Mira Variable Spectroscopy

Executive Summary

Our work shows that slit-less filter-wheel grating spectroscopy can provide useful data for tracking the cycles of Mira and other long period variable. We suggest several guidelines that should be followed to employ this technique as part of a crowd-sourcing program to monitor these types of stars. See the paper in the proceedings of the 2016 Society for Astronomical Sciences Symposium or the slides from the talk.

Papers

Here are video presentations on YouTube of talks we have given at the Symposium of the Society for Astronomical Sciences:

Grating Spectroscopy

Visit http://go.uis.edu/gratingspectra for more information about using filter-wheel gratings to do spectroscopy.

Contributors

John C Martin, University of Illinois Springfield
Bill Rea, Christchurch, NZ
Matthew Templeton, Dedham, MA
Rob McFarland (student), University of Illinois Springfield

Graphics

A series of spectra that show the evolution of the spectrum of Mira variable R Cen across half of its cycle. Note that the plotted spectra have been normalized to have the same flux at 925 nm while the brightness of the target fluctuates.

Animation of R Cen's spectrum over most of its period

Suggestions for Crowd Sourcing

As a result of our pilot study, we suggest the following guidelines for any crowd-sourced Mira variable spectroscopy project:

Filter wheel grating spectra are sensitive to changes in:
- Spectral class / Surface Temperature
- Differences in Mira type
- Different phases in a Mira variable's cycle.
Emission due to mass loss is difficult to detect at this spectral resolution.
Pick targets that are not too faint for the telescopes used by your participants.
Restrict crowd-sourcing efforts to reflectors and apochromatic refractors.
Keep in mind the factors that influence effective spectral resolution. Encourage observing under good seeing and good focus.
Archives of crowd-sourced spectra should provide tools to facilitate comparison of spectra with different resolutions.
The continuum at 920 nm is a good point to normalize the flux of most Mira variables for comparison.
We recommend masking half of the grating in order to get better results in crowded fields.

Ongoing Work

We have continued to work with Bill Rea on further development of effective crowd-sourcing of Mira variable spectroscopy with filter-wheel gratings. Our on-going focus is

Developing "check" stars that provide standard spectra in order to better characterize the differences introduced in the spectrum by different telescope/camera setups.
Writing software to simplify the extraction and calibration of filter-wheel grating spectra.
Exploring the use of the Wing Filter System to measure the changes in TiO bands of Mira's via grating spectroscopy.

Last updated 2021 May 28