Source visibility

In designing an experiment and preparing a schedule, it is important to know when the source of interest is visible to the array. Here we present plots of source elevation vs GST at various declinations for the EVN antennas (these fictional sources all have RA=12h).

• Source visibility at -30 deg Dec
• Source visibility at -30 deg Dec (including Hartebeesthoek)

From the source visibity plots presented below, we can conclude that the observing declination limit of the EVN is around -30 degrees. At this declination a source is visible (elevation > 5 degrees) by more than 3 antennas simultaneously, for only a few hours. The uv-coverage is very poor and the elevation of the source is typically around 10 degress, only rising above 20 degress for Noto and Shanghai. In addition, there is very little mutual visibility between the European and Chinese stations at this declination. The same is true for the EVN and the VLBA. The situtation is much better for Hartebeesthoek, which has a similar longitude to the European telescopes.

• Source visibility at -20 deg Dec
• Source visibility at +10 deg Dec

At source declinations greater than -20 degrees, the mutual visibility coverage of the EVN is much improved. The source is visible by the vast majority of telescpes for around 6 hours. The mutual visibility between the European telescopes and both the Chinese telescopes and VLBA telescopes is still poor (< 2 hours). This improves at higher declinations. At Dec +10 degrees the mutual visibilty of the EVN and the Chinese telescopes is 7 hours for Urumqi and 5 hours for Shanghai. Similarly the mutual visibility between the EVN and the VLBA is 6 hours for Hancock and 3 hours to Owens Valley.

• Source visibility at +50 deg Dec

At declinations greater than 50 degrees sources are circum-polar for most of the EVN telescopes (except Urumqi - 55 deg, Noto - 60 deg, and Shanghai - 65 deg).