The APO 3.5-meter
remote observing program-2002 and beyond
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Bruce Gillespie
Site Operations Manager, Apache Point
Observatory
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Abstract
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The Apache Point Observatory 3.5-meter telescope
is a working model of a modern mid-sized telescope used primarily on
a shared-night, remote-observing basis. After a decade of successful
remote operation and scientific accomplishments, the Astrophysical
Research Consortium, builder and owner of the telescope, is examining
the role by which this university-owned instrument can best serve its
constituency and astronomy at large in the coming years. Various
"niche" scientific capabilities are described for the telescope,
including fast-response observations of transient phenomena, synoptic
observing programs, reactive queue-scheduled observations, temporal
study programs, plus being a capable test bed for new instruments.
While specialized uses of the telescope offer potential for major
scientific discoveries, traditional observing capabilities need to be
sustained for the ongoing and future research programs for the
majority of the consortium astronomers and students, a large and
diverse community. Finding an appropriate balance between the "unique
and specialized" versus the "bread-and-butter" observing models is
discussed, as is the role hands-on remote observing can serve to
support the various operational models.
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Keywords:Astrophysical
Research Consortium, Apache Point Observatory, 3.5-meter telescope,
remote observing
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1. background
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<![if
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The
Astrophysical Research Consortium (ARC or 'consortium'
hereafter) was established in 1984 to build and
operate Apache Point Observatory (APO) at Apache Point, New Mexico,
for the shared use and benefit of consortium astronomers and
students. Two major ARC projects at the site are the 3.5-meter
telescope, which has been in routine operation since 1994, and the
2.5-meter Sloan Digital Sky Survey (SDSS) telescope, in operation
since 1998. The following ARC member institutions
currently fund the operation and capital improvement projects for the
3.5-meter telescope: the University of Chicago, the University of
Colorado, Johns Hopkins University, New Mexico State University,
Princeton University, and the University of Washington. Telescope
time is allocated to these institutions in proportion to their
project contributions, and the telescope has a diverse and
geographically widespread user community of more than 200 astronomers
and students.
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<![if
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telescope and instrument description
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The 3.5-meter telescope has an f/10 Nasmyth
optical design with a 30-arcminute field-of-view, a lightweight
spun-cast 3.5-meter primary mirror, and lightweight secondary and
tertiary mirrors. Rotating the tertiary mirror provides access to
nine parfocal instrument ports. Direct friction drives enable precise
pointing and tracking. The telescope structure and enclosure have low
mass and are kept close to isothermal (at ambient temperature) by
wind and fan-forced air. The secondary mirror is actively controlled
to effect focus and tilt compensation, and the transformation between
the alt-az telescope mount and celestial coordinates is derived from
observational pointing models, while collimation is periodically
adjusted using a Shack-Hartmann wavefront sensor. The telescope has
excellent blind pointing performance, frequently provides
sub-arcsecond images in the visible, and requires unscheduled repairs
less than 2% of the time. Further telescope information is found at
http://www.apo.nmsu.edu/Telescopes/eng.papers/eng.papers.html.
An interior view of the telescope is shown in Figure 1.
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Figure 1.The 3.5-meter telescope from
inside enclosure, photograph by Dan Long
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Several
facility-class instruments are available for routine use on the
telescope, including an infrared imager and grism spectrometer, a
medium-resolution visible-light spectrograph and imager, a
high-resolution visible-light CCD imager, and an echelle
spectrograph. Also, a number of specialized visitor-supplied
instruments have been successfully used with the telescope, some for
limited observing runs and others on a continuing basis. Projects to
upgrade existing instruments and for acquiring next-generation
instruments have either been completed, are well underway, or are at
the proposal stage. These include a detector upgrade to new low-noise
CCDs for the medium-resolution visible-light spectrograph and imager
(completed in 2002), a new IR imager with a medium field detector and
Fabry-Perot etalon (under construction), a near-IR spectrograph
(under construction), a new medium-field visible CCD imager (being
designed), and a low-noise detector upgrade to the echelle
spectrograph (proposed). Continued use of more specialized "visiting"
instrumentation is expected and welcome, which include a Fabry-Perot
tunable narrow-band visible imager, a laser lunar ranging experiment,
and a Fourier Transform Spectrometer, among others. Additional
information on most of the existing and future instruments can be
found at http://www.apo.nmsu.edu/Instruments/.
