NOAO >   Observing Info >   Approved Programs >   2016A-0243

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Program Information for 2016A-0243


PI: Emily Levesque, U. of Washington, emsque@uw.edu
Address: Department of Astronomy, Box 351580, Seattle, WA, 98195-1580 USA

CoI: Philip Massey, Lowell Observatory
CoI: Georges Meynet, Geneva Observatory

Title: Red Supergiants in the Extremely Metal Poor Sextans Galaxies: Local Analogs of Massive Stars in the Early Universe

Abstract: Red supergiants are the He-burning, evolved descendants of massive OB stars; their spectra are characterized by deep bands of TiO. For many years the location of these stars on the H-R diagram was at odds with stellar evolutionary theory; generally the stars were much cooler than allowed, occupying the so-called Hayashi ``forbidden" zone where stars are not in hydrostatic equilibrium. Recently our group has used the new generation of MARCS stellar atmospheres to fit spectrophotometry of these stars, resulting in a significant revision to the effective temperature scale. Here we are proposing to extend this work to unprecedentedly low metallicities, using GMOS on Gemini-N to obtain multislit spectrophotometry of over 100 red supergiants in Sextans A and B. With metallicities of log(O/H) + 12 = 7.5 and 7.6, respectively, the extremely metal-poor stars in these galaxies serve as local analogs of massive stars in the early universe. By determining physical properties for red supergiants in the Sextans, we will be able perform the first rigorous test of the lowest-metallicity evolutionary tracks produced by the Geneva group, the same tracks that are key ingredients in the modeling of high-redshift star-forming galaxies.

Program Type: Standard/Extragalactic

Scheduled Nights:
Run 1 (2016A):  GEM-N/GMOSN -- 2n on Feb 11 - Feb 12 2016


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



NOAO >   Observing Info >   Approved Programs >   2016A-0243

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