2.2-m telescope baffle reports

Because of the installation of new instruments the baffle of the 2.2-m telescope has undergone several modifications/improvement campaigns. The negative aspect of these changes is related to the introduction of configuration changes. Although a reduction to the scattered light properties of an instrument could be considered something positive, it is more important to insure that the instrument is calibratable. To this end we must minimize the number of such changes and introduce them only at the beginning of ESO observing periods. This does not avoid all the troubles associated with configuration changes as some programs extend over multiple periods, but it reduces the impact on the data reduction which otherwise would be unnecessarily complex. The positive aspect of the campaigns reported in these pages is that the characteristics of the telescope baffling have continuosly improved.

The first baffling improvement campaign occured during the adaptation of FEROS to the 2.2-m telescope. The resulting baffle showed a remarkable improvement compared to the previous configuration which had been on the 2.2-m telescope since WFI started operations. The second improvement campaign was due to the installation of GROND, and showed improvements over the FEROS one although not as large as those of the previous campaign. These are reported below in reverse chronological order.

  • 2006-03-08 GROND campaign, phase 3. Report (pdf). This is the same configuration of the previuos phase (Phase 2). Starting from now, M3 and its baffle are permanently mounted on the telescope.

    • Summary: After mounting M3 and its baffle in the final configuration, the telescope was accurately balanced. Pointing, tracking, guiding and dithering tests similar to the ones done during the previous phase were executed on a grid of positions uniformly distributed over the sky, with a total additional weight of 400Kg. Tests were now completely successful. No evidence of degration in telescope behavior nor in IQ was noted. These tests stress the importance of good balance of the telescope.

  • 2006-02-15 GROND campaign, phase 2. Report (pdf). The configuration tested here is the same one defined in the phase 1, but with the M3 on.

    • Summary: Again, the system shows an improvement in its ability to reduce scattered ligh with respect to the previous configuration (FEROS). A new test which uses the moon shows considerable reduction in the quantity and intensity of reflections with the new GROND baffle. In addition to the baffle we also tested the pointing, tracking, guiding, and ability to make precise offsets with the equivalent of the weight of the full GROND instrument mounted on the telescope. These tests were only partly succesful: pointing to 5 pre-selected reference positions succeded in all cases. At each position a dithered sequence of 5 exposures was attempted: two of these dithers failed, once because the telescope could not do the offset at the 4th exposure, and the other because we lost the guide star. During the same night we had one delta interlock episode at airmass 1.2: the balance of the telescope needs to be tuned/improved and further tests done before final acceptance of the system by La Silla SciOps.

  • 2005-12-22 GROND campaign, phase 1. Report (html). Configuration with ray trace, detail with rays, detail no rays: These are the designed configurations. At the moment of these tests no M3 was installed.

    • Summary: The system shows an improvement in its ability to reduce scattered ligh with respect to the previous configuration (FEROS). There are a few minor reflections visible with the previous configuration not seen with the new baffle.

  • 2003-03-18 FEROS Campaign. Report (html). Configuration.

    • Summary: After a first iteration to eliminate vignetting the system showed a major improvement in its ability to reduced scattered light.
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