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VLA Expansion Project Science:
Possible Overall Themes
(Rick Perley)
(19 November 1998)

It is generally agreed that a thematic approach to organizing VLA Expansion Project Science is highly desirable. Paul, in his initial suggested themes, commented that he would be amenable to a different organizational scheme. Below, I circulate a memo from Frazer to Paul, in which he has suggested such an alternate theme set.

Paul has given his strong support to this structure. Essentially, the themes are based on broad physical subjects, each of which then allows a wide range of related physical phenomena to be grouped under it. I think the major advantage of this approach is that subjects which are traditionally grouped under different phenomenological classifications (such as novae, SNRs, solar flares, gamma ray bursters) can be now considered parts of one theme.

Below, I reproduce, with Frazer's permission, his original message. This approach is not perfect -- some important subjects don't easily fit. Following the included message, I list some of these 'misfits', and include an extra theme.

Feel free to comment on these themes, as well as suggesting some of your own. 

From fowen@aoc.nrao.edu Tue Nov 17 08:44:25 1998
Date: Tue, 17 Nov 1998 08:44:09 -0700 (MST)
From: Frazer Owen 
To: pvandenb@aoc.nrao.edu, rperley@aoc.nrao.edu, abridle@aoc.nrao.edu,
        kkellerm@aoc.nrao.edu
Subject: VLA upgrade science

Gentlemen,

I would like to suggest a slightly different approach to presenting the science case for the VLA Upgrade. I believe the strength of the VLA and the Upgrade Science is not best described as a few science problems but in terms of the different sorts of information which the Upgraded VLA can provide. That unique information, combined with other wavelength bands, is really what is important about the Upgrade. While in developing the case one needs to assemble the experts in each subarea these themes cut across the narrow science areas. Thus like the NASA themes, I think they are best presented in a way to emphasize the strengths of radio astronomy without claiming that radio astronmy is the only tool to attack these problems.

To make what I am suggesting clearer I will outline one such division of the topics/themes although this list is not unique or complete. I want mainly to push this approach:

Topics:

  1. The Magnetic Universe
    Galactic, Extragalactic Faraday rotation from 10 to 1,000,000 rad/m^2, cluster halos, Zeeman effect, stellar flares
    This includes the galactic center, high and low z galaxies, the cluster medium, and the general IGM. It also includes stars, SNR's and just about every sort of environment. The Upgrade enhances this area greatly from the increased sensitivity, the wavelength coverage (S-band especially) the E array, and the flexible channel widths and spacings in the correlator.
  2. The Obscured Universe
    This area include hidden AGN's, star formation, as well as the obscuration processes themselves: free-free, dust, electron-scattering, self-absorption. The Upgrade aids this by sensitivity, frequency coverage, and A+ resolution.
  3. The Transient Universe
    Gamma ray Bursters, SN's, transient galactic jets, solar/stellar flares. The Upgrade gives us sensitivity, much faster response times, and high quality, rapid imaging at A+ resolution.
  4. The Forming Universe
    This includes starformation at high z and in the galaxy (this overlaps a bit with 2 as written) and HI observations of galaxies/groups and high and low z. Also molecular lines redshifted into the VLA bands are in this category. The Upgrade gives sensitivity, the wide specral line bands needed for this sort of thing, and the frequency coverage.
  5. The High Resolution Universe
    This includes the environment of AGN's, galactic and extragalactic jets, star forming regions, etc. The Upgrade gives us the sensitivity and the A+ resolution and imaging quality to address many problems the VLA and VLBA cannot deal with now. The A+ gives us high quality, high resolution high sensitivity imaging which no other instrument being pushed can match.

    If we organize this way, we emphasize why astronomy needs the Upgrade without claiming we alone will solve all the problems. We have the individual cases to support each of the cases above but each single case is not as strong as the big picture of what the VLA Upgrade provides. I think this will sell better to a wide-band panel in the Decade Review than a few key projects.

    ---Frazer

    ----- End Included Message -----

    My own view is this: The first four themes are excellent -- they are based on physical phenomena or subjects. The fifth is based on a technical characteristic -- primarily the potential of the A+ configuration. But it is important to underscore the potential science of the A+, as well as its importance to the VLBA.

    Another problem is that planetary science doesn't fit well into these themes. Subjects such as the thermal emission of planets or asteroids, or the characteristics of the atmospheres of gas giants don't seem to fit into the 5 suggested themes.

    And, what to do with HI imaging of local galaxies? Perhaps this subject has been well enough explored that it won't, by itself, justify a separate 'bullet'.

    Another suggested 'universe theme' is: The Invisible Universe. Here we could group subjects that can only, or primarily, be detected by radio astronomy. Dark matter halos, for example.

    Rick Perley

    VLA Expansion Project Science
    VLA Expansion Project Home Page

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