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OCR for page 133
id
New Programs
The New Programs recommended by the Committee for approval
and funding during the coming decade have been divided into three
categories according to the scale of resources required for their com-
pletion.
A. Major New Programs The Committee believes that four major
programs are critically important for the rapid and effective progress
of astronomical research in the 1980's and is unanimous in recom-
mending the following order of priority:
1. An Advanced X-Ray Astrophysics Facility (AXAF) operated as a
permanent national observatory in space;
2. A Very-Long-Baseline (CAB) Array of radio telescopes designed
to produce images with an angular resolution of 0.3 milliarc-
second;
3. A New Technology Telescope (N=) of the 15-m class operating
from the ground at wavelengths of 0.3 to 20 ~m, with rel-
evant design studies to be undertaken immediately; and
4. A Large Deployable Reflector (LDR) in space, for spectroscopic
and imaging observations in the far-infrared and submilli-
meter regions of the spectrum that are inaccessible to study
from the ground.
B. Moderate New Programs In rough order of priority, these are:
133
OCR for page 134
134
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
1. An augmentation to the National Aeronautics and Space
Administration (NASA) Explorer program,
2. A far-ultraviolet spectrograph in space,
3. A space VERB interferometry antenna in low-Earth orbit,
4. The construction of optical/infrared telescopes in the 2-5-m
class,
An Advanced Solar Observatory in space,
6. A series of cosmic-ray experiments in space, and
7. An astronomical Search for Extraterrestrial Intelligence (SETI).
C. Small New Programs The program of highest priority is:
· A 10-m submillimeter-wave antenna.
5.
Other programs of outstanding scientific merit, in which the order
of listing carries no implication of priority, are as follows:
· A spatial interferometer for the mid-infrared region,
· A program of high-precision optical astrometry, and
· A temporary program to maintain scientific expertise at U.S.
universities during the 1980's through a series of competitive
awards to young astronomers.
. ~
A. MAJOR NEW PROGRAMS
1. Advanced X-Ray Astrophysics Facility
The Astronomy Survey Committee recommends the construction of
an Advanced X-Ray Astrophysics Facility (AXAF) to be operated as a
permanent, national observatory in space and urges the National
Aeronautics and Space Administration (NASA) to begin its develop-
ment in time to ensure AXAF operation by the end of the decade.
In less than 20 years, x-ray astronomy has advanced from the
discovery of the first extrasolar x-ray source (through a brief, ex-
ploratory rocket experiment) to the detailed study of thousands of
Galactic and extragalactic sources with the image-forming x-ray tele-
scope on the Einstein (HEAo-2) Observatory. X-ray observations have
revealed important new classes of astronomical objects and have
dramatically advanced our understanding of astrophysical processes
in virtually every field of astronomical research, from stellar physics
to studies of quasars and the formation and evolution of galaxies.
Finding x-ray observations to be of vital significance in their work,
many astronomers from other fields participated in planning and
interpreting the Einstein observations during its two years of oper-
ation, and x-ray observations have now attained an importance in
contemporary astronomy comparable with those in other wavelength
OCR for page 135
New Programs
135
regions. An urgent scientific need therefore exists for a long-lived
satellite observatory with capabilities for x-ray astronomy that com-
plement those of Space Telescope (ST) in the optical/ultraviolet region
and those of the Very Large Array in the radio region of the spectrum.
The AXAF will fulfill that need with an instrument that utilizes the
same basic principles that were tested and proved in the Einstein
mission but which is capable of providing up to a hundredfold greater
sensitivity for the study of faint stellar or quasistellar objects and a
tenfold increase in angular resolution for the study of structure in
extended objects. Major improvements will be achieved in spectro-
scopic sensitivity and resolution, and a capability for sensitive po-
larimetry will also be provided. The Space Shuttle will provide the
means for launching AXAF, maintaining it in orbit, and retrieving it
for major refurbishments. Thus, like ST, AXAF will be a national facility
that can meet fundamental needs of astronomy for a decade or more.
AXAF will permit the observation of sources with x-ray luminosities
as small as 1 percent of the Sun's total luminosity lying in the farthest
reaches of our Galaxy, as well as the study of all the individual high-
luminosity x-ray sources in the hundreds of galaxies of the Virgo
cluster. The composition and dynamics of extended sources such as
supernova remnants, galaxy halos, and clusters of galaxies can be
revealed by spectroscopic and polarimetric observations of high an-
gular resolution. The great sensitivity of AXAF will permit investi-
gation of x-ray galaxies and clusters of galaxies out to distances so
large that the effects of evolution in the early Universe should be
apparent. Because of its power and versatility, AXAF will profoundly
influence and enhance the development of nearly all areas of Galactic
and extragalactic astronomy.
The Committee also suggests that NASA consider the establishment
of special institutional arrangements similar to those embodied in
the Space Telescope Science Institute, to provide scientific guidance
for the development and maintenance of AXAF, to manage the sci-
entific direction of the mission during orbital operations, and to
facilitate the participation of the scientific community in the acqui-
sition and interpretation of x-ray observations. Consideration should
be given, as in the case of the Space Telescope Science Institute, to
appropriate international participation.
2. A Very-Long-Baseli?~e NAB) Array of Radio Telescopes
The Astronomy Survey Committee recommends the construction of
a ground-based Very-Long-Baseline (VERB) Array of radio telescopes
OCR for page 136
136
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
designed to produce images with an angular resolution of 0.3 mil-
liarcsecond. Because the Array utilizes proven technology, this proj-
ect may be begun immediately after completion of final management
and design studies.
