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135
heliosphere, its variation in structure, and its effect
on the modulation of cosmic rays. In situ observations
with the International Solar Polar Mission and the Origin
of Plasmas in the Earth's Neighborhood (OPEN) mission will
provide needed information on these questions and on the
solar spindown due to the solar-wind transport of angular
momentum.
IV. DETAILED DESCRIPTION OF THE WOIR PROGRAM
FOR THE 1980 'S
We now give a detailed justification of the new initi-
atives in our proposed WOIR program for the 1980'S . In
Section A we describe and justify our major recommen-
dations; in Sections B and C we discuss other categories
of W OIR projects that we believe are also vitally
important to the health of astronomy.
A. Major Recommendations
1. The 15-Meter New Technology Telescope and Closely
Related Projects
The time is now ripe for a full-scale attack on the prob-
lems of the formation and evolution of galaxies and
clusters of galaxies, the nature of nonluminous matter in
galactic halos, the character of supermassive objects in
galactic cores; the evolution of molecular clouds; and
the formation and evolution of galaxies, stars, and
planetary systems. Ground-based observations are a key
element in all of these areas of research. The optical
and infrared (JR) regions of the spectrum are unique in
their ability to provide morphological studies and
spectral diagnostics of velocities, compositions, and
excitation that are crucial to the interpretation of
astronomical phenomena. New space observatories of all
types, as well as radio facilities on the ground, will
increase the demand for ground-based optical and IR
observations--particularly for high-resolution spectro-
photometry of faint sources.
Space Telescope (ST) will permit astronomers to image
galaxies and stars with spatial resolution an order of
magnitude greater than that routinely achievable on the
ground. This capability will result in the detection of
unresolved objects up to 100 times fainter than has been
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136
possible in the past. This tremendous gain in spatial
resolution, coupled with access to the ultraviolet (W)
region of the spectrum, are the main reasons that moti-
vated the astronomical community to unite behind ST as a
major initiative for the 1980's. We expect ST to provide
fundamental new insights into the scale and geometry of
the Universe and into the formation and evolution of gal-
axies. For example, ST will provide a glimpse of objects
at the very limits of the observable cosmos. However,
many of the sources to be discovered will be too faint
for effective spectroscopic and spectrophotometric analy-
sis by ST itself. Such analysis is essential for the
proper understanding of the basic physical properties--
temperature, density, excitation, chemical composition,
velocity--of the newly discovered objects. Rapid vari-
ability is a common feature of matter near compact objects
and makes high time resolution an important additional
consideration. Hence, for many programs, we also require
a very much larger ground-based telescope to complement,
fully utilize, and understand the discoveries made by ST.
As ST will do in the optical and W regions, the
Shuttle Infrared Telescope Facility (SIRTF), a 0.85-m
cryogenically cooled telescope in space, will vastly
extend our capabilities in the IR spectral region. At
wavelengths beyond 3 ~m, the low thermal background of
SIRTF will permit a gain in sensitivity for low-resolution
spectrophotometry between 100 and 1000 times that of the
largest ground-based facilities. This telescope will
greatly expand our knowledge of luminous objects in galac-
tic nuclei, the early evolution of stars, and the proper-
ties of star-forming regions through imaging, photoelec-
tric, and moderate spectral resolution observations.
SIRTF will lift the gray-body curtain of thermal
radiation generated by warmer telescopes and by our own
Earth's atmosphere to reveal a new thermal view of our
Galaxy and Universe. However, the capabilities of SIRTF
in the areas of very high spectral and spatial resolution
are limited by its relatively small aperture. For obser-
vations of high spectral resolution, SIRTF will generally
be strongly detector-noise limited. While improvements
in this area can be achieved by development and use of
more sensitive detectors (both discrete and array), it is
nevertheless likely that the detailed study of kinematics
and chemical abundances will depend in large measure on
the availability of a very large telescope capable of
carrying out spectroscopic observations at a spectral
resolution of about 105.
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137
The SIRTF telescope is intended to be diffraction
limited beyond 5 Em. A 15-m telescope located at a
good site can be diffraction limited at 20 Em during
periods of excellent seeing and will provide more than 10
times the spatial resolution of SIRTF in the near- and
mid-infrared regions. Thus, a large ground-based
telescope can also provide an essential, high-resolution
imaging capability as a complement to the SIRTF observing
program.
High-energy observations, especially those from the
Einstein x-ray observatory, have demonstrated that the
full utilization of x-ray data demands extensive optical
work. Samples of quasars and galaxy clusters selected by
x-ray criteria require extensive optical analysis for
determinations of magnitudes, spectra, and red shifts.
While this work is within the reach of ground-based
telescopes of moderate size, not enough telescope time is
available at present to carry it out effectively.
Finally, we note that the Very Large Array (VLA)--a
centerpiece of the astronomy program for the 1970's--is
now in nearly full operation. It has begun to map the
radio sky at spatial resolutions once thought to be the
province of optical astronomy alone. Critical problems
such as the origin and evolution of energetic galactic
nuclei are receiving major impetus from VLA observations.
