Sky coverage

The DR7 contains that part of the SDSS imaging and spectroscopy taken through July 14, 2008. Here we give coverage plots and the detailed coverage tables from which they were constructed, though excluding the supplemental imaging scans released through DRsup. Further below, we outline the future sky coverage of SDSS. The survey terms are explained in the sections on imaging coverage and spectroscopic coverage below.

For data interfaces, see the data access page.

Anomalies in the DR7 Footprint

Several stripes, when examined in detail, have anomalies (or errors) in the definition of the PRIMARY (mode = 1) footprint. Usually objects which should be in the primary footprint are missing. The links here provide a guide to the anomalies on a stripe-by-stripe basis, and in most cases, show sample SQL query clauses in which may be executed on the RunsDB database in order to recover objects uniquely within the full DR7 footprint.

Known anomalies in stripe: 26 1100 1100-79 1100-82 1140-72 1188-72 1220-72 1260-72 1260-76 1300-76 1356-72 1356-86

Anomalies in the Astrometry

The quoted astrometric errors for SDSS are about 100 mas per coordinate or better, on average, around the sky. To check this, we have compared the positions of objects between the SDSS catalog and the 2MASS catalog, adn between the SDSS and the USNO-NOMAD catalogs, and we find a few positions within the SDSS footprint, especially some scans at high declination, where the errors are larger than the nominal values. In the following link we provide are some information about these astrometry anomalies, and how to find them.

Anomalies

SDSS DR7 Footprint Summary

	Full Footprint with Stripe Labels
Equatorial
	Imaging (ps)
	Legacy Footprint
Equatorial
	Imaging (ps)	Spectroscopy (ps)
Galactic
	Imaging (ps)	Spectroscopy (ps)
	SEGUE Footprint
Equatorial
	Imaging (ps)	Spectroscopy (ps)
Galactic
	Imaging (ps)	Spectroscopy (ps)

Additional Contents

Open and Globular Clusters

Repeat scans of the Celestial Equator

Coverage tables

For reference, the coverage tables describe the sky coverage in terms of survey coordinates. To translate the sky coverage into celestial coordinates, please refer to the coordinates section of the EDR paper and the description below.

Note: The coverage tables, and a number of other files we distribute, are given as ASCII parameter (.par) files.

All imaging runs	DR7,Stripe82,Runs CAS + DAS Runs Table of all the imaging
DR7 CAS Runs	allrunsdr7db.par Table of all runs in the DR7 CAS (Legacy and SEGUE)
DAS only runs	DAS only RUNS Table of runs only available in the DAS (not in the CAS)
Stripe 82 Runs	allRunsStripe82DB.par Table of Stripe 82 CAS DB runs, including coadd; see SN DR7
RunsDB Table	allRunsRunsDB.par Table of Runs in the RunsDB CAS
Runs in CAS only	CASonly.par Table of run/reruns which are in one of the 3 CAS DBs only (i.e. no in the DAS)
Special Scans	Special/Supplemental Table of Special/Supplemental Runs in the CAS and DAS

DR7 DAS	All DAS Runs Link to all runs in the DR7 DAS
DR7 CAS	AllCASRuns.dr7.par All scanline segments in the DR7 CAS
Legacy Best	tsChunk.dr7.best.par (great circle coordinates) - see Target and Best below
Legacy Target	tsChunk.dr7.target.par (great circle coordinates) - see Target and Best below
SEGUE DR7	SEGUERuns.dr7.par List of SEGUE scanline segments
Stripe 82	Stripe82.dr7.par Stripe 82 scanline segments; see SN DR7
Runs DB	RunsDB.dr7.par List of scanline segments in Runs DB
Spectroscopy	DR7 contains additional plates beyond the main survey plates: "extra" plates which are reobservations of main survey plates; "special" plates which take spectra beyond the main survey targets, and "extraspecial" reobservations of special plates. There is a separate page descriging the special plates.There are 5 coverage files: one for all the plates, and 4 for each of the categories. The coverage files give plate centers by plate number and MJD of observation. All plates alldr72spectro.par Main survey plates maindr72spectro.par Extra plates extradr72spectro.par SEGUE/Special plates specialdr72spectro.par

Note also the list of list of quality "holes" (small areas of bad seeing etc.) and missing data, the list of fields which are missing only apparently (e.g., data from different runs were used in target and best) and the list of differences in sky coverage between target and best.

