We describe some of the science programs that drive the need for the next generation ground-based OIR telescope. The programs are chosen to illustrate the power of such a telescope to enable new kinds of science via combinations of sensitivity, field-of-view, wavelength coverage, and spectral resolution.

Stellar proper motions, radial velocities and accelarations obtained with high angular resolution techniques over the past decade have convincingly proven the presence of a central compact dark mass of 3x10⁶ M. This mass is most likely associated with the compact radio source Sagittarius A* and represents one of the best candidates for a super massive Black Hole. This contribution summarizes some important observational facts and outlines the future possibilities for interferometric observations of the Galactic Center. In the near future interferometric observations of that region with the LBT, VLTI and the Keck Interferometer will be possible. Detailed measurements of the stellar orbits close to the center will allow us to precisely determine the compactness, extent and shape of any extended mass contribution e.g. due to a central stellar cusp. Emphasis will be put on the potential of the NIR LBT interferometric camera LINC. Given the combination of large telescope apertures, adaptive optics, and interferometry it is likely that stars with orbital time scales of the order of one year will be detected. Theses sources, however, will most likely not be on simple Keplerian orbits. The effects of measurable prograde relativistic and retrograde Newtonian periastron shifts will result in rosetta shaped orbits. An increased interferometric point source sensitivity will also allow for an effective search and monitoring of an IR counterpart of SgrA*.

The bulk of the hard X-ray background has been resolved into discrete sources by ultradeep surveys with the Chandra X-ray Observatory. We have carried out multiwavelength follow-up observations of the active galactic nuclei that make up the background to ascertain their nature. With the addition of optical, submillimeter, and radio data, the bolometric luminosities of the sources can be estimated and used to map the history of supermassive black hole accretion from the earliest times to the present.

Visual-wavelength focal plane mosaics with 10 to 100 gigapixels may become available within the next several decades. Silicon sensor read-outs may also enable the reliable detection of individual visual wavelength photons in the near future. Such solid-state photon-counting mosaics, fed by integral-field spectrographs (IFSs) which simultaneously record the spectrum of every image element, may enable astronomers to chart the 3D structure of the entire visible Universe, and trace its physical and chemical evolution from soon after the birth of the first stars to the present. We explore the requirements of a 'cosmic atlas' sensitive to objects having 0.1 times the luminosity of the Milky Way. The proposed cosmic survey has a spatial resolution of about 0.1", a spectral resolution of R ≈ 10² to 10³, and cover the wavelength range from the near-UV to the near-IR.

We present early results on starts of the galatic spheroid obtained using UVES, the cross dispersed echelle spectrography of VLT. Within its two first years of operation, UVES has already allowed major progresses in our views of the early galactic spheroid, including significant improvements in the age estimates and a deeper insight into the processes that lead to metal-enrichment in the Galaxy. Perspectives for the next few years, with the possible use of the multiobject fiber facility FLAMES coupled with both UVES and the new Giraffe spectrographs are briefly outlines.

In the distant universe, we can map the evolution of galaxies by observing how their global properties change with time. High-resolution studies of nearby galaxies afford a complementary view: for a few galaxies, we can study their star formation histories directly by the application of stellar evolution theory to their observed color-magnitude diagrams. Nearby objects offer a powerful and unique opportunity for understanding galaxy formation and evolution. The individual stars within these galaxies can provide a detailed record of the start formation and chemical history and kinematics: information critical (but unavailable) to the interpretation of galaxies at high redshift, a driving scientific motivation for the Next Generation Space Telescope, for example. Future high-resolution studies will address a number of outstanding questions: what is the range in formation times? Can the assembly of halos be traced for evidence of subclumps hierarchically built up over time as suggested by current cold dark matter models. Did some galaxies form early in the universe and continue to evolve passively to the present day? Do spiral disks form from the inside out or the reverse? When do disks form relative to the halos of galaxies?

ELT science drivers stress aperture, Strehl ratio, PSF definition and stability, field of view, wavelength range, flexibility, low polarisation and thermal emittance, auxiliary instruments, site and infrastructure. Applicable science categories are planets and planetary systems, stars and stellar systems, galaxies and galaxy clusters, and cosmology. ELT observations are needed for our own and other planetary systems. The study of planetary disks and formation requires ELT data. ELT results, with emphasis on PSF quality and stability, are crucial to the search for earth-like planets, especially those favourable for life. Investigation of star formation and stellar evolution requires ELT performance, as does the study of final stellar stages. ELTs are necessary for extremely high time resolution, details of stellar surfaces and astroseismology. Galaxy formation studies will benefit dramatically from ELT data, as will studies of large-scale development of galaxies and galaxy clusters over cosmological time scales. Detecting active galactic nuclei requires ELTs. ELT data are crucial for examining the structure and evolution of the universe. Observations of supernovae and other standard sources over very large distances are necessary for mapping the expansion of the universe and determining its acceleration or deceleration. Comparisons of Euro50 with VLTs and HST show a dramatic gain. The complementarity of Euro50, NGST and ALMA is noted.

