RR Lyrae
The RR Lyrae stars are pulsating giant stars. They are bluer than the Sun, with an A or F spectral type. While they have a mass only about half the Sun's, as giants, they are forty to fifty times as bright. RR Lyrae have typical pulsation periods of about half a day. Based on the shape of their light curves, they are conventionally divided into three main types. Below each brief description are links to videos of a phased light curve and an optical spectrum for that type of RR Lyra star. RRab variables are the most common, making up 91% of all observed RR Lyrae, and display the steep rise in brightness typical of RR Lyrae. RRc are less common, making up 9% of observed RR Lyrae, and have shorter periods and more sinusoidal variation RRd are rare, double-mode pulsators, with two overlapping pulsation periods.
RRd-type RR Lyra
Below is a video with sound of the observed light curve of a RRd-type RR Lyra. This video scans across a plot of brightness measured in magnitudes (y axis) versus time (x axis), in Modified Julian Days or M.J.D. Brighter magnitudes are represented by higher pitches. The 1 minute 11 second video corresponds to measurements made across about 600 days, so time is compressed in the video by a factor of about 73,000. Some of the gaps between measurements are large during the season when this star was not visible at night.
Below is a video with sound of the phased light curve of a RRd-type RR Lyra. This video scans across a plot of brightness measured in magnitudes (y axis) versus phase (x axis), covering two periods. The period for this RR Lyra is 9.2 hours, and the amplitude of variability is 0.5 magnitudes.
Below is a video with sound of the optical spectrum of a RRd-type RR Lyra star. This video scans from blue to red 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. An RR Lyra stellar spectrum is typically blue, so the flux gets weaker (and the audio pitch lower) moving along the spectrum toward the red end. Strong absorption lines of hydrogen can be seen and heard in the spectra of RR Lyrae stars.
This RR Lyra D, J171344.82+352756.1 was targeted for SDSS-IV spectroscopy as a variable in the TDSS project (Roulston in prep.). The light curve is an optical g-band from the ZTF.
RRc-type RR Lyra
Below is a sonified video of photometric observations of a RRc-type RR Lyra. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Higher pitch represents brighter magnitude. The 1 minute long video contains 105 measurements made across about 500 days, where each second in the video corresponds to over 8 days in real time. During the first half of the video an extended silence can be heard during the season when this star is not visible at night.
Shown next is the phased light curve for a RRc-type RR Lyra star. Listen and hear two full phases, each consisting of the secondary minimum followed by the primary minimum with smooth transitions in between the two eclipses. One phase corresponds to a period of about 8 hours, while the amplitude of variability is 0.5 magnitudes. The video scans over phase (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes. The phased light curve is almost perfectly sinusoidal, which is heard as regular variation in brightness.
Below is the spectrum for the observed RRc-type RR Lyra star. 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 decrease in flux (pitch) as wavelength increases, punctuated by large dips in flux corresponding to hydrogen absorption lines.
This RR Lyra C, J153306.36+365042.9 was targeted for SDSS-IV spectroscopy as a variable in the TDSS project (Roulston in prep.). The light curve is an optical g-band from the ZTF.
RRab-type RR Lyra
Below is a sonified video of photometric observations of a RRab-type RR Lyra. The 48 second long video contains 71 measurements across nearly 400 days. Each beat corresponds to 1 day in real time. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Higher pitch represents brighter magnitude. During the second half of the video an extended silence can be heard during the season when this star is not visible at night. No discernible trends can be heard in this video, but the listener gains a good idea for how much the star varies in brightness.
Shown next is the phased light curve for a RRd-type RR Lyra star. Listen and hear two full phases, each consisting of the secondary minimum followed by the primary minimum with smooth transitions in between the two eclipses. One phase corresponds to a period of about 12 hours, while the amplitude of variability is 1.5 magnitudes. The video scans over phase (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes. During one phase, the RRd-type RR Lyra star first exhibits small oscillations around a baseline brightness of about 16.8 magnitudes, then a pulsation event occurs and the brightness increases rapidly to about 15.4 magnitudes, before dimming linearly back to the baseline.
Below is the spectrum for the observed RRd-type RR Lyra star. 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 decrease in flux (pitch) as wavelength increases, punctuated by large dips in flux corresponding to hydrogen absorption lines.
This RR Lyra AB, J080123.37+533537.8 was targeted for SDSS-IV spectroscopy as a variable in the TDSS project (Roulston in prep.). The light curve is an optical g-band from the ZTF.
Please send us your comments, feedback or suggestions! CONTACT US: sdu@cfa.harvard.edu