On Tue, 21 Oct 2003, Anita Richards wrote:
> Thus, to keep the 'decades', this seems more suitable:
> XRAY 0.12 - 12 keV (as per UCD2)
> GAMMARAY > 12 keV
> but maybe a high energy astronomer can advise....
I think that boundary between the two is reasonable: some past instruments called 'X-ray' have some coverage up to maybe 15 keV, but most modern telescopes depend on grazing-incidence reflection, which practically stops working above about 10 or 12 keV.
> OVERLAPPING DATA
> How will the UCDs be used? As I understand it, in order to use Vizier or
> the Aladin SED tool to search for e.g. radio observations between 1.3 and
> 1.7 GHz (radio L-band), the software would look for UCDs
> em.radio.750-1500MHz and em.radio.1.5-3GHz.
I think the way it has to work is this: the UCD defined for some dataset should be as specific as possible, so if the data fall practically within a single band (say within 750-1500 MHz) then you declare the UCD as "em.radio.750-1500MHz". If not then you have to fall back on a less specific UCD of "em.radio". A user wanting radio measurments at some frequency should be prepared to search for both _the_ most specific UCD and the less specific UCD, i.e. "em.radio". This may bring up some false positives, but so will any scheme that we can devise.
The alternative, as you say, is to apply a two or more UCDs to a dataset. That might be better in principle, but difficult in practice.
> * not use the fine divisions in UCDs, but treat frequency like position
> and treat every query as a 1D cone search, ie a linear segment search.
Well that's similar to a proposal I made some time ago (maybe in a Data Models context). Datasets should specify the range of frequencies they cover (which requires two numbers for the min frequency and max frequency, which doesn't imply that coverage between the limits is continuous, gaps should be ignored); then users also specify the range of interest. It's then a trivial exercise for a computer to compare the two intervals and work out which resources overlap the range of interest. All this without us having to dream up any artificial divisions between wavebands. But that doesn't fit in with UCDs as devised up to now, and I don't see any easy way to make it fit.
-- Clive Page Dept of Physics & Astronomy, University of Leicester, Tel +44 116 252 3551 Leicester, LE1 7RH, U.K. Fax +44 116 252 3311Received on 2003-10-21Z11:31:40