» Preparatory Surveys » First epoch results » Parallax results

Preparatory Surveys

In the first few years of the project, we will conduct two surveys in preparation for parallax observations. Results from these surveys will be placed on the BeSSeL website a the data is analyzed.

1) A VLA snapshot mapping of ~400 water masers to obtain recent spectra and absolute positions. We started with the Arcetri Catalog (Valdettaro et al 2001, A&A, 368, 845) and selected only those listed as from star forming regions (SFR). A small number of sources far from the Galactic plane, presumably low-mass SFRs or stellar masers, were removed. The source list and results for the survey can be obtained by clicking here.

Based on the survey results, we will select targets for parallax observation.

2) We will search for background calibrators (presumably QSOs with compact radio emission). Calibrator candidates within about 1.5 degrees from a target maser and stronger than 30 to 50 mJy will be obtained from unresolved sources in the CORNISH or NVSS surveys. We will observe these candidates with the VLBA at X-band and, for detected sources, measure positions and make visibility versus baseline-length plots (as in the VLBA calibrator lists). The results of the calibrator survey can be obtained by clicking here.

Non-detected (resolved) sources are likely to be extended extragalactic radio sources, along with some Galactic HII regions. Detected (compact) sources must have high brightness temperatures (>10^7 K) and, therefore, be non-thermal sources. Almost all will be AGN and many will be suitable for VLBI phase-reference sources.

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