Using on-line resources to find information on a star

Originally posted to vsnet-chat by Brian Skiff

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:

...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:

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:

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.