective telescope sites. Several methods exist to quantify seeing,
one among them is by measuring the scintillation of solar or lunar
light using a photodiode. A shadow band ranger (SHABAR) analyses the
covariance of the signals from an array of such photodiodes, which
allows for the spatial resolution of the index of refraction above
the SHABAR device. This allows one to estimate the index of refraction
structure parameter as a function of height, C<SUP>2</SUP>n(h). Although
a SHABAR has a limited range compared to a differential image motion
monitor (DIMM) or the latest wavefront sensors, the advantage is that it
does not need telescope optics to work. A SHABAR device can be made very
compact and can operate independent of other instruments. We describe
the design of such a SHABAR device with six photodiodes that can
operate virtually indefinitely without requiring human intervention. An
inversion algorithm is used to convert the raw scintillation signals of
the photodiodes to the desired C<SUP>2</SUP>n(h) profile and a value for
the Fried parameter r0 at height zero. We show that it is possible to
perform inversions of 10 s periods in real time on relatively low-end
hardware, such as an Intel Atom based computer, which allows the results
to be presented live to astronomers, who can use this information to
help make decisions about their observation schedule.
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Title: The enclosure for the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Codina, R.; Hammerschlag, R. H.;
Jägers, A. P. L.; Kommers, J. N. M.; van Leverink, S. J.; Sliepen,
G.; Visser, S.
2010SPIE.7733E..33B Altcode: 2010SPIE.7733E..96B
The European Solar Telescope (EST) is a 4-m class solar telescope, which
is currently in the conceptual design phase. EST will be located in the
Canary Islands and aims at observations with high spectral, spatial and
temporal resolution of the solar photosphere and chromosphere. The main
purpose of the enclosure is to protect the telescope and instruments
from severe weather conditions. An enclosure is also often needed for
reducing wind buffeting on the telescope and primary mirror cell, but
on the other hand enclosures are generally considered to degrade local
seeing. In this contribution we will present the conceptual design
of the enclosure for EST. Two different concepts have been studied
in more detail: the first being a dome concept with vent gates to
enhance local flushing, the other being a retractable enclosure, with
an optional windshield. Technically both alternatives seem feasible,
but we conclude that the retractable enclosure is the less risky
solution, since it allows easier local seeing control and allows
the use of a reflecting heat stop in the primary focus. A windshield
is effective in reducing wind load on the primary mirror; although
preliminary analysis indicate that there are feasible solutions to
keep the deformation caused by wind buffeting within the requirements.
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Title: Open Principle for Large High-Resolution Solar Telescopes
Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Jägers,
Aswin P. L.; Sliepen, Guus
2009EM&P..104...83H Altcode: 2008EM&P..tmp...38H
Vacuum solar telescopes solve the problem of image deterioration
inside the telescope due to refractive index fluctuations of the air
heated by the solar light. However, such telescopes have a practical
diameter limit somewhat over 1 m. The Dutch Open Telescope (DOT) was the
pioneering demonstrator of the open-telescope technology without need
of vacuum, now pursued in the German GREGOR. Important ingredients for
this technology are primary beam completely open to natural wind flow,
stiff but still open design by principal stiff overall geometries in
combination with carefully designed joints and completely open-foldable
dome constructions based on tensioned strong cloth. Further developments
to large sizes are made within the framework of the design study for
a European Solar Telescope (EST).
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Title: Large fully retractable telescope enclosures still closable
in strong wind
Authors: Bettonvil, Felix C. M.; Hammerschlag, Robert H.; Jägers,
Aswin P. L.; Sliepen, Guus
2008SPIE.7018E..1NB Altcode: 2008SPIE.7018E..52B
Two prototypes of fully retractable enclosures with diameters of 7 and
9 m have been built for the high-resolution solar telescopes DOT (Dutch
Open Telescope) and GREGOR, both located at the Canary Islands. These
enclosures protect the instruments for bad weather and are fully open
when the telescopes are in operation. The telescopes and enclosures
also operate in hard wind. The prototypes are based on tensioned
membrane between movable but stiff bows, which fold together to a ring
when opened. The height of the ring is small. The prototypes already
survived several storms, with often snow and ice, without any damage,
including hurricane Delta with wind speeds up to 68 m/s. The enclosures
can still be closed and opened with wind speeds of 20 m/s without any
problems or restrictions. The DOT successfully demonstrated the open,
wind-flushing concept for astronomical telescopes. It is now widely
recognized that also large future telescopes benefit from wind-flushing
and retractable enclosures. These telescopes require enclosures with
diameters of 30 m until roughly 100 m, the largest sizes for the ELTs
(Extreme Large Telescopes), which will be built in the near future. We
discuss developments and required technology for the realization of
these large sizes.
