Method for using shadow altitude to remove geocoronal H α
Year: 2026
Type: article
Abstract: Spatially resolved spectroscopic surveys enable the interstellar medium (ISM) of galaxies to be studied. However, observations of Galactic H α emission are contaminated by geocoronal H α emission. The latter is known to depend on the shadow altitude, a geometric parameter that relates the line of sight to Earth’s shadow cone. Using fibres on blank skys from the MaNGA Stellar Library (MaStar) project of the Sloan Digital Sky Survey IV (SDSS-IV), we establish an empirical relation between the geocoronal H α emission and the shadow altitude, with a root mean square fractional scatter of 24.41%. This relation can be used to predict geocoronal H α emission so that it can be removed from observed spectra. This removal method is advantageous when the observed targets are extensive in the sky, and it does not require a large velocity separation between the observed target and the local standard of rest. This will enable reliable studies of Galactic H α in intermediate spectral resolution integral field spectroscopic surveys. We also find tentative evidence for the dependence of geocoronal emission on solar activity and the distance between the Earth and the Sun.
Source: Astronomy and Astrophysics
Authors: Wai-Kiu Ricky Wong, Renbin Yan, Zesen Lin
Institutions: Chinese University of Hong Kong, Zhengzhou University
Language: English
Subfield: Instrumentation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: Smithsonian Institution, U.S. Department of Energy, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, York University, University of Oxford, National Natural Science Foundation of China, Ministério da Ciência, Tecnologia e Inovação, Universidad Nacional Autónoma de México, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, University of Colorado Boulder, Leibniz-Gemeinschaft, Lawrence Berkeley National Laboratory
Award: G4044983565
OpenAlex ID: W7127325453