Northern Sample

To create this catalog, we first adopt the SDSS Quasar Catalog V (DR7QSOcatalog, Schneider et al. 2010) as the list of the primary observations, which lists SDSS BEST DR7 photometry for 105,783 spectroscopically confirmed QSOs. For each primary observation, all secondary observations are obtained by finding all point sources (ie. PhotoObj "type" = 6) within 1 arcsecond in RA and Dec of the primary using the following query:

select as id, round(p.ra,6) as ra, round(p.dec,6) as dec, 
round(p.rowc,3) as rowc, round(p.extinction_r,3) as rExt,
round(p.psfMag_u,3) as upsf, round(p.psfMag_g,3) as gpsf,
round(p.psfMag_r,3) as rpsf, round(p.psfMag_i,3) as ipsf,
round(p.psfMag_z,3) as zpsf,
round(p.psfMagErr_u,3) as uErr, round(p.psfMagErr_g,3) as gErr,
round(p.psfMagErr_r,3) as rErr, round(p.psfMagErr_i,3) as iErr,
round(p.psfMagErr_z,3) as zErr, p.objID as objID2,  
round(f.mjd_r, 4) as mjd_r
from mydb.DR7QSOcatalog q cross apply dbo.fGetNearbyObjAllEq(q.ra, q.dec, 0.016) N, photoobj p, field f
where p.objID = N.objID and f.fieldID = p.fieldID and p.type = 6

The QSOs are put in separate lists depending on whether they have only 1, at least 2, or at least 3 total photometric observations. Less than 0.2% of the total number of QSOs (Ntot = 105,783) had at least 4 observations. In addition to the repeatedly observed QSOs over the Northern Galactic Cap, we include Stripe 82 QSOs in this sample, for which we list the two observations with the maximum time difference.

The Catalog Format

For each of these lists (ie. QSOs with only one observation, at least two, and at least three) a "master" file and a "mag" file are constructed. The master file is simply a list of the QSOs (1 QSO per row) with exactly the same format as the SDSS Quasar Catalog V (Table 2 in Schneider et al. 2010). The "mag" file contains magnitude measurements (along with the time of observation) and selected data for the same set of QSOs. For the list with at least 2 observations, the primary and latest secondary observation are listed. For the list with at least 3 observations, the same two observations as in the dm_2obsDR7.dat file are listed, along with a third observation (picked at random if there are yet additional observations).

Please click on the following for the format for each file:

Master file format     Mag file format

Data files

The following table contains links to the compressed gzip files. The files for QSOs with only 1 observation cannot be used for variability study but are included for completeness. Note that the latter files may include QSOs with multiple observations if all secondary observations are resolved (type=3).

Note: The following files have been revised as of Feb. 2012. For details, see the revisions page. The old files are available here.

QSOs with at least 2 observations, Master file master_2obsDR7.dat (33881 rows x 74 columns) gzip
QSOs with at least 2 observations, Mag file dm_2obsDR7.dat       (33881 rows x 40 columns) gzip
QSOs with at least 3 observations, Master file master_3obsDR7.dat (11680 rows x 74 columns) gzip
QSOs with at least 3 observations, Mag file dm_3obsDR7.dat       (11680 rows x 51 columns) gzip
QSOs with only 1 observation, Master file master_1obsDR7.dat (67794 rows x 74 columns) gzip
QSOs with only 1 observation, Mag file dm_1obsDR7.dat       (67794 rows x 29 columns) gzip

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