Extraordinarily high angular resolution is now possible at radio
frequencies. Precision atomic clocks, more sensitive and reliable re-
ceivers, high-speed tape recorders, sophisticated image-processing
techniques, and modern antennas now make it feasible to build a
radio array with the angular resolution of a telescope covering an
entire continent. This may be done by synchronizing the operation
of about ten widely spaced antennas of approximately 25-m diameter,
whose outputs are recorded and later combined in a central com-
puter.
This VLB Array will produce high-quality radio images capable of
resolving features down to 0.3 milliarcsecond (the size of a dime in
New York as seen from Los Angeles). This is a hundred times better
angular resolution than that of any other image-forming telescope at
any wavelength and will yield detailed new radio images of a wide
range of astronomical objects at the frontiers of modern astrophysical
research. These include quasars and the nuclei of galaxies, features
of interstellar molecular clouds, the center of our Galaxy, and a
variety of energetic Galactic objects such as x-ray, binary, and flare
stars. The high angular resolution of the VERB Array will permit the
direct study of small-scale structure surrounding the central regions
of quasars and stars in the process of formation. Through the method
of statistical parallaxes, it will furthermore permit direct measure-
ments of distances to many objects throughout our Galaxy and even
to some in nearby galaxies. The VERB Array can also be applied to
important problems in Earth science (including precision geodesy
and geophysics), to the navigation of interplanetary spacecraft, and
to tests of the General Theory of Relativity.
Although the VERB Array is a complex and sophisticated instrument,
it will make use of proven concepts and instrumentation. Construc-
tion should begin immediately upon completion of management and
design studies with the building of the antennas and the develop-
ment of the data-reduction system and other instrumentation. Col-
laboration with groups in other countries, particularly in Europe and
North America, would improve the performance of the instrument
by increasing the resolution even further (particularly in the north-
south direction) and by improving the image quality at low decli-
nations.
OCR for page 137
New Programs
137
3. A New Technology Telescope (NTT) of the 15-Meter Class
The Astronomy Survey Committee recommends the construction of
a New Technology Telescope (NTT) of the 15-m class on the ground
for observations in the optical and in the near- and mid-infrared
regions of the spectrum (0.3- to 20-~m wavelength). The design studies
needed before the NTT can be constructed are of the highest priority and should
be undertaken immediately.
Recent progress in optical fabrication techniques, design concepts,
and electronics now make it possible to build a large optical/infrared
telescope at a cost much lower than was possible a decade ago. Such
a New Technology Telescope (NTT), having a diameter of approxi-
mately 15 m, will increase our observing capabilities in the critical
0.3~20-~m spectral region in two important ways. First, throughout
this spectral region, the vast area of the mirror-nine times larger
than that of the 5-m Mt.Palomar reflector-will collect light at a rate
exceeding the combined capabilities of the world's 20 largest existing
optical telescopes, furnishing the image brightness needed for a new
generation of spectroscopic observations. Second, at a good site, the
NTT should frequently achieve 0.3-arcsec resolution at 20-~m wave-
length; in the absence of special speckle or interferometric tech-
niques, this angular resolution can generally be surpassed only by
Space Telescope, at much shorter wavelengths. For many infrared
applications, NTT'S combination of large collecting area and high
angular resolution will lead to a tenfold increase in limiting sensitivity
and a hundredfold increase in speed over present capabilities.
NTT'S large collecting area will make it an enormously powerful
tool for the spectroscopy of faint astronomical sources. For example,
detailed spectra of faint, old stars on the fringes of our Galaxy will
outline for us the early history of element building and nucleosyn-
thesis during the birth of our Galaxy. Similar observations in nearby
dwarf spheroidal galaxies, satellite systems of the Milky Way, will
tell us how the formation and early evolution of these small sister
galaxies differed from that of our own Galaxy. In yet a third such
study, astronomers will determine the compositions and motions of
the equally old swarms of globular clusters that surround many
neighboring galaxies. These clusters, currently believed to be prod-
ucts of the initial galactic collapse phase, hold still further clues to
the mysteries of galactic birth and evolution. All of these are thresh-
old problems, in the sense that there are no brighter objects nearby
that are suitable for study; without the light-gathering power of NTT,
OCR for page 138
38
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
an insufficient number of photons can be collected to mount the
decisive spectroscopic programs needed to address these important
issues.
In addition, spectroscopic observations of the most distant galaxies
and quasars will greatly advance our understanding of cosmic evo-
lution. For example, NTT studies of quasar absorption lines will permit
measurements of the distribution and composition of intergalactic
gas as it existed very early in the history of the Universe. These
measurements offer the exciting possibility of tracing back the origin
of the chemical elements and the birth of clusters and superclusters
of galaxies to a time much earlier than we can currently see directly;
indeed, we should be able to study the large-scale properties of the
Universe when it was only one quarter as old as it is now. Such
studies are completely impossible with present optical telescopes
because of their inadequate collecting areas; the faintness of quasars,
in particular, requires the enormous light-gathering power of NTT for
systematic spectroscopic study.
