At present, there are a number of radio astronomy projects in progress which promise to revolutionize our understanding of astrophysical masers and their environments. Masers form only a small part of the impressive science programmes for these new telescopes, so this chapter contains a considerable amount of general material about the instruments and their capabilities.

EVLA

Introduction to the EVLA

The Expanded Very Large Array (EVLA) is a two-phase development of the existing VLA, situated in New Mexico, USA, and operated by the National Radio Astronomy Observatory. The general capabilities of the EVLA can be found at the website http://www.aoc.nrao.edu/evla/. Phase 1 developments are technological, upgrading the existing array to a wide-band system, whilst Phase 2 involves the construction of new antennas, to provide significantly improved spatial resolution, and improved linkage to the VLBA. The technological developments are similar to those of e-MERLIN (see Section 10.2).

Continuum sensitivity improvements range from a factor of 5 at low frequencies to 20 or more above 10 GHz. This is important for maser, and all spectral line, observations, because the spectral line observations rely on continuum sources for calibration. Spectral line sensitivity increases in Phase 1 are modest below 10 GHz, but up to a factor of 3 at higher frequencies. The EVLA will also move to a wide-band receiver system with fibreoptic cabling and digital electronics, allowing complete frequency coverage from 1 to 50 GHz, with a bandwidth of up to 8 GHz per polarization.