Author name code: dunn
ADS astronomy entries on 2022-09-14
=author:"Dunn, Richard B." OR =author:"Dunn, R.B." OR =author:"Dunn, Dick"
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Title: Obituary John Wainwright Evans, Jr.
Authors: Dunn, Richard B.; Smartt, Raymond N.; Zirker, Jack B.
Bibcode: 2000PhT....53c..94D
Altcode:
No abstract at ADS
Title: John W. Evans died 31 October 1999.
Authors: Dunn, R. B.; Simon, G. W.; Smartt, R. N.; Zirker, J. B.
Bibcode: 2000SoPh..191..227D
Altcode:
No abstract at ADS
Title: The GSFC Lyot Filter for Night Time Astronomy (Poster)
Authors: Woodgate, P. Palunas. B. E.; Danks, A. C.; Klingesmith,
D. A.; Dunn, R. B.
Bibcode: 2000ASPC..195..605W
Altcode: 2000iutd.conf..605W
No abstract at ADS
Title: Obituary: John Wainwright Evans, 1909-1999
Authors: Dunn, Richard B.; Simon, George W.; Smartt, Raymond N.;
Zirker, Jack B.
Bibcode: 2000BAAS...32.1663D
Altcode:
No abstract at ADS
Title: The NSO Solar Adaptive Optics Program: First Results.
Authors: Rimmele, T. R.; Radick, R. R.; Richards, K.; Dunn, R. B.
Bibcode: 1999AAS...19410307R
Altcode: 1999BAAS...31Q1002R
The National Solar Observatory is developing solar adaptive optics at
the R.B. Dunn Solar Telescope (DST). The project recently achieved
a key milestone when the atmospheric control loop was closed at the
DST. The system currently compensates about 20 spatial modes with a
loop bandwidth of about 30 Hz. A 97-actuator deformable mirror is used
for wavefront correction. A correlating Shack-Hartmann wavefront sensor
provides real-time estimates of the wavefront errors using arbitrary
scenes, such as solar granulation and small pores, as the wavefront
sensing target. We will describe the system design and present results
from first engineering runs at the DST.
Title: Image improvement program at the NSO/SP Vacuum Tower Solar
Telescope
Authors: Radick, Richard R.; Rimmele, Thomas R.; Dunn, Richard B.
Bibcode: 1998SPIE.3353..621R
Altcode:
Over the past several years, a number of steps have been taken to
improve the optical performance of the Vacuum Tower Solar Telescope at
Sacramento Peak. We believe that the optical system of the telescope
is now corrected to better than 1/10 wave rms after these improvements.
Title: In Pursuit of High Resolution in Solar Physics
Authors: Dunn, R. B.
Bibcode: 1997AAS...19110201D
Altcode: 1997BAAS...29Q1372D
Current observations of tiny key processes on the Sun, for example,
spicules, prominences, granulation, magnetic ropes, sunspots and flares
lack the spatial resolution to support present theoretical models. Time
series with better than 0.1 arcsecond resolution over a field of view
on the order of 50 arcsecond are needed together with a wide range
of narrow-band filter and spectrographic observations that define the
temperature, magnetic and velocity fields. It is extremely difficult
to achieve the required telescopic resolution for making precision
measurements of these tiny structures on the Sun that are so fundamental
to Solar Physics. Even without the problems caused by turbulence in the
Earth's atmosphere, solar telescopes rarely achieve diffraction-limited
performance due to the heating of the optical system. In this talk I
describe our attempts over the last 25 years to improve the performance
of the vacuum tower telescope at Sac Peak. I discuss problems with the
vacuum window, dome-caused turbulence, resolution tests, and active
optics (deformable mirrors). With a perfect telescope (Strehl Ratio >
0.6) and short exposures ( 20ms) the "frame selection" technique can
produce a promising time series. "Destretching" the selected frames
improves the uniformity of the series. Long exposures, for example,
those required for spectroscopy of sub-arcsecond phenomena, require
adaptive optics (AO). I have spent the past decade pursuing this
field. I will discuss the problems that make solar AO so difficult,
and how close we are to realizing a practical system.
Title: Image Quality Improvements at the NSO/Sacramento Peak Vacuum
Tower Telescope
Authors: Radick, R. R.; Dunn, R. B.; Rimmele, T. R.; Stauffer, F. R.;
Wilkins, L. M.
Bibcode: 1996AAS...188.8503R
Altcode: 1996BAAS...28..961R
Recently, an effort has been underway at NSO/Sacramento Peak to improve
the imaging performance of the vacuum tower solar telescope (VTT) by
identifying, characterizing, and correcting optical problems in the
system. Considerable attention has been given to thermal control of
the entrance window to alleviate focus changes and other time-varying
aberrations in the wavefront, and development of a second generation
solar correlation tracker, based on commercially available components,
to eliminate tip-tilt image motion. We are also refiguring one of the
45deg turning flats in the telescope turret, primarily to eliminate
a turned edge that introduces astigmatism. In the next year, we
plan to implement a low-bandwidth active optics system, based on
a workstation-hosted Shack-Hartmann wavefront sensor, generalized
to operate using solar granulation as its target, and a 97 element
deformable mirror, recently purchased from Xinetics Inc. with Air
Force and NSO funds, to correct any remaining residual aberrations in
the VTT optical system.
Title: Wavefront Sensing for Solar Adaptive Optics
Authors: Rimmele, T. R.; Dunn, R. B.; Radick, R. R.
Bibcode: 1996AAS...188.8504R
Altcode: 1996BAAS...28..962R
The National Solar Observatory is developing an adaptive optics
system with the goal to correct atmospheric aberrations in real time
and allow for diffraction limited observations of solar features. A
key component of the AO system is the wavefront sensor (WFS). The Sun
presents unusual problems for wavefront sensing. Unlike the nighttime
sky, the Sun does not provide natural, high-contrast point sources,
and creation of laser beacons bright enough to be visible against the
solar disk poses major technical and operational problems. Wavefront
sensing at arbitrary locations on the Sun requires a sensor capable of
using the solar granulation as its target. We discuss two approaches
to the solar wavefront sensing problem: (a) a modified Shack-Hartmann
sensor, which is based on correlation tracking on images formed by
an array of subapertures , and (b) an amplitude modulation or spatial
filtering procedure, understandable in terms of the classic Foucault
knife-edge test. We compare measurements of atmospheric wavefront
distortions performed simultaneously with a Shack-Hartmann WFS and a
knife-edge WFS. We discuss the performance, limitations and practical
considerations of the two wavefront sensor concepts.