Imaging coverage: stripes, runs, reruns

The survey coverage is defined in survey coordinates, as described in the coordinates section of the EDR paper. For detailed astrometry please see the following note about parts of the survey which have a slightly different survey coordinate system from the rest.

Stripes

The imaging survey scans the sky along great circles, which are circles of constant survey latitude eta. Scans are obtained along stripes spaced 2.5° in survey latitude. Each stripe has an integer stripe number n such that the inclination of a stripe with respect to the celestial equator is -25° + 2.5° × n. The boundaries of the region eventually to be surveyed by the SDSS are defined in terms of survey longitude lambda in atStripeDef.par.

Runs cover strips, two strips cover a stripe

An imaging run designates a continuous scan of the imaging telescope. The survey camera's focal plane has six columns of CCDs, so that a single run consists of six camera columns (camcols) (see the instrument descriptions). The camera columns have a gap which is filled by an offset second run. The six camcols taken together are called a strip. Thus to completely cover the two strips making up one stripe, at least two runs are required. The imaging data reduction is done on a run-by-run basis, hence the imaging data in our Data Archive are accessible by run number.

Great circle coordinates

Every stripe has its own great circle coordinate system. The coordinate along a great circle is called mu. The range of data actually obtained for a given stripe is reported in terms of a range in great circle mu along that stripe as startMu and endMu in the coverage tables above. Both startMu and endMu are given in integer arcseconds.

The calibrated object lists are accessible in the archive by stripe number and startMu on that stripe.

For historical reasons, DR1 contained both photometric and spectroscopic data which lay outside the official survey limits, i.e., the startMu/endMu for some runs extend beyond the lambda limits for the stripes they cover. Since DR3, only the target data in those areas are still marked non-primary, but the best data are primary. Please refer to this note about DR7 data outside the SDSS survey area for details on how to retrieve these.

Fields

A run is divided into images 2048 pix × 1361 pix which are called fields. Each field then has the first 128 rows of the following field attached to it, so that all survey images actually have a size of 2048 pix × 1489 pix.

Object detection, photometry and classification are done field by field. In particular, the calibrated object lists and survey images are distributed separately for each field. To account for the overlap, object detection is not performed on the first 64 rows or the last 64 rows of each corrected frame.

Note that one therefore should use only objects in the "primary" area of each survey field, in order to avoid duplicate area and duplicate object detections. Near the center of a stripe, the primary area will be the full 2048 pix × 1361 pix, but frames overlap near the ends of stripes, reducing the primary area there. Please refer to how "primary" is set in the "status" flag of an object and please also see the details of how overlapping areas are resolved. The primary area of each field is recorded as entry stripeArea in the tsField*.fit file

Reruns

Every time we (re)process our imaging data, we assign the outputs a new rerun number. Thus, a rerun does not imply re-observation, but is simply a re-reduction of the same run. The re-reduction can use more recent software or calibrations than a previous rerun, or both. Across runs, the rerun is an arbitrary index, so the same rerun of different runs does not have to be produced with the same software or calibrations.

Target and Best

1. A target rerun, which is the reduction used to select targets for the spectroscopic survey. This is referred to as skyVersion = 0.
2. A best rerun, which is the best available reduction. This is usually a different rerun from the target version, since our photometric pipelines have been evolving. The best rerun is referred to as skyVersion = 1. All best reruns have rerun >=40.

• The survey area on the sky, given as a stripe number and a range for the mu coordinate (startmu <= mu <= endmu). These were used to create the plots above.
• The runs and reruns and the range of fields which cover the given area. This is the information needed to find data for a given part of the sky in the Data archive.

• In general, the target and best version of a particular region of the sky come from the same run. However, there are some exceptions which are explained in the list of runs differing for target and best.
• If it seems that other data are missing from some run, look at the list of fields which are meant to be missing.

Spectroscopy

Incremental sky coverage of SDSS

A map of the incremental coverage of the numbered Data Releases (i.e., excluding the EDR) by DR number.

Imaging

Spectroscopy

Future sky coverage of SDSS

Imaging of the Southern Galactic hemisphere and further spectroscopy is continuing as part of SDSS-3.

*Text and figures on this page come from an author-created, un-copyedited version of the SDSS Data Release 7 paper, an article submitted to Astrophysical Journal Supplements. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. A preprint of the DR7 paper is available from the arXiv preprint server.