Method for using shadow altitude to remove geocoronal H α
4 affiliations
- 1Department of Physics, The Chinese University of Hong Kong, Shatin, N.T.
- 2JC STEM Lab of Astronomical Instrumentation, The Chinese University of Hong Kong, Shatin, N.T.
- 3CUHK Shenzhen Research Institute
- 4Institute for Astrophysics, School of Physics, Zhengzhou University
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.
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BibTeX
@article{wong2026method,
title = {{Method for using shadow altitude to remove geocoronal H α}},
author = {Wai-Kiu Ricky Wong and Renbin Yan and Zesen Lin},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202659124},
url = {https://www.aanda.org/10.1051/0004-6361/202659124},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Method for using shadow altitude to remove geocoronal H α
AU - Wai-Kiu Ricky Wong
AU - Renbin Yan
AU - Zesen Lin
PY - 2026
DA - 2026/10/27
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202659124
UR - https://www.aanda.org/10.1051/0004-6361/202659124
AB - 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.
SN - 0004-6361
SN - 1432-0746
ER -