A crisis is now confronting space astronomy. Many current and future investigations at UV and Extreme-UV wavelengths with space observatories such as the International Ultraviolet Explorer (IUE), Hubble Space Telescope (HST), Extreme UV Explorer, and Lyman are limited by the current availability of good fundamental atomic data such as accurate energy levels, wavelengths, and oscillator strengths.

Until very recently, spectroscopic studies using the IUE of hot O-subdwarfs have revealed the vast majority of the photospheric features could not be identified. Our recent detection of species such as Fe V, VI, and VII in very hot white dwarfs was unexpected and has definite implications for observations to be obtained by the EUVE and Lyman. Coadded spectra of these degenerate objects show many other unidentified features. Accurate atomic data for these highly ionized species will be a prerequisite to doing any quantitative analysis of these species and understanding the flux distributions in the EUV, where the strongest lines of these highly-ionized species are located.

Astrophysics bears a distinct relation to Robin Hood’s robbing from the data rich and giving to the poor, in this case, observers. The basic data obtained from laboratory investigation is essential to the understanding of the diverse cosmic environments with which observers and modelers have to deal.

The broad areas of investigation pioneered in the ultraviolet by the International Ultraviolet Explorer satellite (IUE) and certain to be the focus of the spectrographs on the Hubble Space Telescope and FUSE/Lyman are: 1. planetary atmospheres, magnetospheres and comets; 2. stellar atmospheres; and 3. H II regions and diffuse interstellar gas. The last of these is to be understood in both Galactic and extragalactic contexts. These illustrate the diversity of the required data, and also highlight the existing lacunae in the available data sets. I shall touch briefly in this note on each of them.

Since the birth of astronomical spectroscopy in the last century astronomers have appealed for atomic and molecular data. As capabilities at astronomical observatories have grown, and now as a large orbiting telescope equipped with a high-resolution ultraviolet spectrometer is returning novel data, our appeals continue. The appeals are not rooted in exotic chemical compositions and severely extreme physical conditions to be found in stellar atmospheres. Rather the appeals arise very often because stellar atmospheres are more extensive light sources than can be attained in laboratories. The inability to replicate stellar conditions in the laboratory applies to all types of stars. The theoretical quantum chemist/physicist is not so limited as the experimental spectroscopist. Although much vital data can now be supplied through computations, experimental data is absolutely required in many areas: e.g., detailed lists of classified lines, accurate cross-sections for a variety of collisional processes needed for studies of non-LTE line formation.

The Goddard High Resolution Spectrograph (GHRS) on the HST, with resolving powers up to 94000 or 3.2 km s−1, is giving us a new look at interstellar absorption lines in the range 1090 to 3350 Å (Savage et al 1991, Cardelli et al 1991, Smith et al 1991). The high signal-to-noise ratios possible with the digicon detectors provide precise line profiles suitable for studying individual velocity components. Morton (1991) has summarized the relevant laboratory data on wavelengths and f-values for the atomic absorptions from the ground term likely to be detected by the HST, and Hsu and Hayden Smith (1977) have provided a useful list of candidate molecular electronic transitions.

This talk will focus on the information to be gained through UV reflectance spectroscopy of atmospheres in the outer solar system. Here, we are concerned with the spectral region below 3000 Å, where many interesting molecular species have significant absorption cross sections, and observations must be made from sounding rockets or space-based observatories. With the exception of a few important rocket measurements the bulk of the observations in this region to dat have been made with the Voyager spacecraft and IUE observatories. The Voyager Ultraviolet Spectrometer (UVS) measurements offer the advantage of relatively high spatial resolution while IUE permits repeated measurements over a long time base. HST will combine both features and should led to a significant advancement in our understanding of outer solar system atmospheres.

