[vsnet-chat 4829] More on using on-line resources

[Brian Skiff <bas@lowell.edu>]

     Well, I've received already two requests for additional details about
what I did for the on-line bibliographic searches for the two bright suspected
variable stars.  That must mean there are others who are interested, but who
haven't/won't write.  I'm pretty familiar with these services since I use them
daily and contribute to them as part of my work, so it was easy for me to
navigate around to get essential items.  If interested I suggest you retrace
the steps outlined below to get a feel for what's available.
     For stars, the first stop is SIMBAD.  I use an old-fashioned telnet
connection to this, mainly since it is very fast and parsimonious of bandwidth
(flat text only), but requires an account.  The Web version is however freely
available:

http://simbad.u-strasbg.fr/Simbad

...and has other functionality that some folks may find useful, such as
connections to scanned journal articles, sky survey images, and so on.
     HD 37519 is a fairly bright star, so I simply searched SIMBAD by keying-in
the name ("search by identifier" on the Web page).  If the star did not have
a common name such an HD or BD number, I would have searched instead by
coordinates, since SIMBAD unfortunately does not always link a single object
with several designations in the literature.  So sometimes there will be
multiple entries for the same object with slightly different or even identical
positions; these will get picked up by searching on a position with a small
search radius, like 2' or 3'.  For well-catalogued stars this usually not a
problem, however.
     So simply key HD 37519 into the top window of the SIMBAD query page,
take all the defaults, and hit the "SUBMIT" button.  What comes up is a page
with basic catalogue data in a header, and links to other stuff underneath.
Included in the header is the Hipparcos position, proper motion, and parallax.
Below this are links to "plots and image tools".  These won't tell you a thing
about the variability of the star, but only show what a grossly overexposed
star looks like on Schmidt survey plates.
     The next region is the one with the references, which is what's really
useful in this case.  The system defaults to showing references since 1983,
but you can change the dates.  Change the start-date to 1960 and hit the
"display" button.  The next page that comes up is a list of all papers from the
database that mention the star, showing a 19-digit 'bibcode', titles, and
authors.  The bibcodes are highlighted, and clicking on these will bring up
the abstract for the paper.  If the paper itself is scanned-in or otherwise
available on-line (e.g. directly from a journal Web site), then there will be
a link here for this.  The citation to the 1996 Irish AJ paper discussed
previously doesn't have such a link apart from the abstract, but the paper
right above it does ("ROSAT all-sky survey....").  In general one can read 
journal articles up to within a few years of the current issue without having
a subscription.
     The two papers in the bibliography that caught my eye (by their titles)
were the Andrews paper and the one by Jerzykiewicz with high-precision
differential photometry.  I went to our library to look at the Andrews paper,
but read through the other one using the ADS article service:

http://adsabs.harvard.edu/article_service.html

Here I keyed-in the journal volume and start-page number, clicked the
journal title, and hit the "Send Request" button.  This brings up scanned
images of the journal pages.  There's a table there with a list of the stars
observed, and another with the results from the differential photometry that
I quoted.
     Next I used VizieR to look up the stars in the NSV and in Hipparcos:

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

VizieR is a catalogue-query utility that allows you to get (usually) complete
data from over 3000 catalogues and data-tables without actually having to have
the bulk files on your own machine or on CD.  It is so fast that I see little
point in having bulk catalogues locally.  One can for instance look up a
position in USNO-A2.0 (526 million entries), 2MASS (165 million entries), and
GSC-ACT (25 million entries) all at the same time, and have the report back
before I could have decided which of the eleven A2.0 CDs to stick in my
machine, much less any of the others---and no CDs available at all for 2MASS.
     It was easy to search both Hipparcos and the NSV at the same time for
the stars of interest.  I happen to know that the Hipparcos stuff is item
i/239 and the NSV is under ii/214a (which I simply keyed-in to the top line
of the VizieR page), but you can use the second window to do a more general
search.  Typing 'NSV' in the second window will bring up the various bits of
the GCVS IV including the NSV (and even the NSV supplement).  After selecting
catalogues, the query page allows input of either a position or object name
(which will search around the position of that given in SIMBAD).  The
information linked through VizieR into Hipparcos is quite complete (including
the epoch photometry), but the text notes and references for the NSV are not
available.  The NSV files do include the range of the variable, and so you can
see what's been reported at least.  A digest of the catalogue information is
displayed by default, but by clicking the 'full' button, and hitting "Display
full selected rows", you get a complete listing of what's in the all the
catalogue entry.  Try this using Hipparcos for HD 37519 and see what you get.
     Another reminder here is that the default search radius is 10'.  For
large catalogues like A2.0 this is way too large, and the report list will
truncate after 50 rows.  You can change the report length to a larger figure,
but then you get a huge list of mostly "faintest" stars that doesn't really
help you if you're looking for a particular one.  For such catalogues change
the radius to something reasonable like 30 arcsec---having a pretty good
position in hand to start with is obviously helpful.  Since Hipparcos is
relatively small (the stars far apart on the sky), the default 10' search
brings up only one star in the case of HD 37519.
     Go back to the top level VizieR page.  Notice that about midway down the
page there is a window to enter an object name or position.  This can be handy
for some searches.  Hitting "Find Data" with a position entered here (remember
to set the search radius to something reasonable) will begin a search of _all_
the catalogues in VizieR, and return a report of whatever it finds.  Again
try this for HD 37519 with a 1' search radius and see what turns up!
Impressive, eh?

     Apart from the interpretation that's pretty much it.  The best thing to
do is to poke around in these systems for an object you're familiar with to see
what shows up.  There are numerous other features at each of these sites I have
not mentioned.  I hope you'll agree this is really quite a powerful set-up.

\Brian

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