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: http://www.adass.org/adass/proceedings/adass02/P1-8/
Дата изменения: Thu Mar 13 02:27:22 2003 Дата индексирования: Tue Oct 2 04:03:43 2012 Кодировка: Поисковые слова: hydrogen |
MySQL databases are created from broad searches of SDSS and 2MASS data. Broad queries on the SDSS and 2MASS database servers are run weekly so that observers have the most up-to-date information from which to select candidates for observation. Observers can look at detailed information about specific objects including finding charts, images, and available spectra. In addition, updates from previous observations can be added by any collaborators; this format makes observational collaboration simple. Observers can also restrict the database search, just before or during an observing run, to select objects of special interest.
The coolest brown dwarfs require both SDSS and 2MASS
photometry for selection. In the 2MASS catalog (JHK
photometry), the
rare T
dwarfs have the same colors as much more common M dwarfs and are hard
to find
for that reason (Hawley et al. 2002). Also, T
dwarfs are sometimes detected by SDSS only in the z-band, and so are
hard to distinguish from cosmic rays and high redshift quasars. Fortunately, T dwarfs occupy a sparsely populated region in
the i
J, zJ color space and can be selected with these color cuts: iJ 
3.5
and zJ 2.2.
Red stellar objects are selected from the SDSS database with sdssQT, an SQL-based query tool for the SDSS science database. Photometry and astrometry for the selected objects are loaded into a MySQL SDSS subset database using Python. This list is then used as input to Gator, a 2MASS database interface, which finds 2MASS objects within five arc seconds of the SDSS subset objects. These are loaded into a MySQL 2MASS subset database.
Brown dwarfs are nearby so we need a relatively large search radius to catch high proper motion objects. Multiple hits (binaries or cosmic rays) are resolved with a visual inspection of the SDSS images.
Automated weekly updates are run:
(
) a query is performed on the SDSS database,
(
) a script is run which appropriately formats the data,
(
) a query is performed on the 2MASS data using Gator, and
(
) a second script is run to format the data and insert it into the database.
Our color criteria for selecting objects from SDSS are:
() objects detected in r, i, and z, ri 2 and iz 1.5,
() objects detected only in i and z, iz 1.75, and
() objects detected only in z, iz 2.
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When the link is clicked, the rest of the information on the object is displayed. This includes the atlas images, a finding chart, spectra when available, and any notes left regarding the object. There is also an option to add notes, as well as to delete the object if it is not of interest. While this does not delete the object from the database, is does prevent it from being viewed from the main page. An observer can view the list of objects that have been deleted, and can restore them.
Each of these pages are created dynamically using Php. The candidate number, a unique value in the database, is passed from one page to the next, and the data are pulled from the database after the selection is made.
Color-color plots are created using IDL. An observer can look at the plots to determine whether the query run was appropriate.
Users can also select objects based on colors or positions, to customize the main page just before an observing run, making it easier to locate objects of special interest.
Hawley, S. L. et al. 2002, AJ, 123, 3409
