2003ApJ...590..573K

Emissions of the methane ν₃band and the ethane ν₇band were detected in the high-dispersion infrared spectra of comet 153P/Ikeya-Zhang taken by the Subaru Telescope with the Infrared Camera and Spectrograph (IRCS) on 2002 May 28 and 29 UT. The rotational temperature is estimated to be about 40-50 K from R₀and R₁lines of the methane ν₃band. The production rates of methane and ethane were estimated by applying the rotational temperature of 50 K. Resultant production rates of methane and ethane are (2.13±0.40)x10²⁶ and (1.75±0.48)x10²⁶ molecules.s^–1, respectively. The abundance ratio between ethane and methane is 0.82±0.27, which is comparable with other comets within error bars. Although the emissions of monodeuterio-methane (CH₃D) were searched for carefully, there is no evidence of them. The 2 σ (95% confidence) upper limit of the CH₃D/CH₄ratio is 0.3 in comet 153P/Ikeya-Zhang. Comparing the relative abundance of methane and ethane in the interstellar ices, we discussed the formation conditions of cometary nuclei.