Forward-Modeling Method

Spectrum and forward-model of J0136+0933 (Hsu et al. 2021)

I use a Markov Chain Monte Carlo (MCMC) forward-modeling method to model the high-resolution spectra and extract precise radial and projected rotational velocities, as well as surface temperatures and surface gravities for hundreds of nearby ultracool dwarfs.
This method is powerful for measuring these low-temperature stellar/substellar objects because they have abundant absorption lines, and using the earth's atmosphere methane absorption could provide a simultaneous wavelength calibration imprinted on the data. The figure is an example fit (magenta and blue) and spectrum (black) of a young T dwarf J0136+0933. The best-fit forward model with (magenta) and without (blue) earth absorption matches well with the observed spectrum, as can be seen in the residual (data - model) in the bottom panel, consistent with the noise (grey).
I led the development of an open-source, Python-based package called SMART (Spectral Modeling Analysis and Rv Tool), published in Hsu et al. (2021). This tool can model several spectrometers, including high-resolution Keck/NIRSPEC, SDSS/APOGEE, Keck/HIRES, Gemini/IGRINS, Lick/APF, and medium-resolution Keck/OSIRIS. Feel free to contact me if you would like to use the code!