chihchunhsu.github.io/research1.html at master · chihchunhsu/chihchunhsu.github.io · GitHub

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							<h1 class="major">Forward-Modeling Method</h1>
							<figure><span class="image fit"><img src="images/J0136+0933_spectrum.png" style="width:460px" alt="" />
							<figcaption>Spectrum and forward-model of J0136+0933 (<a href="https://ui.adsabs.harvard.edu/abs/2021ApJS..257...45H/abstract">Hsu et al. 2021)</a></figcaption>
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							<p>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. <br>

							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).<br>

							I led the development of an open-source, Python-based package called <a href="https://github.com/chihchunhsu/smart">SMART (Spectral Modeling Analysis and Rv Tool)</a>, published in <a href="https://ui.adsabs.harvard.edu/abs/2021zndo...4765258H/abstract">Hsu et al. (2021)</a>. 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!
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