Title: White-Light Reflecting Corona graph for the SWATH Mission
Authors: Smartt, Raymond N.; Dunn, Richard B.; Carmichael, Roger
B.; Gregory, B. Scott; Plum, Douglas W.; Neidig, Donald F.; Golub,
Leon; Bookbinder, Jay A.; Koutchmy, George U.; Nystrom, Serge L.;
Zimmermann, Jean-Paul
Bibcode: 1996ASPC...95..531S
Altcode: 1996sdit.conf..531S
No abstract at ADS
Title: 256-channel digital wavefront reconstructor
Authors: Hull, William C.; Dunn, Richard B.; Small, M.
Bibcode: 1993SPIE.1920..200H
Altcode:
A 256-channel Digital Wavefront Reconstructor System (DRS) has been
developed for the Sacramento Peak Adaptive Optics System. The system may
be configured with 16 to 256 channels in a single VME chassis. Several
thousand channels can be accommodated by adding more VME chassis. The
system architecture supports both parallel and serial processing
combinations. This flexibility allows it to be adapted to various
wavefront sensors or used in other applications that require high-speed
parallel data processing in real time. Algorithms may be implemented
that perform matrix multiplication, FIR and IIR filters, gain and
offset corrections, table lookups, and polynomial evaluations. The
use of the DRS in the Sac Peak Adaptive Optics System is presented,
followed by a detailed description of the DRS hardware design.
Title: Solar imaging at National Solar Observatory using a segmented
adaptive optics system
Authors: Acton, Daniel S.; Dunn, Richard B.
Bibcode: 1993SPIE.1920..348A
Altcode:
The Lockheed Missiles and Space Co. (LMSC) has developed a 57-actuator
segmented adaptive optics (AO) system to compensate for atmospheric
turbulence encountered in ground- based solar astronomy. While working
with the National Solar Observatory (NSO), this system has been
successfully tested in several observing runs on the Tower Telescope
at Sacramento Peak. This paper gives a brief description of the AO
system with emphasis on recent developments. Images from a recent
observing run with the AO system are also presented.
Title: The Advanced Stokes Polarimeter - A new instrument for solar
magnetic field research
Authors: Elmore, D. F.; Lites, B. W.; Tomczyk, S.; Skumanich,
A. P.; Dunn, R. B.; Schuenke, J. A.; Streander, K. V.; Leach, T. W.;
Chambellan, C. W.; Hull, H. K.
Bibcode: 1992SPIE.1746...22E
Altcode:
A new Stokes polarimeter for high spatial resolution quantitative
measurement of magnetic fields at multiple heights in the solar
atmosphere has been constructed by the National Center for Atmospheric
Research and the National Solar Observatory. The instrument uses
the Vacuum Tower Telescope at Sunspot, New Mexico, and its existing
horizontal spectrograph, universal birefringment filter, and image
motion stabilization system. The polarimeter uses a rotating retarder
polarization modulator with polarization calibration optics. Multiple
paired CCDs are used for detection followed by video processing to
produce spatial maps of the full state of polarization in restricted
regions of the solar spectrum. Two spectral regions encompassing
lines sensitive to the Zeeman effect, which form in the photosphere
and low chromosphere, are recorded simultaneously. Significant
developments include: construction of the new telescope post
focus optical arrangement, creation of a polarization model for the
telescope, construction of high-speed, low-noise solid state cameras,
and construction of computer hardware for receiving and processing
high-rate 12-bit digital data.
Title: The Advanced Stokes Polarimeter: A New Instrument for Solar
Magnetic Field Research
Authors: Tomczyk, S.; Elmore, D. F.; Lites, B. W.; Dunn, R. B.;
Skumanich, A.; Schuenke, J. A.; Streander, K. V.; Leach, T. W.;
Chambellan, C. W.; Lacey, L. B.
Bibcode: 1992AAS...180.5108T
Altcode: 1992BAAS...24..814T
A new Stokes polarimeter for high spatial resolution quantitative
measurement of magnetic fields at multiple heights in the solar
atmosphere has been constructed by the National Center for Atmospheric
Research and the National Solar Observatory. The instrument has become
operational at the Vacuum Tower Telescope at Sunspot, New Mexico
and uses its existing horizontal spectrograph, universal birefringent
filter, and image motion stabilization system. To these optical systems
we have added a rotating wave plate polarimeter and polarization
calibration optics. Multiple CCDs are used for detection followed by
video processing in order to produce polarization maps of solar regions
from several spectrum lines simultaneously. Significant developments
include: a) construction of the new VTT post focus optical arrangement,
b) creation of a polarization model for the VTT, c) construction of
high speed, low noise CCD cameras, and d) construction of computer
hardware for receiving and processing high rate 12-bit digital data.
Title: First Results from the Advanced Stokes Polarimeter
Authors: Lites, B. W.; Dunn, R. B.; Elmore, D. F.; Tomczyk, S.;
Skumanich, A.; Streander, K. V.
Bibcode: 1992AAS...180.1201L
Altcode: 1992BAAS...24..747L
The Advanced Stokes Polarimeter (ASP) is a collaborative program between
the High Altitude Observatory (HAO) and the National Solar Observatory
(NSO) to investigate the physics of solar active regions though
quantitative measurements of vector magnetic fields. First scientific
results from the ASP were obtained during an observing run in March,
1992, when high resolution Stokes profile maps of active regions were
obtained under good seeing conditions. The ASP measures simultaneously
the full Stokes profiles in photospheric Fe I lines near 630 nm and in
the temperature minimum/low chromospheric Mg I b-lines at 517 nm. We
present scans of an isolated small sunspot near disk center, and we
discuss the fine structure of the vector field within this sunspot
and in the magnetic elements surrounding it. Observations of a complex
active region near the east limb will also be presented. This active
region produced a flare during the observational sequence.
