Hans Ulrich Käufl and Andreas Glindemann
OPTICAL VERY LONG BASELINE INTERFEROMETRY: THE QUEST FOR NANO-ARCSEC RESOLUTION IN ASTRONOMY (Poster)

OPTICAL VERY LONG BASELINE INTERFEROMETRY: THE QUEST FOR NANO-ARCSEC RESOLUTION IN ASTRONOMY

Hans Ulrich Käufl and Andreas Glindemann
European Southern Observatory D-85748 Garching b. München, Germany

A new generation of frequency standards based on the principle of the ``Frequency Comb'' will soon be readily available for field-use. With such a frequency standard $CO_2$ or $NH_3$-lasers operating in the astronomical N-band ( $8 \mu m \leq \lambda \leq 13\mu m$) can be frequency and phase stabilized with unprecendented precision. Heterodyne receivers based on such lasers as local oscillators have been used for more than 2 decades in astronomy.


We describe at the conceptual design level a Very-Long-Baseline Interferometer working at $\lambda \approx 10 \mu m$. Data reduction (correlation, phase-closure and image reconstruction) could be based either on micro-wave links or on the European VLBI Network (EVN) and the Joint Institute for VLBI in Europe (JIVE) in Dwingeloo. Extrapolating the demonstrated performance of the ISI-interferometer (e.g. Hale et al. APJ 537 p. 998, 2000) to 8m-class telescopes we discuss the realisation and sensitivity of a VLBI network. Basically such a system could have a sensitivity of few Jansky per resolution element. The spatial resolution could approach 100 nano-arcsec, if a link between telescopes in Chile and Hawaii is considered. Science cases for such a system, ranging from AGB-star imaging to AGN-research will be elaborated. In a similar sense propagation effects limiting the spatial resolution in radio-VLBI will be discussed and scaled for infrared VLBI.