SEGUE Stellar Parameter Pipeline (SSPP)

Introduction

SDSS/SEGUE stellar spectra are processed through the SEGUE Stellar Parameter Pipeline (SSPP), and three primary stellar parameters, effective temperature (T_eff), surface gravity (log g), and metallicity ([Fe/H]) are reported for most stars in the temperature range 4000 - 10,000 K and with spectral S/N ratios exceeding 10/1. In that process, the line indices of various atomic and molecular lines are also measured. The detailed descriptions of the SSPP can be found in a series of papers (Lee et al. 2008a, Lee et al. 2008b, and Allende Prieto et al. 2008). The changes and improvements made on the SSPP since the DR7 are described in Smolinski et al. (2010). The following links highlight some important features of the SSPP.

Two Output Files in SSPP

Note that the FITS files linked to below are very large as they include all DR8 products.

ssppOut (1.7 Gb) contains information on stellar parameters from individual pipes in the SSPP (datamodel). Among the various parameters, it is mostly recommended to use the adopted T_eff, log g, and [Fe/H] unless one wants to use the parameters from a specific method for a very good reason. These are named "TEFF_ADOP", "LOGG_ADOP", and "FEH_ADOP", respectively, in the data model.
ssppOut_lineindex (2.2 Gb) includes line index measurements for various atomic and molecular lines (datamodel).

Details

[α/Fe] Measurements

Although the [α/Fe] ratio is determined by the SSPP, the estimate is not available in the DR8. A detailed description of the alpha measurement can be found in Lee et al. (2011). Note that the [α/Fe] ratio was released in DR7. However, it is not recommend to use it as its measurement and error were not well characterized as decribed in Lee et al. (2011).

Caveats on Temperature and Gravity Estimates

The effective temperatures for cool metal-poor giant stars (less than 4800 K), derived by the SSPP are higher by about 100 - 200 K than the high-resolution analysis of the same SDSS/SEGUE stellar spectra, and surface gravities for metal-rich giants (log g less than 3.0 or so) are gradually larger by about 0.1 - 0.7 dex.

Extinction Calculations

SSPP reports extinction values in the SDSS's ugriz filter system. The pipeline calculates these values by converting from standard extinction E(B-V) values (Schlegel, Finkbeiner, & Davis 1998), using the following conversions:

Extinction_u = 5.155*E(B-V)

Extinction_g = 3.793*E(B-V)

Extinction_r = 2.751*E(B-V)

Extinction_i = 2.086*E(B-V)

Extinction_z = 1.479*E(B-V)