SUBSTELLAR COMPANIONS TO BROWN DWARFS: 1ST STEPS TOWARDS A DIRECT DETECTION OF EXO-PLANETS

摘要

Direct detection of planets around other stars requires both observations with high angular resolution and with a high dynamic range. The angular resolution of a few 0.1″, which is a prerequisite to resolve physical scales of the order of ≈1 A.U. around nearby stars, is now routinely achieved with modern telescopes like HST or ground-based telescopes equipped with adaptive optics systems. Achieving a high dynamic range presents a bigger challenge, as it requires highly optimized telescope-instrument configurations. For a typical Jupiter-Sun system, the brightness contrast is in the range 1:10~9 (visual) to 1:10~6 (at 5 μm). The task of a direct detection of sub-stellar mass companions to nearby objects becomes easier when one moves to less luminous, later-type primaries, and higher-mass (brown dwarf) companions. Indeed, with present instrumentation, the direct detection of brown dwarf companions to late-types stars and brown dwarfs themselves has become possible. Observations of brown dwarfs are expected to provide important feedback on theories of atmospheres and inner structure of substellar objects. In addition, brown dwarf binary systems offer the unique opportunity to determine the mass of individual brown dwarfs, which is one of the fundamental astrophysical quantities. We summarize ongoing surveys for brown dwarf binaries, and present first results of follow-up studies. A brief outlook on prospects of contrast enhancement techniques by means of differential imaging concludes this contribution.