An evolving astronomical landscape
Twenty-five years after the inauguration of the
INT and
JKT, and 20 years after
WHT started science
operations, the Isaac Newton Group of Telescopes (ING) is discussing its role for the coming
decade. The ING telescopes, thanks to the vitality of the astronomical communities served by them,
have amply fulfilled the ING mission of fostering major advances in our knowledge of the Universe.
Owing to a versatile set of instruments, and to our commitment to a classical, visitor-oriented
operating mode, world-class science has emerged in virtually all areas of astronomy. Our focus on
PI science tailored to small groups has meant that the majority of our astronomers, residing in
University groups, have had regular access to world-class observational facilities. By
welcoming visitor instruments, ING has facilitated the development of innovative instrumentation,
thereby contributing to the training of generations of instrumentalists. The multi-national nature
of our clients has fostered international collaboration and has decisively contributed to the
emergence of Spanish astronomy in the past two decades.
The global astronomical landscape has evolved tremendously during the thirty years
throughout which the
International Agreements have articulated astronomy in the Canary Islands. As many as twelve
optical-infrared telescopes with apertures above 8m are in operation worldwide. Plans are underway in the USA
and in Europe for the construction of the next generation of giant telescopes, with apertures of 30m
to 42m, which could start observations within one decade. The cost of these larger facilities, and
that of projects at other wavelengths on the ground
(ALMA,
SKA) and in space
(JWST,
LISA)
forces the communities to re-evaluate the roles of the smaller facilities
in order to open the way for the larger telescopes.
The following sections portray our vision of the role the WHT should play in the coming decade.
Our challenge is to remain a world-class facility, while maintaining the
current level of service to the community and the cost effectiveness of our operation
for our funding agencies.
The WHT, like other 4m-class telescopes, provides observing capabilities that larger telescopes cannot
deliver
Both the ING Board and the ING Science Advisory Committee concur that 4m telescopes have an
important role to play among 10m-class telescopes, namely to deliver
an efficient capability for wide-field (WF) astronomy.
Typical fields of view (FOV) on 10m telescopes are below 20 arcmin in diameter.
On 4m telescopes, FOV can reach diameters of 2 degrees at prime focus (PF).
Survey speeds are greatly enhanced, both in imaging and multi-object spectroscopy (MOS).
We are in agreement with the conclusions of the
OPTICON-ASTRONET-led
ETSRC
Infrastructure Roadmap for European medium-sized telescopes.
In this context, the WHT has an important role to play as a 4m complement of the 10m GTC on the ORM.
The three ING partners are all members of ESO, and ESO provides ample access to observational
capabilities in the Southern sky. The ING has a crucial role to play in
providing access to the Northern sky. Access to the Northern sky is crucial for several science areas. These include
the Northern Milky Way, nearby galaxies such as M31, M32 and M33, Local Group dwarf spheroidals,
the Coma cluster, follow-up of radio surveys in the North such as
LOFAR,
and important cosmological fields
such as the GOODS-North field,
the Lockman Hole and the ELAIS fields.
Of strategic importance, access to the Northern sky is essential for
follow-up of space-based surveys such as GAIA and Herschel in the
North, in support of our communities' investment in space astrophysics.
WEAVE, a wide-field multi-object spectrograph for the WHT
It has become clear in recent years that, among WF instruments,
our communities have a strong interest in a WF MOS. The rationale for this is
based on the fact that, in the coming years, many imaging and photometric surveys will be carried out on a
variety of platforms at a wide range of wavelengths. Examples include the
VST and
VISTA surveys, the
Pan-STARRS maps
of the sky, the
GAIA map of the Milky Way, and the
LOFAR radio survey,
in addition to the ongoing UKIDSS surveys.
For all of these, obtaining useful physical information from the sources requires extensive optical
spectroscopy to obtain redshifts and physical characterization of millions of targets.
With a new corrector, now in the design stage, the WHT will deliver a FOV of 2 degrees in diameter.
Due to this, the ING is proposing the construction of WEAVE, a wide-field MOS at WHT. The science cases call for a spectrograph fed with 1000 fibres and delivering spectra of resolving power of 5,000 covering from 370 nm to 1000 nm. A high-resolution mode will also be available, with resolving power 20,000 over a smaller wavelength range. WEAVE will provide for single-fibre input as well as mini-IFUs and a monolythic IFU. A science team and an instrumental team will develop the instrument design and construction. ING is working with the WEAVE team to ensure support from the funding agencies for the project, and to expand including non-ING partners to make WEAVE and its scientific exploitation a truly European project. Updated information on this project can be found at the WEAVE web site.
