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News and updates

Bug in synthetic magnitudes of spectra: mag_0,mag_1,mag_2 --> u,g,r (not g, r,i)

There is a bug in the tabulating of synthetic magnitudes of objects based on their integrated, flux calibrated spectra convolved with the SDSS filter curves. In the CAS table specObjAll (and its subset table specObj), the three quantities: mag_0, mag_1, and mag_2 are intended to be the synthetic g, r, and i band magnitudes of each object. In fact, in DR6 they are the u, g, and r band synthetic magnitudes. The wavelength coverage of the u band (centered on 3551 Angstroms) does not overlap (except at the few percent level) the wavelength coverage of the spectrographs (which start at about 3800 Angstroms), and the synthetic u band is only a very rough estimate. Thus, the i synthetic magnitude is not directly available in the DR6 CAS database.

If you currently need access to the i band synthetic magnitude, they are currently only available in the DR6 DAS: You may find them in HDU# 7 of the spPlate-$plate-$mjd.fits file in the form of a 640x5 (row x col) size image extension table containing the u,g,r,i,z synthetic magnitudes for all 640 objects with spectra, in fiber number order (i.e. the first 5 numbers are for the ugriz synthetic mags for the object at fiber#1, etc). You may download the full spPlate-$plate-$mjd.fits file from the DAS and extract this 'imaging region' from HDU#7 to access these numbers. The u and z synthetic magnitudes are generally not to be used since, as mentioned above, the overlap of the wavelength coverage of the spectrographs with these filter bandpasses is minimal.

Note that the DR5 CAS has correct g,r,i synthetic values in mag_0,mag_1,mag_2, however, an older version of the spectroscopic pipeline was used to process these data and the handling of reddening is different. Also note that the synthetic magnitude values may need an AB correction applied to put them onto the SDSS gri system.

The spSpec-$mjd-$plate-$fiber.fit files have header keywords MAG_G, MAG_R, MAG_I which are intended to be the same as mag_0, mag_1, mag_2 in the specObjAll table of the CAS. These synthetic numbers are also 'shifted by one filter' in DR6, thus, they actually are synthetic mags u, g and r (instead of g,r, and i) respectively.

Please note this bug. It will be corrected for the DR7 release of the DAS and CAS.

DR6 paper in print

The DR6 paper (Adelman-McCarthy, J.K. et al. 2008, ApJS, 175, 297-313) has appeared in print.

Old "news"

Proper motions update announcement.

Proper motions are not correct.

Bug in SEGUE primTarget flag

PrimTarget flag in SEGUE plates is trunctated in the CAS

SDSS-III announced

A new collaboration based on the legacy of SDSS and SDSS-II has been formed to pursue a number of new science goals. See the SDSS-III web site at www.sdss3.org.

Patch applied to DR6

This patch, applied the week of Aug 27,2007, corrects several bugs in the database. The list of patches to DR6 is as follows:
  1. 6 segments in Stripe 36 had a bug in their startMu/endMu, resulting in ~1500 duplicate primary objects in the main database. This has been corrected, and the previously duplicate primaries have been made secondary.
  2. The 'Propermotions' table has been incremented for BESTDR6 from DR5 to the full DR6 dataset. Additionally, propermotions have been added for a large number of objects which previously had been missed because they were targeted as galaxies (but turned out to be stars). Additionally, propermotions have been added for Segue imaging to the SEGUEDR6 database context in a parallel propermotions table. Note that all these propermotions have been 're-zeropointed' from their USNO-B source by matching to the SDSS positions for objects with zero proper motion (distant galaxies and quasars), and thus are of overall higher accuracy than those in the 'USNO' table.
  3. The 'Match' and 'MatchHead' tables in the CAS, which connects duplicate measurements of the same physical object on the sky, observed at different times (for instance, objects in the overlap between scanlines), were incompletely populated prior to Aug 31, 2007. They have now been updated.
  4. The sppParams table incorrectly computed the derived parameter velgal (the velocity of a star in the Galactic frame of reference, subtracting out the suns motion of (v_x,v_y,v_z) = (7,224,10) km/s prior to Aug 31, 2007. The table is now correct. The velgal velocities now also reflect the 7.3 km/s offset determined by absolute reference to known globular clusters and other Radial velocity standards. The best radial velocity for stars in the DR6 dataset is the 'rva' value in the sppParams table. It is reliable when the rvaerr is strictly > 0.
  5. A view (subset) of the sppParams table, called 'spbsparams' has been generated for easy access to Galaxy spectral parameters, including redshift (along with redshift confidence) and velocity dispersion (measured two different ways). These parameters are available on a plate-by-plate basis in the DAS as part of the spZbest* binary FITS tables, and on a fiber-by-fiber basis in the spSpec* FITS spectra as header keywords, but they are gathered here in a SQL searchable table.
  6. Documentation has been updated on matching photometry to spectroscopy on the SEGUE website. Magnitudes in the sppParams table are 'PSF target' magnitudes, the best available at the time an object was targetted for spectroscopic followup. Since then, the imaging data for an object may be remeasured (recorded as the best photometry). Finally, ubercal photometry is also available for many objects.
  7. The prepackaged tarballs of spectra, organized by object category (galaxy, qso, star, etc), are now available again, and include updates for DR6.

DR6 is available

About DR6 explains what is new in DR6.

SEGUE spectroscopic parameters available

DR6 includes a slew of new SEGUE data, including new stellar atmospheric parameters ([Fe/H], log g, Teff) and line indices in the CAS BESTDR6 database. See About SEGUE.

DRsup - Data Release Supplemental - is available

DRsup contains additional SEGUE, M31/Perseus and stripe 82 imaging. About DRsup explains what DRsup is and how to get it.

SDSS acknowledgements updated

The SDSS has entered a second phase of funding and operations, SDSS-II, with new participating institutions. Please use the updated SDSS acknowledgement statement in your publications using SDSS data.

DAS hardware is up and healthy.

Last modified: Mon Mar 31 17:06:47 CEST 2008