RAEGE ASTRONOMICAL CAPABILITIES

The RAEGE network is an homogeneous VLBI network composed by 4 antennas with similar characteristics: 13.2m in diameter, dual linear polarisation cryogenic receivers operating between 2 to 14 GHz developed at Yebes Observatory, and ring focus mount specially adapted to the Quadruple-Ridged Flared (QRFH) feed.

The usage of linear polarization is one of the drawbacks of the broadband receivers and implies the need to observe in both polarizations to recover the whole signal, for astronomical studies. Different solutions can be adopted, either by software or by hardware, to perform the conversion from linear to circular polarization. One advantage of the homogeneous network is that there is no need to perform primary beam corrections.

For a 30º declination source the shortest projected baseline is 593.5 km between Santa Maria and Flores, both in Azores, and the longest projected baseline is 2380.8 km between Yebes, in the Iberian Peninsula, and Flores in Azores (see Fig. 1, table 1). The 4 antennas provide a total of 6 baselines, with 3 closure phases and 2 closure amplitudes, “good” observables to derive maps of the radio sources using self-calibration techniques.

Despite the size of the radio telescopes, the network is sensitive enough to detect above 50 mJy/beam per time integration (2 sec) in continuum at S-band, and is capable of resolving out emission on angular scales larger than 12.5 mas in X-band. Table 2 summarizes the scientific capabilities of the RAEGE network for usual frequency bands in astronomical observations: S-band (2.3 GHz), C-band (5 GHz), M-band (6 GHz) and X-band (8.4 GHz). 

Assuming a usual geodetic 24h observation in which a 30º declination target is observed 20% of the total time, the uv-coverage, that represents the distance between all possible pair of telescopes or baselines in units of the observed wavelength (lambda), is represented in Figure 2 for S and X bands. The uv-coverage is where the complex visibility function for each baseline is sampled. The better the sampling of the visibility function in the uv plane, the better the fidelity of the sky images derived from the observation. 

Figure 3 shows the dirty beams for S (top) and X band (bottom), that represents the effective angular resolution at each frequency and the response of the network that needs to be deconvolved from the sky images.