The combination of NTT'S high spatial resolution with sufficient
photon-collecting power to achieve very high spectral resolution will
also permit definitive studies of molecular clouds and obscured pro-
tostars in the near- and mid-infrared regions of the spectrum. The
fundamental vibration-rotation transitions of molecules are found
primarily in the 2-10-llm wavelength region. The study of these and
of molecular rotational transitions and continuum radiation will lead
to a much better understanding of the composition, abundances,
excitation, and dynamics of collapsing gas clouds. NTT will provide
a probe of gas dynamics in regions of star formation by permitting
the examination of optical and infrared spectral lines at very high
spectral resolution on an exceedingly fine spatial scale. Present ob-
servations indicate that the brightest protostellar candidates are about
1 arcsec in diameter in the 2-10-~m wavelength region, whereas the
diffraction limit of a filled-aperture 15-m telescope is about 0.0~0.15
arcsec over the same range; thus, the use of NTT with interferometric
techniques will permit detailed study of the geometry and structure
of such objects. In addition, NTT'S high spatial resolution will allow
the isolation and study of individual source components. All of these
studies will be complementary to those that can be carried out by
the Shuttle Infrared Telescope Facility (SIRTF), which has high sen-
sitivity but low angular resolution; by ST, which has high angular
resolution but limited collecting area; and by the Large Deployable
Reflector in space, which will be designed for far-infrared work at
wavelengths longer than 20 ~m.
OCR for page 139
New Programs
139
Because most of the known objects in the Universe either emit
visible or infrared radiation or are associated with objects that do,
optical and infrared spectroscopy provide powerful and versatile
techniques for investigations of the Universe. As the worldJs most
capable instrument for such spectroscopic observations, NIT will be
an extraordinarily productive facility. The Survey Committee finds
the scientific importance of NIT to be equal to that of any other
facility considered and regards it as one of the cornerstones of the
recommended research program for the 1980's.
4. A Large Deployable Reflector in Space
The Astronomy Survey Committee recommends the construction of
a Large Deployable Reflector (LDR) of the 10-m class in space to carry
out observations in the far-infrared and submillimeter regions of the
spectrum that are inaccessible from the ground. Design studies for
such a facility should begin at once.
Much of the matter in the Universe is relatively cool, from cool
stars at a few thousand degrees to dense interstellar clouds at tens
of degrees. Radiation from these objects lies in the infrared and
submillimeter regions of the spectrum, at wavelengths from a few
to a few hundred micrometers. Instruments in space are essential
for observations at wavelengths between the atmospheric windows
and at wavelengths beyond 20 ~m, for which the elimination of
atmospheric absorption and background thermal noise is critical.
STRTF will offer a thousandfold improvement in our ability to detect
infrared sources, bringing many millions of them into view. How-
ever, the requirements of cryogenic cooling put a practical limit on
the aperture of the STRTF telescope; as a result, it cannot collect enough
photons for high-resolution spectroscopy, and its angular resolution
is high only at shorter infrared wavelengths.
A LDR in space of approximately 10-m diameter, for observations
at the longer infrared and submillimeter wavelengths inaccessible
from the ground, is needed to collect enough photons for high-
resolution spectroscopy and to provide high angular resolution at
these long wavelengths. Such a telescope could carry out detailed
morphological and spectroscopic studies of all the far-infrared sources
discovered in the forthcoming Infrared Astronomy Satellite (IRAS) all-
sky survey and of the brighter objects discovered by SIRTF. Because
mirror-figure and pointing requirements are a hundred times more
OCR for page 140
140
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
relaxed than for ST, a 10-m-class LDR capable of arcsecond resolution
at 20-~m wavelength should be less expensive.
A number of important scientific problems are uniquely accessible
to such a LDR in space. For distances less than 500 parsecs, the
projected beam diameter will be less than 1000 astronomical units.
Direct measurements of the sizes of nearby clouds collapsing to
become stars will thus be possible at far-infrared wavelengths, which
can penetrate the surrounding clouds of dust that invariably obscure
small-scale features at optical wavelengths. In addition, the wave-
length regions accessible to a LDR contain spectral lines of atoms,
ions, and molecules that reflect a wide range of astrophysical con-
ditions. Studies of these features will yield otherwise unobtainable
information about the structure and dynamics of planetary atmo-
spheres; the heating, cooling, and chemical composition of the in-
terstellar medium; and because of the penetrating power of long-
wavelength radiation- chemical abundances in the highly luminous
but optically obscured nuclei of active galaxies.
The sensitivity and high angular resolution of a LDR will also make
it possible to study newly forming stars in optically obscured regions
of nearby external galaxies, enhancing our understanding of galactic
evolution and of the dynamical processes that stimulate star for-
mation. Such an instrument can also probe the structure of the early
Universe and the mechanisms of galaxy formation through studies
of small-scale spatial fluctuations in the cosmic microwave back-
ground radiation.
The capabilities of a LDR in space will complement those of ST,
which is optimized for observations in the ultraviolet, optical, and
near-infrared spectral regions, and those of the NIT, which will offer
large collecting area and high angular resolution but will be restricted
to the atmospheric windows between 0.3- and 20-~m wavelength.
The Committee believes that design studies for a LDR should begin
at once.
B. MODERATE NEW PROGRAMS
1. Explorer Program Augmentation
The Astronomy Survey Committee recommends an immediate and
substantial augmentation to the NASA Explorer satellite program, with
the aim of restoring it to at least the healthy real level of effort of
1970.