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<![if
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overview
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The telescope systems were designed and built
for real-time remote operation through the Internet. Most (about three-quarters) of all observing is done
remotely, with in-person visits to the site by astronomers being
mainly for installation and testing of new instruments or for
training purposes. Multiple independent science programs
share the telescope in turn on the same night, often using more than
one scientific instrument. Remote users also collaboratively use the
telescope simultaneously from different off-site locations. Synoptic
observing programs and rapid-response observations are frequently
accommodated.
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The manner in which observatories support users
ranges from "help-yourself" to "full-service." The APO user support
model is somewhere in the middle, and is often described as an equal
partnership between the consortium astronomers and the observatory
staff. User support is helped by easy telescope access afforded by
the remote observing capability and on-line user information systems.
Operational costs are kept low by allowing and encouraging the direct
involvement of the astronomers in the operations and engineering
projects. Also, consortium astronomers have first-hand involvement
with the data acquisition process and can more readily understand and
appreciate the quality of their data. The APO remote observing
systems promote this hands-on observing approach while enabling
flexible and semi-reactive telescope use, which saves a significant
amount of astronomers' time (and funds) by greatly reducing the
amount of travel necessary to observe. While Principal Investigators
of the science programs are from ARC-affiliate institutions,
collaborations with scientists and students from outside the
consortium institutions are welcome and numerous.
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The telescope is scheduled by quarters using
proposals solicited and prioritized within each of the consortium
institutions. Except for brief synoptic observations and target of
opportunity programs, each night is typically divided into halves.
These half-night blocks provide adequate on-target and calibration
time, plus simplify the manual scheduling process. Several nights of
Director's Discretionary Time are reserved in each quarter and are
allocated ad hoc for a variety
of special science programs, targets-of-opportunity, or engineering.
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The
observing proposal form is relatively simple, requiring only the
science justification information necessary for selection and
prioritization by the PI's institution, PI contact information, and
brief observational and scheduling parameters. After selection and
prioritization, the institutional schedulers electronically submit
the proposals to the Director, who manually constructs a three-month
schedule. Proposal priorities, lunar and other scheduling
constraints, the balance between institutional allocations, and
inclusion of engineering time, etc., are reasonably well
accommodated. Most of the scheduled programs are allocated one or
more half- or full-nights, unless they require a shorter observing
duration such as synoptic or target-of-opportunity programs. These
shorter programs are in the minority but do involve a significant
amount of observing time. The proposal oversubscription rate varies
somewhat between the ARC institutions, but typically runs about a
factor of two.
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<![if
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modes
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Typically,
two or three observing programs are scheduled for adjoining time
intervals in the same night. These science programs often employ
different instruments, observers, and institutional affiliations.
While observers can elect to either use the telescope in person or
remotely through the Internet, most choose to observe remotely.
Remote observing is conducted using a Macintosh-based application
program, which is downloaded in advance to the remote observing
stations from the site. A new platform-independent remote-observing
software program is under development. Data communications with the
site are handled through a dedicated T1 line from Apache Point to Las
Cruces, New Mexico; from which point the data and command packets are
transferred back and forth from the remote observing stations through
Internet2.
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The remote
observer can carry out nearly all essential observing functions,
including telescope and instrument control, guiding, quick-look
quality assurance, and data retrieval.However,
all telescope operations are attended and supported by an on-duty
Observing Specialist, who is responsible for telescope safety as well
as providing technical assistance to the on-site or remote astronomer
who is using the telescope. Observing Specialists perform all
instrument changes at night single-handedly, typically in a few
minutes per change. The telescope design also enables some instrument
changes to be performed quickly without human assistance, and allows
for multiple instruments to be mounted on the telescope
simultaneously and kept ready in a "standby" mode. For a number of
programs, Observing Specialists are active collaborators in that they
conduct the observing and participate in data reduction and analysis.
In principle, the telescope could be operated without an on-site
Observing Specialist, but the value of having staff experts assisting
the remote astronomers has proven to be worth the cost for efficiency
and telescope safety reasons-many remote astronomers use the
telescope only occasionally and find they can use the telescope time
more effectively when they work together with Observing Specialists,
even though the partnership is virtual.