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Title: Contactless sub-millimeter displacement measurements
Authors: Sliepen, Guus; Jägers, Aswin P. L.; Bettonvil, Felix C. M.;
Hammerschlag, Robert H.
2008SPIE.7018E..1CS Altcode: 2008SPIE.7018E..41S
Weather effects on foldable domes, as used at the DOT and GREGOR, are
investigated, in particular the correlation between the wind field and
the stresses caused to both metal framework and tent clothing. Camera
systems measure contactless the displacement of several dome points. The
stresses follow from the measured deformation pattern. The cameras
placed near the dome floor do not disturb telescope operations. In
the set-ups of DOT and GREGOR, these cameras are up to 8 meters away
from the measured points and must be able to detect displacements of
less than 0.1 mm. The cameras have a FireWire (IEEE1394) interface
to eliminate the need for frame grabbers. Each camera captures
15 images of 640 × 480 pixels per second. All data is processed
on-site in real-time. In order to get the best estimate for the
displacement within the constraints of available processing power,
all image processing is done in Fourier-space, with all convolution
operations being pre-computed once. A sub-pixel estimate of the peak
of the correlation function is made. This enables to process the
images of four cameras using only one commodity PC with a dual-core
processor, and achieve an effective sensitivity of up to 0.01 mm. The
deformation measurements are well correlated to the simultaneous wind
measurements. The results are of high interest to upscaling the dome
design (ELTs and solar telescopes).
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Title: Cornelis Zwaan, open principle, and the future of
high-resolution solar telescopes
Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Jägers,
Aswin P. L.; Sliepen, Guus
2008SPIE.7012E..0MH Altcode: 2008SPIE.7012E..20H
It was in the years around 1970 that during site-test campaigns for
JOSO masts were erected up till 30 m height with sensors at several
heights for the measurement of temperature fluctuations. Cornelis
(Kees) Zwaan discovered that the fluctuations decrease drastically
at heights from about 15 m and upward when there is some wind. The
conclusion from this experience was the open telescope principle: the
telescope should be completely free in the air 15 m or more above the
ground. The Dutch Open Telescope (DOT) was the pioneering demonstrator
of the open-telescope technology. Now that larger high-resolution
telescopes come in view, it is time to analyze again the principle:
(i) the essentials for proper working of the open principle; (ii)
the differences with nighttime observations particularly concerning
the seeing; (iii) the design consequences for the new generation of
high-resolution solar telescopes.
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Title: Fast foldable tent domes
Authors: Jägers, Aswin P. L.; Sliepen, Guus; Bettonvil, Felix C. M.;
Hammerschlag, Robert H.
2008SPIE.7018E..1RJ Altcode: 2008SPIE.7018E..56J
In the near future ELTs (Extreme Large Telescopes) will be
built. Preferably these telescopes should operate without
obstructions in the near surrounding to reach optimal seeing
conditions and avoid large turbulences with wind-gust accelerations
around large obstacles. This applies also to future large solar
telescopes. At present two foldable dome prototypes have been
built on the Canary Islands: the Dutch Open Telescope (DOT, La
Palma) and the GREGOR Telescope (Tenerife), having a diameter of
7 and 9 meter, respectively. The domes are usually fully retracted
during observations. The research consists of measurements on the two
domes. New camera systems are developed and placed inside the domes for
precise dome deformation measurements within 0.1 mm over the whole dome
size. Simultaneously, a variety of wind-speed and -direction sensors
measure the wind field around the dome. In addition, fast sensitive
air-pressure sensors placed on the supporting bows measure the wind
pressure. The aim is to predict accurately the expected forces and
deformations on up-scaled, fully retractable domes to make their
construction more economically. The dimensions of 7 and 9 meter are
large enough for realistic on-site tests in gusty wind and will give
much more information than wind tunnel experiments.
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Title: Aperture Increase Options for the Dutch Open Telescope
Authors: Hammerschlag, R. H.; Bettonvil, F. C. M.; Jägers, A. P. L.;
Rutten, R. J.