HARPS-NEF
The Harvard-led
HARPS-NEF
high-resolution stabilized spectrograph was part of our strategy of providing the WHT with competitive, front-line instrumentation. Funding issues prevented HARPS-NEF from coming to WHT. It is our understanding that the instrument, now named
HARPS-N, is being built by a consortium led by Observatory of Geneva and is planned for deployment at TNG. We regret not being able to host HARPS-N on the WHT, and wish the team full success in the detection of planets by the radial velocity technique.
Balancing classical observing with large surveys
The ING will strive for a middle ground approach between allocating time for classical, TAC-based time
allocation to small-size proposals, and large allocations to survey-type science.
Whilst the former has been at the root of ING's past successes, and oversubscription factors of 4
indicate that this mode of observation is in much demand, it is only through large time allocations
that the full power of some of our instruments can be harvested and solutions for key
astrophysical questions can be sought. The spectroscopic follow-up to large surveys which we
suggest above is one such example.
The exact balance between the two observing modes
is a matter of debate, and indeed it is the communities we serve who have to decide the amount of time
allocated to surveys.
How many instruments
A diversity of common-user instruments is a natural wish of classical observing, and the WHT has
excelled in this regard in the past. At the same time, more instruments imply greater
maintenance costs. Furthermore, having more instruments results in each instrument
sitting unused in storage for a larger fraction of each year. Obtaining full
benefits from the construction of forefront, expensive instruments, requires generous access to
telescope time. For all of these reasons, it is likely that ING will reduce the number of supported
common-user instruments in the near future. Instrument selection will be guided by the statistics
of instrument requests by our users, among other considerations. For the past 5 years,
50% of all requested time at the WHT has been
for
ISIS or
LIRIS,
which rightly qualify as the work-horse instruments of the WHT.
Enhancing the visitor instrument programme
In our view, the ING mission of providing telescopes for world-class astronomical research is
strongly served by continuing our successful visitor instrument programme. Within this programme, small
groups have been able to complete the entire instrument building cycle, from idea
through design and construction to exploitation on a world-class telescope, in the time span of a
few years. Over the years, this programme has fostered the training of generations of
instrumentalists; today it is these scientists who are leading the design of the complex instruments
needed for future giant telescopes. Furthermore, data from visitor instruments have led to some of
the most highly cited papers coming from the WHT. And it is a common remark from teams who have
deployed their instruments at the WHT that their programme could not possibly have been carried out at
any other major observatory to which they have access.
For these reasons we believe that maintaining and enhancing the visitor instrument programme is of
immense benefit to our communities, and we plan to do so in the future.
Training
Through our visitor observer, classically scheduled mode, and our resident student programme,
students and young astronomers gain a direct exposure to optical-infrared observing.
We believe this is an important contribution of ING to present and future astronomy,
and we plan to continue our programme.
Use of the WHT for technology development
We believe that our mission of supporting forefront astronomical research benefits from our offering
a fraction of WHT time to activities aimed at developing technologies that do not immediately yield
astrophysical knowledge but which will be used in future instruments. In particular, we plan to
facilitate technology development aimed at instrumentation for E-ELT.
European-wide rationalisation of observing capabilities
European astronomy holds an important potential for better coordination of national-level strategic
plans. For medium-size telescopes, such coordination is fundamental if we are to survive under the
funding pressure driven by the larger facilities. ING is engaged in the
OPTICON-ASTRONET-led
ETSRC
study, whose
final report is expected in the first quarter of 2010. ING already has instrument and observing
time-sharing experience, which we are eager to contribute in order to make the process a success.
For the multi-object spectrograph we plan to take into consideration the
recommendations of the ETSRC and its MOS working group.
The Adaptive Optics programme at the WHT
Promoting wide-field spectroscopy represents a change of strategic direction for ING. In the past
decade, ING has focussed on developing technologies and observing capabilities
(NAOMI) for
high-spatial resolution imaging
(INGRID)
and integral-field spectroscopy
(OASIS)
based on natural guide star (NGS) and laser-assisted (LGS) adaptive optics (AO). While
the WHT ground-layer laser system
GLAS
was a good choice when initially planned, it is no
longer competitive now when several 8 and 10m telescopes have sodium-layer laser systems. Our
AO systems will continue operational with a priority below that of other
instruments. We note that the investment in AO has led to a high knowledge level on AO systems,
which will come in handy for technology developments aimed at the E-ELT, as described above.
