Lunar Occultations, Setting the Stage for VLTI: The Case Study of CW-Leo (aka IRC+10216)

Abstract.

Lunar occultation allows for a sneak preview of what the VLTI will observe, both with comparable angular resolution and sensitivity. In the thermal infrared ( $\lambda \approx 10\mu m$, angular resolution $\le 0.03^{\prime \prime}$) the technique has been pioneered with TIMMI on La Silla. Using this technique several dust shells around Asymptotic Giant Branch stars have been resolved. For the Carbon star CW-Leo (IRC+10 216) high S/N scans will allow for ‘$1\frac{1}{2}$-dimensional’ imaging of the source. At the present state of data reduction the light curves already provide for a very convincing proof of theories on the milli-arcsec scale. In combination with VLTI the technique allows for checks of the visibility calibration and related issues. Moreover, in the (u,v)-plane both techniques are extremely complementary, so that a merging of the data sets appear highly desirable. At La Silla and Paranal ESO a suite of instruments which can be (ab)used for this project is under construction.