Again, appropriate complementary studies at optical and
IR wavelengths require spatial and spectral resolutions
difficult to achieve with current ground-based tele-
scopes. Already half of the requests for use of the 4-m
telescope at Kitt Peak National Laboratory (KPNO) are for
programs directly related to, or stimulated by, space-
craft and radio observations. The reason for this is
clear--observations at optical and IR wavelengths are
necessary for a broad understanding of the physical mech-
anisms responsible for the peculiar behavior of these
unusual and newly discovered objects.
a. The Scientific Impact of the New Technology
Telescope
A 15-m New Technology Telescope (NTT) will have
capabilities unique in the long history of astronomy. It
will increase by an order of magnitude the photon-
gathering power of our largest telescopes; with the use
of interferometric techniques it will furthermore achieve
angular resolution of 0.03 arcsec at the shorter IR
wavelengths and resolution of about 0.3 arcsec near 20
Em. NTT will provide the spectroscopic capability that
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will be absolutely essential to follow
observations and will provide high angular resolution at
IR wavelengths less than 20 Em. For spectroscopy, a
15-m telescope is superior to ST at all wavelengths acces-
sible from the ground except for observations requiring
high angular resolution (e.g., galactic nuclei).
Spectra of faint stars are necessary for an under-
standing of the chemical evolution of our Galaxy, the
dynamics of the Galactic halo, and the ages of dwarf
spheroidal galaxies. With a 15-m telescope, halo stars
down to magnitude 25 can be found by broadband photo-
graphy and studied using abundance-sensitive intermediate-
band spectrophotometry. White dwarfs in the nearest glob-
ular clusters can be studied, and the main sequence can
be reached in nearby dwarf spheroidal galaxies. All of
these problems are threshold problems in the sense that
there are no nearby bright objects suitable for study.
Without the light-gathering power of a 15-m NTT there
will be insufficient photons to mount these decisive
spectroscopic programs.
Distant galaxies and dim quasars provide their own
challenge to image and to study spectroscopically. When
did clusters collapse? Inhomogeneities in the surface
density of galaxies can be measured out to a red shift of
unity. Spectrophotometry of high-red-shift galaxies will
allow us to see the 2000-3000-l region in the spectra
of distant galaxies and search for spectral evidence of
young stars. Study of QSO absorption lines will allow us
to measure directly the chemical and isotopic composition
of gas at large red shifts. Present-day spectra do not
achieve a high enough signal-to-noise ratio at high dis-
persion to determine the strengths of faint lines needed
to obtain accurate chemical composition; for example,
neither H2 nor D has been detected with certainty in
quasar spectra.
m e combination of high spatial resolution with suf-
ficient photon-collecting power to achieve spectral
resolution on the order of 105 will permit definitive
IR studies of molecular clouds and imbedded objects. For
studies at wavelengths less than 20 Am, the 15-m NTT
will provide an important programmatic and scientific
link between SIRTF and a Large Deployable Reflector in
space.
and SIRTF
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b. Technical Considerations for a 15-Meter New
Technology Telescope
The New Technology Telescope will almost certainly
take a form rather different from that of the traditional
telescope, which has a long primary focal length and
thick, monolithic primary mirror. A short-focal-length
telescope based on the MMT concept, or a segmented pri-
mary mirror, or perhaps even a thin monolith are examples
of new approaches that can substantially reduce the
weight, dome size, and, hence, cost of very large tele-
scopes. There are, furthermore, compelling reasons for
constructing a very large collecting aperture in the form
of a single telescope, rather than simply combining data
obtained by all the existing ground-based telescopes.
To begin with, we anticipate that one important class
of applications of such a facility will center around its
power for infrared observations. The IR scientific impact
of a 15-m-class ground-based telescope is based primarily
on two aspects of its performance: photon-collecting
power and spatial resolution capability.
Photon-collecting power is particularly crucial for IR
spectroscopy. At wavelengths less than 2.5 ~m, the
thermal emission of the telescope itself is very small,
and the performance of present-day large telescopes and
of the proposed SIRTF facility is detector-noise limited
at these shorter wavelengths. A 15-m telescope will
provide the aperture for at least an order-of-magnitude
increase in sensitivity for a wide range of spectral
observations, ranging from moderate-resolution studies of
continuum and emission lines from atoms and molecules to
very high spectral-resolution studies of atomic and
molecular emission and absorption systems. In the
3-25-pm wavelength range, thermal emission by the
telescope will generally limit performance at low and
moderate spectral-resolutions, but at a resolution of
105 or greater, similar order-of-magnitude gains are
possible. In addition, as mentioned earlier, the spatial-
resolution capabilities of a 15-m telescope, utilizing
interferometric techniques, will permit observations at
spatial resolutions of about 0.03 arcsec or less at the
shorter IR wavelengths, while resolutions of about
0.3 arcsec will be possible near 20 ~m.
In order to realize the scientific potential of such a
New Technology Telescope, it appears necessary that the
collecting area be placed on a single mount rather than
distributed among individual telescopes, for the
following reasons:
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1. Present IR detectors and near-future prospects for
the 1-25-pm range are such that moderate- and high-
resolution spectroscopy will be detector-noise limited.
Thus, an efficient, convenient system for focusing
photons from the entire collecting area onto a single
detector element is required to take full advantage of
the larger collecting area. - ~
The gain in signal-to-noise
ratio (S/N) tor a collecting area focused on a single
detector, compared with n separate elements/detectors of
the same total collecting area, is equal to the square
root of n. The most straightforward configuration for
this arrangement would place the entire collecting area
on a single mount.
2. m e capability for high-spatial-resolution obser-
vations at the shorter IR wavelengths requires phased
beam combining for interferometric purposes at wavelengths
of about 1 Am or greater.