NASA is now proceeding with four Explorer missions in the areas
OCR for page 141
New Programs
of astronomy and astrophysics. The Infrared Astronomy Satellite
MORASS is at present under development; the Cosmic Background Ex-
plorer (COBE), Extreme Ultraviolet Explorer (EUVE), and X-Ray Timing
Explorer (XTE) are in various stages of final planning in preparation
for development. Unless the present Explorer funding level is in-
creased, however, these are likely to be the only Explorer satellites
dedicated to astronomical observations that can be flown in the 1980's.
The Astronomy Survey Committee believes that such a limitation
would present a serious obstacle to the progress of space astronomy
during the coming decade.
Today's Explorer budget, as currently charged for mission costs,
provides only about half the support in real terms that was available
to the Explorer program a decade ago. As a consequence, the flight
of new Explorer missions has in recent years fallen much below the
rate needed for healthy advance. The rate will decline even more
drastically during the early 1980's if present budget levels are not
increased. The Astronomy Survey Committee thus recommends an
immediate and substantial augmentation to the Explorer program to
restore it to at least the real level of effort of 1970.
As emphasized in Chapter 4, the Explorer program has been a
vital component of the NASA space-science program for over 15 years,
and it promises to continue to provide the best means for pursuing
a wide range of scientific problems in the years ahead. Determination
of priorities among the most promising individual Explorer mission
possibilities in astronomy and astrophysics for the 1980's remains
the responsibility of other advisory groups, particularly the Space
Science Board's Committee on Space Astronomy and Astrophysics
(CSAA). However, among the scientific areas that at present appear
to offer special promise for additional Explorer-class missions are the
following, in which the order of listing carries no implication of
priority:
141
· A spectroscopic study of physical conditions and element abun-
dances in a wide variety of x-ray sources. Such a study could address
one or more of the regimes of spectroscopy that may not or will not
be addressed by AXAF, e.g., observations of spectral lines (such as
Fe lines) with exceptionally high spectral resolution or with the spa-
tial resolution permitted by large apertures, the study of spectral
lines emitted by newly synthesized matter and of cyclotron-reso-
nance features at energies above 10 keV, and wide-field spectroscopic
studies of the interstellar medium. These investigations would yield
important new information on the structure and composition of young
OCR for page 142
142
ASTRONOMY AND ASTROPHYSICS FOR THE 1980
s
supernova remnants and the interstellar medium; the structure and
dynamical behavior of the coronas of nearby stars; the nature of the
plasmas associated with compact x-ray sources in Galactic x-ray bi-
naries and in quasars; and the distribution, composition, and origin
of the hot intergalactic gas pervading clusters of galaxies.
· A study of the isotopic and elemental composition of low-energy
Galactic cosmic rays and solar energetic particles in the interplanetary
medium. A primary aim of such an investigation is an accurate
determination of the isotopic composition of the elements through
nickel in a direct sample of contemporary solar and Galactic inter-
stellar matter. In addition, it should be possible to analyze the com-
position of solar energetic particles through uranium and to study
the processes that accelerate particles on the Sun and in the inter-
stellar medium. These measurements hold the key to understanding
the processes that synthesized and accelerated both solar and Galactic
matter.
· A study in soft x rays (preferably with moderate-resolution spec-
troscopic capability) of those objects now known to radiate predom-
inantly in the 100-2000-eV energy range, including cataclysmic var-
iable stars, AM Herculis-type systems, RS CVn binary stars, stellar
coronas, isolated white dwarfs, central stars in planetary nebulae,
hot neutron-star remnants of recent supernovae, and x-ray pulsars.
Such an investigation should include extended searches for, and
studies of, regular and quasi-regular pulsations as well as aperiodic
variability, studies of binary orbital light curves, measurements of
spectral-line ratios (to determine temperatures and densities in the
hot, emitting plasmas), and observations correlated with measure-
ments at other wavelengths. The results of these studies would have
an important bearing on our understanding of the evolution of com-
pact binary systems, the composition and cooling of isolated very
hot stars, and stellar activity and variability cycles.
· A study of high-energy transient phenomena, particularly ob-
servations of cosmic and solar gamma-ray bursts up to 10 MeV with
high resolution and sensitivity, in conjunction with a program of
wide-field x-ray imaging with fine angular resolution. Such a com-
bination will provide both accurate timing and location of the burst
sources from the same spacecraft and very probably lead to their
identification. The cosmic gamma-ray observations will also provide
probes of nuclear and electromagnetic processes in compact objects
and measure spectral features that have been reported in burst mea-
surements, including cyclotron-resonance features, red-shifted 511-
keV photons, and nuclear lines. Continuous observations of solar
OCR for page 143
New Programs
gamma-ray lines may also be possible from the same spacecraft; such
observations, carried out over a several-year period bracketing a solar
maximum and with the highest energy resolution obtainable, would
greatly advance our understanding of solar flares.
· A study of the physical processes that deposit both energy and
momentum into the solar corona and the solar wind, through mea-
surements of the structure, expansion velocity, electron-density dis-
tribution, transition-region plasma density, and magnetic properties
of the corona. Such investigations will furnish essential new infor-
mation on the detailed relation of coronal structure to x-ray bright
points and coronal holes through studies of the fate of newly emerg-
ing magnetic-flux tubes; the interaction of coronal plasma with the
solar magnetic field in general; and mechanisms for the acceleration
of the solar wind, which are best studied in conjunction with si-
multaneous observations of the evolution of coronal holes, bright
points, transients, active regions, and magnetic structures on all
scales.
