The DESI Y1 RR Lyrae Catalog. II. The Metallicity Dependency of Pulsational Properties, the Shape of the RR Lyrae Instability Strip, and Metal Rich RR Lyrae
Abstract
Abstract RR Lyrae stars (RRLs) are valuable probes of both Milky Way assembly and stellar-evolution physics. Using a sample 6240 RRLs obtained in the first year of the Dark Energy Spectroscopic Instrument (DESI) survey, we investigate the metallicity of RRLs and its correlation with their pulsation properties. We find that (1) a clear correlation between period and [Fe/H] reinforces the view that the long-standing Oosterhoff dichotomy arises from the scarcity of intermediate-metallicity Galactic globular clusters hosting sizeable RRL samples; (2) high-amplitude short-period and small-amplitude short-period variables are comparatively metal-rich, with mean [Fe/H] = −1.39 ± 0.27 and −1.30 ± 0.28, respectively; (3) in double-mode pulsators (RRd), the metallicity declines smoothly with increasing fundamental-mode period, and anomalous RRd stars occupy a remarkably narrow [Fe/H] range relative to classical RRd stars; (4) this spectroscopic sample lets us, for the first time, place empirical constraints on the metallicity-dependent topology of the instability strip using phase-corrected effective temperatures and a large number of RRLs, where we observe an instability strip that moves towards cooler T eff with declining [Fe/H] with a width roughly consistent with stellar-evolution models; and (5) a subset of metal-rich RRLs exhibits orbits consistent with disk membership and halo kinematics. Our results confirm the tantalizing potential of DESI for Galactic and stellar astrophysics and highlight the importance of the even larger samples of RRLs and data-processing improvements forthcoming in future DESI data releases.
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Authors: G. E. Medina, Ting S. Li, Carlos Allende Prieto, Leandro José Beraldo e Silva, Amanda Byström, R. G. Carlberg, Sergey E. Koposov, Mika Lambert, Joan Najita, Connie M. Rockosi, Namitha Kizhuprakkat, Alexander H. Riley, J. Aguilar, Steven P. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, Andrew P. Cooper, Axel de la Macorra, A. Dey, P. Doel, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, Mustapha Ishak, R. Kehoe, Theodore S. Kisner, Martin Landriau, Laurent Le Guillou, Aaron Meisner, R. Miquel, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, D. J. Schlegel, David Sprayberry, G. Tarle, B. A. Weaver
Institutions: Universidad Nacional Autónoma de México, University of Michigan, University of Toronto, Boston University, Consejo Superior de Investigaciones Científicas, University College London, University of Edinburgh, University of Arizona, Sorbonne Université, University of Cambridge, Institució Catalana de Recerca i Estudis Avançats, Durham University, Universitat Politècnica de Catalunya, University of Milan, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, National Tsing Hua University, University of Portsmouth, The University of Texas at Dallas, Sejong University, Universidad de La Laguna, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, Institut d'Estudis Espacials de Catalunya, NSF NOIRLab, Southern Methodist University, Instituto de Astrofísica de Canarias, Instituto de Astrofísica de Andalucía, National Institute for Astrophysics, Universidad de Los Andes, Brera Astronomical Observatory, Institute for High Energy Physics, National Observatory, University of California Observatories