_ This can be most easily
achieved with a single mount. The gain in spatial
resolution is approximately the maximum separation of
phased elements divided by the diameter of a coherent
array element, which is also equal to the square root of
n if the n elements are combined into a filled phaseable
aperture.
3. m e potential of improved seeing or seeing correc-
tions at the longer IR wavelengths, particularly at 10
and 20 Em, can lead to smaller beam sizes for photom-
etry, imaging, and spectroscopy. In order to realize
this, coherent beam combining over a significant field of
view is required, which again leads to a single mount if
not a single dish. The potential gain in S/N is again
equal to the square root of n if the n elements are
combined into a filled aperture.
In addition, at optical wavelengths there will also be
some spectroscopic applications that will be detector-
noise limited, and for such problems arguments similar to
those made for the IR program apply. But of perhaps
greater importance is the fact that the emerging field of
speckle interferometry promises outstanding capabilities
for large single-mount telescopes.
Speckle techniques for faint objects have so far been
limited to the derivation of simple quantities such as
angular size or the separation of two or three components
of a multiple stellar system. For example, studies
employing two telescopes have already resolved Pluto.
Full image reconstruction is available and appears to
have been achieved for a star both by simple crude
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techniques and by detailed computer processing. The
limiting magnitude for speckle studies is independent of
telescope size but depends strongly on seeing.
The limiting angular resolution of a 15-m equivalent
aperture telescope will depend on how the aperture is
arranged, but it may well be about 4 milliarcsec at
5000 A. Note that at 10 Em the corresponding resolu-
tion will be 0.08 arcsec, or almost as good as the
performance of ST at visual wavelengths. The visual
angular resolution is comparable with that which can be
achieved by radio interferometry using intercontinental
baselines.
A study of possible goals for these new techniques
reveals that they are so advanced that they will cer-
tainly open up entirely new areas of research. The use
of the highest possible resolution at all wavelengths
would be helpful in trying to understand the process of
star formation and the origin of protoplanetary conden-
sations. At a distance of 200 pa, the range of angular
resolution available would cover the linear range from
0.75 AU in the visible to 30 AU at 20 Am.
The fundamental requirement that the NTT be optimized
for both IR and optical observations places a number of
constraints on its design and location:
Field of View. A large field of view for NTT is
desirable both to complement the relatively small field
(2.7 aramin) of ST and to take advantage of instruments
that can obtain simultaneously the spectra of many
objects in the same field.
Coherence. NTT should be diffraction limited at 20
Am. A diffraction limit of 1 arcsec at 20 Am requires
that the diameter of an individual coherent element be at
least 5 m; it would be preferable for the entire collect-
ing area to be coherent, since coherence over larger sizes
achieved in excellent seeing or by interferometric methods
will allow even better spatial resolution.
Geometry. If NTT is not of a single-dish design, then
for spectroscopy in both the optical and IR regions the
light from the program object(s) must be brought with
high efficiency to a common instrument. This is required
to realize fully the low-noise potential of silicon detec-
tors and to provide an optical configuration that will
allow detector-noise-limited performance from existing
near-IA detectors and projected arrays.
Emissivity. For telescope-background-limited observa-
tions in the thermal IR region, a reduction of the emis-
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sivity by a given factor is equivalent to an increase in
collecting area by the same factor. The effective emis-
sivity of NTT should be as low as possible--5 percent is
a difficult but realizable goal. In addition, the tele-
scope emission must be steady to avoid introduction of
excess noise.
Image Quality.
Seeing is of extreme importance in
determining the limiting magnitude of a ground-based
telescope. A reduction of a factor of 2 in the diameter
of the seeing disk reduces the threshold brightness by a
factor of 2; for sky-limited observations this is equiv-
alent to doubling the telescope aperture. Good seeing is
also important for spectroscopy, where the efficiency of
a spectrograph is controlled principally by the size of
the slit that is required to pass most of the light.
Since for a well-designed telescope the site sets the
limit to seeing, it is absolutely critical that the
15-m-class NTT be located at a site of known excellent
seeing. At some sites already in use, the optical seeing
is occasionally observed to be 0.5 arcsec or better. In
the IR the seeing might be even better. Experience with
the Multiple-Mirror Telescope (MMT) has shown that, if
care is taken to minimize the effects of local dome and
mirror seeing and to make the optics of very high quality,
images of this size will be achieved for a useful frac-
tion of the time. The effect of mirror seeing (convec-
tion from the mirror surface) can be minimized through
the use of thin mirrors, which reach thermal equilibrium
in 2-3 h.
Site Selection. Choice of a site is critical in
obtaining optimum performance from the 15-m-class NTT--
or, indeed, from any telescope. In addition to seeing
factors (such as low water vapor), absence of light pol-
lution, accessibility, and reasonable cost of development
are important. We note that the National Science Founda-
tion (NSF) has undertaken a program of identifying and
protecting excellent astronomical sites. This is an
important effort because the majority of sites now in use
are either overcrowded and/or threatened with light
pollution. We therefore strongly endorse the NSF efforts
in this area and recommend that the program proceed
vigorously enough to allow selection of a site for the
15-m-class NTT by the mid-1980's.
