News from the 30-m Telescope

  

Figure 1: Aperture plane phase distribution a) in September 1998, and b) in September 1999

Visitor Information

From now on, the operators will perform the data backup for our observers at the end of their run. You may choose between a DAT tape or a CD-ROM as storage device, and have the option to include your raw data. The data will remain on disk for a couple of days and can be accessed from the computers at the Pico Veleta Observatory and our office in Granada. In case our visitors have to catch the transport immediately at the end of their observing run, the data backup will be written to a storage device at the Granada office on the same day.

In the past months air traffic in Spain has been a disaster. If you have a choice, we recommend to fly directly into Malaga instead of having a stopover in Madrid or Barcelona. There are excellent direct connections and cheap fares from many European cities. From Malaga take the airport bus to the bus station (135 ptas, every 30 minutes). At the Alsina counter buy a ticket to Granada (1100 ptas). Buses leave every hour, the last one at 21:00. Travel time is about 2 hours. For your orientation: the taxi fare from Malaga to Granada is approximately 13000 ptas. At the Granada bus station take a taxi to Jardines del Triunfo (400 ptas).

Rainer MAUERSBERGER

Observing with the 30m

We have a new pointing scheme at the 30-m telescope. Pointing runs are done more often now (twice a week) with fewer sources and using additional information from inclinometer readings.

We have been observing through the "millennium" at the 30-m telescope with a system performing better than ever, thanks to the computer group who helped to avoid any big Y2K problems so far.

Have a look on our web site (http://www.iram.es). We have updated the system summary, and the link to the Telescope Characteristics contains many recent data on the receiver parameters. We have added a picture gallery (visitors are encouraged to send us their own photos from the telescope to be included). Our weather page now contains the most recent measurements of wind speed, temperature and humidity from our weather station as well as a symbol representing the cloud coverage. We have added a link to the weather page of the nearby Sierra Nevada Ski station which contains a detailed weather forecast tailored for the site (in Spanish). The telescope operator has similar information and can be contacted by remote observers.

Rainer MAUERSBERGER

Telescope Surface Quality

A surface adjustment was made in October 1998 and again in July 1999. Both settings were made on the basis of holographic measurements made in September 1998 with the new 39 GHz phase coherent receiver operating at the prime focus (Mattiocco et al. IRAM Internal Report March 1996). An opportunity to check the new surface occured during the installation of the new receivers C and D in September 1999. Several good quality maps of the aperture plane phase distribution were obtained. They yield a root mean square error of 52 microns for the paraboloid, when projected onto the aperture plane and amplitude weighted. The value appropriate for secondary focus operation is then 55 microns, after correction for the estimated errors in the subreflector. This new result is a significant improvement over the corresponding value of 74 microns, measured in September 1998 before the latest surface adjustments. It should be noted that all these estimates of surface error refer to elevation 43 degrees and to calm nightime conditions. In daytime under full solar illumination the surface error rises to about 66 microns.

Measurements of beam efficiency made in January 2000 (Lisenfeld and Mauersberger) show an improvement at 235 GHz from 42 % (see Newsletter 38, January 1999) to 51 %, with corresponding increases at 86 GHz (73 to 78 %) and 150 GHz (54 to 65 %). The improvement in surface quality is displayed visually in Fig. 1 which shows the aperture plane phase distributions before, (a) on the left, and (b) after the last adjustments (on the right). For a clearer display of the fine surface structure, the time variable astigmatism has been removed from these plots. The range of the grey scale is $\pm 0.2$ radians at 39 GHz ($\pm 120$ microns). The visual aspect of these distributions is dominated by an almost regular scalloping of the surface mainly due to the manufacturing errors of individual panels, which contributes about 40 microns to the error budget.

Dave MORRIS