Title: NSO/Sac Peak continuous-face-plate adaptive mirror
Authors: Dunn, Richard B.; Streander, George W.; Hull, William;
Wilkins, Larry
Bibcode: 1992SPIE.1543...88D
Altcode:
The National Solar Observatory is constructing a continuous-face-plate
mirror with 61 actuators. The mirror, which has a clear aperture of
218 mm, features a detachable face plate and replaceable actuators
that are servoed to maintain a position measured by capacitors which
are within the actuators themselves. The actuators, manufactured by
Queensgate Instruments Ltd., are 20 mm diameter and are placed on 32
mm centers. Each has a range of 6.4 (mu) for a voltage swing of +/- 175
volts. The servos have a bandwidth of 1 KHz (-3 db). In order to couple
the face plate to the actuators, each actuator has a rare-earth magnet
on its end that attracts a steel button cemented to the 3 mm thick
glass faceplate. The mirror is a contender for those systems needing
a relatively large adaptive mirror with relatively few actuators, for
example, to replace the secondary mirror of a Cassegrain telescope. At
Sacramento Peak the mirror will be used with the 76 cm aperture Vacuum
Tower Telescope to observe small details on the sun.
Title: Solar feature correlation tracker.
Authors: Rimmele, Th.; von der Luehe, O.; Wiborg, P. H.; Widener,
A. L.; Dunn, R. B.; Spence, G.
Bibcode: 1991SPIE.1542..186R
Altcode:
The authors present a tracking system that stabilizes atmospheric
and instrumental image motion at the vacuum tower telescopes of the
National Solar Observatory at Sacramento Peak and the Kiepenheuer
Institut für Sonnenphysik at Tenerife. A matrix diode array rapidly
scans the scene of interest, usually with a field of 5 arcsec. Images
are cross-correlated in real time with a previously recorded reference
image of the same area. Reference pictures are updated every 30
s. Recent performance tests show that the residual image motion in the
tracked image is 0.05 arcsec rms compared to a typical 0.5 arcsec rms
for the untracked image. The correlation tracker also includes a seeing
monitor providing a relative seeing measure at a two millisecond rate,
which can be used for frame selection and shutter control.
Title: Results from a Recent Observing Run with the Lockheed Solar
Adaptive Optics System
Authors: Acton, D. S.; Tarbell, T. D.; Dunn, R. B.
Bibcode: 1991BAAS...23.1453A
Altcode:
No abstract at ADS
Title: High resolution telescopes at the National Solar Observatory
Authors: Dunn, R. B.; Smartt, R. N.
Bibcode: 1991AdSpR..11e.139D
Altcode: 1991AdSpR..11..139D
The principal high-resolution telescopes of the National Solar
Observatory are its two evacuated telescopes of 61-cm aperture (Kitt
Peak) and 75-cm aperture (Sac Peak). The 61-cm telescope is used for
making full-disk magnetograms, spectromagnetograms and λ10830 maps
that show coronal holes, and is dedicated to synoptic programs. We
describe the 75-cm telescope at Sac Peak. Upgrades that are underway
include an adaptive mirror and fast mirror system that will feed
several focal-plane instruments including the Universal Spectrograph,
a new spectrograph whose detectors are CCD cameras, the Universal
Birefringent Filter, a Fabry-Perot Interferometer and an Advanced
Stokes Polarimeter (ASP), is being constructed at the High Altitude
Observatory. Additional equipment planned for this telescope includes
an improved temperature control subsystem for the entrance window, an
instrument that continually measures Fried's parameter, r0,
and integrating more advanced data collection systems into a computer
network. The observatory is also pursuing a mirror coronagraph, which
should have high resolution and which could be built in apertures
larger than a meter. Operated by the Association of Universities
for Research in Astronomy, Inc. (AURA) under cooperative agreement
with the National Science Foundation.
Title: Window considerations for LEST: an update.
Authors: Dunn, R. B.
Bibcode: 1991ewst.conf...31D
Altcode:
In LEST Technical Report No. 3, "Window considerations for LEST"
(1984), the author evaluated the formulas of Mehltretter for the thermal
gradient in the window, and Bernat's formula for birefringence due to
temperature and vacuum load for three thicknesses and two materials
for a 2.5-meter-diameter window for LEST. He estimated the variation
in path length and birefringence due to these factors. The author
concluded that the window should be made from fused silica and should
be as thin as could be manufactured and handled, perhaps even as thin
as 1 centimeter. Because it could not support the load from the vacuum,
it would have to be used with a helium-filled telescope.
Title: Preliminary results from the HAO/NSO Advanced Stokes
Polarimeter prototype observing run.
Authors: Lites, B. W.; Elmore, D.; Murphy, G.; Skumanich, A.; Tomczyk,
S.; Dunn, R. B.
Bibcode: 1991sopo.work....3L
Altcode:
A prototype version of the Advanced Stokes Polarimeter was operated at
the Sunspot Vacuum Tower Telescope of the National Solar Observatory
in May und June, 1990. Although the prototype instrument does not
have the capability of the final instrument to be deployed in 1991,
it nonetheless provided high spatial resolution Stokes profiles
observations of a small symmetric sunspot. Analysis of these
observations shows that the magnetic field at the outer edge of
the penumbra of this sunspot is highly inclined with respect to the
local normal (γ = 70 - 80°), in agreement with previous Stokes II
measurements of larger sunspots. In addition, the axial field and flux
distribution was found to be nearly identical to that of the previous
Stokes II measurement.
Title: The Large Earth-Based Solar Telescope (LEST) - Its Scientific
Objectives and Status
Authors: Linsky, J. L.; Leibacher, J.; Smithson, R.; Dunn, R. B.
Bibcode: 1990BAAS...22.1238L
Altcode:
No abstract at ADS
Title: NSO/SP adaptive optics program.
Authors: Dunn, Richard B.
Bibcode: 1990SPIE.1271..216D
Altcode:
The author describes the current status of the adaptive optics system
for the National Solar Observatory 75-cm aperture, evacuated solar
telescope at Sunspot, New Mexico. This system is interfaced to a
birefringent filter and two solar spectrographs. The optical system
provides for the High Altitude Observatory Advanced Stokes Polarimeter
that measures solar vector magnetic fields. Recently the optical design
has been modified to accommodate the Lockheed 19-segment adaptive
mirror and its 19-segment quad-cell tracker.
Title: Solar feature correlation tracker for ground-based telescopes
Authors: von der Luehe, O.; Widener, A. L.; Rimmele, Th.; Spence,
G.; Dunn, R. B.