Instrument Changes and Scheduling. The 15-m-class NTT
will be capable of doing more in an hour than present
large telescopes can do in a night, and in some cases
more than can be done in an observing run of several
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nights. To take the best advantage of the varying
conditions that arise at ground-based observatories--
changes in seeing, in cloud cover and photometric con-
ditions, and in sky brightness from moon and twilight--
provision for rapid interchange of key instruments should
be an integral part of the telescope design. (For
example, sky-limited imaging or spectroscopy should be
carried out in the best seeing. Again, it would be advan-
tageous to change instruments at moonrise or moonset and
again at dawn and dusk.) It follows that NTT should be
queue-scheduled for at least a large fraction of its
operation, with several programs interleaved. The pattern
of use will probably be rather different from what is now
customary; one can anticipate scheduled programs that
require as little as an hour of integration, given the
enormous power of the telescope, and in many cases the
observer will not need to come to the telescope.
Construction. The experience gained from the building
of this decade's 4-m-class telescopes allows the design
and construction of much larger telescopes that will be
substantially less expensive than the extrapolated costs
of the traditionally designed facilities constructed in
the past. Indeed, there is now general agreement that,
through the use of thin mirrors (10 cm) and altazimuth
mounts, the weight and dome size of 10- to 15-m telescopes
can be kept comparable with those of 4-m telescopes built
in the last decade.
A number of groups are already considering the prob-
lems associated with the construction of 7- to 15-m-class
instruments. The concepts that now appear most viable
are a multiple-mirror telescope with 5- to 6-m monolithic
elements or a single-mirror telescope of short focal
ratio, probably synthesized from separately constructed
off-axis segments. During the early 1980's, support
should be provided for a coordinated program of technology
development leading to the selection of a specific tele-
scope design. With these studies in hand, it should be
possible to select an appropriate design for a 15-m NTT
in the mid-1980's and to begin construction with a goal
of First light" by the end of the decade.
The New Technology Telescope: Summary
Broad support exists within the astronomical com-
munity for construction of larger telescopes. Evidence
for this support comes from the initiatives already taken
by the Universities of California, Texas, and Arizona and
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by KPNO to carry out design studies and tests of various
concepts for building very large telescopes. Indeed, it
is precisely because of these initiatives that we have a
clearer picture of the performance standards for a 15-m
NTT and confidence that these standards can be met. If
the steps outlined in this recommendation are taken, we
will enter the 1990's with the first dramatic increase in
telescope aperture since the completion of the 5-m Hale
telescope 35 years ago.
d. Support Telescope Program for the 1980's
Most of the NTT observing time will of necessity be
dedicated to those frontier and threshold programs that
require the enormous photon-gathering power and high spa-
tial resolution of this magnificent instrument. However,
each of these scientific programs encompasses a continuum
of sources; for each quasar, star, and galaxy of the 20th
magnitude, there are objects in the magnitude range 17-19
that are just accessible to the largest telescopes cur-
rently available. Observations of these still-faint
objects will teach us the astrophysics of quasars at a
variety of lookback times. Other observations will
determine the shapes of color-magnitude relations of
stars in external galaxies and hence delineate the his-
tory and evolution of stellar populations external to our
own. Still other observations of halo stars in our own
Galaxy in the magnitude range 17-20 will yield insights
into the early history of galactic formation. It is
reasonable to expect NTT to work only at the limits of
these populations. The combination of the 15-m threshold
observations with those from the ~smaller" telescopes
will be crucial in solving many of the frontier problems
of the 1980's.
These "smaller" telescopes might range in sizes from
about 2.5 m to larger than 7 m, but they must be state-of-
the-art facilities with the capability of producing
results competitive with the largest telescopes in use
today. For the National Astronomy Centers, dedicated
telescopes of the 4- to 5-m class seem more appropriate
than a versatile, fully instrumented telescope. Such new
telescopes should be dedicated to one or two primary
programs. This will result in decreased construction,
instrumentation, and operating costs.
Scientific results obtained with the 2.5-m telescope
at Las Campanas offer convincing evidence that a well-
constructed, imaginatively instrumented telescope of this
size at a superb site can attack and solve problems at
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the forefront of astronomy. Telescopes of this class are
attractive to university groups and offer the opportunity
for a wholesome diversity of styles and approaches to
observational astronomy. They could accommodate the
needs of specialized programs and would also encourage
technical innovation. One telescope might concentrate on
long-term, large-scale programs or on astrometry or on
observations coordinated with those from space vehicles.
Still another might arrange its scheduling to emphasize
speed of response to sudden events such as the appear-
ances of comets or supernovae or maximum coverage of
periodic phenomena in predictable systems. Instrumental
innovations such as the development of the pulse-counting
Reticon system often grow out of such environments, where
technically adventurous projects can be attempted.
As emphasized at the beginning of the section on
scientific opportunities for the 1980's, the problem of
access to telescopes with sufficient aperture to attack
the important problems perceived by the astronomical
community as scientifically exciting and fruitful has
reached a critical state. The need is so severe that
university groups have begun on their own to search for
nonfederal funding for large telescopes to serve their
needs. The federal government can play an important role
here by providing matching funds and encouragement through
the National Centers. Other large instruments should be
part of our national facilities.
The selection of new telescopes for construction during
the 1980's will depend on a variety of considerations,
including the impact on major scientific objectives,
state of the relevant technology, cost, and timeliness.
