SDSS DR7 Stellar SED and Dust Extinction Catalogs

Abstract

We utilize SDSS photometry (and 2MASS photometry when available) for unresolved sources from SDSS Data Release 7 to simultaneously fit a main-sequence stellar energy distribution (SED) and the amount of dust extinction towards each star. The empirical SEDs are extracted from the main stellar color locus at high Galactic latitudes (Covey et al. 2007), and the dust is parametrized by Av (total column along the line of sight) and Rv (the parametrization for the shape of extinction curve). The best-fit SEDs, Av and Rv, together with measured and best-fit model photometry, are made available here for about 75 million stars from SDSS Data Release 7 (23 million stars also have 2MASS data). This site describes the catalog format and provides links to data files. A detailed description of all the processing and preliminary analysis of results is presented in Berry et al. 2012 , which should be referenced when using these data products. Here we only provide a brief description of the main steps, but describe catalog format in full detail.

Introduction

The main purpose of this catalog is to enable studies of the spatial distribution and properties of stars and interstellar dust close to the Galactic plane. For completeness, we distribute SDSS and 2MASS data used in our analysis (although they are available from the survey data release sites), as well as the best-fit model parameter and photometry predicted by the best-fit models. Models only include SEDs extracted from the main stellar locus and thus are representative of main sequence stars (red giants have similar SEDs as main sequence stars in SDSS bands, but often can be recognized with the aid of 2MASS photometry, or as outliers in the extinction vs. distance diagrams). One way of interpreting our catalogs is that they are an excellent filter for finding objects with SEDs that are not consistent with main sequence stars. For example, subsets of unresolved SDSS sources that are white dwarfs, binary stars, quasars, L/T dwarfs, etc. are all easily recognized as entries with bad chi2 statistic.

Catalogs are defined by selection based purely on SDSS measurements.

Data Selection

For methods of accessing SDSS data products, and detailed product description, please see SDSS EDR paper (Stoughton et al. 2002, Astronomical Journal, 123, 485). This catalog contains all SDSS Data Release 7 objects that satisfy the following query:


SDSS sources in the catalog are not SATURATed, BRIGHT, BLENDED, NODEBLENDed, DEBLENDED_AS_MOVING, and 
must have nchild == 0 and rModelMag < 21:

WHERE (
   (objFlags & (OBJECT_SATUR | OBJECT_BRIGHT | OBJECT_BLENDED | OBJECT_NODEBLEND | OBJECT_DEBLENDED_AS_MOVING )) == 0 
     && (nchild) == 0 && (objc_type == 6) && (psfCounts[2] < 21) 
)

The first line excludes all saturated and "bright" objects (the latter are always duplicates of physical objects produced by processing software), as well as various flavors of blended objects, and the second line requires that the object is unresolved and within adopted r band magnitude limits.

The selected objects cover sky regions included in the SDSS-I survey (approximately 10,000 sq.deg. at Galactic latitudes b>+30) and in the SDSS-II survey (so-called SEGUE survey, which obtained ten 2.5 deg wide strips that cross the Galactic plane at a range of Galactic longitudes). 2MASS objects are positionally matched to all SDSS objects using a matching radius of 1.5 arcsec (for justification and other details, see Covey et al. 2007).

Due to two fitting methods and relatively large data volume, we separate our catalogs into four groups. We fit stellar SEDs twice: once with the selective extinction fixed to Rv=3.0 (using Cardelli, Clayton & Mathis 1989 model; see the paper for details) and the second time with Rv as a free-fitting parameter (confined to the 1-8 range). For users interested only in objects with 8-band SDSS/2MASS photometry, we distribute this smaller data subset separately. For the Rv=3.0 case, the data files in each dataset (only-SDSS and SDSS-2MASS) are defined by Galactic coordinates, and are designed to contain fewer than 10 million stars each. For the free Rv case, we distribute only the data from SEGUE strips with |b|<30 deg. because Rv is poorly constrained at higher galactic latitudes with small extinction. This data organization allows users to download data for a relatively small region of sky without the burden of downloading the whole dataset.

The data files containing astrometric and photometric data, best-fit parameters, and detailed descriptions of their format, are accessible by following these links:

1) All SDSS stars, assuming a fixed Rv of 3.0

2) Stars with SDSS and 2MASS data, assuming a fixed Rv of 3.0 (most reliable fits)

3) Stars with SDSS and 2MASS data, with a best-fit Rv

4) All SDSS stars, with a best-fit Rv (WARNING: unreliable!)

5) ** Table with Stellar Locus Parametrization used in the paper ** (different than Covey et al. table!)

** NOT ALL FITS ARE USABLE FOR SCIENTIFIC ANALYSIS: PLEASE READ Berry et al. (2012) paper **

Funding

This research has been supported by NSF grants AST-0707901 and AST-1008784 to the University of Washington, and by NSF grant AST-0551161 to LSST for design and development activity.

Referencing

The reference entry for this catalog is Berry et al. (2012, Astrophysical Journal 757, 166). In addition, we would greatly appreciate if you add the standard SDSS and 2MASS acknowledgements to your paper:

Acknowledgements

Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS Web site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Thank you very much! Your friendly purveyors of fine astronomical catalogs,


   Michael Berry (1,2)
   Željko Ivezić  (1)
   Branimir Sesar (1,3)
   Mario Jurić (4,5)

   and  the SDSS Collaboration

(1) University of Washington
(2) Now at Amazon
(3) Now at Max Planck Institute for Astronomy
(4) Harvard University
(5) Now at University of Washington

If you need more information, please do let us know!

Version 1.2 from December 14, 2015 ( revision history)