DISSERTATION DEFENSE
"Spectroscopy of Earth and Stellar Atmospheres"
Manish Bhusal
Old Dominion University
OCNPS 304 Physics Conference Room
Tuesday, October 27, 2026
3:00 pm
Abstract:
Molecular spectroscopy is an important tool to determine the abundances of various molecules in the atmospheres of the Earth and beyond. S-type stars are characterized by the presence of ZrO bands, M-type stars have TiO bands, and carbon stars have C2 bands as their characteristic spectra. A modern spectral fitting program, PGOPHER, was used to analyze the spectra of astrophysically important molecules: ZrO, TiO, YO, and CH. The high-resolution experimental spectrum of YO was recorded in this study using a hollow-cathode method, and the spectrum for ZrO was obtained from the National Solar Observatory in Kitt Peak, Arizona, through a carbon furnace method. The ACE-FTS solar spectrum served as the experimental spectrum for the analysis of CH, while the calculated cross-sections of TiO were used as the experimental spectrum for analyzing TiO. The spectroscopic constants calculated for various vibrational bands of these molecules were used to calculate their equilibrium constants, which were then used, along with ab initio calculations of transition dipole moment functions, in the RKR1 and LEVEL programs to calculate band strengths. These band strengths were used to produce a line list with line strengths, which is expected to aid in estimating the abundance of these molecules in various stellar atmospheres. Infrared transmittance spectra recorded by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) were analyzed to examine variations in the weight percentage of sulfuric acid (H2SO4 ), size distribution, and column density of stratospheric sulfate aerosols. The observed weight percentage of sulfuric acid ranges from about 40% to 91%, and the median radius varies from about 0.05 μm to 0.47 μm. When the temperature fluctuates, sulfuric acid droplets absorb or release water vapor to maintain equilibrium with the surrounding vapor. At high temperatures, the water present in sulfate aerosols evaporates, increasing the sulfuric acid content. In addition, low water vapor pressure accelerates the evaporation of water from sulfate aerosols, further enhancing the weight percentage of sulfuric acid. The empirical relationship between the weight percentage of sulfuric acid, temperature, and water vapor pressure has been updated. Weight percentages have been calculated using this new relation and compared with observed values. A new empirical relation was derived that estimates the median radius of stratospheric sulfate aerosol particles. Large volcanic eruptions significantly increase the number density of stratospheric sulfate aerosols. Large wildfires increase the size distributions of the stratospheric sulfate aerosols and decrease the composition of sulfuric acid in sulfate aerosols. Additionally, the ACE-FTS observations show that there is a hotspot of SO2 at around 24 km above the tropics where the percentage of sulfuric acid in stratospheric sulfate aerosol is maximum. This higher abundance of SO2 VMR at mid-stratosphere is mainly due to the photolysis of stratospheric sulfate aerosols.
All interested persons are cordially invited to attend.