Constraining Balmer Alpha Fine Structure Excitation Measured in Geocoronal Hydrogen Observations

Gardner, D. D.; Mierkiewicz, E. J.; Roesler, F. L.; Nossal, S. M.; Haffner, L. M.

doi:10.1002/2017ja024055

Cited by 5 publications

(8 citation statements)

References 56 publications

(119 reference statements)

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“…Based on the observational data from the WHAM survey, the intensities of Hα sky have been found to gradually decline with the line-of-sight shadow height (Nossal et al 2001). As geocoronal Hα sky emission mainly originates in the thermosphere and exosphere (Mierkiewicz et al 2006), while the OH λ6554 comes from the mesopause region (Gardner et al 2017;Xu et al 2012), it's expected that F(Hα sky )/F(λ6554) ratio should be correlated with solar altitude (sunalt). Because all the observations were made at night, the sunalt varies from -90 to 0 degree.…”

Section: Correlation Between F(hα Sky )/F(λ6554) Ratio and Solar Alti...mentioning

confidence: 99%

“…Besides, the line ratios are usually used to classify the ISMs into H II regions, supernova remnants (SNRs), and planetary nebulae (PNe) (Sabbadin et al 1977;Riesgo & López 2006). However, the Hα nebular line (Hα neb ) is blended with geocoronal Hα sky line (Hα sky ) which is the result of solar Lyman β scattering by atomic hydrogen in the Earth's upper atmosphere (Mierkiewicz et al 2006;Gardner et al 2017). The sky component should be subtracted before we derive the parameters based on the Hα nebular line.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang,

Wu,

et al. 2021

Preprint

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We introduce a method of subtracting geocoronal Hα emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Hα sky line to the adjacent OH λ6554 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 Hα 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 Hα 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.

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Section: Correlation Between F(hα Sky )/F(λ6554) Ratio and Solar Alti...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Zhang,

Wu,

et al. 2021

Preprint

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“…The Galactic spectra also contain the terrestrial emission and can be used for geocoronal studies provided that there is a sufficiently large Doppler separation between the Galactic and terrestrial emission lines (Nossal et al, ). Additional observations have been made in low Galactic emission regions (Nossal et al, ) and in the zenith direction for geocoronal investigations and observations have been made of both the geocoronal Balmer‐α and Balmer‐β column emission intensity (Gardner, Mierkiewicz, Roesler, Nossal, & Haffner, ; Roesler et al, ).…”

Section: Ground‐based Hydrogen Balmer‐alpha Emission Observationsmentioning

confidence: 99%

“…Additionally, there is contribution to the Balmer‐α signal from cascade excitation whereby higher‐energy solar Lyman line radiation excites the electron in the hydrogen atom to energy levels higher than the n = 3 state followed by cascade transitions of the electron back to the n = 3 level. This process results in Balmer‐α emission along all seven of the fine structure paths from the n = 3 to n = 2 levels of the hydrogen atom resulting in an approximate 4–5% cascade contribution to the total hydrogen Balmer‐α emission intensity (Mierkiewicz et al, ; Roesler et al, ) that is depended on shadow altitude (Gardner, Mierkiewicz, Roesler, Nossal, & Haffner, ).…”

Section: Introductionmentioning

confidence: 99%

Geocoronal Hydrogen Emission Variation Over Two Solar Cycles

et al. 2019

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Ground-based hydrogen Balmer-α observations from Northern midlatitudes span multiple solar cycles, facilitating investigation of decadal scale variations, including natural variability in the hydrogen response to solar geophysical changes. Here we present a reanalysis of ground-based hydrogen emission observations from the early 1990s and their comparison with observations obtained in [2000][2001] in the context of the extended Northern Hemisphere midlatitude geocoronal hydrogen emission data set. This work suggests an increase in hydrogen emission intensity between the solar-maximum period of 1990-1991 (Solar Cycle 22) and the near-solar-maximum period of 2000-2001 (Solar Cycle 23), with the caveat that this is a limited data set and that there are calibration uncertainties discussed in this paper. Solar activity was higher during the earlier solar maximum period. Thus, the apparent increase in intensity is counter to previous observations from midlatitudes in which the observed intensity increases with higher solar activity. This increase was also not seen in comparison of intensities from three solar minima periods. Further, the apparent increase in intensity is also likely of larger magnitude than model simulations would predict due to increases in methane and carbon dioxide. We will discuss the reanalysis and recalibration of the 1990-1991 observations using current analysis approaches and the interpretation of these observations in the context of observations and modeling of hydrogen variation over different time scales. The detailed review of the calibration procedures has also provided insights to guide design of future observations. Plain Language Summary Atomic hydrogen is a key constituent of the thermosphere and exosphere, the uppermost region of the Earth's atmosphere. Hydrogen in this region is a by-product of molecules at lower altitudes that contain hydrogen such as water vapor and methane, two of the greenhouse gases most important to the energy balance of the Earth. The 11-year solar cycle is a major source of natural variability in the upper atmosphere. Here we present observations of geocoronal hydrogen emissions (~400 km and above) taken by ground-based Fabry-Perot instruments at Wisconsin and at the Kitt Peak, Observatory in Arizona. These observations span two solar cycles and suggest an increase in the geocoronal hydrogen emission intensity between the 1990-1991 solar maximum (Solar Cycle 22) and the 2000-2001 near-solar-maximum (Solar Cycle 23) periods, with the caveat that this is a limited data set and there are calibration uncertainties. Solar activity was higher during the earlier solar maximum period. The apparent increase in intensity is counter to previous observations from midlatitudes in which the observed intensity increases with higher solar activity. Further, the apparent increase in intensity is also likely of larger magnitude than model simulations would predict due to increases in methane and carbon dioxide.

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Section: Introductionmentioning

confidence: 99%

LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N): subtraction of geocoronal Hα emission

Zhang

et al. 2021

Res. Astron. Astrophys.

View full text Add to dashboard Cite

We introduce a method of subtracting geocoronal Hα emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Hα sky line to the adjacent OH λ6554 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 Earthʼs 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 Hα 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 Hα 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.

show abstract

Constraining Balmer Alpha Fine Structure Excitation Measured in Geocoronal Hydrogen Observations

Cited by 5 publications

References 56 publications

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

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

Geocoronal Hydrogen Emission Variation Over Two Solar Cycles

LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N): subtraction of geocoronal Hα emission

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