2007ASPC..368..573H Altcode: 2007astro.ph..3638H
This paper is an invitation to the international community to
participate in the usage and a substantial upgrade of the Dutch Open
Telescope on La Palma (DOT, http://dot.astro.uu.nl). <P />We first
give a brief overview of the approach, design, and current science
capabilities of the DOT. It became a successful 0.2-arcsec-resolution
solar movie producer through its combination of (i) an excellent
site, (ii) effective wind flushing through the fully open design and
construction of both the 45-cm telescope and the 15-m support tower,
(iii) special designs which produce extraordinary pointing stability of
the tower, equatorial mount, and telescope, (iv) simple and excellent
optics with minimum wavefront distortion, and (v) large-volume
speckle reconstruction including narrow-band processing. The DOT's
multi-camera multi-wavelength speckle imaging system samples the
solar photosphere and chromosphere simultaneously in various optical
continua, the G band, Ca II H (tunable throughout the blue wing),
and Hα (tunable throughout the line). The resulting DOT data sets
are all public. The DOT database (http://dotdb.phys.uu.nl/DOT)
now contains many tomographic image sequences with 0.2-0.3 arcsec
resolution and up to multi-hour duration. You are welcome to pull them
over for analysis. <P />The main part of this contribution outlines
DOT upgrade designs implementing larger aperture. The motivation
for aperture increase is the recognition that optical solar physics
needs the substantially larger telescope apertures that became useful
with the advent of adaptive optics and viable through the DOT's open
principle, both for photospheric polarimetry at high resolution and
high sensitivity and for chromospheric fine-structure diagnosis at
high cadence and full spectral sampling. <P />Our upgrade designs for
the DOT are presented in an incremental sequence of five options of
which the simplest (Option I) achieves 1.4 m aperture using the present
tower, mount, fold-away canopy, and multi-wavelength speckle imaging
and processing systems. The most advanced (Option V) offers unblocked
2.5 m aperture in an off-axis design with a large canopy, a wide 30-m
high support tower, and image transfer to a groundbased optics lab for
advanced instrumentation. All five designs employ adaptive optics. The
important advantages of fully open, wind-transparent and wind-flushed
structure, polarimetric constancy, and absence of primary-image rotation
remain. All designs are relatively cheap through re-using as much of
the existing DOT hardware as possible. <P />Realization of an upgrade
requires external partnership(s). This report about DOT upgrade options
therefore serves also as initial documentation for potential partners.
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Title: Towers for Antarctic Telescopes
Authors: Hammerschlag, R. H.; Bettonvil, F. C. M.; Jägers, A. P. L.;
Nielsen, G.
2007EAS....25..265H Altcode:
To take advantage of the exceptional seeing above the boundary layer
on Antarctic sites, a high-resolution telescope must be mounted on
a support tower. An open transparent tower of framework minimizes
the upward temperature-disturbed airflow. A typical minimum height is
30m. The tower platform has to be extremely stable against wind-induced
rotational motions, which have to be less than fractions of an arc
second, unusually small from a mechanical engineering viewpoint. In
a traditional structure, structural deflections result in angular
deflections of the telescope platform, which introduce tip and tilt
motions in the telescope. However, a structure that is designed to
deflect with parallel motion relative to the horizontal plane will
undergo solely translation deflections in the telescope platform and
thus will not degrade the image. The use of a parallel motion structure
has been effectively demonstrated in the design of the 15-m tower
for the Dutch Open Telescope (DOT) on La Palma. Special framework
geometries are developed, which make it possible to construct high
towers in stories having platforms with extreme stability against
wind-induced tilt. These geometric solutions lead to constructions,
being no more massive than a normal steel framework carrying the
same load. Consequently, these lightweight towers are well suited to
difficult sites as on Antarctica. A geometry with 4 stories has been
worked out.
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Title: The Ba II 4554 / Hβ Imaging Polarimeter for the Dutch Open
Telescope
Authors: Snik, F.; Bettonvil, F. C. M.; Jägers, A. P. L.;
Hammerschlag, R. H.; Rutten, R. J.; Keller, C. U.
