Chemical Components Analysis of Atmospheres of Ultracool Objects using Laboratory Spectra

Substellar objects have ultracool atmospheres where molecules significantly contribute to the complexity of the spectra. 

To help with spectroscopic analysis, we are building a library of optical to near-infrared molecular absorption spectra using gas cells and a spectrometer at our laboratories.  We  already have room-temperature spectra of water vapor, ammonia, methane, hydrogen cyanide, hydrogen sulfide, and several other carbohydrades and deuterated molecules as well.

Recently we have investigated ammonia-to-methane ratios from a specific window in H-band near-infrared spectra which minimizes contamination from other chemicals in late-T and Y dwarfs, using laboratory gas spectra and tens of object spectra from different observatories like the Hubble Space Telescope. The results are concordant with the theoretical abundance model and suggest that all the late-T and Y dwarfs considered in this work have ammonia-to-methane ratios consistent with that of Jupiter within the uncertainties, suggesting that they have similar chemical abundances, and the overall trend also shows ammonia-to-methane ratio increases when spectral type goes from T7 to Y2.

In the future, we are going to explore more specific spectral window for certain combination of chemicals in our library and we will obtain higher-resolution spectra of objects. Besides, with future deep-sky infrared survey like Euclid, which will be launched into space in 2023. we will have to deal with the spectra of thousands of ultracool objects. Those objects will need to be classified spectroscopically, and our research may provide optimized spectral indices.