Particularly important initiatives are as follows:
A 2-Meter-Class Telescope Dedicated to High-Resolution
Spectroscopy for Solar-Stellar Studies. The application
of advanced spectroscopic-diagnostic techniques makes it
possible to extract, from subtle features of spectral-line
contours, information concerning such properties as the
distribution of temperature and density in the atmosphere,
the amplitude and structure of velocity and magnetic
fields, the abundances of the elements, and the rotation
rate of the star. The reliable inference of some of
these properties from stellar spectral lines requires
very-high-resolution, high-S/N data of the kind routinely
obtained in solar studies but hitherto unobtainable with
stellar instrumentation. The spectroscopic resolution
should be high enough (greater than 2 X 105) to over-
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Universe and the objects in it. We give here a brief dis-
cussion and endorsement without implication of priority
of some of the other programs and initiatives that we
believe are vital to the health of astronomy in the
1980's.
1. Solar-Physics Program
In addition to launching the SOT and ASO, it is necessary
to initiate two other programs that address important
problems that ASO and SOT cannot study.
a. Solar Coronal Explorer Satellite
The basic physics of solar-wind acceleration and the
time-evolution of solar coronal structures in response to
changing magnetic-field configurations are two fundamental
problems that can be addressed by a solar coronal mission
of the Explorer class. Measurements provided by this mis-
sion will provide unique insight into the more general
astrophysical problems of mass loss from stars and the
energy and momentum balance of stellar coronas, topics
that are becoming increasingly important as a result of
recent Einstein x-ray observatory and IUE discoveries.
The Solar Coronal Explorer (SCE) should contain at
least five complementary instruments:
1. A resonance-line coronagraph operating at Lyman-
alpha and the O VI resonance line at 1032 ~ is a new type
of instrument recently flown successfully on a rocket but
not yet orbited. This instrument provides a new capabil-
ity for directly measuring expansion velocities low in the
corona. It also yields information on hydrogen column
densities and measures coronal kinetic temperatures from
line widths.
2. A white-light coronagraph on SCE will provide elec-
tron column densities.
3. A soft x-ray telescope will delineate the basic
coronal structures--coronal holes in which the magnetic
fields are open, loops in which the fields are closed, and
x-ray bright points where new fields are emerging--and the
temperatures and emission measured in these structures.
4. A coronagraph operating at the He+ 304-A resonance
line will, in combination with the hydrogen Lyman-alpha
coronagraph, give the observations necessary to determine
the probably variable He/H abundance ratio in the solar
corona and inner solar wind. The mechanisms leading to
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the fractionization of atomic species in the solar wind
should be elucidated by these coronal observations.
5. Finally, a magnetograph aboard SCE will measure
the input of magnetic flux to the corona.
Together, these five instruments will measure a com-
plete set of coronal plasma parameters (temperatures,
densities, magnetic fields, abundance differentiation,
and expansion velocities) as a function of radial dis-
tance from 1 to 5 solar radii with which to test in
detail our present theory of the solar wind.
While the SCE is a unique facility in its own right,
which ideally should fly during the next solar minimum
(1986) when the wind structures are relatively simple, it
takes on added importance if flown simultaneously with
solar polar passages of the spacecraft of the Inter-
national Solar Polar Mission (ISPM) and the operation of
the Interplanetary Plasma Laboratory (IPL) spacecraft at
the Sun-Earth libration point. Simultaneous observations
by the coronagraphs and x-ray telescopes on SCE and ISPM
would give stereo views of the solar corona, which is
absolutely fundamental for understanding the three-
dim!ensional structure and evolution of coronal structures
and transients.
b. Solar Interior Dynamics Program
The discovery of an unexpectedly low neutrino flux
from the Sun has stimulated a broad re-evaluation of our
ideas about the structure and dynamics of the solar inte-
rior. Such questions as whether the Sun has a rapidly
rotating core or whether the interior undergoes episodes
of mixing have an important bearing on our understanding
of solar and stellar activity cycles. Solar seismology,
the measurement of the frequencies and amplitudes of
various solar modes of oscillation, is an important new
tool for the study of the structure and dynamics of the
solar interior.
The Solar Interior Dynamics Program has the following
four major goals:
1. m e determination of the interior dynamics and
structure of the Sun (e.g., rotation versus depth,
large-scale flows, pulsations, properties of the
radiative core);
2. The combination of the resulting models with
dynamo theories to illucidate the global magnetic
behavior of the Sun and specifically to explain the
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observations of the solar activity cycle;
3. The development of a more physically self-con-
sistent theory of convection; and
4. The application of these results to other stars on
which activity cycles, surface activity, and rotation
have been observed as the result of high-resolution
spectroscopy and x-ray observations by satellites.
Components of the Solar Interior Dynamics Program are
as follows:
1. Theoretic modeling, including computer simulations
of solar interior dynamics with dynamo processes.
2. High-precision observation of solar surface behav-
ior, specifically solar-surface motions by means of
Doppler shifts with accuracies of about 1 m/sec. The
development of a tachometer capable of 1 m/see precision
on an absolute scale is crucial. We also require mea-
surements of large-scale magnetic patterns, of large-
scale brightness patterns related to interior circula-
tions with relative accuracies of about 0.01 percent, and
of solar-diameter measurements with accuracies of 1 milli-
arcsec. The accurate measurement and identification of
the frequencies of oscillation necessary for the solar
internal temperature stratification will require continu-
ous observing sequences of a week or more. Such obser-
vations can best be obtained from experiments in Sun-
synchronous orbits. The program should begin with
long-duration observations from the South Pole, followed
by a two-week Shuttle experiment, followed later by a
longer-duration experiment (6 months or more) flown on a
free-flyer (Solar Interior Dynamics Mission) or in
conjunction with the ASO.