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2. future considerations & plans
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2.1 Overview
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The present availability of 6- to 10-meter
telescopes, with more and larger ones planned, will clearly influence
the future role of mid-sized telescopes-the number of 4-meter size
telescopes is probably less than the number of existing and planned
6- to 10-meter telescopes! Although the ARC 3.5-meter telescope is
used mostly as a general-purpose facility for a wide range of smaller
projects, it has potential capabilities and modes of operation that
support unique and/or larger investigations not easily accommodated
on the largest telescopes. One of the planning issues for ARC is
whether a long-range strategy should maintain and emphasize the
current mode of operation, or to place more priority and resources
toward dedicated and specialized projects that are uniquely matched
to the telescope and its instrumentation. Such projects include
development of new specialized instrumentation, changes in telescope
scheduling and observing modes, implementation of long-term survey
projects, optimization of rapid follow-up, etc. The combination of
remote observing access plus its fast instrument change capability
enables new observing modes with the 3.5-meter telescope, opening
unique classes of scientific exploration and educational
experiences.
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As attractive as these new observing modes and
specialized projects seem, many of the consortium astronomers
understandably wish to retain the current operational model generally
as it is, adding and upgrading instruments and preserving most of the
observing time for individual projects, especially those conducted by
graduate students. These users feel that careful consideration of new
observing modes and specialized projects should be given, but that
the observatory should not be tempted into chasing "fad" science at
the expense of established research areas. For these traditionally
minded users, the cost-effective operation of the ARC 3.5-meter
telescope and remote observing capability uniquely allow many small
projects to get significant amounts of telescope time, possibly more
than would be accessible with the new generation of larger telescopes
for which the user demand and oversubscription are naturally
greater.
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ARC widely recognizes the importance of
obtaining next-generation instruments for the 3.5-meter
telescope-whatever balance of science priorities is chosen for the
future use of 4-meter telescopes, instrumentation is generally what
drives scientific productivity over the longer term. Many of the ARC
astronomers have interests in wide-field imaging, multi-object
spectroscopy, and infrared spectroscopy, observation types not
provided by the current suite of facility instrumentation. Bringing
the existing imagers and spectrographs to near state-of-the-art
capability is already underway, a faster, cheaper way of keeping the
instrumentation current. But part of the long-range planning for any
modern telescope must include a program for replacement of
instrumentation, except for those instruments dedicated to long-term
survey and temporal study programs. As given later, upgrading and
replacing facility instrumentation can involve making tradeoffs that
work counter to specialization.
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In the remainder of this section, some of the
possible specialized science uses of the ARC 3.5-meter telescope are
given and contrasted with a discussion of maintaining and upgrading
the telescope for general-purpose observing programs.
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2.2 Niche science opportunities
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Several niche science and observing modes are
possible with the ARC 3.5-meter telescope, which capitalize on its
several unique strengths.
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Fast-response observations of transient
phenomena:The ARC 3.5-meter telescope is ideally
suited for "fast-attack" observations of transient and
target-of-opportunity programs. Remote operability, rapid instrument
change capability, and good telecommunication with a broad user
community promote the use of the telescope and instruments for rapid
follow-up of time-critical phenomena. The telescope has been used
successfully for optical observations of gamma-ray bursts,
gravitational lens events, and extra-galactic supernovae. Coordinated
observations with other ground- and space-based telescopes are often
undertaken. As an example, a program is currently underway to obtain
high-resolution echelle spectra of gamma-ray bursts using an
automatic spacecraft alert to trigger an alarm at APO. If conditions
warrant, the telescope is diverted from whatever program is running
to take a high-resolution echelle spectrum of the gamma-ray source.
The time from the alert to the start of the echelle exposure can be
less than a few minutes.
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Remote-control, queue-scheduled observations:Since it is possible to change
instruments rapidly with the ARC 3.5-meter telescope, many remote
(and on-site) users opt to not specify in advance which instrument or
exact program they plan to use, but rather adapt their observing
plans in real time based on observing conditions. This is tantamount
to running a small queue-scheduled observing program by one
astronomer. One limitation is that an individual astronomer's private
queue of programs may not take full advantage of all possible
observing conditions, nor contain any of the highest-ranked programs
that require the most rare seeing or transparency conditions.