The name Opacity Project (OP) refers to an international collaboration that was formed in 1984 to calculate the extensive atomic data required to estimate stellar envelope opacities. The project has involved research groups from France, Germany, the United Kingdom, the United States and Venezuela. The approach adopted by the OP to calculate opacities is based on a new equation-of-state formalism (see the series of papers “The equation of state for stellar envelopes”, ref. [1] and contributions thereafter) and on the calculation of accurate atomic properties such as energy levels, fvalues and photoionisation cross sections (see the series of papers “Atomic Data for Opacity Calculations”, ref. [2] and contributions thereafter). The theoretical framework used to compute ionic states (bound and free) and their radiative properties is based on the close-coupling formalism of scattering theory [3] and on the R-matrix numerical approach developed by Burke and collaborators [4]. Considerable improvements and extensions were introduced in the R-matrix package to adapt it for this task, thus producing a powerful computational tool to study both collisional and radiative properties of electronion systems. In particular, an innovative treatment of the asymptotic region has led to high efficiency and speed in computation, and allows unobserved bound states to be calculated since initial energy estimates are no longer required [5].

Several of the larger and more inclusive atomic data centers and databases useful for space astronomy are briefly described here. Bibliographic reports on atomic and molecular data useful for astronomy are given in Ref. [1].

The satellites ISO and SIRTF are cryogenically-cooled infrared observatories. These telescopes will provide a tremendous increase in sensitivity and will, therefore, require new laboratory data to support their missions. A survey of some of the necessary atomic and moelcular data is presented.

The UV and X-ray wavelength ranges are rich in emission unes from the transition region and the corona, formed at temperatures from 104 K to 107 K. Fortunately, these emission lines, absorbed by the earth upper atmosphere, can be observed by some solar space observatories. In particular, the NASA SMM satellite, from 1980 to 1990, has obtained very interesting spectra from which important solar results were derived. In a close future, they will be again observed but with improved spectral, spatial and temporal resolution by SOLAR-A and SOHO.

The important atomic and molecular data needed by astrophysicists who analyze far ultraviolet spectra include accurate wavelengths, ocsillator strengths, molecular data for six molecules, and especially electron collisional exciatation cross sections.

The astronomical X-ray and EUV satellites of the past generally had low enough spectral resolution that atomic data of modest quality was sufficient for most interpretation of the data. Typical proportional counter resolution Δ E/E ~ 1 permits a determination of the spectral shape sufficient for an estimate of the temperature of the emitting gas, but only the Fe K feature at 6.7 keV stands out as a distinct emission line. The higher spectral resolution Einstein Transmission Grating, Solid State Spectrometer, and Focal Plane Crystal Spectrometer instruments measured a score of emission lines or line blends, permitting determinations of the elemental abundances, temperature, and ionization state of the emitting gas. The higher spectral resolution and throughput of the BBXRT aboard the ASTRO mission and the instruments planned for EUVE, ASTRO-D, AXAF, and XMM will make possible a far more detailed analysis of the data. It should be possible to derive better abundances for more elements, accurate temperature distributions, electron densities, and accurate ionization states.

The Antarctic Plateau is the best site on Earth for astrophysical research from millimetre to near-infrared wavelengths. The low temperature, high elevation on top of the ice sheet, and the Polar Vortex, which blocks the infusion of moist air, result in extremely low column densities of atmospheric water vapour. These unique conditions may result in the clearest and darkest sky available from the surface of the Earth in this wavelength range.

Scientific work at the South Pole during austral winter began in 1957, the International Geophysical Year. Interest in a polar observatory was already expressed in the survey of polar research conducted by the Committee of Polar Research (Gould, 1970). But not until 1986, was photoelectric photometry of variable stars made at the South Pole (Chen et al 1988); and in 1988, stellar observations for atmospheric extinction were made. The optical telescope used for stellar observations at the South Pole is a twin-mirror siderostat with an 8 cm lens (Chen et al 1986; Taylor 1988). The computer-controlled automated telescope made the polar observations possible.

