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| Auteurs principaux: | , , , |
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| Format: | Preprint |
| Publié: |
2024
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| Accès en ligne: | https://arxiv.org/abs/2401.06343 |
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| _version_ | 1866913233248452608 |
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| author | Shimojo, Masumi Bastian, Timothy S. Kameno, Seiji Hales, Antonio S. |
| author_facet | Shimojo, Masumi Bastian, Timothy S. Kameno, Seiji Hales, Antonio S. |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2401_06343 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Polarization Observations at 3 mm Shimojo, Masumi Bastian, Timothy S. Kameno, Seiji Hales, Antonio S. Solar and Stellar Astrophysics Instrumentation and Methods for Astrophysics 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. |
| title | Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Polarization Observations at 3 mm |
| topic | Solar and Stellar Astrophysics Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2401.06343 |