NOAO >   Observing Info >   Approved Programs >   2014A-0411

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Proposal Information for 2014A-0411


PI: Annalisa Calamida, Space Telescope Science Institute, calamida@stsci.edu
Address: 3700 San Martin Drive, Baltimore, MD 21218, USA

CoI: Kailash Sahu, Space Telescope Science Institute
CoI: Stefano Casertano, Space Telescope Science Institute
CoI: Jay Anderson, Space Telescope Science Institute
CoI: Tom Brown, Space Telescope Science Institute
CoI: Howard Bond, Space Telescope Science Institute
CoI: Harry Ferguson, Space Telescope Science Institute
CoI: Mario Livio, Space Telescope Science Institute
CoI: Josh Sokol, Space Telescope Science Institute
CoI: Jeff Valenti, Space Telescope Science Institute
CoI: Santino Cassisi, Osservatorio Astronomico di Teramo (OACTe-INAF)
CoI: Maurizio Salaris, Astrophysics Research Institute, Liverpool John Moores University

Title: The nature of hot horizontal branch and blue straggler stars in the Galactic bulge

Abstract: We propose to collect multi-epoch, medium-resolution spectra of about 50 candidate extreme horizontal branch (EHB) and blue straggler stars (BSS) in the SWEEPS (Sagittarius Window Eclipsing Extrasolar Planet Search) field of the Galactic bulge. The candidates were identified through F606W (V), F814W (I)-band photometry and proper motions, estimated from HST images of the SWEEPS field taken in 2004 and 2012 (Clarkson et al. 2011; Calamida et al. 2013). The spectra will help in confirming the nature of these candidates through spectral classification, and in determining the fraction of close binaries through radial velocities. The true binary fraction of the bulge EHBs, along with their abundances, will reveal if they share a similar origin as in the high-density, low-metallicity environments of globular clusters, where stellar collisions play an important role, or if they are more similar to the field disk population, where the binary scenario is favored. We identified indeed two ellipsoidal variables among the EHBs, with periods < 0.5 d, and four W UMa-type BSS with period < 10 d. The radial velocity measurements will allow us to estimate the masses of the components of these, as well as other, close binary systems in the sample.


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NOAO >   Observing Info >   Approved Programs >   2014A-0411

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