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Larger, more complex, queue-observing models
have been prototyped and tested on smaller and mid-sized telescopes,
and queue observing has since been implemented on some of the largest
new telescopes. "Service" queue scheduling (where the PI team is not
directly involved with the data taking) can often make better use of
the more expensive telescope resources, and it facilitates the
completion of the higher priority science programs that require rare
observing conditions. This is in contrast to the classical observing
scenario where the scheduled astronomer attends the observing and
makes best use of whatever the conditions and equipment allow.
Running a large queue-observing program in service mode is expensive
and labor-intensive, suitable for only the largest telescopes. For a
full-blown queue operation, the on-site service observing staff must
have extensive scientific expertise to make the numerous necessary
tactical decisions, and the proposers need to prepare a fairly
detailed explanation of their observing requirements. Complex
software is needed to plan and prioritize the various observing
program options between dozens, if not hundreds, of competing
observing proposals. Satisfaction with the data products is not
always universal, as the end customer is often unfamiliar with the
trade-offs necessary to obtain the data, or is psychologically
disinclined to trust others to take observations in their place.
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Hands-on remote observing allows for a form of
queue observing that would alleviate these problems. For those
astronomers prepared to take their chances, a block of
queue-scheduled time on a remote-accessible telescope would be
allocated to a handful of remote astronomers who together have
programs requiring a wide range of observing conditions and
scientific priority. The astronomers would be on-call during weeklong
blocks of time, and offered the time for their program(s) on a
prioritized first-refusal basis if the observing conditions were
suitable. If the highest priority program were untenable because of
conditions, then the next astronomer needing the existing conditions
would be given the option for remote use of the telescope. In the
case where all the astronomers in the queue declined to use the time
and if conditions allowed, the telescope would then be used for
synoptic or other observatory programs with site staff conducting the
prescribed observing. Although this relatively simple model of remote
queue-observing has not yet been attempted at APO, in principle it is
a way to optimize observations to better match changing observing
conditions using a richer queue of programs than can be provided by a
single observer.
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Large (and backup) programs:Three of the
recognized strengths of modern 4-meter class telescopes are
wide-field imaging, spectroscopy of medium-faint objects, and
high-dispersion spectroscopy of brighter targets. "Large" science
programs of these types can require huge blocks of telescope time.
Although it is difficult for individual ARC astronomers to win more
than a few nights per year of time on the 3.5-meter telescope, groups
of astronomers could submit proposals to conduct large projects on
the telescope by pooling their allocations. In practice, however, the
typical ARC astronomer seems to prefer smaller observing projects,
usually with two or three collaborators at most, which use about a
week of telescope time to complete over a year or so. Also, many of
the ARC astronomers are already engaged in pursuing other major
projects with data from the SDSS, which is in itself a large project.
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A formidable, though attainable, goal is to
build and promote large observing programs for the 3.5-meter
telescope that would win the interest of sizeable groups of ARC
users. As an example, one suggested large program would be to create
a high-resolution echelle spectroscopic catalog of several thousand
of the brightest stars. This program would be executed in "backup"
service mode by observatory staff using observing conditions
unsuitable for other projects. It is clearly the role of the Director
to make a case for the importance of such programs and to solicit the
collaborative involvement of the user community, especially if it is
felt that the promotion of large programs is an important niche
priority for the telescope's future. It is also conceivable that
large observing programs would be undertaken with the 3.5-meter
telescope in collaboration with other facilities.
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Synergy with other telescopes, follow-up
observations:In
the past few years, synergism between the consortium's 3.5-meter
telescope and the SDSS project has been a major scientific success.
Many of the most spectacular and important scientific results
produced by both projects have resulted from 3.5-meter follow-up
observations of SDSS discoveries. The SDSS is continuing to provide
the 3.5-meter telescope with a steadily growing source of fairly
faint and interesting spectroscopic targets. Also, other telescopes
could be effectively used in tandem with the 3.5-meter telescope in
complementary ways. This is particularly true for follow-up
observations, which usually can be quickly accommodated with the
3.5-meter telescope.
