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RR Lyrae Stars in the Galactic Nuclear Bulge: Constraining its Assembly History with Roman GBTDS
Program ID 19024
Science Category Stellar Populations
Program Type Analysis
Category Medium
Principal Investigator Q. Daniel Wang
PI Institution University of Massachusetts, Amherst
Co-Investigators
  • Ron Renda (University of Massachusetts, Amherst)
  • Doris He (Smith College)
Abstract Understanding how stellar bulges assemble around supermassive black holes remains an outstanding challenge in astrophysics. The Galactic center serves as an exceptional laboratory for studying these processes through resolved stellar populations in a dense nuclear environment. We propose a data-analysis project using data from the Roman Galactic Bulge Time-Domain Survey (GBTDS) to carry out the first systematic census and metallicity investigation of RR Lyrae (RRL) stars in the Galactic nuclear bulge (NB). These variables fall squarely within the optimal dynamic range of GBTDS, delivering high-signal-to-noise-ratio measurements while avoiding saturation. Infrared imaging of the GBTDS will alleviate the severe interstellar extinction toward the NB. By capitalizing on the survey’s coverage in the off-NB field, where extensive ground-based RRL light-curve templates and metallicity measurements are already available, we will establish empirical transformations connecting Roman F146 light-curve characteristics to standard photometric systems. This cross-band calibration will enable the reliable application of Period–Phase–Metallicity relations to the GBTDS sample and will permit analogous studies with data from the Roman Galactic Plane Survey. We will verify these metallicity estimates using reddening-insensitive Wesenheit magnitudes. Such a high-precision chemical abundance map of RRL stars, combined with the survey's accurate proper motion measurements, will discriminate between the two proposed primary formation channels for the NB: primordial in situ collapse versus hierarchical disruption of globular clusters. We will further constrain the fraction of the ancient stellar mass, uncover phase-space gradients and/or substructures left by past accretion events, and reconstruct the assembly history of the NB. The resulting constraints will probe the interplay of the nuclear stellar components with the central supermassive black hole, Sgr A*.