2006ASPC..358..205S Altcode:
In order to expand the high-resolution, multi-wavelength imaging
capabilities of the Dutch Open Telescope (DOT), an additional
polarimetric channel based on a 80 mÅ tunable Lyot filter for Ba
II 4554 and Hβ has been designed and constructed. The large atomic
mass and the resulting steep line wings, make Ba II 4554 particularly
suitable for the creation of photospheric Dopplergrams and Stokes-V
magnetograms. The line also yields a significant degree of linear
(scattering) polarization for observations near the limb of the Sun,
which is modified by both horizontal and vertical weak-field topologies
through the Hanle effect and hyperfine-structure level crossing. The
polarimeter is based on liquid crystal variable retarders (LCVRs)
as polarization modulators in combination with the Lyot filter's
entrance polarizer. The tunability of the LCVRs is exploited to enable
specific wavelength calibration, selection of the reference frame of
linear polarization, and optimization of instrumental polarization
cross-talk, which for the DOT is constant in time. With the future
Ba II 4554 photospheric magnetograms, we expect to be able to discern
magnetic structures of about 150 km with field strengths down to 100 G,
and that Hanle-type observations can be performed at a resolution of
about 1 arcsec. The range of applicability of Hβ imaging polarimetry
has to be explored after installation.
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Title: Tunable H-alpha Lyot filter with advanced servo system and
image processing: instrument design and new scientific results with
the Dutch Open Telescope
Authors: Bettonvil, Felix C. M.; Hammerschlag, Robert H.; Sütterlin,
Peter; Rutten, Robert J.; Jägers, Aswin P. L.; Sliepen, Guus
2006SPIE.6269E..0EB Altcode: 2006SPIE.6269E..12B
The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma
is a revolutionary open solar telescope, on an excellent site, on
top of a transparent tower of steel framework, and uses natural
air flow to minimize local seeing. The DOT is a high-resolution
multi-wavelength imager capable of long-duration time series aiming
at magnetic fine structure, topology and dynamics in the photosphere
and low- and high chromosphere. In this paper we describe the latest
addition to the multi-wavelength imaging system: a Lyot H-alpha
camera channel operating at a wavelength of 656.3 nm, being of major
interest for high-chromospheric phenomena. The channel is operated
strictly synchronous with the other channels and all data are speckle
reconstructed. The channel permits profile sampling and delivers
Dopplergrams in a 15 second time cadence, up to several hours long
and adding up to a total data amount of 1.6 Terabyte/day. A dedicated
computer (DSP, DOT Speckle Processor) has been built for processing
the data overnight.
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Title: Concept study and validation of Antarctic telescope tower
Authors: Lanford, Ephraim; Swain, Mark; Meyers, Catherine; Muramatsu,
Tamao; Nielson, Greg; Olson, Valerie; Ronsse, Sebastien; Vinding Nyden,
Emily; Hammerschlag, Robert; Little, Patrick
2006SPIE.6268E..14L Altcode: 2006SPIE.6268E..36L
Studies by Mark Swain and a colleague at the Max Planck Institut
fur Astronomie, coupled with results from past and ongoing projects
at Harvey Mudd College, strongly suggest that it may be possible to
achieve imaging performance comparable to the Hubble Space Telescope
at relatively low cost using available, commercial products. This is
achievable by placing a 2.4 m telescope, with readily available adaptive
optics, on a 30 m tower located at a high-elevation geological "dome"
in Antarctica. An initial project surveyed relevant tower design
approaches, then generated and evaluated six concept designs for
telescope towers. Using data for typical and extreme wind at Dome C to
generate wind loads, finite element analysis yielded lateral deflections
at the top of 0.3 mm for typical winds and 12.1 mm for extreme gusts,
with the lowest resonant frequency at 0.7 Hz; some tower concepts
are innovative and allow for easy shipment, setup, and relocation. A
subsequent project analyzed a tower designed by Hammerschlag and found
fundamental resonance frequencies at 4.3 Hz for bending and 5.9 Hz for
torsion; this project also designed and simulated an active telescope
control system that maintained 17 milliarcsecond pointing error for
the telescope atop the tower during typical wind conditions.
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Title: Towers for telescopes with extreme stability: Active or
passive?
Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Jägers,
Aswin P. L.