Bibcode: 1989A&A...224..351V
Altcode:
A tracking system that stabilizes atmospheric and instrumental image
motion has been tested at the vacuum tower telescope of the National
Solar Observatory at Sacramento Peak. The system locks anywhere on
the sun, using solar granulation or other small scale structures as
tracers. A matrix diode array rapidly scans the scene of interest;
pictures are cross-correlated in real time with a previously recorded
reference image of the same area on the sun.
Title: Adaptive optical system at Sac Peak: a progress update
Authors: Dunn, R. B.; Streander, G.; Lühe, O. V. D.
Bibcode: 1989hsrs.conf...53D
Altcode:
No abstract at ADS
Title: NSO/SP Adaptive Optics Program
Authors: Dunn, R. B.
Bibcode: 1989BAAS...21..847D
Altcode:
No abstract at ADS
Title: National Solar Observatory polarimeter
Authors: Dunn, Richard B.; November, Laurence J.; Colley, Stephen A.;
Streander, George W.
Bibcode: 1989OptEn..28..126D
Altcode:
A general polarimeter for the precise measurement of Stokes intensities
was developed and was used for testing the Sacramento Peak Vacuum Tower
Telescope and other optical instrumentation. The design is based upon
the polarimeter described by Orrall (1971) and Makita et al.(1982),
with some simplifications. A control computer sets parameters in the
integration electronics and provides a simple readout for an experiment
control or analysis computer. Calibration of the polarimeter is defined
by a Mueller matrix for the system; the calibration matrix compensates
for the systematics of the polarimeter. The calibration matrix was
derived using an optical wheel containing many orientations of sheet
polarizers, partial polarizers, and insertable wave plates. The rms of
the calibration solution is about 0.6 percent. The calibration procedure
as it is presently defined limits the accuracy of the polarimeter.
Title: Observational Results in Solar Astronomy with the Improved
Lockheed Active Mirror System
Authors: Smithson, R. C.; Acton, D. S.; Peri, M. L.; Sharbaugh, R. J.;
Dunn, R. B.; van der Lühe, O.; Keil, S. L.
Bibcode: 1988BAAS...20R.710S
Altcode:
No abstract at ADS
Title: Proposal for an alignment system for the primary and secondary
mirrorof LEST.
Authors: Heier, H.; Engvold, O.; Dunn, R. B.
Bibcode: 1988LFTR...32.....H
Altcode:
The tolerances of tilt and decentration of the secondary mirror of LEST
relative to the primary mirror are very tight. The tilt tolerance is 10
arc sec and the decentration tolerance is 80 μm. In order to be able to
align the secondary and primary mirrors to these tolerances, the authors
propose to equip the telescope with two auxiliary optical systems.
Title: Solar granulation power spectra from speckle interferometry
Authors: von der Luhe, O.; Dunn, R. B.
Bibcode: 1987A&A...177..265V
Altcode:
Granulation was observed with a CCD array at the SPO tower telescope
in a quiet region near the solar center. Time series of short exposure
(4 ms) pictures of a 14 by 14 arcsec region were taken. Consecutive
frames were separated by 0.55 s in time. Labeyrie's (1970) speckle
interferometry technique was applied in order to recover power spectra
of the intensity fluctuations at high spatial frequencies. The spectral
ratio technique (von der Luhe, 1984) was applied to correct for seeing
attenaution of the power spectra. It is possible to recover a signal
up to spatial frequency of 2.5 line pairs per arcsec, corresponding
to a wave number of 22/Mm or 40 percent of the diffraction limit of
the telescope under 1.3 arcsec average seeing conditions. A corrected
rms granulation contrast of 0.127 + or - 0.01 is estimated, and an
exponential falloff of power density toward higher spatial frequencies
is observed.
Title: The Foucault Test for Solar Telescopes
Authors: Darvann, T. A.; Dunn, R. B.
Bibcode: 1987LFTR...26...71D
Altcode:
The purpose of this note is to describe the Foucault technique and to
review and encourage its application to solar telescopes.
Title: Site Testing Telescope Configurations
Authors: Dunn, R. B.
Bibcode: 1987LFTR...26...79D
Altcode:
For an optical site survey for a solar telescope, one might like to
observe or measure: (1) Granulation at the center of the disk, (2)
R0, or some other characteristic of the distribution of
turbulence cells across the image of the aperture, and (3) Size of
isoplanatic patch. The author discusses some telescope options for
these three measurements.
Title: Specifications of the LEST adaptive optical system.
Authors: Dunn, R. B.
Bibcode: 1987LFTR...28..243D
Altcode:
The author defines a performance specification for the adaptive mirror
system for LEST. He then comments on a system that might meet this
specification in terms of today's adaptive mirror technology and shows
that much of current research is directly applicable to the components
needed for LEST. He concludes that the adaptive mirror system for
LEST will not need to be a state-of-the-art advance over existing or
planned adaptive mirror systems.
Title: Conclusions (definition of immediate and long term actions)
[related to the LEST adaptive mirror system].
Authors: Dunn, R. B.
Bibcode: 1987LFTR...28..263D
Altcode:
The author defines a number of technological areas related to the LEST
adaptive mirror system that can be studied with existing telescopes
and modest equipment.
Title: Optical telescope for LEST site survey.
Authors: Bonaccini, D.; Dunn, R. B.; Engvold, O.
Bibcode: 1987LFTR...28..233B
Altcode:
The authors propose a telescope of 40-cm aperture for the optical
site-testing campaign for the LEST. They have chosen a helium-filled
compact design with a f/2.54 spherical primary whose aberrations are
corrected by a lens-mirror combination with all spherical surfaces. A
scheme for taking TV images of the granulation, determining Ro and
measuring the size of the isoplanatic patch is proposed.
Title: Summary of the Round Table Discussion
Authors: Dunn, R. B.
Bibcode: 1987rfsm.conf..374D
Altcode:
Two broad areas were to be addressed: "What can be done best,
with what restriction, and what cannot be done with the presently
foreseen facilities on the Canary Islands? What extensions of these
facilities are desirable?" and "What are the candidate problems for
future integrated observational experiments, for which all available
solar observing facilities could be used simultaneously?
Title: Image Enhancement Techniques Applied to Solar Granulation Data
Authors: von der Luehe, O.; Dunn, R. B.; November, L. J.