3. An understanding of other causes of spectral line
shifts, which, if misinterpreted, may lead to systematic
errors in the surface-motion observations. SOT will make
major contribution toward this understanding and will, in
addition, provide important information on the relation-
ship between plasma motions and magnetic fields at small
spatial scales and the variation of surface convection
across the solar surface in both space and time.
2. Sky Surveys Needed to Support Major Missions
ST, SIRTF, and the 15-m ground-based telescope are all
expensive facilities that require the support of surveys
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directed to discovering important rare objects that will
be studied in greater detail by these more powerful
instruments. A number of important survey programs have
been proposed. The W OIR Panel notes and endorses the
following.
a. Infrared Surveys from Space
Deep, all-sky surveys covering the IR from 5 to 130
Am at various spatial resolutions are essential as a
foundation for the orderly progress of IR astronomy in the
1980's. Present survey experiments include the Infrared
Astronomy Satellite (IRAS) to be launched in 1982, the
Spacelab Small Infrared Telescope to follow in 1984, and
military programs. By virtue of their unbiased sky cover-
age and high sensitivity, these surveys will vastly
increase our knowledge of the IR sky and will identify
significant classes of IR emitters in the Universe, some
of which may represent the discovery of new types of
objects. It is of the utmost importance that deep-IA
surveys from space be successfully completed.
b. Moderate and Wide-Field Imaging in the
1200-10,000-' Wavelength Region
The ST Wide-Field/Planetary Camera and Faint Object
Camera will provide a capability for imagery in the
visible and W wavelength ranges with 10 times better
than ground-based resolution and with correspondingly
improved point-source detection sensitivity. However,
the Wide-Field Camera (WFC) has a maximum field of view
of 2.7 arcmin square, and there is a demonstrated need
for imagery over larger fields in the 1200-10,000-[
range from space-based telescopes, supplemental to the
imagery to be provided by ST. This imagery would tenta-
tively have two characteristic combinations of field and
resolution: (1) high-resolution, moderate-field (nominal
0.5° field of view, 0.3 arcsec resolution) and (2) wide-
field, moderate-resolution (roughly 5° field of view,
1 to 2 arcsec resolution). In the following discussion,
we present the scientific rationale and justification for
these two types of supplemental imagery.
High-Resolution, Moderate-Field Imagery. There are a
number of important astrophysical problems requiring
photometric-quality imagery at considerably better than
ground-based resolution but with a much wider field of
view than provided by ST. Additional advantages of such
imagery, in comparison with ground-based imagery, include
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accessibility to the W and the darker sky background.
The particular advantages of a wide field of view (0.5°,
or 10 times that of the ST WFC) are for programs requir-
ing the observation of objects of large angular extent
(e.g., star clusters, nearby external galaxies, cluster
of galaxies); programs requiring large statistical sam-
ptes; study of positional dependencies; and searches for
rare objects. Such programs would require inordinately
large amounts of observing time with the ST cameras and
also would represent inefficient and perhaps inappro-
priate use of such observing time in comparison with the
programs likely to be of highest priority for ST.
The use of a "grism" with the imaging camera on the
wide-field telescope would allow spectrographic surveys
over large fields. This capability permits more accurate
determinations of spectral type and effective tempera-
ture, correction for interstellar extinction, and easier
identification of QSO's and other peculiar objects than
would be possible with imaging photometry alone. Inclu-
~ _ g . .
· · . .
Sian of the W (1200-3000 A) is especially important
for grism surveys.
Wide-Field, Moderate-Resolution Imagery. The scien-
tific problems addressed by a space-based telescope with
a wide field (5°) and ground-based resolution (1-2 arcsec)
are primarily (1) deep surveys in the ground-inaccessible
W region and (2) studies of extended, low-surface-
brightness objects at all optical wavelengths, for which
a fast focal ratio (f/3 or faster) and observations above
the terrestrial airglow are especially important.
Deep- W surveys provide a much more sensitive means
for mapping the spatial distributions of high-temperature
objects than is possible in ground-based surveys. Also,
for specific problems, far- W observations can provide
quantitative photometric data that are much more useful
than those obtained from the ground. This is particu-
larly true in the cases of hot, subluminous objects near
the end points of their evolutionary cycles, in the
central bulges or disks of external galaxies, and in
crowded regions of the Milky Way, where the far more
numerous late-type stars dominate ground-based measure-
ments.
In addition, a wide-field telescope would be appli-
cable to many of the problems discussed in connection
with the high-resolution, moderate-field telescope;
although the lower resolution would make it less useful
in crowded fields, the wider field of view would allow
collection of a larger statistical sample of a given type
of object in the observing time.
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Ground-Based Survey. There is a need to improve the
Palomar Sky Survey by repeating it on fine-grained emul-
sions. There have been several proposals to construct a
large Schmidt telescope to undertake such a survey. The
W OIR Panel suggests, however, that the Palomar Schmidt,
finished in 1948, be upgraded and used instead. To permit
the use of the fine-grained emulsions, the Palomar Schmidt
should be upgraded with an achromatic corrector that will
reduce the image size at all optical wavelengths to less
than 20 ~m; a IIIaJ sky survey should be then carried
out. Such a survey would be invaluable for ST pointing
and for astrometric purposes. Also, an objective prism
can be mounted without creating balance and weight-
distribution problems. This would permit low-resolution
spectroscopy over a wide field, a valuable capability in
the search for distant, high-red-shift quasars.