As many as 101 extrasolar giant planets (EGPs) have been detected by radial-velocity techniques, but none has been detected directly by its own emission or by reflection of the light from its parent star. We review the current state-of-the-art in the theoretical modeling of the spectra of giant planets outside the solar system and the basic theory of EGP spectra and atmospheres. We are now entering a new era of planet discovery and measurement. This contribution is meant to communicate some of the excitement in the astronomical community as the hunt for these exotic and remarkable objects accelerates.

For the first time in human history the possibility of detecting and studying Earth-like planets is on the horizon. Terrestrial Planet Finder (TPF), with a launch date in the 2015 timeframe, is being planned by NASA to find and characterize planets in the habitable zones of nearby stars. The mission Darwin from ESA has similar goals. The motivation for both of these space missions is the detection and spectroscopic characterization of extrasolar terrestrial planet atmospheres. Of special interest are atmospheric biomarkers-such as O₂, O₃, H₂O, CO and CH₄-which are either indicative of life as we know it, essential to life, or can provide clues to a planet's habitability. A mission capable of measuring these spectral features would also obtain sufficient signal-to-noise to characterize other terrestrial planet properties. For example, physical characteristics such as temperature and planetary radius can be constrained from low-resolution spectra. In addition, planet characteristics such as weather, rotation rate, presence of large oceans or surface ice, and existence of seasons could be derived from photometric measurements of the planet's variability. We will review the potential to characterize terrestrial planets beyond their spectral signatures. We will also discuss the possibility to detect strong surface biomarkers-such as Earth's vegetation red edge near 700 nm-that are different from any known atomic or molecular signature.

A combination of Spergel’s innovative gaussian-shaped pupil masks with future space-based and ground-based adaptive optics telescopes will offer great sensitivity for direct imaging of faint companions including brown dwarfs and extra-solar planets around nearby stars. Here we propose a quick way to fully achieve its potential for deep contrast imaging surveys with a great speed in a conventionally designed telescope. In our approach, two Gaussian pupil masks set on each side of the secondary obscuration, slightly penetrating the telescope spider structures, are placed in a cryogenic pupil plane in an infrared (IR) camera to allow the collimated telescope beams to pass through. This simple design will enable ~10^-6 deep contrast imaging while enjoying diffraction-limited imaging from the full telescope aperture for discovering faint companions closest to the primary. The survey speed with this design will be at least 3-4 times faster than a conventional coronagraph due to its simple alignment. This contrast should allow an image survey for Jupiter-like planets to ~ 20 pc in the thermal IR with next generation large ground-based and space based telescopes. A combination of this shaped pupil mask with an apodizing focal plane mask will enable deeper contrast than the pupil mask alone. However, it takes a much longer time to align the system, so this mode will be used for characterization of faint companion systems from the candidates identified from the survey. A prototype gaussian pupil mask in the Penn State near IR Imager and Spectrograph (PIRIS) has been tested at the Mt. Wilson 100 inch telescope with high order natural guide star adaptive optics (AO) and has demonstrated its tremendous potential. The contrast is about 10^-3-10^-4 beyond 7 λ/Δ. The contrast is about 5 times better than the direct AO image, and comparable to an IR coronagraph in the same instrument. Recent lab experiments show that 3x10^-6 at ~ 4 λ/Δ can be reached with a combination of a Gaussian pupil mask with an apodizing focal plane mask.

We present several scenarios for the development of potential space astronomy missions and instruments over the next fifty years. It has gradually become necessary to extend our planning horizon well beyond the decade scale because of the lengthy development time for ever larger and more complex space missions, especially to enhance the efficient selection of design options for Terrestrial Planet Finder (TPF) and subsequent systems described in NASA's long-term Origins program, such as Life Finder and Planet Imager. Choices between such options should be driven by science goals and priorities, and also by the benefits of coordinating technologies developed in Origins with those needed for other U.S. and international directed-target and survey missions at all wavelengths. Even though there will be inevitable influences of scientific and technical discoveries along the way, sketching out now a variety of possible integrated technology and (to a degree) science roadmaps helps put the potential paths in context, so our early choices may more rapidly lead toward achieving likely science goals in the future.

