News from the 30m Telescope

We monitor the fluxes of quasars used as pointing sources at the IRAM 30m telescope. The most recent results can be found on our WWW pages at:

This list is intended to help with the selection of pointing sources. A publication of the collected flux monitoring data is in preparation. Most results are available on request; please contact UL and HU.

Efficiencies at the 30m telescope

The forward efficiencies, $F_{\rm eff}$ , have changed in December 2000 due to the installation of a new reflecting ring around the subreflector. The new values are:

Receiver	$\mathbf F_{\rm eff}$
A100/B100	0.95
C150/D150	0.93
A230/B230	0.91
C270/D270	0.88

The beam efficiency, $B_{\rm eff}$ , has been measured regularly during the last year. The values can be well fitted (see Fig. 1) by the theoretically predicted Ruze function:

$\begin{displaymath}B_{\rm eff}= 1.2 \epsilon_0 \exp[-(4\pi R\sigma/\lambda)^2] \nonumber \end{displaymath}$

**Figure:** The beam efficiencies measured during the last year together with the best-fit Ruze function. The circles denote measurements carried out in November 2000, triangles and squares measurement done in October 1999 and January 2000 and the diamonds the values of $B_{\rm eff}$ valid before July 1997.
$\begin{figure}\begin{center} \mbox{\psfig{file=feb01_beam_eff.ps,height=7.3cm} }\end{center}\end{figure}$

In Fig. 1 we also include the value of $B_{\rm eff}$ valid before July 1997. The beam efficiency has increased considerably since then, especially at high frequencies due to successful panel adjustment based on the results of the holography measurements during the last years.

Status of the VLBI at Pico Veleta

The October 2000 VLBI campaign was the first time we have used a recording mode of 256 Mbit/second on thin tape. A fringe search done by D. Graham (MPIfR Bonn) shows good quality fringes (SNR 30-100 dB) for different sources and baselines combinations using the 30m telescope as reference. This indicates that both the new recorder r/w head installed last year and the mechanical upgrade to allow thin tape recording are working fine.

OBS News: Equivalent Cold-Load Temperatures

The calibration system for the A, B, C and D receivers has the inconvenient feature that the cold-load temperature ``seen'' by any of the eight receivers varies with the tuned frequency over several degrees Kelvin. Since the beginning of this year OBS interpolates this cold-load temperature from tables. Some of the tables do not completely cover all the tuneable frequency range. If this happens OBS gives a warning and takes the first (or the last) value in the table. The tables are used whenever the RECEIVER command is used in OBS. The interpolated cold-load temperatures can then be overwritten with the SET CHOPPER command.

Latest News from the NIC Development Group

The arrival of new instrumentation and observing modes makes it necessary to keep track with software development. You can follow the progress under http://iram.fr/GS/nic.html, the official IRAM web page for bolometer software.

Due to major changes in the near future, we plan to provide NIC users with latest news on software releases and debugging. Therefore, we kindly invite you to subscribe the NIC users list to keep you regularly informed about the latest developments. Your suggestions and comments are welcome.

Bad weather at the observatory?

In case of bad weather, your stay at the observatory can still be productive and entertaining. If you need any book from the Granada library, just phone Esther Franzin (franzin@iram.es) and we will send it up with the next transport.

We have some interactive CD-ROMs for learning and practising Spanish or English. There is also a copy of the Encyclopedia Britannica on CD-ROM. Just ask the operator.

Souvenirs

T-shirts, polos and sweatshirts are available in the Granada office for purchase. These items are sold at cost price and have printed the 30m logotype. Various ceramic items are also available. Contact either Esther Franzin or Dave John (CdE).