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RAEGE GEODETIC 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 polarisation 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 needed 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.

Figure 1. RAEGE VLBI network. Plot generated with the EVN Observation Planner. Credits: B. Marcote.
Table 1. RAEGE VLBI network coordinates.

Despite the size of the radio telescopes, the network is sensitive enough to detect above 50 mJy/beam per time integration (2s) 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). 

Table 2. Scientific capabilities of the RAEGE network, assuming same characteristics for all the antennas, 512 MHz observed bandwidth per polarisation, with 16 subbands of 32 MHz each, with 1024 channels, 1s Gaussian noise level, and natural weighting.

                                                                                                                                            

Figure 2. shows the difference in uv-coverage for S (left) and X bands (right) for a 24h observation, when the target is observed 20% of the time (4.8h), in lambda units.
Figure 3. shows the dirty beams for S (top and X bands (bottom), for natural and uniform weighting, in mas.
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