Bibcode: 1986BAAS...18..663V
Altcode:
No abstract at ADS
Title: Design Criteria Considerations Objectives and Trade-Offs
Authors: Dunn, R. B.
Bibcode: 1986tswo.work...89D
Altcode:
No abstract at ADS
Title: High Resolution Solar Telescopes
Authors: Dunn, R. B.
Bibcode: 1985SoPh..100....1D
Altcode: 1985SoPh..100.....D
The advantages and disadvantages of the configurations for high
resolution solar telescopes are discussed within two broad groups:
those with steerable mountings and those with fixed mountings. We then
consider simple optical tests, stabilization of the internal optical
path, windows, vibration, guiding and alignment systems, improving
the observations, and solutions for large-aperture telescopes for
Stokes polarimetry observations. This review does not address all
the problems. It is not a compendium of solar telescopes, nor does it
include any discussion of focal-plane instrumentation.
Title: Filigree-Granulation Movie
Authors: Dunn, R. B.
Bibcode: 1985BAAS...17R.633D
Altcode:
No abstract at ADS
Title: Atmospheric Distortion and Blurring
Authors: November, L. J.; Dunn, R. B.
Bibcode: 1985BAAS...17..640N
Altcode:
No abstract at ADS
Title: Solar granulation movie.
Authors: Dunn, R. B.; November, L. J.
Bibcode: 1985MPARp.212...27D
Altcode:
No abstract at ADS
Title: Collages of Granulation Pictures
Authors: Dunn, R. B.; November, L. J.
Bibcode: 1985LNP...233...85D
Altcode: 1985hrsp.proc...85D
Two small-area selection schemes are applied to CCD observations of
solar granulation. One procedure, referred to as mosaic, divides a
128 x 128 array into 64 subarrays of 16 x 16 pixels; the rms contrast
of the fine structure is measured and compared in order to develop
a mosaic of the subarrays. The second technique, collage, involves
calculating rms values within a sliding Gaussian window and gating
the pixel into the final image. Methods for assessing seeing quality,
which involve the calculation of rms after high-pass filtering,
are examined; a simple high-pass filter or an edge-locating function
can be utilized for filtering. The rms map is then formed from the
convolution of a Gaussian with either the high-pass or the Laplacian
filters. The usefulness of the two procedures is demonstrated by
applying the mosaic and collage processes to data recorded on July 17,
1983 with a CCD device on the NSO/Sac Peak Vacuum Tower Telescope.
Title: Professor Rösch, Pic du Midi and High Resolution
Authors: Dunn, R. B.
Bibcode: 1985LNP...233....3D
Altcode: 1985hrsp.proc....3D
No abstract at ADS
Title: The Sacramento Peak Fast Microphotometer.
Authors: Arrambide, M. R.; Dunn, R. B.; Healy, A. W.; Porter, R.;
Widener, A. L.; November, L. J.; Spence, G. E.
Bibcode: 1984NASCP2317..243A
Altcode:
The Sacramento Peak Observatory Fast Microphotometer translates an
optical system that includes a laser and photodiode detector across
the film to scan the Y direction. A stepping motor moves the film gate
in the X direction. This arrangement affords high positional accuracy,
low noise (0.002 RMS density units), modest speed (5000 points/second),
large dynamic range (4.5 density units), high stability (0.005 density
units), and low scattered light. The Fast Microphotometer is interfaced
to the host computer by a 6502 microprocessor.
Title: Window Considerations for Lest
Authors: Dunn, R. B.
Bibcode: 1984LFTR....3P..45D
Altcode:
No abstract at ADS
Title: Window considerations for LEST.
Authors: Dunn, R. B.
Bibcode: 1984LFTR....3.....D
Altcode:
This contribution gathers together material that concerns the 250-cm
diameter vacuum or helium window required for the Large European
Solar Telescope (LEST). The author applies the formulae developed
by Mehltretter and Bernet to the larger LEST window and makes
recommendation on the material and thickness. He discusses material
availability and fabrication problems.
Title: LEST design study.
Authors: Andersen, T. E.; Dunn, R. B.; Engvold, O.
Bibcode: 1984LFTR....7.....A
Altcode:
No abstract at ADS
Title: The Sacramento-Peak Fast Microphotometer
Authors: Arrambide, M. R.; Dunn, R. B.; Healy, A. W.; Porter, R.;
Widener, A. L.; November, I. J.; Spence, G. E.
Bibcode: 1984amd..conf..243A
Altcode:
No abstract at ADS
Title: Granulation Date Set
Authors: Dunn, R. B.
Bibcode: 1984ssdp.conf...88D
Altcode:
No abstract at ADS
Title: A Multiple Diode Array (MDA)
Authors: Widener, A. L.; Dunn, R. B.; Spence, G. E.
Bibcode: 1983BAAS...15Q.718W
Altcode:
No abstract at ADS
Title: Test of vacuum vs helium in a solar telescope.
Authors: Engvold, O.; Dunn, R. B.; Livingston, W. C.; Smartt, R. N.
Bibcode: 1983ApOpt..22...10E
Altcode:
The consequences of filling a solar telescope with helium, a gas with an
exceptionally low index of refraction and a high thermal conductivity,
are reported. All the tests are conducted with the solar beam present to
provide normal heating. Internal seeing of the telescope is evaluated by
viewing the image of an He-Ne laser beam in autocollimation reflected
from the entrance window for different pressures of air or helium. The
total path of the laser beam through the tank (six times) becomes
about 100 m. Quantitative measurements of the wave front distortions
are derived by inserting a point-diffraction interferometer near the
focused image of the laser beam. Excursions of the fringe pattern yield
direct measures of the wave front errors in units of the 0.633-micron
laser wavelength. It is concluded that a helium-filled telescope is a
realistic alternative to a vacuum telescope for solar observations. The
barely detectable tank seeing with helium near atmospheric pressure
could possibly be rectified either by a high reflectivity coating of
the mirrors, which reduces the heat load, or by a forced circulation
of the helium in the tank.
Title: An Air Force/NSF initiative to study the origins of solar
activity.
Authors: Worden, S. P.; Dunn, R. B.; Smith, M. A.; Zirker, J. B.
Bibcode: 1982SAOSR.392B.221W
Altcode: 1982csss....2..221W
No abstract at ADS
Title: Solar Optical Telescope Instrumentation
Authors: Dunn, R. B.
