[vsnet-alert 10379] checking for new objects in big surveys - usno b1.0 now on GATOR

bydra at Safe-mail.net bydra at Safe-mail.net
Wed Jul 30 05:22:05 JST 2008

USNO B1.0 is now available on GATOR



along now with other all sky and major sky surveys such as 2MASS and DENIS, resources at times used when transients occur to look for candidate progenitors.

Although VizieR is usually more than enough for such, and there are several mirrors available now for VizieR should one site be down, there are times when it disappears during maintenance etc, although granted relatively very few nowadays.

An aspect of GATOR however is that not only cone searches are possible, but also full SQL interrogation (with assisting forms for doing most of the field and range selectio), and for the SQL aware relatively bulk subsets of data can be obtained, up to fairly reasonable sizes, at the server end, and then downloaded when processing completed.  Warning : can be big files, and if you get the query wrong, you've wasted bandwidth and their computer processing time.  Target lists can also be uploaded and worked upon.  Thus a bunch of candidate objects could be parameter delimited tested against particular catalogues for predefined colour ranges, whilst flags can be set to ensure only the better quality data is returned.

For people who make things like Astrometrica and Guide this also provides an independent source of automated download as the relational database can be queried directly via HTTP GET, including cone searches, SQL searches, the lot, although timeouts do seem to occur with anything too nontrivial via that route, and even cone searches can be a bit slow.

Several return formats are available including a simple flat ascii tabular format that will import into just about anything.

Once familiarity is gained with using the system, more exotic datasets become available, such as those from SPITZER.  These can be useful for red variables and ysos, not to mention make flux data available for use in SED generation.  For instance some of the candidate YSOs I noted earlier had some of, and in one or two cases all of, glimpse, msx6c, iras and 2mass fluxes available, and these can be compared against models uses this resource http://caravan.astro.wisc.edu/protostars/ .  However, it should be noted that even with SEDs circumstellar discs around ysos and cool circumstellar discs around postAGB stars are apparently still difficult to distinguish with just various forms of infrared data.

In such ways, whole swathes of OGLE II variables, or even stars in general, for instance, can have their magnitudes in various colours returned and the whole checked in various colour spaces.  With USNO B1.0 now included linkage with optical data becomes feasible too, as returned shortlists can be further crossed with that.  Although it should be noted that there is no JOIN capability (well, not that I've ever found).

It takes a bit more learning than most things, and it isn't always needed as other resources exist, but for certain tasks it is invaluable, and now it has USNO B1.0 it will be a useful backup for when VizieR is down (GSC2.3.2 can be investigated via MAST / GALEX, and also supports HTTP GET :-

http://gsss.stsci.edu/webservices/GSC2/GSC2WebForm.aspx )



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