· A study of the interior dynamics of the Sun, as one important
component of a more general program to understand the funda-
mental mechanisms responsible for the solar cycle. The goals of such
an interior-dynamics study include measurements of photospheric
velocities, as a probe of the solar convection zone and the variation
of rotation rate with depth; of radiation from the large-scale convec-
tive pattern in the photosphere, to permit correlations with magnetic
measurements and inferences concerning the influence of magnetic
fields on solar radiative output; of radiation from the entire disk of
the Sun over periods ranging from days to the length of a solar cycle,
to determine the degree of variations in the so-called "solar con-
stant"; and of magnetic activity in the upper solar atmosphere, to
determine the effects of such activity on the atmospheres of both the
Sun and the Earth. These results are also expected to play a role in
the more general effort to understand the nature of stellar convection
and of energy and magnetic-field maintenance.
143
Two further possibilities merit detailed study by NASA and by other
advisory groups for inclusion in the Explorer program. The first is
an Explorer satellite to map the Milky Way at moderate angular
resolution, both in the lines of selected submillimeter-wavelength
transitions thought to be important for the heating and cooling of
interstellar gas clouds and in wavelength bands relevant to deter-
minations of temperature and density distributions in cold clouds.
The second is the Explorer flight of optical and infrared interferom
OCR for page 146
146 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
mits a more complete study of dynamical processes presumed to be
operating at various distances from the central energy sources in
these objects.
Second, a space VERB! antenna greatly facilitates the study of radio
sources at low declination. Any ground-based VERB Array must rely
on the rotation of the Earth to vary the position and length of the
baseline employed; for low-declination sources, the resulting base-
lines lie largely or solely in the east-west direction, thus diminishing
greatly the north-south resolution and degrading the quality of the
radio map. A space antenna can provide north-south resolution of
such sources, allowing full two-dimensional mapping of radio sources
at all declinations.
Third, an Earth-orbiting space antenna will permit the study of
time variation on much shorter time scales than is possible with a
purely ground-based array, which requires up to 24 h to fill in all
the baselines necessary to complete a radio map. An antenna in low-
Earth orbit would allow mapping of sources in a time that is half of
the period of revolution of the satellite (about 1 h) and, thus, the
study of source variations on this much shorter time scale. Such a
capability would be immediately useful, for example, in studying
dramatic relativistic-jet phenomena in SS 433. Many other time-vary-
ing sources will also be accessible.
Finally, a space antenna will in concert with the VERB Array's
southernmost stations, southern hemisphere NASA stations, and an-
tennas in other countries permit the VUB! mapping of the rich south-
ern hemisphere of the sky.
The Committee notes that even the first space VERB! antenna in low-
Earth orbit will additionally provide angular resolution that is nearly
an order of magnitude greater in solid angle than that of the ground-
based SIB Array alone. Moreover, a space VUB! antenna in low-Earth
orbit will provide the first step toward the achievement of baselines
far longer than can ever be achieved on the Earth itself. This requires
the placement of antennas in highly elliptical Earth orbits; in Chapter
7, the Committee recommends the study and development of a more
extensive space VERB} system as part of a program of advanced spatial
interferometry in the radio, optical, and infrared regions of the spec-
trum.
4. Construction of Opticalllnfrared Telescopes in the 2-5-Meter Class
The Astronomy Survey Committee recommends the construction of
optical/infrared telescopes in the 2-5-m class during the coming de
OCR for page 147
New Programs
147
cede as the ground-based facilities of choice for an extensive range
of important observations. The Committee particularly encourages
federal assistance for those projects that will also receive significant
nonfederal funding for construction and operation.
Optical/infrared telescopes in the 2-5-m class have made critically
important contributions to most of our recently acquired knowledge
in a number of key areas, including the following:
· Evidence of galaxy evolution from studies of distant galaxies;
· The crucial quasar observations that established the existence of
the first known gravitational lens;
· A mass estimate for the dense component of an x-ray binary
star, establishing it as the leading black-hole candidate;
· The discovery of quasars in clusters of galaxies, demonstrating
that at least some quasars are at the great cosmological distances
implied by their large red shifts;
· Dynamical studies of hundreds of galaxies in clusters, showing
that the bulk of the matter in the Universe is nonluminous at optical
wavelengths and has therefore escaped direct detection;
· Observations providing strong evidence that interstellar shock
waves play a role in star formation;
· Demonstration that the old stars in our Galaxy are anomalously
rich in oxygen, supporting the hypothesis that the protogalactic gas
was enriched by an early generation of massive, short-lived stars;
· Detection of activity cycles in solar-type stars and observations
of the modulation of chromospheric features by stellar rotation;
· Discovery of a binary-star system (SS 433) emitting huge streams
of matter at about one fourth of the speed of light; and
· Optical confirmation of the existence of pulsars.
In addition, telescopes in the 2-5-m class have furnished essential
follow-on observations and identifications of a multitude of objects
discovered in other wavelength regions by spacecraft or comple-
mentary ground-based facilities. Such telescopes are essential for
timely observations of transient phenomena, long-term survey and
surveillance programs, general support of space astronomy, and the
development of astronomical instrumentation under realistic observ-
ing conditions.
All of these scientific tasks and opportunities will assume even
greater importance during the coming decade. Recent breakthroughs
in telescope technology have radically reduced the cost of construc-
tion of optical/infrared telescopes in the 2-5-m class, enabling a wider
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148
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
group of institutions to consider their acquisition than ever before.
