FreeLists / az-observing / [AZ-Observing] Re: ADS 4112 a multiple star in Auriga

[Brian Skiff <Brian.Skiff@xxxxxxxxxx>]

    I agree the WDS Web site is clumsy, since there's no query utility.
Basically, you download the chunks of RA you need, and either just
look at them or save the files and run them into an editor or something
you can search with.  This is the up-to-the-minute version of the WDS.
For a lot of stuff, such as the stars in nebulae you'll probably be
looking up a lot (stuff that doesn't have orbits or any substantial
motion), the version that's searchable through VizieR is probably          
just fine.  It is item i/237 in VizieR.  It is best when doing searches
in VizieR to have coordinates rather than names---the ADS is poorly
worked into SIMBAD (which is where it looks to get coordinates),
so you might end up not finding what you want.  (SIMBAD probably should be
but is _not_ a catalogue-data look-up device; it is a bibliographic reference
database.)  Since there aren't so many entries in the WDS, set the
search-radius in VizieR to something like 3 arcminutes (rather than the
default 10 arcmin), and that will usually be good enough to snag the WDS
entries you want.
     For pairs bright enough to appear in Tycho-2, you might also 
search in the Tycho double-star catalogue (i/276 in VizieR), which will
give the Tycho sep/pa data and also a link to the WDS info for the same
pairs.

     ADS 4112 is a good example of the problem with finding stuff in
SIMBAD since the stars are in fact listed without coordinates, only by
name.  So if you just put the ADS number in VizieR, it'll show an error
because of this.  There _are_ coords for NGC 1931, so go here:

http://vizier.u-strasbg.fr/viz-bin/VizieR

Up in the top window, type:                            

i/237,i/276

...which will set the thing to search the WDS and TDSC.  Down below,
change the search radius to 3 arcminutes.  I happen not to like the
default html output (really ugly), but let it be for the moment.
Now in the window where it says 'Target name (resolved by SIMBAD)....'
type:

ngc 1931

...then hit the 'find data' button that's over to the right.  The report
comes almost instantly.

Okay,  the WDS coords are a bit over 2' off the NGC 1931 position in SIMBAD
(I don't know which is correct, doesn't matter for the moment), but there
they are.  Nothing from the TDSC, so ignore that.  So, the output shows
some basic stuff from the WDS, but not everything.  It shows some coords,
probably inadequate for some things since they're only to 1' precision
(and probably worse accuracy).  There's the discoverer name, component name,
a date of the first observation, then the specs of position angle and
separation for that date, some magnitudes (notoriously bad in the WDS---
get them from someplace else), and finally a BD name for the primary star
(the BD observers actually probably listed the whole nebular blob).
     Now in the leftmost column, called 'Full', there are hot-linked numbers
for each line.  Click on '1'...and up comes a complete page of the WDS data
that includes the second date, how many observations, and a few other items
if they're available for the star in _this_verison_ of the WDS.  Notice that
the second date is 1902; almost certainly the current on-line WDS has more
recent data, perhaps from the 2MASS catalogue for instance.  
     All of this should be in better shape in the on-line WDS, particularly
the coordinates, which are now given to 1" accuracy and precision, and there
is a lot more basic data in the catalogue, too.
     _My_ approach would be somewhat different.  If I didn't know anything
about the NGC 1931 trapezium, I would first get some DSS or 2MASS images
from the Goddard SkyView utility:

http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl

...and independently determine "pretty good" coordinates from the image for
the group.  In bright nebulae like this, the 2MASS J-band image should show
little or no nebulosity and let you see the stars, whereas the regular DSS1
or DSS2 images will be toasted.  With coordinates in hand, I would then use
VizieR with a small search radius (say 30" or 60") and just look up
"everything", which it will do if you don't put any catalogue designations
in the top window.  This will lead you to photometry (if it's on-line at
VizieR, but not if it ain't!), coordinates, spectral types, etc.

     I just got the necessary images (yes, 2MASS J is the one you want to
look at), and see that the SIMBAD and WDS coordinates are wrong for the
group.  The primary of the trapezium is at:  5 31 27.08 +34 14 49.6 (J2000).
Work from there in VizieR.

     Another possibility is to use the Strasbourg Aladin package:

http://aladin.u-strasbg.fr/aladin.gml

...which allows the superposition of images and catalogue data.
But of course, as we've just seen, this may not be so helpful since the
database itself is a mess for the immediate field.

     A final thing to mention is that all the on-line astro data services
(CDS, ADS, NED) have tutorials (see for instance the links at the top of
any of the Strasbourg pages) that give exmaples of use and capabilities.
See also my Sky & Telescope article in the March 2003 issue (I think) that
gives a quick outline of the three main services, all of which have developed
considerably since then.


\Brian
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