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There is an ongoing community discussion about
combining observatory resources in the U.S., both federal and
private, into a coordinated system. Although a "national observing
system" might avoid some duplication of capability between
observatories, any such system would be compelled to impose complex
and perhaps onerous requirements on instrument specification, user
interfaces, and observing protocols. It could also hamper the
important hands-on aspect of observing and instrument development by
small groups or individuals, and might suppress innovation,
experimentation, and philanthropy by individuals. In contrast,
smaller-scale arrangements for sharing telescope and instrument time
would be somewhat less cumbersome than a national system. At other
private and consortium-based 4-meter telescopes, hands-on remote
observing is under study and development. Telescope-sharing
arrangements can be imagined where the user communities of two or
more telescopes would have limited remote access to each other's
telescopes at different locations and/or with different
instrumentation in return for sharing comparable amounts of time
between telescopes within the combined user communities. If the
remote operation interfaces were largely similar and simple between
the partner telescopes, users would have relatively seamless, though
limited, access to a broader suite of instrumentation and possibly
different sky coverage than would be available at their home
facilities.
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Surveys, synoptic and temporal monitoring
programs:With its moderate aperture, wide field
of view, and easy access to a variety of instruments, the ARC
3.5-meter would undertake several kinds of long-term studies. With a
new wide-field visible or infrared imager, various kinds of imaging
surveys are possible, including extensions of existing surveys taken
with smaller telescopes. Multi-object spectroscopic surveys are also
possible. In addition, studies involving the time domain of
astronomical phenomena have become increasingly interesting. Using
queue scheduling in service mode, the ARC 3.5-meter telescope would
allocate small blocks of time on a frequent time interval for the
execution of a variety of innovative synoptic and temporal monitoring
programs.
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Solar system programs:Studies of solar
system objects are well served by 4-meter class telescopes with good
imaging capabilities, easy user access, and appropriate
instrumentation; it is often the case that a larger aperture
telescope is unnecessary or would be difficult to justify its use.
The ARC 3.5-meter telescope has conducted many solar system science
programs, including cometary impacts on Jupiter, Venusian
atmospherics, and Kuiper Belt Object discoveries. The ease in which
prototype and specialized instruments are integrated with the
telescope enables unique observational opportunities; an
acousto-optic tunable infrared camera has been a frequent and
successful APO visiting instrument for studies of planetary
atmospheres, for example. Also a laser lunar ranging project has been
proposed which would enable earth-moon relative distance measurements
to an accuracy of about 1-millimeter, which could yield an order of
magnitude improvement in the precision of three important tests of
the basic properties of the gravitational interaction.
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New instrument testing:The ARC 3.5-meter
telescope design easily accepts new instrumentation. The Nasmyth
instrument port has been used by several visiting prototype
instruments over the past several years, and instrument developers
have found the telescope well suited and convenient for commissioning
new instruments. We intend in the future to continue encouraging the
use of visitor instruments. This is motivated in part as "community"
support for those instrument builders who need testing time for new
instruments on a telescope of this size. Also, by encouraging the
commissioning of these new instrument at APO, unique science
opportunities are afforded as is the possibility of retaining the new
instrumentation for general use by consortium astronomers as
replacements or upgrades to aging facility instruments. Any mid-sized
telescopes that can afford easy focal plane access for new
instruments will be in demand for commissioning the next-generation
instruments for the largest new telescopes.
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2.3 General-purpose programs
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To maintain the continuing support and
involvement of the majority of its astronomers and students, the ARC
3.5-meter telescope will need to sustain a core capability for
"facility-class" instrumentation and hands-on (both remote and
on-site) observing. The complement of instruments originally
commissioned with the telescope includes a medium-field visible
imager/photometer, a narrow-field IR imager with grism spectrometer,
a low- and medium-dispersion visible spectrometer, and a
high-resolution echelle. As mentioned above, the consortium has found
the resources to upgrade the detectors on the low/medium dispersion
spectrometer, and to replace the IR imager with a device offering a
larger field of view and lower noise. Other projects for the facility
instruments include a low-noise detector upgrade for the echelle
spectrograph, building a near-IR spectrometer, and the development of
a low-noise multi-color visible imager.
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A fundamental problem with astronomical
instruments, both facility and specialized, is that they have
relatively short service lifetimes. With the pace of advances in
technology, instruments have a useful lifetime of less than a decade.
If four or five facility instruments are to be maintained, upgraded,
and replaced on this time scale, an observatory needs to plan and
budget for a major upgrade or replacement averaging every few years.
A typical instrument upgrade or replacement for a 4-meter telescope
can cost about $1M, which is a substantial fraction of the annual
operational and capital development budget for most telescopes in
this class. A telescope can have a lifetime of more than 25 years,
but if the instruments are not kept near the state-of-the-art, user
communities will not be satisfied with the scientific potential of
the observatory as a whole and may lose interest in its continued
support.
