New UCDs for VOEvent please

[Frederic V. "Rick" Hessman]

On 26 Apr 2005, at 4:20 pm, Rob Seaman wrote:

> On Apr 26, 2005, at 3:28 AM, Rick Hessman wrote:
>
>> I've added more VOEvent examples, several suggestions for IVOA/UCD to  
>> the proposed
>> object/event/process UCD list at
>>
>> 	http://monet.uni-sw.gwdg.de/twiki/bin/view/VOEvent/ 
>> UnifiedContentDescriptors
>
> Good start at a list.  A search facility would add immensely to its  
> usefulness as the list grows.  This would also function as a validator  
> for an astronomer's guess as to the proper syntax for a familiar class  
> of objects.
>
>> If something like this list has already been created, I'd appreciate  
>> hearing about
>> it before I put much more work into our own.
>
> This would be a good opportunity for VO to reach out to the larger  
> community.  It really isn't for us to mandate nomenclature.  An  
> interactive dictionary/beastiary of astronomical objects and processes  
> could be useful all by itself, and will be of obvious utility for  
> various VO projects.  A common understanding of each "hypothesis" will  
> indeed be key to VOEvent, for instance.

On the other hand, one can't have TOO many people laying on their  
hands, since there is a need for some level of editorial control.    
We'd be happy to provide our Twiki more-or-less as it is, since it's  
already interactive and available to anyone interested.

> I'm not sure, however, that the ApJ keywords are the best model for  
> constructing this content descriptor list.  Keywords are a way to  
> partition the level of interest a member of the community may have in  
> reading a paper.  A UCD is a way of partitioning the underlying  
> physics.  For instance, given that the interest in working on this is  
> arising out of VOEvent, it isn't surprising that there is a focus on  
> processes more than objects, and that the selection of objects would  
> be weighted toward time variability in various ways.  There are dozens  
> of fine shadings between variable stars.  On the other hand, while one  
> can distinguish between elliptical, irregular and spiral galaxies,  
> there isn't any mechanism (yet) for specifying the precise type of  
> each.

Actually, the ApJ/A&A/MN keywords should really be a GREAT place to  
start, since they are supposed to capture what is eventually done with  
the content. It's clear that they don't provide a uniform and uniformly  
deep level of description, but at least they provide a good and evenly  
distributed place to start.

> I'm leery of encouraging these descriptors to become longer than they  
> are, but it seems inappropriate to specify generally descriptive  
> classes, like:
>
> 	stars.variable.irregular
> 	stars.variable.long_period
> 	stars.variable.semi-regular
>
> at the same level as members of prototypical classes, like:
>
> 	stars.variable.Cepheid
> 	stars.variable.RR_Lyr
> 	stars.variable.RS_CVn
>
> (And where is stars.variable.W_UMa?  Just pointing out that the list  
> will never be complete.)
> Perhaps it should be stars.variable.class.Cepheid?  Or better yet,  
> adjust in the other direction, maybe stars.variable.period.irregular?   
> Or ideally, a general mechanism might be provided for parametrically  
> classifying periodicity.

No no no no : these are individual stars but names commonly used to  
typify a certain variable star behavior (just as we say "Cepheids" and  
really mean "delta Cepheids" = "stars like delta Cep").  There really  
are "W UMa" stars.  Of course, the UCD can't be defined for individual  
objects other than a very few like the Sun, Moon, and major planets.    
Thus, "stars.variable.W_UMa" means the same as  
"stars.variable.class.W_UMa";  I suppose we could add on the "*.class*"  
just as a reminder, but at the cost of an additional hierarchical level  
of detail.

> The challenge here is not only that the list will never be complete,  
> it is that we should be encouraging researchers to actively augment  
> and improve the list.  A workable classification scheme is often the  
> first step in organizing a research program.  But the result of a  
> research program is often to overturn the original classification  
> scheme.  We don't want to provide a mechanism that is only useful for  
> describing objects far removed from the cutting edge.

Fortunately, astronomers - even very good ones - are often rather  
traditional in their use of nomenclature, so we'll need such metadata  
whether someone thinks it's quaint or not.  As a stellar astrophysicist  
interested in variability and accretion, I've included things I'd like  
to have and will leave it to others to include their own metatdata.

Rick

------------------------------------------------------------------------ 
------------------------
Dr. Frederic V. Hessman      Hessman at Astro.physik.Uni-Goettingen.DE
Universitaets-Sternwarte     Tel.  +49-551-39-5052
Geismarlandstr. 11                Fax +49-551-39-5043
37083 Goettingen                 http://www.uni-sw.gwdg.de/~hessman
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http://monet.uni-goettingen.de
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