Bibcode: 1981SSRv...29..341D
Altcode:
NASA has conducted numerous studies to define the concepts of a
workable Solar Optical Telescope (SOT). We describe SOT as it is
envisioned by the U.S. solar community. The final configuration is not
entirely defined, as it is being proposed on the basis of performance
specifications and the instrument configurations for the first flight
are just now being evaluated.
Title: Future directions in ground-based optical observations.
Authors: Dunn, R. B.
Bibcode: 1981BAAS...13..548D
Altcode:
No abstract at ADS
Title: Solar instrumentation: What's next?
Authors: Dunn, Richard B.
Bibcode: 1981siwn.conf.....D
Altcode:
No abstract at ADS
Title: Design and performance of a new emission-line coronograph.
Authors: Smartt, R. N.; Dunn, R. B.; Fisher, R. R.
Bibcode: 1981SPIE..288..395S
Altcode:
A new emission-line solar coronagraph is described that photographically
records coro-nal emission of the Fe XIV (5303 Å) and Fe X (6374 Å)
lines, and prominences and the solar disk in Hα (6563
Å). The basic optical system consists of a 20-cm aperture, f/11
aspheric singlet objective and four secondary optical systems--one
for each image channel--that are sequentially switched into the
beam. Interference filters and a specially-designed Lyot birefringent
filter isolate spectral bands ≍ 1 Å at the three wavelengths. The
efficiency of this filtering and special constructional features
result in an exceptionally small amount of scattered light reaching
the film plane. Coronal images can be recorded in skies some 2.5
times brighter than is typical for earlier designs of emission-line
corona-graphs. Features of the data obtained so far, including high
contrast and high spatial resolution images and the detection of
extremely rapid coronal changes, are discussed.
Title: Science opportunities with the SOT
Authors: Dunn, R. B.
Bibcode: 1980fsoo.conf..245D
Altcode:
No abstract at ADS
Title: Solar Optical Telescope (SOT)
Authors: Dunn, R. B.
Bibcode: 1980fsoo.conf..135D
Altcode:
No abstract at ADS
Title: Trends in solar instrumentation
Authors: Dunn, R. B.
Bibcode: 1980fsoo.conf...23D
Altcode:
No abstract at ADS
Title: Trends in solar instrumentation.
Authors: Dunn, R. B.
Bibcode: 1979MmArc.106...23D
Altcode:
No abstract at ADS
Title: Solar optical telescope (SOT).
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..135D
Altcode:
No abstract at ADS
Title: Science opportunities with the SOT.
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..245D
Altcode:
No abstract at ADS
Title: Transferring a ground-based telescope to the Shuttle
Authors: Dunn, R. B.
Bibcode: 1978guco.conf.....D
Altcode:
The procedure for transferring a ground-based telescope to the Shuttle
is reviewed. Attention is given to equatorial mounts, the bearings
for the right ascension axis, and the precision drive system. Methods
for obtaining subarcsecond pointing are indicated with reference to
bandwidth, a feed-forward servo loop, limit vernier rocket firings,
photographs made from short exposures, and computer deconvolution.
Title: Trends in solar instrumentation
Authors: Dunn, R. B.
Bibcode: 1978fsoo.conf...23D
Altcode:
No abstract at ADS
Title: Science opportunities with the SOT
Authors: Dunn, R. B.
Bibcode: 1978fsoo.conf..245D
Altcode:
No abstract at ADS
Title: Solar Optical Telescope (SOT)
Authors: Dunn, R. B.
Bibcode: 1978fsoo.conf..135D
Altcode:
No abstract at ADS
Title: Preliminary design analysis for the solar optical telescope
main mirror actuator
Authors: Dunn, R. B.
Bibcode: 1977STIN...7821999D
Altcode:
The resolution of the SOT Gregorian telescope was maintained if the
conic foci of the elliptical secondary and parabolic primary were made
to coincide within plus or minus 38 microns across the prime focus plane
and to within 5 microns in focus. An error in coincidence across the
focal plane caused all point images to show additional coma with all
the comatic tails pointing in the same direction. An error in focus
became magnified by the square of the magnification of the secondary
and simply increased the diameter of the point source. Offsetting or
rastering the sun may be accomplished by swinging the primary in an
arc about the point of coincidence of the conic foci so long as the
coincidence is kept to within the tolerance stated.
Title: Solar activity (Activité solaire).
Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.;
Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.;
Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.;
de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman,
G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P.
Bibcode: 1976IAUTA..16b..13N
Altcode:
No abstract at ADS
Title: A Phenomenological Study of High Resolution Granulation
Photography
Authors: Labonte, B. J.; Simon, G. W.; Dunn, R. B.
Bibcode: 1975BAAS....7..366L
Altcode:
No abstract at ADS
Title: A Phenomenological Study of High-Resolution Granulation
Photographs
Authors: LaBonte, Barry J.; Simon, George W.; Dunn, Richard B.
Bibcode: 1974BAAS....6..285L
Altcode:
No abstract at ADS
Title: Preliminary Interpretation of Diode Array Simultaneous
Observations of He I and Ca II Line Profiles in Collaboration with ATM
Authors: Linsky, J. L.; Dunn, R. B.; Rust, D. M.
Bibcode: 1974BAAS....6S.290L
Altcode:
No abstract at ADS
Title: Properties of the Solar Filigree Structure
Authors: Dunn, R. B.; Zirker, J. B.; Beckers, J. M.
Bibcode: 1974IAUS...56...45D
Altcode:
No abstract at ADS
Title: A 512-channel photodiode array for solar observations.
Authors: Dunn, R. B.; Rust, D. M.; Spence, G. E.
Bibcode: 1974inas.conf..109D
Altcode:
No abstract at ADS
Title: A 512-channel photodiode array for solar observations
Authors: Dunn, R. B.; Rust, D. M.; Spence, G. E.
Bibcode: 1974SPIE...44..109D
Altcode:
The Sacramento Peak Observatory has developed and placed in operation
an array of photodiodes in the focal plane of a high dispersion
spectrograph. The diodes record solar phenomena in the 4000-11000 A
range. Signals from the diodes are digitized and computer processed into
photographs or other output forms in real time. By varying the placement
of 32-diode blocks in the spectrograph, any combination of wavelengths
may be used in the construction of spectrograms, spectroheliograms,
magnetograms and tachograms. Spatial resolutions vary between 1/2 and 2
arcsec with a spectral resolution of up to 0.02 A. The signal-to-noise
ratio for a single observation is limited in most cases by scintillation
to 300:1. Several examples of computer processed photograms are given.