Such telescopes, equipped with modern instrumentation and detec-
tors will constitute powerful research tools for the 1980's. The Com
mittee believes that federal funds for such facilities should be awarded
on the basis of peer review of scientific merit. Federal agencies should
be receptive to proposals from all parties that could make effective
use of these telescopes, including private, state, and national insti-
tutions.
The Committee particularly encourages the award of federal funds
for such telescopes to be located at private and state observatories
that can contribute significant nonfederal funding for construction
and operation. It applauds the initiative of astronomy groups that
are currently seeking private and state funds for this purpose and
welcomes private and state agency support of astronomical research.
Some portion of the observing time at these facilities should be
allocated to outside users, the fraction to depend in general on the
level of federal funding. Visitor access is especially important for the
larger telescopes constructed in this class.
5. Advanced Solar Observatory in Space
The Astronomy Survey Committee recommends the establishment
in space of an Advanced Solar Observatory (ASO) to be assembled
near the end of the coming decade from facility-class instruments
developed earlier through the Spacelab program-for simultaneous
observations of a number of important solar properties at optical,
extreme ultraviolet, x-ray, and gamma-ray wavelengths.
The Solar Shuttle Facility endorsed earlier (Chapter 4, Section D)
can achieve a number of the major scientific objectives of space solar
physics. However, other important problems-such as the structure
of the convection zone, large-scale circulation patterns, transient high-
energy phenomena, and long-term evolution of the corona require
observations with-a comprehensive set of high-resolution instru-
ments over much longer periods of time than can be obtained in
Shuttle flights. The Committee therefore recommends that the Solar
Shuttle Facility evolve into a major free-flying observatory, the ASO.
The ASO iS currently planned to consist of five major components:
(1) the Solar Optical Telescope (SOT) truss containing the SOT itself;
(2) a Solar Soft X-Ray Telescope Facility (SSXTF), an EUV Telescope
Facility (EUVTF), and white-light and resonance-line coronagraphs to
be mounted within the SOT truss; (3) a Grazing Incidence Solar Tele-
scope (GRIST) currently under consideration for development by the
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New Programs
149
European Space Agency; (4) a Pinhole/Occulter Facility for hard
x-ray observations and high-resolution studies of the corona; and (5)
a Solar Gamma Ray Telescope. It is hoped that an ASO nucleus
(consisting for example of the SOT/SSXTF/EUVTF assembly and GRIST)
can become operational in the late 1980's, perhaps assembled upon
a space platform. The full ASO, including the Pinhole/Occulter Facility
and the Gamma Ray Telescope, will be necessary for the study of
transient phenomena during the next solar maximum in the early
1990's.
ASO will be the first solar facility with the design goal of achieving
an angular resolution much less than 1 arcsec from the infrared
through the x-ray region (0.1 arcsec or better at many wavelengths),
together with the spectral resolution needed to detect motions of
solar material over the entire span of wavelengths required for study
of such material at a wide range of temperatures. The ASO will be
able to address nearly all of the problems of contemporary solar
physics, including the structure of the solar core; the mechanisms
responsible for the solar magnetic and activity cycles; the energy and
mass-transport mechanisms operating over the full range of tem-
peratures present in the atmosphere; the basic plasma processes
responsible for metastable energy storage, magnetic reconnection,
and particle acceleration in solar flares and related nonthermal phe-
nomena; and the processes involved in the heating and acceleration
of the solar wind.
6. Cosmic-Ray Experiments
The Astronomy Survey Committee recommends a series of cosmic-
ray experiments in space, to promote the study of solar and stellar
activity, the interstellar medium, the origin of the elements, and
violent solar and stellar processes.
Cosmic rays high-energy particles from space that include the
nuclei of all elements of the periodic table, as well as electrons and
antiparticles are a sample of contemporary matter from regions far
beyond the solar system that we can study in detail. For example,
it has now been established that both neon and magnesium in cosmic
rays are enriched in their heavier isotopes by comparison with stan-
dard solar-system abundances. In their composition and energy spec-
tra, cosmic rays carry unique information about the origin of the
elements in stars, the nature of cosmic particle accelerators, and the
interstellar gas. Cosmic-ray research has now reached the stage of
maturity that permits substantial advances in all of these areas.
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
At lower energies, and for the lighter elements, some of the re-
quired studies could be carried out through the Explorer satellite
program, as noted earlier (Section B.1~. However, determinations of
abundances of the rarer isotopes (such as those of elements heavier
than nickel), of the chemical composition of the ultra-heavy nuclei,
and of the elemental composition and spectra of lighter elements at
high energies, all require large collecting areas and the longest fea-
sible exposure times. Dramatic progress in detector technology dur-
ing the past decade, together with the ability of the Space Shuttle
to place heavy payloads in orbit, now makes it feasible to carry out
such measurements with high accuracy over a broad range of ener
g~es.
The Committee therefore recommends that NASA begin a system-
atic program that would pursue the development and construction
of the large instruments required to perform these significant cosmic-
ray measurements and that would ultimately provide long-duration
(approximately 6 months or more) exposures of these instruments
in the most appropriate way, possibly through use of a space plat-
form. The development of these large instruments for long-duration
exposure will in many cases best be carried out through balloon and
Spacelab flights of short duration and through use of ground-based
facilities such as the Bevalac accelerator.
7. Astronomical Search for Extraterrestrial Intelligence
The Astronomy Survey Committee recommends an astronomical
Search for Extraterrestrial Intelligence (SETI), supported at a modest
level, undertaken as a long-term effort rather than as a short-term
project, and open to the participation of the general scientific com-
munity.
