Figure: VLBI detection at 1mm between Plateau de Bure and Pico Veleta
Figure: VLBI detection at 3mm between Plateau de Bure and Pico Veleta
In the IRAM Newsletter No.18 (November 1994) we reported that a first attempt had been made to use the 30m-telescope on Pico Veleta together with one antenna of the Plateau de Bure interferometer for a VLBI experiment. In this first experiment which focussed on 3mm observations, fringes were found from several sources, indicating that the equipment at both sites was fully functional. This prompted us to schedule a second 3mm plus 1.3mm test for early December, in conjunction with an international 3mm VLBI campaign (Europe, USA, Chile) in which the 30m-telescope participated most of the time.
Given the need for good weather conditions at both sites, we had defined a `window' between December 2nd and 12th to carry out the 1.3mm test, using the same equipment (maser, terminal, tape unit) as in the earlier successful observing run. Our main goal was to demonstrate the feasibility of 1.3mm very-long-baseline interferometry on the baseline Bure(France) - Pico Veleta(Spain), corresponding to 1114 km. At 1.3mm this is equivalent to an angular resolution of 0.3 milli-arcseconds.
The observing procedure was the same as outlined in the earlier Newsletter.
The log of the observations where both IRAM stations collected data
reads as follows:
We are happy to report that at 1.3mm fringes have been detected from 3C273B with S/N-ratios of 6.8 and 9.7, from 3C279 with a S/N-ratio of 10.2, and from 2145+067 with a S/N of 7.5 (Fig. 1).
1.3mm-VLBI observations with such S/N-ratios are unprecedented and are indeed a big encouragement to continue with such experiments. This is planned for the near future.
For completeness, we mention also that the 3mm observations yielded fringes (Fig. 2), in several cases with a S/N-ratio in excess of 100 !
We could not have been so successful without the substantial contributions from the engineers and technicians in the receiver and backend groups, the operators at the telescopes, the correlator group, and the astronomers who participated in the preparation and execution of the observations and in the reduction of the data.
These 3mm- plus 1.3mm-VLBI experiments are a joint effort between IRAM and the Centro Astronomico de Yebes/Spain, the Max-Planck-Institute for Radioastronomy/Germany, and the Bordeaux and CERGA Observatories/France, coordinated by Albert Greve (IRAM).
Michael GREWING