Title: The Solar Filigree
Authors: Dunn, Richard B.; Zirker, Jack B.
Bibcode: 1973SoPh...33..281D
Altcode:
As a birefringent filter is tuned from the center of Hα to the
continuum the Hα bright mottles appear to break up into a network of
grains. The name `filigree' is suggested for this bright network. Its
size, shape, contrast and time evolution is described as well as its
relation to the `abnormal' granulation, magnetic field and spicules.
Title: A Morphological Study of Solar Spicules
Authors: Lynch, D. K.; Beckers, J. M.; Dunn, R. B.
Bibcode: 1973SoPh...30...63L
Altcode:
From improved spicule filtergrams obtained with the Sacramento Peak
vacuum telescope we measured some spicule properties. The spicule
diameter of 950 km was well resolved. A small decrease of diameter
with height was observed confirming older observations. The expansion
of the spicule was found to be at least an order of magnitude less
than reported by Mouradian. Spicule counts are very sensitive to the
threshold intensity of the observations. Counts, and their dependence
on threshold intensity, height and wavelength are reported.
Title: A Multichannel Diode Array for Solar Observations
Authors: Dunn, Richard B.; Spence, Glenn E.
Bibcode: 1973BAAS....5T.271D
Altcode:
No abstract at ADS
Title: Cinematography of Solar Granulation
Authors: Dunn, R. B.; Mann, G. R.; Simon, G. W.
Bibcode: 1973BAAS....5S.271D
Altcode:
No abstract at ADS
Title: New Multichannel Spectrometer at Sacramento Peak
Authors: Dunn, R. B.; Epstein, G. L.; Hobbs, R. W.; Maran, S. P.
Bibcode: 1972BAAS....4S.381D
Altcode:
No abstract at ADS
Title: A Search for the Photospheric Origin of Spicules
Authors: Dunn, R. B.; Zirker, J. B.
Bibcode: 1972BAAS....4T.381D
Altcode:
No abstract at ADS
Title: High resolution solar observations.
Authors: Dunn, R. B.
Bibcode: 1972spre.conf.1657D
Altcode: 1972spre....2.1657D
No abstract at ADS
Title: Solar Instrumentation (Part II)
Authors: Dunn, Richard B.
Bibcode: 1971spas.conf...71D
Altcode:
No abstract at ADS
Title: Optical performance of vacuum solar telescope.
Authors: Dunn, R. B.
Bibcode: 1971BAAS....3..267D
Altcode:
No abstract at ADS
Title: Coronal Events Observed in 5303 Å
Authors: Dunn, R. B.
Bibcode: 1971ASSL...27..114D
Altcode: 1971psc..conf..114D
No abstract at ADS
Title: Sacramento Peak Magnetograph
Authors: Dunn, R. B.
Bibcode: 1971IAUS...43...65D
Altcode:
No abstract at ADS
Title: Computer Control of the Vacuum Solar Telescope
Authors: Dunn, R. B.
Bibcode: 1971PROE....8...37D
Altcode: 1971IAUCo..11...37D; 1971auoa.conf...37D
No abstract at ADS
Title: Sacramento Peak's New Solar Telescope
Authors: Dunn, Richard B.
Bibcode: 1969S&T....38..368D
Altcode:
No abstract at ADS
Title: The Chromospheric Spectrum at the 1962 Eclipse
Authors: Dunn, R. B.; Evans, J. W.; Jefferies, J. T.; Orrall, F. Q.;
White, O. R.; Zirker, J. B.
Bibcode: 1968ApJS...15..275D
Altcode:
A joint expedition of the High Altitude Observatory, Sacramento Peak
Observatory, and the National Bureau of Standards obtained slitless
spectrograms of the flash spectrum at the February 5,1962, total eclipse
of the Sun. The spectrograms covered the wavelength range of about
3200 to 9100 A with a height resolution of 100 km. The spectrographic
equipment, the observations, the photometric calibration procedures,
and the methods adopted to reduce the large quantity of data are
described. The results are presented in a set of tables that show the
wavelength and identification (where known) of each of the 3500 lines
recorded. A separate set of tables lists the intensity of each line at
each height. The latter tables are ordered according to the element,
ionization stage, and multiplet number associated with the line.
Title: Recent D2 Spectroheliograms
Authors: Dunn, Richard B.
Bibcode: 1968AJS....73S..59D
Altcode:
No abstract at ADS
Title: Trends in Solar Instrumentation
Authors: Dunn, Richard B.
Bibcode: 1968AJS....73T..59D
Altcode:
No abstract at ADS
Title: A Gyro-Stabilized Airborne Eclipse Spectrograph built at
Sacramento Peak
Authors: Dunn, R. B.
Bibcode: 1966ISAT....5..119D
Altcode:
No abstract at ADS
Title: The Coronal Emission Spectrum During the Solar Eclipse of
May 30 1965
Authors: Curtis, G. Wm.; Dunn, R. B.; Orrall, F. Q.
Bibcode: 1965soec.conf..137C
Altcode:
No abstract at ADS
Title: Coronal Eclipse Spectrographs
Authors: Curtis, G. Wm.; Dunn, R. B.; Orrall, F. Q.
Bibcode: 1965soec.conf..133C
Altcode:
No abstract at ADS
Title: The Structure of the Inner Solar Corona on 30 May 1965
Authors: Curtis, G. Wm.; Dunn, R. B.; Orrall, F. Q.
Bibcode: 1965soec.conf..147C
Altcode:
No abstract at ADS
Title: An evacuated tower telescope
Authors: Dunn, Richard B.
Bibcode: 1964ApOpt...3.1353D
Altcode:
Available from http://www.opticsInfoBase.org/abstract.cfm?id=13582;
Title: Solar Telescope Planned for Sacramento Peak.
Authors: Dunn, Richard B.
