The possibility to spatially filter the wavefronts in the L band and combine them coherently with low dispersion and good interferometric efficiency has been demonstrated successfully for the first time on two stars brighter than =-3.
This first experiment in the thermal infrared looks then encouraging, and a few modifications are under way for future interferometric observations on IOTA in the L and M bands with the TISIS experiment. Using an X coupler dedicated to these wavelengths, with two optimized InSb infrared detectors should help gaining both in accuracy and sensitivity, up to the point where the thermal background will this time dominate. A dedicated chopping and nodding capability will then become mandatory.
More generally, stellar interferometric observations at these intermediate infrared wavelengths look very promising for stellar physics. For instance 5µm long baseline interferometric measurements would have sufficient resolution to directly detect the dust shell warm inner regions located typically 50 to 70 mas away from some late type stars, according to heterodyne observations at longer wavelengths. They should very well constrain envelopes inner radii, mass loss rates and mechanisms. In that sense they are very complementary to observations in K, mostly sensitive to the photosphere, and to the 11 microns observations of cooler regions in extended shells.
© European Southern Observatory (ESO) 1999
Online publication: May 6, 1999