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Also, overall costs increase with the number of
instruments supported. If a modestly funded observatory intends to
keep four or five general-purpose instruments in prime operational
condition, there is little room left in the staffing plan and budget
to support any substantial program of specialized niche
instrumentation. One approach to solving both problems is to
encourage astronomers to independently propose and find resources to
develop new instrumentation, both general-purpose and specialized.
Several of the past, present, and planned ARC instrument upgrades
have followed this approach, including both specialized
instrumentation and general facility-class instruments. ARC will
continue to solicit these kinds of grass-roots instrument
developments and in return, offer instrument developers varying
degrees of support such as cost sharing, telescope time and site
support. In general, ARC assistance to the developers is provided at
a negotiated level that is keyed to whether the instrument
upgrade/replacement is generally useful to the larger ARC user
community or is of more specialized value to a small number of
users.
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Although this approach has worked in the past,
it can be somewhat inefficient. Being "market-driven" and
time-consuming for ARC management, many false starts are suffered. On
the other hand, experience has shown that in general, good
instrumentation is rarely designed and built by committee. Many of
the most productive astronomical instruments have been conceived and
built by individuals or small groups with a particular scientific
project in mind.
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2.4 Outreach and teaching
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Because of their lower on-sky operating costs,
4-meter and smaller telescopes are natural tools for public outreach
and teaching opportunities-remote hands-on observing makes this even
more tenable. The ARC 3.5-meter telescope has been in partnership
with the Adler Planetarium for several years, participating in a
successful remote-access public program. Planetarium and university
astronomers remotely operate the 3.5-meter telescope on Friday
evenings for public display, during evening twilight hours at APO
that are otherwise not used for science observations. Even during
normal science observations, it is conceivable that private or public
eavesdropping would be supported over the Internet with little or no
impact to the science programs.
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Furthermore, the ability to provide astronomy
students with hands-on access to research-grade telescopes is made
easier by remote observing, especially for those students with
limited travel support. Hands-on access to observatory facilities is
declining with the increased use of observing modes such as queue
scheduling and service observing on the new largest telescopes.
Astronomy students in the coming years will have increasingly fewer
opportunities to learn the hands-on aspects of the field, unless easy
access to the smaller telescopes is encouraged. This is extremely
important, because the future telescope and instrument builders will
graduate from the ranks of these students who have been given
extensive observatory experience.
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3. Conclusions
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The ARC 3.5-meter telescope and its baseline
facility instrumentation have been incrementally improved during the
first decade of operation to the level where the observing systems
are mature, reliable, and routinely provide its user community with
useful and often exciting data. Looking forward, the ARC community
has begun discussions on what role this facility can have in the
company of the new large-telescope facilities recently put into
operation, and on the rapidly evolving scientific priorities in the
field as a whole. While the future scientific value of 4-meter class
telescopes will be partly determined by the vision and leadership of
their management and governing bodies, the realization of the
potentials and continued viability of the facilities will be largely
driven by the scientific priorities of the users-especially if these
astronomers and students are actively involved with the telescope and
its instrumentation.
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Two principal ARC priorities for the 3.5-meter
telescope are excellence and innovation in science, and graduate
student education and training. By identifying, maintaining, and
building on the intrinsic strengths of the telescope, the consortium
astronomers and students will continue to benefit from both its
unique and generic scientific capabilities. Some of the more
important future advances in astronomy will come from the innovative
use of state-of-the-art hardware, computer technologies, and new
observing modes-even with modest aperture telescopes. For APO, it is
not presently clear how these kinds of initiatives can be allocated
priority while continuing to serve the wider range of interests of
the ARC user community. The dilemma for the consortium is to
determine the balance between these paradigms, i.e., can they happily
co-exist and be affordable. In the future, telescopes of this size
with large-field, high-resolution imaging capabilities, state-of-the
art CCD imagers and spectrometers, flexible scheduling, remote
operations, and easy access for users, will undoubtedly play a
significant part in the future advancements in astronomy.
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4. Acknowledgements
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The author wishes to thank the many ARC
astronomers and APO staff who provided perceptive input for this
article. Their continued active interest in the long-term planning
process is essential and much appreciated.