Comet C/2022 E3 (ZTF) is the visually brightest long-period comet in several years, making it one of few trans-Neptunian objects accessible to amateur astronomers. Long-period comets almost exclusively originate from the Oort cloud, a spheroidal body of frozen planetesimals which were ejected from the early solar system but remained gravitationally bound to the sun. Oort cloud comets therefore pose a unique opportunity to study the early chemical composition of the solar system, which is important in understanding how the solar system has evolved over billions of years. Specifically, Oort cloud objects are known to possess high concentrations of carbon-chain molecules, water, and nitrogen, species which are critical to biological life. Additionally, Oort cloud objects can help us understand the compositions of other stellar systems. By comparing the compositions of proto-stars and young stars to Oort cloud comets, we can reveal patterns in stellar formation and search for habitable extrasolar systems. Thus, identifying the chemical compositions of Oort cloud comets is the first step towards understanding our world and countless other planetary systems.
Using a Shelyak LISA low-resolution (R~1000) slit spectroscope, Celestron C9.25 schmidt-cassegrain telescope, and ASI2600MM-Pro CMOS camera, I recorded 7 spectra of the outer coma and 15 spectra of the inner coma of C/2022 E3 (ZTF) on February 9, 2023. On the same night, I also captured neon-argon calibration frames, incandescent flat frames, and spectra of an A-type reference star, HIP24160. During data reduction, I preprocessed and wavelength calibrated the cometary spectra, created an instrument response curve from the A-type star, and cropped the spectra to the visible domain. When analyzing the spectra, I subtracted a synthetic dust continuum and identified chemical emission lines from the spectral catalog by Brown et al. (1996).
Across the data, the species C2, C3, CN, NH2, and CH were identified, which suggests that C/2022 E3 (ZTF) is a chemically typical Oort cloud object. C2 and C3 are generally produced from the photodissociation of more complex carbon chain molecules, such as C2H2, C2H6, and C3H4; CN most likely derives from HCN; NH2 most likely derives from NH3; and CH most likely derives from CH4. Observations with a higher resolution spectroscope are necessary to affirm the existence of CH+. Another anomaly was the lack of CO and CO+ detected in C/2022 E3 (ZTF), which contradicts its high [O I] G/R ratios of 0.42 for the outer coma and 0.23 for the inner coma. For example, C/2016 R2 (PanSTARRS), which contained an unusually high abundance of CO+, exhibited a ratio of 0.23 ± 0.03 (Opitom et al. 2019). Since the G/R ratios for C/2022 E3 (ZTF) were uncorrected for Doppler shift and low-resolution line blending, higher resolution observations are required to detect CO and CO+, and to calculate more accurate G/R ratios.
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