2006SPIE.6273E..1OH Altcode: 2006SPIE.6273E..50H
High-resolution telescopes require a mechanical stability of fractions
of an arc second. Placing such a telescope on top of a tower will
improve the local seeing. An open transparent tower of framework
minimizes the upward, temperature disturbed air flow. The tower
platform has to be extremely stable against rotational motions, which
have to be less than fractions of an arc second, unusual in mechanical
engineering. Active systems can improve the stability. However, they
need sensors for position measurements, active actuators and a control
loop. The performance is limited by the available signal-to-noise
ratio. Consequently, improvement of the passive stability of large tower
structures will significantly contribute to the final stability. Special
geometries in steel framework can reach extreme passive stability of
a tower platform, particularly against rotational motions. There are
several groups of basic geometries, which lead to solutions and we
will give a systematic description. The proposed towers can be welded
or screwed together from smaller parts. This makes a construction in
adverse environments like the Antarctic region within good reach.
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Title: Large bearings with incorporated gears, high stiffness,
and precision for the Swedish Solar Telescope (SST) on La Palma
Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Jägers,
Aswin P. L.; Scharmer, Göran B.
2006SPIE.6273E..15H Altcode: 2006SPIE.6273E..34H
The 1-meter Swedish Solar Telescope (SST) obtains images of the solar
surface with an unprecedented resolution of 0.1 arcsec. It consists
of a relatively slender tower with on top only the vacuum turret for
reflecting downward the solar beam and no protective dome. This is a
favourable situation to get good local seeing. Just in the case of some
wind, seeing is best for daytime observations, therefore the precision
bearings and drives of the elevation- and azimuth axis of the turret
have to be stiff against wind. This requires line contact between the
meshing teeth of the large gear wheel and the pinion. High preload
forces to achieve line contact are not allowed because of appearing
stick-slip effects. To reduce the risk on stick-slip a special design
of the teeth for high stiffness combined with low friction and smooth
transition from one tooth to the next was made. Furthermore, extreme
precision in the fabrication was pursued such that relatively small
contact forces give already line contact. This required a special order
of the successive fabrication steps of the combination of bearing and
gear teeth. An additional problem was the relatively thin section
of the bearings required for a compact turret construction, needed
for best local seeing and minimum wind load. Solutions for all these
problems will be discussed. For the large gears the exceptional good
DIN quality class 4 for the pitch precision and straightness plus
direction of the teeth faces was achieved.
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Title: GISOT: a giant solar telescope
Authors: Hammerschlag, Robert H.; von der Lühe, Oskar F.; Bettonvil,
Felix C.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..491H Altcode:
A concept is presented for an extremely large high-resolution solar
telescope with an aperture of 11 m and diffraction limited for visual
wavelengths. The structure of GISOT will be transparent to wind and
placed on a transparent stiff tower. For efficient wind flushing,
all optics, including the primary mirror, will be located above
the elevation axis. The aperture will be of the order of 11 m, not
rotatively symmetrical, but of an elongated shape with dimensions
11 x 4 m. It consists of a central on-axis 4 m mirror with on both
sides 3 pieces of 2 m mirrors. The optical layout will be kept simple
to guarantee quality and minimize stray light. A Coudé room for
instruments is planned below the telescope. The telescope will not
be housed in a dome-like construction, which interferes with the open
principle. Instead the telescope will be protected by a foldable tent
construction with a diameter of the order of 30 m, which doesn"t form
any obstruction during observations, but can withstand the severe
weather circumstances on mountain sites. Because of the nature of
the solar scene, extremely high resolution in only one dimension is
sufficient to solve many exciting problems in solar physics and in
this respect the concept of GISOT is very promising.
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Title: DOT++: the Dutch Open Telescope with 1.4-m aperture
Authors: Bettonvil, Felix C.; Hammerschlag, Robert H.; Sütterlin,
Peter; Rutten, Robert J.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..362B Altcode:
The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is
a revolutionary open solar telescope, on an excellent site, on top
of a transparent steel tower, and uses natural air flow to minimize
local seeing. The aim is long-duration high-resolution imaging with
a multi-wavelength camera system. In order to achieve this, the DOT
is equipped with a diffraction limited imaging system and uses the
speckle reconstruction technique for removing the remaining atmospheric
turbulence. The DOT optical system is simple and consists currently of
a 0.45m/F4.44 parabolic mirror and a 10x enlargement lens system. We
present our plans to increase the aperture of the DOT from 0.45m to
1.4m. The mirror support and telescope top shall be redesigned, but
telescope, tower, multi-wavelength camera system and speckle system
remain intact. The new optical design permits user selectable choice
between angular resolution and field size, as well as transversal pupil
shift introducing the possibility to use obstruction free apertures up
to 65cm. The design will include a low order AO system, which improves
the speckle S/N substantially during moderate seeing conditions.
