ELL Rotating Ellipsoidal Binaries

Rotating ellipsoidal (ELL) binary variables are composed of two stars that orbit so close to each other that both stars take on an ellipsoidal shape because of the strong gravitational pull between them. Unlike the EB-type eclipsing binaries, the two components in an ELL binary do not eclipse each other, but fluctuations in brightness occur due to changes in the light emitting area that is visible to the observer. These fluctuations happen with a period equal to that of the orbital motion of the binary.

Below is a sonified video of observations of a rotating ellipsoidal binary variable. A dense period of observation is shown in the video, with 45 observations occurring within a 20 day span. Each beat of time in the video corresponds to one hour in real time. There are no noticeable trends to be heard in the video besides the quick fluctuations in brightness, which span nearly half a magnitude. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes.

Below is the sonified video for the phased light curve for this rotating ellipsoidal binary variable. The best fit rotation period is found to be 2.57 hours. In the video, you should hear two full phases, where one minimum is deeper (fainter) than the other. 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 rotating ellipsoidal binary variable. 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 3800 to 7200 angstroms. Lower pitch represents weaker flux. The spectrum will gradually increase in flux (pitch) as wavelength increases. This binary’s spectrum peaks at redder wavelengths, which means it is cool and likely composed of dwarf stars.

This ELL, J163713.87+423703.7 was targeted for SDSS-IV spectroscopy as a variable in the TDSS project (Roulston in prep.). The light curve is an optical r-band from the ZTF.