AAS 207th Meeting, 8-12 January 2006
Session 131 Galactic Astronomy in the SDSS
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[131.13] Calibration of the SDSS/SEGUE Spectroscopic Pipeline

T. Sivarani, T. C. Beers, Y. Lee (Michigan State & JINA), C. Rockosi, D. Lai (UCSC), B. Yanny, D. Tucker (FNAL), J.A. Smith (LANL), R. Wilhelm (Texas Tech), C. Allende (UT), J. Norris (ANU, Australia), H. Morrison (CWRU), B. Plez (Montpellier, France)

We describe an ongoing effort to validate the estimated atmospheric parameters (Teff, log g, [Fe/H]) obtained from SDSS spectroscopy (R = 2000) and ugriz photometry, which are being employed for both the previous SDSS-I and the ongoing SEGUE surveys. The spectroscopic pipeline makes use of a number of methods for the estimation of each parameter, with estimated internal errors in the order of \sigma (Teff) = 150 K, \sigma (log g) = 0.4 dex, and \sigma ([Fe/H]) = 0.3 dex. However, several of these methods rely on an uncertain transformation of g-r colors to B-V, and there does not presently exist an external validation of the derived parameters based on high-resolution spectroscopy. In order to address these deficiencies, we have generated two new grids of synthetic spectra and ugriz colors (based on both Kurucz NEWODF models with no covective overshoot and MARCS models) for stellar atmospheric parameters covering the ranges 3500 K \le Teff \le 10000 K, 0.0 \le log g \le 5.0, and -5.0 \le [Fe/H] \le 0.0. The two grids will provide a useful internal check on the dependence of the derived parameters on the adopted stellar models. In addition to these grids, we have also generated a carbon-enriched subgrid, covering the entire parameter space for various values of carbon enhancement ([C/Fe] = 0.5,1.0,1.5,2.0). This subgrid makes use of carbon-enhanced MARCS models instead of scaled solar models, since the atmospheric structures themselves can be altered by enhanced carbon, especially at cooler temperatures. The synthetic colors will be calibrated using a selection of standard stars and open and globular cluster stars covering a wide range of stellar atmospheric parameters. We have already obtained a small number of the high-resolution spectra for SDSS stars needed to calibrate the spectroscopic pipeline; much larger samples of high-resolution data are presently being acquired. Preliminarycomparisons of the estimated atmospheric parameters based on the SDSS/SEGUE spectroscopic pipeline with those derived from the high-resolution specta will be reported.

T.S., Y.L., and T.C.B. acknowledge partial support from grant AST 04-06784, as well as from grant PHY 02-16783, Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation.

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