Zwicky Transient Facility and Globular Clusters: The RR Lyrae gri-band Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations

Creators: Ngeow, Chow-Choong; Bhardwaj, Anupam; Dekany, Richard; Duev, Dmitry A.; Graham, Matthew J.; Groom, Steven L.; Mahabal, Ashish A.; Masci, Frank J.; Medford, Michael S.; Riddle, Reed

Abstract

Based on time-series observations collected from the Zwicky Transient Facility (ZTF), we derived period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyrae located in globular clusters. We have applied various selection criteria to exclude RR Lyrae with problematic or spurious light curves. These selection criteria utilized information on the number of data points per light curve, amplitudes, colors, and residuals on the period–luminosity and/or period–Wesenheit relations. Due to blending, a number of RR Lyrae in globular clusters were found to be anomalously bright and have small amplitudes of their ZTF light curves. We used our final sample of ∼750 RR Lyrae in 46 globular clusters covering a wide metallicity range (−2.36 dex < [Fe/H] gri bands. In addition, we have also derived the period–color–metallicity and, for the first time, the period-Q-index-metallicity relations, where the Q-index is extinction-free by construction. We have compared our various relations to empirical and theoretical relations available in the literature and found a good agreement with most studies. Finally, we applied our derived PLZ relation to a dwarf galaxy, Crater II, and found that its true distance modulus should be larger than the most recent determination.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 January 29; revised 2022 March 24; accepted 2022 March 25; published 2022 April 28. We are thankful for the useful discussions and comments from an anonymous referee that improved the manuscript and from H. Baumgardt regarding the distance to the globular clusters. We are thankful for funding from the Ministry of Science and Technology (Taiwan) under contracts 107-2119-M-008-014-MY2, 107-2119-M-008-012, 108-2628-M-007-005-RSP, and 109-2112-M-008-014-MY3. Based on observations (prior to 2020 December 1) obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratory. Operations are conducted by COO, IPAC, and UW. Based on observations (after 2020 December 1) obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratory, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. This research has made use of the SIMBAD database and the VizieR catalog access tool, operated at CDS, Strasbourg, France. This research made use of Astropy, 27 a community-developed core Python package for astronomy (Astropy Collaboration et al. 2013, 2018). Facility: PO:1.2m - Palomar Observatory's 1.2 meter Samuel Oschin Telescope. Software: astropy (Astropy Collaboration et al. 2013, 2018), dustmaps (Green 2018), gatspy (VanderPlas and Ivezić 2015), Matplotlib (Hunter 2007), NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020), boundfit (Cardiel 2009), corner (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013).

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