{
  "id": "2309.03263",
  "version": "v1",
  "published": "2023-09-06T18:00:00.000Z",
  "updated": "2023-09-06T18:00:00.000Z",
  "title": "High-resolution Spectroscopic Metallicities of Milky Way Cepheid Standards and their impact on the Leavitt Law and the Hubble constant",
  "authors": [
    "Anupam Bhardwaj",
    "Adam G. Riess",
    "Giovanni Catanzaro",
    "Erasmo Trentin",
    "Vincenzo Ripepi",
    "Marina Rejkuba",
    "Marcella Marconi",
    "Chow-Choong Ngeow",
    "Lucas M. Macri",
    "Martino Romaniello",
    "Roberto Molinaro",
    "Harinder P. Singh",
    "Shashi M. Kanbur"
  ],
  "comment": "14 pages, 4 figures, Accepted for publication in The Astrophysical Journal Letters",
  "categories": [
    "astro-ph.SR",
    "astro-ph.CO",
    "astro-ph.GA"
  ],
  "abstract": "Milky Way Cepheid variables with accurate {\\it Hubble Space Telescope} photometry have been established as standards for primary calibration of the cosmic distance ladder to achieve a percent-level determination of the Hubble constant ($H_0$). These 75 Cepheid standards are the fundamental sample for investigation of possible residual systematics in the local $H_0$ determination due to metallicity effects on their period-luminosity relations. We obtained new high-resolution ($R\\sim81,000$), high signal-to-noise ($S/N\\sim50-150$) multi-epoch spectra of 42 out of 75 Cepheid standards using ESPaDOnS instrument at the 3.6-m Canada-France-Hawaii Telescope. Our spectroscopic metallicity measurements are in good agreement with the literature values with systematic differences up to $0.1$ dex due to different metallicity scales. We homogenized and updated the spectroscopic metallicities of all 75 Milky Way Cepheid standards and derived their multiwavelength ($GVIJHK_s$) period-luminosity-metallicity and period-Wesenheit-metallicity relations using the latest {\\it Gaia} parallaxes. The metallicity coefficients of these empirically calibrated relations exhibit large uncertainties due to low statistics and a narrow metallicity range ($\\Delta\\textrm{[Fe/H]}=0.6$~dex). These metallicity coefficients are up to three times better constrained if we include Cepheids in the Large Magellanic Cloud and range between $-0.21\\pm0.07$ and $-0.43\\pm0.06$ mag/dex. The updated spectroscopic metallicities of these Milky Way Cepheid standards were used in the Cepheid-Supernovae distance ladder formalism to determine $H_0=72.9~\\pm 1.0$\\textrm{~km~s$^{-1}$~Mpc$^{-1}$}, suggesting little variation ($\\sim 0.1$ ~km~s$^{-1}$~Mpc$^{-1}$) in the local $H_0$ measurements due to different Cepheid metallicity scales.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-09-06T18:00:00.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "milky way cepheid standards",
      "spectroscopic metallicity",
      "high-resolution spectroscopic metallicities",
      "hubble constant",
      "leavitt law"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}