The Sun has been observed at South Pole nearly every austral summer since 1979. This experience shows that the duration of uninterrupted observations is limited by clouds to runs of at best ~150 hours. Impressively high duty cycles can be achieved over longer periods. Sky clarity is often superb but even in cloudless conditions, ice crystal precipitation storms can be a problem. Daytime observations of the Sun and bright stars show that visible seeing quality is limited to about 2-3 arc seconds at altitudes of 15-20 degrees. Nearer the zenith, the seeing quality approaches 1 arc second in light wind. Seeing quality appears to vary with wind speed and direction and also diurnally with changing solar illumination of the surface ridges (sastrugi). Seeing is degraded by turbulence in the exceptionally large temperature gradient in the first few hundred meters above the surface. There are suggestions that both daytime and, perhaps more so, nighttime cloudiness increased over the last decade. This may be related to increasing amounts of CO2, CH4 and CFCs in the polar atmosphere.

During the winters of 1989 and 1990, the Observatorio Astronomico de Cordoba conducted observational site testing in the Antarctic. The search was carried out amongst the Argentinian stations to take advantage of existing logistic facilities. Belgrano II was chosen because it is the most southerly one, has the most stable climatological conditions, and is ground-based. The results are not very promising for astronomical work, but we have obtained important experience for this kind of task in the Antarctic.

Seeing degradation is almost entirely the result of thermal inhomogeneity in the atmosphere and at most observatory sites, a major contributor to this inhomogeneity is the diurnal variation in temperature. In addition to its effects on the free atmosphere, the daily temperature variation leads to local seeing degradation, especially with large telescopes, because the temperatures of massive components tend to lag behind the temperature of the surrounding air and give rise to convective disturbances.

The Antarctic submillimetre Telescope and Remote Observatory (AST/RO), a 1.7 m offset Gregorian, is scheduled for installation at the South Pole in November 1993. It is a collaboration including the Smithsonian Astrophysical Observatory, AT&T Bell Laboratories, Boston University, the University of Illinois, the University of Colorado, and the University of Cologne. Observational tests (Pajot 1990; Dragovan et al 1990) and modeling (Bally 1990) of atmospheric transparency over the Pole indicate that it is the best accessible submillimetre-wave site in the world. The immediate scientific goals are heterodyne spectroscopy of galactic molecular clouds and molecular lines in the earth’s stratosphere at wavelengths near 600 μm. Two early observational programs are a large-scale survey of the CI line at 609 μm and monitoring of the 2.8 mm O3 line arising in the stratosphere. Under the newly-formed Center for Astrophysical Research in Antarctica (centred at Yerkes Observatory), AST/RO will become a general-purpose instrument for the millimetre, sub-millimetre and far-infrared.

In the standard cosmology of the Big Bang theory the cosmic microwave background (CMB) is the remnant radiation from the hot early universe. The sky signal is comprised of radiation from the CMB, from Galactic emission, from atmospheric emission, and from instrument sidelobes seeing the ground and man-made interference. One observes in directions of minimum galactic signal. The antarctic polar plateau provides the best site in the world for low atmospheric emission, low horizons, low man-made interference, and reasonable accessibility. The low column density of precipitable water and extreme stability for periods exceeding a week, combined with low RFI are critical. A very important secondary benefit for anisotropy experiments is the ability to observe the same part of the sky continuously at a high elevation angle.

The Infrared and Submillimetric OASI Observatory is the first permanent telescope installed in Antarctica. The installation was completed in 1989 at Terra Nova Bay. The diameter of the primary mirror is 2.6 m and the receiver is a cryogenic multichannel bolometric photometer. The OASI Observatory takes advantage of the privileged position in Antarctica, where the atmosphere is very clear and the transmission is very high (≥ 90% at 2 mm wavelength). It has been designed mainly to investigate the small scale anisotropics of the Cosmic Background Radiation and Galactic and extragalactic diffuse emission.