LAMOST Medium-Resolution Spectral Survey of Galactic Nebulae (LAMOST-MRS-N): Subtraction of Geocoronal Halpha Emission

Abstract

We introduce a method of subtracting geocoronal Halpha emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Halpha sky line to the adjacent OH lambda6554 single line do not show a pattern or gradient distribution in a plate. More interestingly, the ratio is well correlated to solar altitude, which is the angle of the sun relative to the Earth's horizon. It is found that the ratio decreases from 0.8 to 0.2 with the decreasing solar altitude from -17 to -73 degree. Based on this relation, which is described by a linear function, we can construct the Halpha sky component and subtract it from the science spectrum. This method has been applied to the LAMOST-MRS-N data, and the contamination level of the Halpha sky to nebula is reduced from 40% to less than 10%. The new generated spectra will significantly improve the accuracy of the classifications and the measurements of physical parameters of Galactic nebulae.

arXiv comment12 pages, 10 figures, accepted for publication in Research in Astronomy and Astrophysics

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Cited by in corpus (5)

• Stellar Parameters and Chemical Abundances Estimated from LAMOST-II DR8 MRS based on Cycle-StarNet
• The Data Processing of the LAMOST Medium-Resolution Spectral Survey of Galactic Nebulae (LAMOST MRS-N Pipeline)
• Diffuse Ionized Gas in the Anti-center of the Milky Way
• Spatially-resolved Galactic HII regions observed by LAMOST medium-Resolution Spectroscopic Survey of Nebulae (LAMOST MRS-N)
• LAMOST MRS-N Observations of the W80 Region