EUROPEAN SOUTHERN OBSERVATORY La Silla - Science Operation Department

M1 ventilation

From the impression that the seeing on the images is considerable higher than the DIMM in times without or very low wind, the idea was born to install fans along the main mirror, similar to 3p6 where this measure improved the seeing a lot. To install fans for a laminar stream, the mirror cover needs to be changed. A rising of the cover above the fans would result in more counterweights and might also cause problems with GROND. Figure 1 shows the measured FWHM versus the difference in temperature between M1 and surroundings. Only a few points show a really large difference between FWHM and DIMM, hence it is probably not worth to perform mayor changes to the telescope.

Actions to be taken:

A larger analysis of the database to get in particular the effect of the wind speed and wind direction shall be conducted. If a test of fans is possible without major modifications on the mirror cover, it shall be performed.