3. Planetary Observations
a. Dedicated Orbital Telescope for Solar-System
Studies
The power of remote sensing from Earth-orbiting
telescopes is now receiving wide recognition in planetary
science as a result of the successful application of
OAO-2, Copernicus, and IUE to a selection of planetary
and cometary problems. Consequently, there is great
anticipation for solar-system studies with ST and SIRTF.
However, in spite of the capability of these facilities
to attack many solar-system problems, there are also many
drawbacks and mismatches. Many solar-system observations
require telescopes to be pointed in the close vicinity of
the Sun or the Earth or require special orientations of a
spectrograph slit or require complex attitude maneuvers.
There are solar-system observations that need to be made
in spectral regions (such as shortward of 912 A), or
with combinations of spectral and spatial resolutions,
that are not necessarily appropriate for astrophysical
problems. In addition, there is clearly a problem with
the restricted time available. Many solar-system obser-
vations have either special timing requirements or need
extended periods of observations, particularly if the
observations are associated with an interplanetary
mission in progress.
Our assessment is that special consideration should be
given in the future to the concept of a dedicated orbital
telescope for solar-system studies. However, we believe
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that it is essential that this concept be developed by
NASA in the context of the overall priorities for an
integrated program of solar-system exploration.
b. Extrasolar Planetary Detection
The detection and accumulation of statistics on other
planetary systems would be an important development for
planetary astronomy; given the likelihood of reaching the
required accuracy by means of astrometric techniques, we
support the start of a cautious program in this field.
The development that we envisage should include at least
two independent research programs in order to ensure
adequate cross-checking of apparently positive results.
At present, it is generally assumed that the formation
of planetary systems is common during star formation, but,
in fact, no proof exists. The statistics of planetary
formation will reflect directly on the physical status
and the relative peculiarity of our own solar system.
They are also involved in the estimation of the prob-
ability of other life in the Galaxy. While attempts have
been made in the past to detect planetary systems by
astrometric means, these efforts have not attained the
required accuracy. A precision of 10 4 to 10 5
arcsec--one to two orders of magnitude better than what
is possible now--is required, and this precision must be
maintained over a time scale of 10 years.
Recent studies in NASA-sponsored workshops have indi-
cated that such precision may now be technically possible
through use of a dedicated astrometric facility. Other
methods include the detection of small periodicities in
radial velocity, spacecraft interferometry, and direct
detection by means of specially apodized telescopes of
larger aperture.
At present, it appears that the two
most likely candidate instruments are a dedicated astro-
metric telescope or a high-spatial-resolution IR tele-
scope that might detect fragmentation in collapsing proto-
stars. While it is not now possible to identify a specif-
ic instrument concept, it is likely that there will be a
convergence of opinion on instrumentation for this prob-
lem in the next two or three years.
4. Observatory Support
Optical astronomy is in a transitional period. The
optical facilities approved and proposed for spaceflight
in the 1980's will provide a capability in the decade
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that far exceeds the capabilities of the 1970's. mere
is good reason for this evolution--astronomy from space
is free from the deleterious effects of the Earth's atmo-
sphere. Nevertheless, ground-based astronomy will con-
tinue to play a pivotal role in the 1980's. On an abso-
lute scale, space astronomy will continue to be very
expensive; there are many astronomical problems that can
be solved using ground-based techniques, and many space
programs will require ground-based support observations.
For a telescope to be useful, it must be properly
instrumented and used. Ground-based astronomy is now
suffering from a lack of adequate support funds. Both at
the National Astronomy Centers and in the universities,
the corrosive effects of inflation have seriously reduced
the capabilities of observatory staffs to maintain instru-
mentation at a high level of efficiency. Observatories
that derive a major portion of the core support from pri-
vate endowments or state funds are particularly hard hit,
as is the Cerro Tololo Inter-American Observatory, which
has suffered from the effects of isolation from the
United States, Chilean inflation, and changes in the U.S.
tax laws. Observatory groups are responding to the finan-
cial pressures by carefully examining their budgets and
operations to find areas of cost savings. Nevertheless,
it is clear that the current support of observatories is
not adequate. Therefore, the W OIR Panel urges NSF and
NASA to increase substantially their support of observa-
tory operations. We recognize that, traditionally, NASA
has been required to link this support to a space mission,
but we see no difficulty in doing so, particularly since
SIRTF, ST, and x-ray observations will require even more
ground-based backup observations.
The KAO has been extremely productive scientifically
and provides a unique and flexible access to the IR
region beyond 30 Em. Until the space IR telescopes are
fully operational, the KAO provides one of the major
facilities for observation in the 30-300 Am wavelength
band. It also provides a means of rapidly testing new
instruments. Flight durations have recently been cur-
tailed owing to lack of funds for jet fuel. This has
severely restricted the amount of observing time avail-
able on this important national facility. Augmentation
of the KAO flight program would increase its productivity
and should be undertaken.
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5. 2.5-5-Meter Telescope Program
There is a demonstrated need for a number of small
special-purpose instruments. Perhaps most of these would
be operated by university groups that are likely to be
successful in attracting state and private funding,
particularly if some federal matching funds could be
obtained. We have noted and particularly endorse the
following:
(a) A dedicated 4-m-class IR telescope in the southern
hemisphere. The cost of such a telescope need not be
large if advanced construction techniques are used. This
telescope should be viewed in the perspective that Amer-
ica, and indeed the world, has no large IR telescope in
the southern hemisphere, the hemisphere that is often
said to be the more important hemisphere for modern
astrophysics.