It is hard to imagine a more exciting astronomical discovery or one
that would have greater impact on human perceptions than the
detection of extraterrestrial intelligence. After reviewing the argu-
ments for and against SETI, the Committee has concluded that the
time is ripe for initiating a modest program that might include a
survey in the microwave region of the electromagnetic spectrum
while maintaining an openness to support of other innovative studies
as they are proposed.
Since the chance for a successful detection in the next decade is
quite uncertain and may be small, it should be understood that the
SET! effort is to be undertaken on a long-term, evolutionary basis. In
the coming decade it has been proposed to use a million-channel
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New Programs
analyzer in the microwave region of the spectrum; such a program
seems appropriate for an initial assay. While exploration of this re-
gion of the electromagnetic spectrum appears to make best use of
our current technology, other approaches such as searches using
radiation of shorter wavelengths-can also provide interesting op-
portunities, and the SET! program should allow for the possible sup-
port of the ingenious new ideas and proposals that are likely to
appear.
Modest support of such programs by U.S. funding agencies is a
legitimate scientific activity, and choice of programs within each
agency should be made through the normal process of peer review.
As a number of other nations have initiated steps toward SET! pro-
grams, the opportunities for international collaboration are substan-
tial.
151
C. SMALL NEW PROGRAMS
A 10-Meter Submillimeter-Wave Antenna
The Astronomy Survey Committee recommends the construction of
a submillimeter-wave telescope of about 10-m aperture at a high, dry
site.
Recent advances in the design and fabrication of ultraprecise an-
tennas and low-noise receivers make possible an instrument that can
observe a substantial portion of the almost completely unexplored
submillimeter-wavelength band. Such an instrument will allow de-
tailed study of this rich region of the spectrum with an angular
resolution as fine as 8.5 arcsec, which is a factor of 2 better than that
of any existing single-element millimeter-wave antenna. The portion
of the electromagnetic spectrum accessible to this antenna contains
the fine-structure transition of atomic carbon and many rotational
lines of important molecules. The facility will be particularly useful
for observing higher molecular rotational transitions, such as those
of the well-studied interstellar molecules CO and HCN, which are
important for cooling processes. Information from a range of molec-
ular levels will make possible a detailed examination of the physical
structure of molecular clouds-especially the hot, dynamically active
clouds where stars are formed. Since the 10-m telescope will achieve
high angular resolution, the transitions of abundant species like car-
bon and carbon monoxide can be used for studies of objects of small
angular extent, such as external galaxies and the envelopes of evolved
stars displaying mass loss. The study of the distribution of molecular
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
clouds in external galaxies should, when combined with optical/
infrared results, greatly improve our knowledge of star formation in
nearby galaxies. If both the 25-Meter Millimeter-Wave Radio Tele-
scope and the 10-m submillimeter-wave antenna are placed at the
same site, they may be used together as an interferometer within
the short-wavelength range of the former and the long-wavelength
range of the latter.
The fascinating problems of star formation, stellar mass loss, and
galactic structure stand at the center of many of the controversial
issues of astrophysics today. The important information that this
instrument can provide on these topics through observations of the
more energetic molecular rotational transitions elevates it to an im-
portance much greater than would be suggested by its modest cost.
A Spatial Interferometer for the Mid-Infrared Region
The Astronomy Survey Committee recommends the construction
during the early 1980's of a dedicated two-element spatial interfer-
ometer for the mid-infrared spectral region with design parameters
optimized for operation at a wavelength of 10 ~m.
The spectacular success of radio interferometry since World War
II has illustrated forcefully the benefits of interferometry to astron-
omy. Experiments during the last decade have demonstrated the
feasibility of spatial interferometry in the infrared region at wave-
lengths from 2 to 20 Am and have shown that there are a number
of important applications for such techniques. Atmospheric propa-
gation characteristics have been shown to be excellent for the 10-~m
region in particular, and heterodyne detection techniques have been
developed that permit sensitive, coherent detection in this wave-
length region.
The Committee supports the construction of a 10-~m heterodyne
interferometer for the exciting scientific promise it offers in the near
term and as a significant step toward the goal of extending interfer-
ometric technology to a wide range of wavelengths. With the later
possible addition of an infrared delay line, the interferometer could
be made suitable for use with incoherent detectors, when the highest
sensitivities to continuum radiation are required.
A dedicated infrared interferometer will have many important as-
tronomical applications. It will permit detailed mapping of infrared
sources, many of which are invisible optically because of obscuration
by intervening interstellar dust. Of special interest is the circumstellar
distribution of dust and molecules shed during episodes of mass loss
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153
by many stars during certain stages of their evolution. High-reso-
lution maps of regions of star formation are essential to our under-
standing of the birth of stars and planetary systems. The angular
diameters of large numbers of stars can be measured. Such an in-
terferometer is also well suited to search for an accretion disk around
a black hole in the Galactic center a possibility suggested by recent
observations- and to probe the intense infrared sources in the nuclei
of active galaxies.
A 10-~m heterodyne interferometer furthermore shows great promise
as an astrometric instrument. It will measure precisely the location
of infrared sources, aid in the determination of an accurate celestial
coordinate system over the entire sky, allow proper motions of stars
and other infrared objects to be determined with high precision, and
test the General Theory of Relativity to a new order of accuracy by
measuring the bending of 10-~m radiation from sources seen near
the limb of the Sun.