Bibcode: 1964AJ.....69..540D
Altcode:
A new solar telescope is planned for the Sacramento Park Observatory,
Sunspot, New Mexico. The telescope configuration is as follows: Light
from the sun passes through a quartz window to two quartz flat mirrors,
all mounted in the turret. The turret is servo-operated in elevation and
azimuth to track objects in different parts of the sky. Light from the
turret passes through an iris that controls the size of the aperture
and then passes downward inside a tube that extends approximately
130 ft to the table and an additional 200 ft below. The diameter of
the tube from the upper portion of the telescope is 4 ft. Below table
level the tube expands to 10 ft diameter. At the bottom of the tube
the light falls upon a spherical objective mirror that reflects the
sunlight 180 ft back up the tube, and forms an image of the sun at
ground level. The approximate diameter of this mirror is 64 in. Its
focal length is 180 ft. The main mirror, or objective mirror, may be
tilted to send the light through any of five exit windows. It is also
tilted to correct for errors in tilt when the focus of the mirror is
changed. The sunlight passes through the exit windows to auxiliary
instruments that are mounted in a cluster around the center of the
telescope at ground level. The entire optical system, including the
space between the entrance window in the turret and the five exit
windows is evacuated to eliminate turbulance inside of the telescope
caused by sunlight heating the air. In order to control the rotation of
the image, all the vacuum tubes and auxiliary instruments are rotated
around a vertical axis by a servo motor mounted at ground level. This
entire movable mass of 250 tons is supported on a mercury mass float.
Title: Astronomers Gather for Eclipse in New Guinea
Authors: Dunn, Richard B.
Bibcode: 1962S&T....23..124D
Altcode:
No abstract at ADS
Title: The line and continuous emission observed in two limb flares
Authors: Dunn, R. B.; Jefferies, J. T.; Orrall, F. Q.
Bibcode: 1960Obs....80...31D
Altcode:
No abstract at ADS
Title: Solar Limb Darkening Near λ 6563 from 0.9 to 1.00 R.
Authors: Dunn, Richard B.
Bibcode: 1959ApJ...130..972D
Altcode:
A curve of solar limb darkening from 0.9 to 1.00 radius has been
obtained in the continuum near Ha. The observation has been corrected
for the instrumental profile of a point distribution of light.
Title: Hα chromosphere gradients.
Authors: Dunn, Richard B.
Bibcode: 1957AJ.....62..141D
Altcode:
A method of reduction is worked out for obtaining Ha gradients in
the solar chromosphere from films taken during 1955 at the Sacramento
Peak Observatory with the chromosphere camera described at the Troy
A.A.S. meeting. The films are photographed through a 3.4 A half-width
birefringent filter. The individual frames include a simultaneously
photographed "off-band" picture that represents the limb, the diffuse
scattered light, and the continuum. By subtracting the light in the
off-band picture from that in the "on-band" picture and by correcting
for line profiles, different absolute intensities, zero points
and seeing, Ha gradients are derived for various features on the
limb. Due mainly to the wide pass band of the filter compared to that
of the Ha line the corrections are found to be reasonably small and
relatively unaffected by any of the known variations in line profiles
and observed radial velocities. Points of large radial velocities
are easily avoided. According to the observed Ha line profiles on
the disk, disk light should very nearly cancel out. Minor variations
in the Ha Fraunhofer profiles do not affect the results. The seeing
is inferred from the widths of the spicules in the pictures. These
widths are on the order of 500-600 km. Corrections to the gradients
for seeing are very small. About 6o of these gradients are measured
and corrected. Many of the curves of intensity versus height turn out
to be essentially straight lines in the 1000 to 7000 km region. Many of
these gradients can be almost exactly superimposed by height shifts up
to 1500 km. According to these results gradients measured close together
over regions 1500 km wide are found to reproduce all current Ha results
measured during eclipse. Somewhat steeper and flatter gradients are
also observed. Sacramento Peak Observatory, Sunspot, N. M.
Title: A multiple-image camera for chromosphere photometry.
Authors: Dunn, Richard B.
Bibcode: 1956AJ.....61....3D
Altcode:
A new camera has been constructed and is in operation at Sacramento
Peak solely for the study of the Ha chromosphere. This camera utilizes
a i5-inch singlet lens of ~56-inch equivalent focal length and a 3.4
A Ha birefringent filter. The optical system employs a series of beam
splitters that enable four pictures of a single 120 region of the
chromosphere to be taken simultaneously. These pictures differ from
each other in occulting, intensity and wave length. The multiple-image
feature enables an evaluation of the scattered light and the seeing,
and permits a greater usable density range. A complete absolute
standardization system is provided. Two types of 35 mm pictures are
taken, one a survey completely around the limb and the ~ther a movie
at the rate of 16 frames per minute. Upper Air Research Observatory,
Sunspot N. Men.
Title: Solar Instrumentation
Authors: Evans, J. W.; Dunn, R. B.
Bibcode: 1956SCoA....1....5E
Altcode:
No abstract at ADS
Title: New stars with proper motion exceeding 0.5 annually.
Authors: Dunn, R. B.; Hugues, H.; Luyten, W. J.
Bibcode: 1955AJ.....60..274D
Altcode:
No abstract at ADS
Title: A quartz polaroid birefringent filter for the K line.
Authors: Dunn, Richard B.
Bibcode: 1953AJ.....58R..38D
Altcode:
Since the birefringent filters for the Ha line have been so
successful in showing prominences and disc features on the sun it
seemed worthwhile to build a filter for the K line. The filter should
be very effective because the K line is such a wide absorption line
in the solar spectrum. On the other hand, scattered light is about
eight times more intense at the K line than at the Ha line. A 4A
half-width filter was designed and constructed at the Harvard College
Observatory. It consists of 13 quartz plates and 5 polaroids arranged
in the Evans' split-element design that reduces the number of polaroids
required. The thickest plate is 17.8 mm, which is about one- third the
thickness of the equivalent Ha plate. Type KN 36 polaroid was selected
for the polarizing elements. Prominences and some disc features have
been photographed with SA I film and a 2~21 mm thick Corning 5874
glass filter and the birefringent filter. The speed of the system is
about ten times slower than the corresponding Ha filter. This low speed
results in part from absorption in the telescope and polaroid, and from
the slower film. Present plans include trying different polaroids,
and various auxiliary filters to improve the speed and contrast of
the filter. Additional plates may be added to narrow the filter to
I A. The research reported in this paper has been sponsored by the
Geophysics Research Directorate of Air Force Cambridge Research Center,
Air Research and Development Command. Harvard College Observatory,
Cambridge, Mass.