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Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
K.; de Wijn, A. G.
2004IAUS..223..597R Altcode: 2005IAUS..223..597R
The Dutch Open Telescope (DOT) on La Palma is an innovative solar
telescope combining open telescope structure and an open support tower
with a multi-wavelength imaging assembly and with synchronous speckle
cameras to generate high-resolution movies which sample different
layers of the solar atmosphere simultaneously and co-spatially at high
resolution over long durations. The DOT test and development phase is
nearly concluded. The installation of an advanced speckle processor
enables full science utilization including "Open-DOT" time allocation
to the international community. Co-pointing with spectropolarimeters
at other Canary Island telescopes and with TRACE furnishes valuable
Solar-B precursor capabilities.
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Title: DOT tomography of the solar atmosphere. I. Telescope summary
and program definition
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
Sütterlin, P.; de Wijn, A. G.
2004A&A...413.1183R Altcode:
The Dutch Open Telescope (DOT) on La Palma is an innovative optical
solar telescope capable of reaching 0.2 arcsec angular resolution
over extended durations. The DOT presently progresses from technology
testbed to a stable science configuration providing multi-wavelength
imaging and multi-camera speckle data acquisition for tomographic
mapping of the solar atmosphere. Large-volume speckle processing will
soon enable frequent usage and community-wide time allocation, in
particular for tandem operation with other solar telescopes pursuing
spectropolarimetry and EUV imaging. We summarize the DOT hardware and
software in the context of this increasing availability and outline
the corresponding “open-DOT” program.
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Title: Multi-wavelength imaging system for the Dutch Open Telescope
Authors: Bettonvil, Felix C.; Suetterlin, Peter; Hammerschlag, Robert
H.; Jagers, Aswin P.; Rutten, Robert J.
2003SPIE.4853..306B Altcode:
The Dutch Open Telescope (DOT) is an innovative solar telescope,
completely open, on an open steel tower, without a vacuum system. The
aim is long-duration high resolution imaging and in order to achieve
this the DOT is equipped with a diffraction limited imaging system
in combination with a data acquisition system designed for use with
the speckle masking reconstruction technique for removing atmospheric
aberrations. Currently the DOT is being equipped with a multi-wavelength
system forming a high-resolution tomographic imager of magnetic
fine structure, topology and dynamics in the photosphere and low-
and high chromosphere. Finally the system will contain 6 channels:
G-band (430.5 nm), Ca II H (K) (396.8 nm), H-α (656.3 nm), Ba II
(455.4 nm), and two continuum channels (432 and 651 nm). Two channels
are in full operation now and observations show that the DOT produces
real diffraction limited movies (with 0.2" resolution) over hours in
G-band (430.5 nm) and continuum (432 nm).
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Title: Large open telescope: size-upscaling from DOT to LOT
Authors: Hammerschlag, Robert H.; Jaegers, Aswin P. L.; Bettonvil,
Felix C. M.
2003SPIE.4853..294H Altcode:
The design characteristics of a large open telescope (LOT) are: (i)
an open tower with only pure translations of the platform under wind
load; (ii) an open telescope construction with extremely stiff geometry
and drives; (iii) simple optics with easy aligning and testing, but
nevertheless suitable for large auxiliary equipment like spectrographs.
---------------------------------------------------------
Title: Dutch Open Telescope: status, results, prospects
Authors: Rutten, Robert J.; Sütterlin, Peter; de Wijn, Alfred G.;
Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Hoogendoorn, Piet W.;
Jägers, Aswin P. L.
2002ESASP.506..903R Altcode: 2002svco.conf..903R; 2002ESPM...10..903R
The Dutch Open Telescope (DOT) on La Palma is a revolutionary telescope
achieving high-resolution imaging of the solar surface. The DOT combines
a pioneering open design at an excellent wind-swept site with image
restoration through speckle interferometry. Its open principle is now
followed in major solar-telescope projects elsewhere. In the past three
years the DOT became the first solar telescope to regularly obtain 0.2"
resolution in extended image sequences, i.e., reaching the diffraction
limit of its 45-cm primary mirror. Our aim for 2003-2005 is to turn
the DOT into a 0.2" tomographic mapper of the solar atmosphere with
frequent partnership in international multi-telescope campaigns through
student-serviced time allocation. After 2005 we aim to triple the DOT
resolution to 0.07" by increasing the aperture to 140 cm and to renew
the speckle cameras and the speckle pipeline in order to increase
the field size and sequence duration appreciably. These upgrades will
maintain the DOT's niche as a tomographic high-resolution mapper in
the era when GREGOR, Solar-B and SDO set the stage.