In the coming decades, astronomical breakthroughs will increasingly come from observations from the best ground-based locations and from space observatories. At infrared and sub-millimetre wavelengths in particular, Antarctica offers site conditions that are found nowhere else on earth. There are two implications of this. First, for tackling some of the most crucial problems in astrophysics, a large telescope in Antarctica can outperform any other ground-based facility. Second, with infrared backgrounds between one and two orders of magnitude below those at other sites, superior sub-mm transmission and extraordinary low atmospheric turbulence above the boundary layer, Antartical offers designers of space missions a unique test-bed for their ideas and instrumentation.

Four teams incorporating scientists and engineers from more than 50 universities and 20 engineering firms have assessed techniques for detecting and characterizing terrestrial planets orbiting nearby stars. The primary conclusion from the effort of the past two years is that with suitable technology investment starting now, a mission to detect terrestrial planets around 150 nearby stars could be launched within a decade. Missions of smaller scale could carry out more modest programs capable of detecting and characterizing gas giant planets around tens of stars and of detecting terrestrial planets around the nearest stars.

A generation 8-m telescopes, particularly the Keck telescopes in the 1990s have played a crucial role in many scientific programs carried out with the Hubble Space Telescope. The Next Generation Space Telescope, scheduled for launch at the end of this decade, may form a similar relationship with the next generation of ground-based telescopes, for example, CELT, or the NRC Decadal Report's GSMT. Core science programs for ground-based telescopes are now becoming clear. Drawing on these studies, I will address the question of to what degree CELT, GSMT, and perhaps eventually OWL, will share the same important symbiotic relationship to NGST that HST and the 8-m telescopes have enjoyed, or to what extent they will carry out largely independent astronomical research.

The SuperNova / Acceleration Probe (SNAP) is a space-based experiment to measure the expansion history of the Universe and study both its dark energy and the dark matter. The experiment is motivated by the startling discovery that the expansion of the Universe is accelerating. A 0.7~square-degree imager comprised of 36 large format fully-depleted n-type CCD's sharing a focal plane with 36 HgCdTe detectors forms the heart of SNAP, allowing discovery and lightcurve measurements simultaneously for many supernovae. The imager and a high-efficiency low-resolution integral field spectrograph are coupled to a 2-m three mirror anastigmat wide-field telescope, which will be placed in a high-earth orbit. The SNAP mission can obtain high-signal-to-noise calibrated light-curves and spectra for over 2000 Type Ia supernovae at redshifts between z = 0.1 and 1.7. The resulting data set can not only determine the amount of dark energy with high precision, but test the nature of the dark energy by examining its equation of state. In particular, dark energy due to a cosmological constant can be differentiated from alternatives such as "quintessence", by measuring the dark energy's equation of state to an accuracy of ± 0.05, and by studying its time dependence.

The principal science objectives of the major new telescope initiatives at radio, millimeter and sub-millimeter wavelengths are shown to correspond in large measure with the major science objectives of the new space astronomy observing facilities. The complementary insight that is achievable using combinations of these instruments is emphasized. It is noted that in most cases, these science objectives involve a discovery space based on a large sample of objects or of a particular large area of sky. In order to optimize the science return of each new telescope it is argued that the "design" of the science program for that telescope would benefit if it were done in concert with that of other contemporary telescopes.

Recent results from XMM-Newton and Chandra show that sufficiently sensitive x_ray imaging and spectroscopic capabilities allow one to observe the evolution of active galaxies out to z ~ 6, the x-ray signature of luminous star forming galaxies at z~3, as well as the origin and evolution of cosmic structure. With the advent of new optical/UV/IR and radio capabilities in the next decade, it is appropriate to evaluate the future capabilities of planned x-ray missions (e.g., Constellation_X and Astro-E2) as well as other missions being developed (e.g., Gen-X, XEUS, and Astro-G) or under advance planning (MAXIM and EXIST). I will present a summary of the present status of the field and the capabilities of these missions for extragalactic x-ray astronomy.

The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy at large ground-based telescopes. Fabrication of high quality silicon grisms and immersion gratings up to 2 inches in dimension has become a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ~ 4 inches are being developed at Penn State. This immersion grating will be able to provide diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. To take full advantage of this high dispersing device for high resolution IR spectroscopy at high efficiency, high order adaptive optics is required to fully correct wavefronts distorted by atmospheric turbulence, to reach Strehl ratio of at least ~50%. IR spectroscopy with R > 100,000 opens up new possibilities in investigating the total mass and location of protoplanets through observing absorption lines from the CO fundamental bands at 4.6 microns and other molecular bands formed in the dynamic gaps created by protoplanets. It can also be used to study the density, temperature and composition of the environment where planets form. Large aperture telescopes with low thermal background are essential for ground-based observations to have enough sensitivity for observing thousands of nearby T Tauri stars to study planet formation. The results of protoplanet mass and location distribution will be compared to those of planets obtained from Doppler radial velocity surveys to investigate whether orbital migration and dynamical scattering play a significant role in planet formation and evolution. Future perspectives for developing silicon immersion gratings with sizes larger than 4 inches will also be discussed.

