Mira

Mira variables are long-period pulsating giant stars on the second, or asymptotic giant branch (AGB) phase of their evolution. They are extremely red, cool giants, pulsating with a period of 100 days or more, with large variability amplitudes of 4 to 6 magnitudes. Pulsating AGB stars like Mira variables bring up material from deeper layers of the star that have been processed by the stellar nuclear fusion, in a process called dredge-up. Dredge-ups enrich the outer atmosphere with heavier elements like carbon. The pulsations eventually blow away a substantial fraction of the stellar mass in powerful dusty winds. The Mira variable R Bootis, whose light curve and spectrum are shown below, has a period of 223 days, with an amplitude of about 5 magnitudes. It's very red and cool, with a spectral type M6.

Below is a sonified video of observations of R Bootis, our Mira variable star. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes. The video spans 4 and a half years, during which 189 observations were taken. The periodic oscillations in brightness can be heard clearly in the video a few times, during spans when the sampling frequency is sufficiently high.

Shown next is a sonified video of the phased light curve for R Bootis. R Boo's period is 223 days, and nearly sinusoidal in its brightness variation. The amplitude of its variation is about 5 magnitudes. Listen and hear two full phases corresponding to a year and 3 months on Earth. The video scans over phase (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes.

Below is the spectrum for the observed Mira variable R Bootis. This video scans across a plot of brightness measured in flux or intensity of light (y axis) versus wavelength (x axis), moving from blue to red wavelengths from 4050 to 8800 angstroms. Lower pitch represents weaker flux. During the video, the spectrum increases gradually in flux (pitch) as wavelength increases. Some unique spectral features called P Cygni profiles can be heard as the video plays. P-Cygni profiles are the presence of both absorption and emission features in the same spectral line profile indicating powerful stellar winds blowing a gaseous envelope away from the central star. A P-Cygni profile will be heard as a small decrease in flux – the absorption, followed by a large spike in flux – the emission.

The spectrum for R Bootis is provided thanks to Michael Castelaz, Ph.D., Professor of Physics, Brevard College. Reference: Castelaz, M.~W., Luttermoser, D.~G., Caton, D.~B., et al.\ 2000, \aj, 120, 2627 (link). The light curve is an optical v-band from ASAS-SN.