(b) A 2-m-class astrometric telescope in the southern
hemisphere. There has long been felt a need for a tele-
scope optimized for astrometry in the southern hemisphere.
In fact, such an instrument was recommended in the 1972
report of the Greenstein Committee. This instrument
would complement the U.S. Naval Observatory instrument at
Flagstaff, Arizona, and rectify a major imbalance in
positional astronomy in the southern hemisphere. This
program is particularly important in view of the need for
accurate astrometric data to support space missions that
view both hemispheres.
(c) Interferometric telescopes. For some specialized
applications, substantial increases in our ground-based
capability can be obtained with relatively modest invest-
ments. Spatial interferometry in the IR region using
speckle, Michelson, and heterodyne techniques has produced
highly interesting results. A specialized facility for
this purpose, capable of resolving structure in the
0.1-0.01-arcsec range over a wide range of wavelengths,
would be extremely exciting for the detailed study of the
structure of late-type stars, circumstellar shells, and
embedded objects. Atmospheric windows exist from 300
Em to 1 mm, which can be effectively exploited with
innovative far-IR and submillimeter telescopes.
(d) University telescopes. A number of universities
are seeking funds for the contraction of general-purpose,
intermediate-sized (2-m-class) telescopes at good sites
to support faculty research and graduate-student instruc-
tion. It has been shown that such instruments can be
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constructed economically with today's technology. m e
scientific utility of such instruments is high because
they have sufficient aperture to attack frontier problems
in astronomical research. Among other uses, they will
permit university groups to carry out observing programs
in support of space observations by staff scientists.
Since major support funds for these instruments will flow
from private or state sources, they are, from the federal
point of view, a very cost-effective way of advancing
astronomical research.
(e) Balloon facilities. At present, IR experiments
account for a substantial portion of the astronomical use
of the National Scientific Balloon Facility. Balloon
altitudes offer excellent sensitivity and atmospheric
transparency at the longer wavelengths. Balloon tech-
niques are especially suited to specialized experiments,
the testing of new ideas, and new-technology development.
Balloonborne IR astronomy warrants continued and expanded
support.
6. Moderate Cost Space Missions
a. Astronomy Payloads on Space Shuttle
Spacelab II is intended to demonstrate the effective-
ness of the Space Shuttle for carrying a variety of astro-
nomical instruments on short missions. Instruments on
Spacelab II include a small cryogenically cooled IR tele-
scope, a W telescope, solar telescopes, and others. The
Shuttle promises to be an important means for orbiting
small experiments with far longer observing times than
rockets provide and at a cost less than that of free-
flying satellites.
Unfortunately, despite the outstanding promise of the
Space Shuttle for astronomical research, funding for
Spacelab experiments has still not reached substantial
levels; moreover, funding for a number of experiments
that had already been approved was recently reduced, and
the selection of additional experiments in the Principal
Investigator class has been deferred. These programmatic
constraints have affected Shuttle flight opportunities
for a wide range of programs. However, they have had a
particularly serious impact on prospects for a coherent
program of W astronomy during the 1980's, which should
be based to a significant extent on small, special-purpose
instruments designed for Shuttle flights to obtain data
in areas not well covered by IUE, ST, or the far- W
spectrograph in space recommended in this report.
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We therefore urge an augmentation of the Shuttle small-
payload program at NASA as a minimum requirement to allow
currently foreseen, high-quality investigations to be
carried out through reasonably frequent flight opportu-
nities during the 1980's. In addition, we urge NASA to
give high priority to implementation of methods for in-
creasing the flight duration of individual missions, so
that the observing time available can be increased without
a proportionate increase in launch costs. Such methods
could include extension of the orbital-stay times of Shut-
tle missions or transfer of the instruments to long-
duration space platforms or free-flyers that could be
revisited by the Shuttle at intervals of 3 to 6 months.
b. Explorer Program
The NASA Explorer program provides for a class of
exploratory science missions involving small, free-flying
satellites, generally not recoverable, dedicated to spe-
cific new types of investigations (e.g., IUE, IRAS). Such
satellites are most suitable for missions requiring very
long observing times with relatively simple and routine
measurement techniques and not requiring instrument
changes or film recovery. The only currently approved
Explorer mission in the area of W astronomy is the
Extreme Ultraviolet Explorer. This mission is intended
to survey the sky for sources of radiation in the
loo-9oo-A (E W) wavelength range and provide relatively
broadband photometric measurements of the sources
detected.
It is expected that all Explorer-class satellites
(after the IRAS launch) will use the Shuttle as a launch
vehicle, along with an Inertial Upper Stage (IUS) if even
higher orbits are required. Although we can foresee sev-
eral areas in which Explorer-class satellites would be
extremely valuable to WOIR astronomy, many of these will
be more expensive than the historical cost of Explorer
missions.
We therefore urge that both the total Explorer funding
level and the cost limit for individual Explorer missions
be substantially increased. Also, we urge that NASA look
into means for providing the high-capability pointing
systems required for astronomical observations with tele-
scopes in the 1-m-aperture class and strive to minimize
the cost of such pointing systems. Despite attempts at
economy, it is clear that inflation and the increased
sophistication required of exploratory science missions
are seriously compromising the effectiveness of a highly
Representative terms from entire chapter:
angular resolution