---------------------------------------------------------
Title: Opening the Dutch Open Telescope
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.; Bettonvil,
F. C. M.; Hammerschlag, R. H.
2002ESASP.505..565R Altcode: 2002IAUCo.188..565R; 2002solm.conf..565R
We hope to "open the DOT" to the international solar physics
community as a facility for high-resolution tomography of the solar
atmosphere. Our aim is to do so combining peer-review time allocation
with service-mode operation in a "hands-on-telescope" education
program bringing students to La Palma to assist in the observing and
processing. The largest step needed is considerable speedup of the
DOT speckle processing.
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Title: Proxy Magnetometry with the Dutch Open Telescope
Authors: Rutten, R. J.; Hammerschlag, R. H.; Sütterlin, P.; Bettonvil,
F. C. M.
2001ASPC..236...25R Altcode: 2001aspt.conf...25R
No abstract at ADS
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Title: A Multi-Channel Speckle Imaging System for the DOT
Authors: Sütterlin, P.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
Rutten, R. J.; Skomorovsky, V. I.; Domyshev, G. N.
2001ASPC..236..431S Altcode: 2001aspt.conf..431S
No abstract at ADS
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Title: Dutch Open Telescope: Status and Prospects
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M.;
Suetterlin, P.
2000SPD....3102107R Altcode: 2000BAAS...32.1290R
The Dutch Open Telescope (DOT) on La Palma in the Canary Islands is
a small but revolutionary solar telescope of which the image quality
matches the superb imaging of the Swedish Vacuum Solar Telescope (from
whose building the DOT is operated). The DOT is an open parabolic 45cm
reflector on an open 15m high tower, relying on mirror flushing by the
trade winds that bring the best seeing at La Palma to avoid internal
turbulence. A water-cooled field stop in the primary image reflects
most sunlight and heat out of the telescope. The first data from the
DOT combined with speckle reconstruction have yielded sunspot movies
of outstanding quality. At present, a multi-channel imaging system is
in construction for simultaneous registration of speckle sequences in
the G band, in Ca II K and in Hα. The data pipeline permits continuous
speckle data acquisition up to 0.5 Tb per day. The advantage of speckle
reconstruction over adaptive optics is the much larger field of the
restored scene, with the DOT camera's 100x130 arcsec at 0.2 arcsec
resolution. The DOT science program is to study magnetic topology and
dynamics throughout the photosphere and chromosphere.
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Title: Solar Magnetometry with the Dutch Open Telescope
Authors: Rutten, R.; Hammerschlag, R. H.; Sutterlin, P.; Bettonvil,
F. C. M.; van der Zalm, E. B. J.
2000ESASP.463..611R Altcode: 2000sctc.proc..611R
No abstract at ADS
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Title: The Dutch Open Telescope
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.
1999ASPC..158...57R Altcode: 1999ssa..conf...57R
No abstract at ADS
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Title: The Dutch Open Telescope at the Roque de los Muchachos
Observatory
Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.
1998NewAR..42..485H Altcode:
We briefly describe the Dutch Open Telescope, whose innovative design
tries to get the most out of the good La Palma seeing.
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Title: The Dutch Open Telescope
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M.
1997ASSL..225..289R Altcode: 1997scor.proc..289R
The Dutch Open Telescope is now being installed at La Palma. It
is intended for optical solar observations with high spatial
resolution. Its open design aims to minimize disturbances of the
local air flow and so reduce the locally-generated component of
the atmospheric seeing. This paper briefly describes the design,
construction, short-term plans, and longer-term prospects.
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Title: De Dutch Open Telescope: nieuwe zonnentelescoop op La Palma.
Authors: Rutten, R.; Hammerschlag, R.; Bettonvil, F.
1997Zenit..24..481R Altcode:
No abstract at ADS
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Title: Dutch Open Telescope: Status and Prospects
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.
1997ASPC..118..335R Altcode: 1997fasp.conf..335R
The Dutch Open Telescope represents a new solar telescope concept. Being
open rather than evacuated, it leads the way to large-aperture high
resolution telescopes. It is now being installed on La Palma.
