With this fifth issue of the Calar Alto Newsletter, we are able to report on a number of most promising activities and results which have been carried out in the last half year, and which will further improve our service to the community.
As described in more detail in the contribution by Ulrich Thiele, we have optimised the image quality at the 3.5m telescope. It was known to us for quite some time already that the 3.5m telescope suffered from static telescope aberrations, which have caused a degradation of the image quality that can theoretically be achieved. While it was clear that a de-centering of the primary and secondary mirror was the major contributor to the aberrations, it was not obvious what the cause of the de-centering was. After a number of meticulous tests and observations in the June - September period, we could finally trace the cause to a tilt of the primary mirror by 0.035 degrees. The tilt arose from a fault in the mirror support system. Special thanks goes to Peter Bizenberger from MPIA for his assistance in nailing down the fault. As that system has been declared maintenance-free by ZEISS, it took some intellectual enterprise to identify its failure.
As noted earlier, the differential image motion monitor (DIMM) acquired in September 2000 from Lhesa Electronique has caused us quite some headaches. The instrument did not work on Calar Alto as advertised, and severe hardware and software problems prevented its operation altogether before June 2001. Regular seeing measurements were assumed in June 2001, with full trust that the seeing values delivered were correct. Suspicion arose pretty soon after June 2001 that this was not so, and indeed it turned out that the airmass correction of the seeing measurements was not correctly implemented. Previous measurements were retroactively corrected, and after a lot of hazzle, our DIMM is in a proper state now. The accuracy of our DIMM measurements was confirmed during a campaign of the generalised seeing monitor (GSM) of the research group at the Université Sofia Antipolis at Nice on Calar Alto, in May 2002. The GSM uses 4 Maksutov telescopes and allows a study of the spatial and temporal properties of wavefronts by means of measurements of angle of arrival (AA) fluctuations. The angle of arrival is derived from rapid scanning of the stellar images over Ronchi gratings. The temporal spectrum of the AA fluctuations is sampled at 5 ms. AA variances are then computed for a degraded temporal resolution of 10 ms and are used to extrapolate to AA variances at zero integration time. The comparison of the GSM measurements and the Calar Alto DIMM is perfect. The seeing data gathered during the April 2001 - December 2002 period on Calar Alto show that the median seeing on Calar Alto is 0.82 arcseconds (see diagram). This value compares very well with the seeing at the most competitive sites. For instance, the median seeing on Paranal, as obtained during the 1992 - 2002 period, is 0.78 arcseconds. It is a great pleasure to thank Aziz Ziad, Irbah Abdanour and Julien Borgnino for their most pleasing interactions with the CA astronomy group.
A comparison of the night sky brightness over different astronomical sites (F. Patat, astro-ph/030115) shows that Calar Alto is as dark as Paranal. Very good seeing, very good transparency except in times of Calima (see article by Hopp & Fernandez in the previous issue of the Calar Alto Newsletter). Despite the relatively poor weather, Calar Alto is producing some 100 refereed papers per year, and about 200 non-refereed publications. At total annual operating costs of some 4 Million Euros, the cost per refereed paper on Calar Alto is of the order of 40.000 Euros. This number compares very well with the observing costs on sites such as Hawaii, where UKIRT has some 85.000 Euro per refereed paper. The ING on La Palma has a very good cost/benefit ratio if measured in this terms, at 245 refereed papers the cost is down at 25.000 Euro per paper. From the comparison with La Palma, it becomes clear that it is not the time lost to weather, but the fraction of programmes affected by weather (which on Calar Alto is of the order of 70-80%), which determines the productivity. We thus trust that with service observations we will be able to significantly increase the scientific efficiency and productivity on Calar Alto.
In the future, Calar Alto will form part of a network of European observatories. A proposal to the 6th Framework Programme of the European Union has been discussed extensively during recent Opticon meetings in Paris (September 2002), Cambridge (November 2002), and Tenerife (January 2003). If successful, a fraction of 5-10% of the observing time on Calar Alto will be offered to European astronomers, with a special emphasis to colleagues from Central and Eastern European states. The possibility to apply at Calar Alto will be advertised extensively via JENAM, road-shows, and direct contacts to those institutes which do not have a priviledged access to a modern observatory.
As far as Calar Alto instrumentation is concerned, LAICA is now available on a regular basis at the 3.5m telescope. The image given below gives a taste of the future possibilities with LAICA. PMAS, another powerhouse instrument at the 3.5m telescope, has been put up and running by Martin Roth and his crew. An overview of PMAS with links to more detailed information is given in the article by Martin. A first and most successful technical commissioning run with Omega2000 has been carried out in January. After a second technical commissioning run in March and a scientific commissioning in April, Omega2000 should be delivered to the community in the second semester of this year.
The scientific contributions include a description of a ToO programme on supernovae Ia, with the observation of SN2002er in UGC 10743 through maximum as a very first and most impressive success, as well a a summary of the Calar Alto key programme for the SDSS.