A Program of High-Precision Optical Astrometry
The Astronomy Survey Committee recommends support for the de-
sign and construction of innovative devices that offer the promise
of greatly improved astrometric precision, particularly those that may
help permit the detection of planets around other stars. Since the
1960's, the typical accuracy of observed stellar parallaxes has im-
proved from +16 milliarcseconds to +3 milliarcseconds; the Com-
mittee recommends support for the design and construction of in-
novative devices that offer the potential for obtaining relative positions
with an accuracy of +0.1 milliarcsecond. If the Earth's atmosphere
allows the achievement of such accuracy but existing telescopes prove
to be inadequate, serious consideration should be given to the con-
struction of a specialized astrometric telescope.
The major advances in astrometry during the past decade have
been due to the introduction of new instrumentation and the up-
grading of existing instruments. These, together with the advent of
new detector technologies and data-analysis techniques, have pro-
vided the astronomical community with the tools for decisive ad-
vances in the accuracy that can be obtained through ground-based
astrometric measurements. For example, one may now look forward
to a tenfold improvement in our knowledge of relative stellar posi-
tions. Such an advance would permit distance determinations of stars
out to 1 kiloparsec, leading to improved luminosities, radii, and
masses of stars of virtually all types and ages, including objects such
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
as RR Lyrae stars and members of star clusters that are crucial for
calibration of the distance scale to extragalactic objects. Moreover, a
substantial improvement in the accuracy of stellar-velocity measure-
ments also seems possible, with important consequences for studies
of stellar dynamics.
Such advances can be exploited to search for evidence of extrasolar
planetary systems. The detection of such systems would have a
significant intellectual impact, removing immediately the apparent
uniqueness of our own solar system; systematic observations would
enable us to begin the accumulation of data for eventual statistical
studies of planetary-formation rates, planetary multiplicity, correla-
tions of physical properties with those of the parent star, and the
effects of planetary formation on stellar evolution. An important goal
for ground-based astrometry during the coming decade is the de-
tection of Jupiter-like planets around nearby stars, if indeed they
exist. The detection of Earth-like planets around other stars appears
to require astrometric measurements from space, and the Committee
encourages design studies of focal-plane detectors and astrometric
telescopes that will yield a positional accuracy sufficient for such
measurements.
A
The Committee also calls attention to the potential for astrometry
of a very large space telescope and the advanced interferometers for
the radio, infrared, and optical regions of the spectrum recommended
for study and development in Chapter 7 of this report.
A Temporary Program to Maintain Scientific Expertise at U S. Universities
The sharp decline in the anticipated number of university under-
graduates in the 1980's, coupled with the unusually small number of
faculty retirements anticipated over the same period, will cause a
temporary but serious reduction in the number of junior astronomy
faculty members that will be appointed by U.S. universities. The
intellectual energy that such faculty members bring to astronomy is
crucial to progress; moreover, as explained in Chapter 4, basic re-
search at U.S. universities is a critically important component of the
national effort in astronomical research. The Astronomy Survey Com-
mittee therefore recommends that urgent steps be taken to maintain
scientific expertise at U.S. universities by ensuring that excellent
younger researchers continue to flow into them during the critical
decade ahead.
In particular, the Committee recommends that the Astronomy Di-
vision of the National Science Foundation initiate a temporary pro
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155
gram of "Astronomy Excellence Awards." Ten to twenty 5-year po-
sitions would be awarded to individuals each year on the basis of
an open national competition. Each award would be for one half of
the salary of a position at the assistant-professor level and would be
contingent on commitment of matching funds in the form of the
other half of the salary for the same period by a recognized univer-
sity. It is anticipated that the status and qualifications of successful
candidates would be similar to those of regular faculty members at
the host institutions and would include the improvements described
below. The anticipated cost of this program, which we recommend
as a new initiative, would be $0.5 million to $1.0 million per year.
It would generate an equal amount of matching funds from univer-
sities on a short-term basis and also, the Committee believes, lead
to the establishment of new, long-term positions in astronomy. In-
asmuch as the problem of declining enrollments and reduced retire-
ments is anticipated to abate starting in about 1990, this program
should be terminated at that time.
The Committee furthermore urges the universities themselves to
take the following steps to respond to the declining student enroll-
ments and reduced faculty retirements anticipated during the 1980's:
implementing procedures that encourage the early retirement of fac-
ulty, the establishment of "parallel track" positions of high prestige,
and the permitting of non-tenure-track scientists with appropriate
qualifications to serve as Principal Investigators on contracts and
grants. Some universities have also experimented with so-called "rolling
tenure," by which a scientist is granted tenure for the duration of
supporting funding from a contract or grant, with tenure extended
in step with funding renewal. Since this scheme raises broad issues
of university policy, its consideration by a more broadly based com-
mittee than the present one would be helpful.
A much more detailed discussion of the issues underlying the
present recommendation may be found in the report of the Panel
on Organization, Education, and Personnel, to be published in Vol-
ume 2 of this survey.
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Speckle interferometry permits resolution of a stellar disk. The top
frame represents a short-exposure stellar image of ~ Ceti; at the
lower right is the speckle image of an unresolved star, ~ Ceti; and
at the lower lefties the resolved image of the surface of a red giant
star, Mira, or 0 Ceti. (Photo courtesy of R. Stachnik and P.
Nisenson, Harvard-Smithsonian Center for Astrophysics)
Representative terms from entire chapter:
survey committee