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Title: De Utrechtse open toren telescoop.
Authors: Bettonvil, F. C. M.; Hammerschlag, R. H.
1993Zenit..20..327B Altcode:
No abstract at ADS
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Title: Analysis of Jovian decamteric data: Study of radio emission
mechanisms
Authors: Staelin, D. H.; Rosenkranz, P. W.; Arias, T. A.; Garnavich,
P. N.; Hammerschlag, R.
1986mit..reptQ....S Altcode:
This research effort involved careful examination of Jovian
radio emission data below 40 MHz, with emphasis on the informative
observations of the Planetary Radio Astronomy experiment (PRA) on the
Voyager 1 and 2 spacecraft. The work is divided into three sections,
decametric arcs, decametric V bursts, and hectometric modulated spectral
activity (MSA).
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Title: A telescope drive with emphasis on stability.
Authors: Hammerschlag, R. H.
1983SPIE..444..138H Altcode:
A solar telescope, which consists of an open steel framework, is under
construction. The telescope will operate without a dome in order
to improve the local seeing. The telescope drives should be stable
against the fluctuating wind forces. The described design may be of
interest for future large telescopes because it reduces the telescope
vibrations caused by wind buffeting.
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Title: Excursion: Tower, Parking Lot, Geostationary Orbit
Authors: Hammerschlag, R.
1981siwn.conf..583H Altcode:
No abstract at ADS
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Title: Construction Outlines of the Utrecht Open Solar Telescope
Authors: Hammerschlag, R.
1981siwn.conf..547H Altcode:
No abstract at ADS
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Title: Aperture Screens for Solar Telescopes
Authors: Hammerschlag, R.
1981siwn.conf..274H Altcode:
No abstract at ADS
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Title: An open LEST?
Authors: Hammerschlag, R. H.; Rutten, R. J.
1980fsoo.conf..115H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An open LEST (Large European Solar Telescope)?
Authors: Hammerschlag, R. H.; Rutten, R. J.
1979MmArc.106..115H Altcode:
No abstract at ADS
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Title: An open LEST?
Authors: Hammerschlag, R. H.; Rutten, R. J.
1978fsoo.conf..115H Altcode:
No abstract at ADS
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Title: Book reviews
Authors: Reijnen, G. C. M.; Kleczek, J.; Millman, Peter M.; Vesseur,
H. J. A.; Bar-Nun, Akiva; de Jager, C.; van Albada, T. S.; Rawer,
K.; Hinze, J. O.; Trümper, J.; de Jager, Cornelis; Müller, O.;
Kovalevsky, J.; Hammerschlag, R. H.; Hoyng, Peter
1977SSRv...20..235R Altcode:
No abstract at ADS
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Title: Interferometric recording of the deflections of towers and
telescopes
Authors: Hammerschlag, R. H.
1975ApOpt..14..885H Altcode:
Wind generates vibrations in towers and in telescopes placed
in the open air. Interferometers for measuring these vibrations
were developed. Applications to scale models of a telescope led to
improvements of the telescope design. An optoelectronic system using
three photocells for scanning the interferometer fringes allows the
application of an inexpensive laser with several longitudinal modes
as a light source for the interferometers.
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Title: HD 206267, a candidate star for the transient X-ray source
Cepheus X-4?
Authors: Hensberge, G.; Hammerschlag, R. H.
1975A&A....39..157H Altcode:
Summary. The spectrum of the 3.7 day spectroscopic binary HD 206267
shows no evidence for large mass loss. No emission lines could be
detected in the wavelength region 37506680 A. The orbital elements of
the system suggest a massive secondary which can be interpreted as a
normal non-degenerate star. Key words: X-ray sources radial velocities
---------------------------------------------------------
Title: An Efficient Wind Shield for the Protection of Telescopes
Authors: Hammerschlag, R. H.; Zwaan, C.
1973PASP...85..468H Altcode:
A semitransparent wind shield to protect telescopes against wind is
described and some measurements and experiences during a site-testing
campaign are reported. Key words: instrumentation - telescope protection
- seeing
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Title: Jones-Vektoren geschrieben in rechts- und linkszirkularen
Komponenten.
Authors: Hammerschlag, R. H.
1972Optik..34..595H Altcode:
No abstract at ADS
