High-resolution spectroscopy provides a source of large amounts of astrophysical information. A combination of large spectral coverage and high spectral resolution is a powerful tool. A spectrograph with a resolving power of 50,000 and wavelength coverage from 3000 to 8900Å represents such a combination for a variety of studies. The design of STELES, being at the Nasmyth focus of the SOAR telescope, will allow the instrument to be slit-fed, and thus it can be optimized for near-UV work. This would be a powerful addition to Southern Hemisphere astronomy. There is no other 4-m telescope in the Southern Hemisphere with high spectral resolution optimized for the near-UV. The high-resolution spectrometer for Gemini South is planned to be fiber-fed (fiber losses in the UV restrict their use to wavelengths bluer than about 3500Å).

    The STELES design takes advantage of the excellent image quality of the SOAR telescope, and will provide high efficiency, such that stars as faint as V=16-17 would be observable at R=50,000. Estimates show that the spectrum of a star with V=14, having a S/N=100 per 3 km/s bin, can be obtainable in a one hour exposure (or S/N=10 at V=17). High-resolution spectroscopy at the magnitude limits described above could be applied to such projects as studies of large numbers of metal-poor stars in the Galaxy, or even to stars in nearby galaxies.

    In addition, as it will be coupled to the telescope mounting and fed by the Nasmyth focus, STELES is expected to be very stable. Such a configuration can be used for asteroseismological studies or precise determinations of radial velocities, possibly aiding the search for extra-solar planets. In the following, we list some examples of research projects that would benefit from the facilities offered by the STELES coupled to the SOAR telescope.

    Abundance analyses in the near-UV: Key projects requiring good efficiency in the near-UV include spectroscopy of the strong electronic OH lines near 3100Å. These particular OH lines are detectable to very low metallicity and are useful in attempts to derive oxygen abundances in the oldest stars in the Galaxy: such O abundances probe the very earliest chemical evolution in the Milky Way. In addition to OH, the element beryllium is only detectable in the near-UV, via Be II lines near 3130Å. Beryllium is produced only through cosmic-ray spallation reactions and is a key probe in understanding cosmic-ray nucleosynthesis over the chemical evolutionary history of the Galaxy.

    Chemical Evolution of the Galaxy: The chemical evolution of the Galaxy follows the changes in elemental abundances from their initial values into the present compositions of the disk, bulge and halo. Some examples of specific topics related to this subject are the gradients of metallicity and radial and temporal variations of the star formation rate. Concerning the major components of the Galaxy, the study of the bulge is essential to understand the mechanisms of formation of our Galaxy: the bulge may have been formed in the beginning of our Galaxy, although part of the bulge may have formed significantly later. The study of the oldest halo stars provides crucial lithium abundances which result from primordial Big Bang nucleosynthesis. Young stars in the Galactic disk trace the present distribution of chemical abundances and can be used to determine abundance gradients: these gradients provide constraints to Galactic models of star formation and chemical evolution.

    r-Process Enriched Stars: It has been suggested that one likely explanation for the highly r-process enhanced stars that have been identified recently is that they are members of a binary system with a massive companion that exploded as a type II supernova, which would now be a collapsed object such as a black hole. Radial velocity monitoring of the many examples of these stars we hope to find in the near future will be of extreme importance. The same applies to the metal-deficient stars that are moderately enhanced in their r-process elements.

    Light Element Abundances: The primordial abundance of light elements and their subsequent Galactic enrichment requires high-quality data to constrain and test their production and evolutionary models. One important problem in this subject is the intrinsic dispersion of Li abundances in dwarf stars of halo globular clusters. Given that globular clusters are among the oldest objects in the Galaxy, their initial Li abundance must be very close to the primordial value. Precise abundance determinations for Li (both 6Li and 7Li) and Be (with only one stable isotope, 9Be) provide essential information relevant to early Galactic cosmic-ray fusion and spallation nucleosynthesis, as well as primordial BBN. Beryllium is an important addition to lithium, however, Be is much more difficult to observe. The spectral regions containing the Be II (3130.41Å and 3131.06Å) and Be I lines (3312Å) are crowded and close to the atmosphere cutoff: a near-UV optimized spectrograph, such as STELES, would be an important addition to light element studies.

    Cluster Analyses: The determination of accurate abundances in globular cluster stars over a range of magnitudes, covering effective temperatures from 4000 to 6000 K, can address the issue of possible variations in chemical composition existing among stars belonging to the same cluster. This topic is particularly relevant in investigating possible stellar processes, such as diffusion, dredge-up. STELES will be able to investigate stars down to the main-sequence turn-off (V=17) in several clusters, combining high efficiency with a wide spectral range. Superb image quality, will also allow for spectroscopy in relatively crowded cluster fields.

    Long-Term Velocity Monitoring of Carbon-Enriched Metal-Poor stars: A large fraction of the stars with [Fe/H] < -2.5 exhibit anomalously strong CH G-bands (and often C2 and CN features) indicative of very high carbon abundance, despite the star's overall low metallicity. It seems quite unlikely that all of the stars involved are participants in close binaries that have undergone mass transfer of carbon-enriched material from their companions. Hence, sorting out which of the stars are radial velocity variables and which are not is an important program. Since the periods of known mass-transfer binaries can reach up to 7-8 years (or more, in some cases), gathering data for their study is a challenge with most telescopes. Correlations between measured abundances of (e.g., s-process) elements and orbital properties would provide invaluable clues for understanding the range of phenomena and the nature of the progenitors in these systems.

    Asteroseismology of Stars: Certain structural properties of stellar interiors can be probed by the study of the weak non-radial pulsations in solar-like stars, which cause small radial velocity variations. The simultaneous measurement of many spectral lines leads to the detection of small radial velocity variations.

    Search for Extra-Solar Planets: The detections and follow-up observations of extra-solar planetary systems will bring new constraints to bear on the formation and evolution of stars and planetary systems. This task has been accomplished for Jupiter-like planets revolving around solar-type stars through high-resolution spectroscopy. The current major instrument in the Southern Hemisphere, CORALIE, mounted on the Swiss 1.2m telescope, is limited to only the brighter stars. A potential application of STELES is to the detection of extra-solar planets.

    These are only a few ideas for projects for high-resolution spectroscopy, but many more of high scientific caliber are certainly possible (isotopic ratios; carbon abundance in planetary nebulae; heavy metals abundances in low [Fe/H] stars; stellar rotation, line variability studies, emission lines of novae, SN, H II regions, planetary nebulae, AGN; analysis of absorption spectra of high redshift QSO's; kinematics in galactic nuclei and star clusters, etc). In summary, a high-resolution spectroscopic capability for SOAR will be an important addition to its scientific potential