Using MiraFitter to Identify Circumstellar Dust Around Optically-Thin Oxygen-Rich Mira Variables

Both ground-based and space-based observatories are capable of measuring infrared spectra
of dust in space. There are various studies of dusty environments that focus on the shape and
strength of silicate features near 10μm and 18μm. The study I present may impact how people
interpret silicate dust in their observations. Radiative Transfer (RT) modeling has often been
used to analyze spectra and obtain a match to the overall spectral energy distribution with
certain parameters. While RT modeling should allow us to build a spectrum that includes all
contributions to the observed spectra, we are hampered by a lack of detailed or appropriate
laboratory data for such modeling. This limits the application of RT modeling if we want to
determine the detailed mineralogy of the dust.

In some cases (usually very optically-thin scenarios), we can simply eliminate a continuous
contribution to the observed spectrum to isolate any observed features and measure their basic
spectral parameters. I created a program called MiraFitter to investigate several methods of
continuum elimination using spectroscopy data for the archetypal dusty AGB star, Mira. I have
investigated the ∼10μm and ∼18μm spectral features in the continuum-eliminated spectrum
including peak position, barycenter, and full width half maxima (FWHM). The positions and
widths of observed spectral features were compared with those seen in laboratory spectra. The
results show that the method of continuum elimination matters for correct identification of dust
minerals, while varying the temperature and precise continuum shapes do not have a major
effect on the positions of spectral features.