Telescope Tilt Paul Gensheimer 2 Mar 01 Over the last couple of years (observing seasons 99-00 and 00-01) it has been recognized that the tilt of the Heinrich Hertz Telescope has been one of the more erratic terms in the pointing model. Consequently, some effort has been put into stabilizing or characterizing this part of the pointing model. At the SMTO, the tilt of the telescope has been modelled as two orthogonal components, one in a North-South direction and the other in an East-West direction. The history of these two terms can be viewed by running the macro /home/paulg/gag/pro/pointing_history under GRAPHIC. The second page shows the history of the inclinations terms (IncN for the N-S term, IncW for the E-W term). The triangles connected by a dashed line are determined from observations with the SIS and bolometer radio receivers, the squares connected by a dotted line are from optical telescope observations, the filled circles connected by a dot-dash line are from simultaneous solutions of the radio and optical pointing data, and the solid line is from the inclinometers placed on the fork mount of the telescope. During the summer of 2000 (months 42 to 44 on the plot) the pier of the telescope was wrapped in insulation and one can see a marked improvement in the stability of the inclination of the telescope from the 1999-2000 observing year (months 32-42) versus the 2000-2001 observing year (months 44-50), especially in the inclinometer data. It also appears that during the course of the observing season 2000-2001 the telescope tilt has been slowly migrating from (IncW,IncN)=(7.5,15) to (incW,IncN) =(3,7.5). It will be interesting to see if the tilt slowly migrates back to (IncW,IncN)=(7.5,15) as the observing season continues (temperature effect?). Plots of IncW versus IncN can be viewed by running the macro /home/paulg/gag/pro/incwvsincn. Again, one can see a marked improvement in the inclination of the telescope from the 1999-2000 observing year to the 2000-2001 observing year in that there is much less scatter in the migration of the inclination after the pier was wrapped in insulation. In the observing year 2000-2001, the inclination of the telescope appears to have been confined to a narrow band running from (IncW,IncN)=(7.5,15) to (IncW,IncN)=(3,7.5). We should continue to monitor the inclination of the pier, particularly by making regular inclinometer observations; the procedure only takes a few minutes but it will greatly help in keeping track of the most erratic component in our pointing model. Additionally, we may wish to contemplate for the future whether it would be worthwhile to have some sort of temperature control inside the pier. Temperature sensors are already in place. For modest expenditures we may be able to control the temperature and thus stabilize the tilt of the telescope still further. Addendum: In order to more easily access and run the GRAPHIC macros described above, one may configure the .gag.dico file in their home directory to include the line PG: /home/paulg/gag/pro/ Then under their directory /home//gag/gag-init there should be an init.graphic file. In this file should be inserted the lines symbol pnt_history "SIC\@ PG:pointing_history" symbol incwvsincn "SIC\@ PG:incwvsincn" Then the macros described in the text above can be accessed by merely typing their names, pnt_history and incwvsincn.