{
  "id": "2401.06343",
  "version": "v1",
  "published": "2024-01-12T03:21:46.000Z",
  "updated": "2024-01-12T03:21:46.000Z",
  "title": "Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Polarization Observations at 3 mm",
  "authors": [
    "Masumi Shimojo",
    "Timothy S. Bastian",
    "Seiji Kameno",
    "Antonio S. Hales"
  ],
  "comment": "30 pages, 16 figures, Accepted for publication in Solar Physics",
  "categories": [
    "astro-ph.SR",
    "astro-ph.IM"
  ],
  "abstract": "The Atacama Large Millimeter-submillimeter Array (ALMA) is a general purpose telescope that performs a broad program of astrophysical observations. Beginning in late-2016, solar observations with ALMA became available, thereby opening a new window onto solar physics. Since then, the number of solar observing capabilities has increased substantially but polarimetric observations, a community priority, have not been available. Weakly circularly polarized emission is expected from the chromosphere where magnetic fields are strong. Hence, maps of Stokes V provide critical new constraints on the longitudinal component of the chromospheric magnetic field. Between 2019-2022, an ALMA solar development effort dedicated to making solar polarimetry at millimeter wavelengths a reality was carried out. Here, we discuss the development effort to enable solar polarimetry in the 3 mm band (ALMA Band 3) in detail and present a number of results that emerge from the development program. These include tests that validate polarization calibration, including evaluation of instrumental polarization: both antenna based \"leakage\" terms and off-axis effects (termed \"beam squint\" for Stokes V). We also present test polarimetric observations of a magnetized source on the Sun, the following sunspot in a solar active region, which shows a significant Stokes V signature in line with expectations. Finally, we provide some cautions and guidance to users contemplating the use of polarization observations with ALMA.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-01-12T03:21:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "atacama large millimeter/submillimeter array",
      "polarization observations",
      "solar development effort",
      "polarimetric observations",
      "solar polarimetry"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 30,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}