Globular and Open Clusters Observed by SDSS/SEGUE: the Giant Stars

TL;DR

This paper provides detailed photometric and spectroscopic data for several globular and open clusters, focusing on red giant stars, to aid calibration of SDSS/SEGUE surveys and improve cluster membership identification.

Contribution

It introduces new membership identifications, reddening maps, and photometric transformations for cluster giants, enhancing calibration accuracy for SDSS/SEGUE.

Findings

New spectroscopic membership lists for clusters

Reddening map for M71

Transformation from Teff to g-r for giants

Abstract

We present griz observations for the clusters M92, M13 and NGC 6791 and gr photometry for M71, Be 29 and NGC 7789. In addition we present new membership identifications for all these clusters, which have been observed spectroscopically as calibrators for the SDSS/SEGUE survey; this paper focuses in particular on the red giant branch stars in the clusters. In a number of cases, these giants were too bright to be observed in the normal SDSS survey operations, and we describe the procedure used to obtain spectra for these stars. For M71, also present a new variable reddening map and a new fiducial for the gr giant branch. For NGC 7789, we derived a transformation from Teff to g-r for giants of near solar abundance, using IRFM Teff measures of stars with good ugriz and 2MASS photometry and SEGUE spectra. The result of our analysis is a robust list of known cluster members with correctly dereddened and (if needed) transformed gr photometry for crucial calibration efforts for SDSS and SEGUE.