Characterization of extra-solar planetary systems requires surveying for planets around hundreds of thousands of nearby stars of all types, with different metalicities, environments (star cluster and multiple star systems), ages etc. Space missions such as SIM, NGST and TPF will identify many of these systems. However, these missions need ground-based surveys to find candidates to improve their efficiency and provide complementary work. Among these surveys, Doppler radial velocity (RV) surveys, which have detected almost all of ~ 100 known planetary systems, will continue to be the most efficient for detecting planets. Though the cross-dispersed echelle spectroscopy has demonstrated high sensitivity and good efficiency for observing thousands of stars, (limited to late F,G, K and M type), it would be tremendously challenging to search for hundreds of thousands of stars since this would require more than 2 orders of magnitude improvement in observing efficiency. New techniques with high throughput and multi-object capability for high precision RV surveys are crucial in solving this problem. Here we introduce a new technique based on a multi-object fixed-delay interferometer with a first order grating postdisperser which provides the potential for all sky radial velocity surveys for planets. This kind of instrument is a combination of a fixed-delay interferometer with a moderate resolution post-disperser. Doppler measurements are conducted by monitoring stellar interferometric fringe phase shifts instead of absorption line centroid shifts as in the echelle. High Doppler sensitivity is achieved by optimizing the optical delay in the interferometer and reducing photon noise by measuring multiple fringes over a broadband realized by the post-disperser. Since the resulting Doppler sensitivity is independent of the dispersion power of the post-disperser, the whole instrument can be designed for multiple objects, high throughput, and high Doppler sensitivity, while the instrument can be made very compact, thermally and mechanically rigid, and low-cost compared to the echelles. Its superior stability and simple instrument response allow its easy adaptation to other wavelengths such as UV and IR. Once a multi-object instrument of this type, with possible UV, visible and near-IR instrument channels, is coupled with a wide field telescope (a few degree, such as Sloan and WIYN), it will produce hundreds of fringing spectra to allow simultaneous searching for planets around late type F, G, and K stars in the visible, early type B and A-type stars, and white dwarfs in UV and late M-dwarfs in near-IR. The first light observations of our prototype interferometer at the Hobby-Eberly 9m and Palomar 5m telescopes in 2001 have demonstrated that this new technique can approach high Doppler precision mainly determined by photon statistics (Ge et al. 2001; van Eyken et al. 2001; Ge et al. 2002). For instance, a stellar intrinsic Doppler precision of ~ 3 m/s has been achieved with a wavelength coverage of ~ 140 Å and S/N ~ 120 per pixel. The overall short-term Doppler measurement error is ~ 9 m/s. This is mainly caused by low fringe contrast (or visibility) of the iodine absorption lines (~ 2.5% vs. ~7% in stellar lines) for wavelength calibration. Recent observing at the KPNO 2.1-m telescope demonstrated good instrument throughput and increased wavelength coverage. The total detection efficiency including the sky, telescope and fiber transmission losses, the instrument and iodine transmission losses and detector quantum efficiency is 3.4% under 1.5 arcsec seeing conditions. This efficiency is already comparable to all of the echelle spectrometers for planet detection.

We describe a new three-reflection telescope (TRT) prototype, where the 30-cm primary mirror is acting as the first and the third reflecting surfaces with different figurings. The two surfaces were realized and polished separately, and then accurately aligned and glued together. This technique has added more flexibility to the original design. The telescope provides: wide (2°x2° square degrees) corrected and unvignetted field of view, flat-field focal surface, small encumbrance, and easy access to the focal plane instrumentation. These characteristics make the TRT in combination with large area CCD cameras, a useful instrument for wide-field observations from remote and hostile ground sites, such as the Antarctic Plateau. The prototype has been equipped with a 2kx2k thermoelectric cooled CCD camera using the San Diego State University SDSU controller. A second custom controller prototype has been developed for ongoing space and Antarctica applications, characterized by synchronous fast readout capabilities (two 14-bit channels each sampled at 3.3 Msamples/s) and suitable to be scaled to large array mosaic applications. This project is aimed at the discovery and tracking of potentially hazardous NEOs, and identification of transient events such as GRBs.

This paper reviews our current understanding of the process of re-ionization of the Universe, focusing especially on those models where re-ionization is caused by UV radiation from massive stars. After reviewing the expected properties of stars at zero metallicity, I discuss the properties of primordial HII regions and their observability