Pulsating Variables
Pulsating Variables (puls)¶
Pulsating variables are stars whose brightness variations are caused by periodic expansion and contraction of the stellar envelope. Pulsation is driven by opacity-related instabilities (the kappa mechanism) in specific temperature and luminosity regimes, defining the classical instability strip in the HR diagram.
Classification and numbers¶
- Supertypes
- variable
- periodic
- Subtypes
- RR Lyrae (rrlyr): horizontal branch pulsators, P = 0.2-1 d
- Delta Scuti (dscu): main sequence / subgiant A/F pulsators, P = 0.03-0.3 d
- Classical Cepheids (ceph): young supergiant pulsators, P = 1-100 d
- Long Period Variables (lpv): cool luminous giants, P = 100-1000 d
- Occurrence rate: very common; pulsators are among the most numerous periodic variables in ZTF
Description¶
Pulsating stars occupy distinct regions of the HR diagram depending on their evolutionary state, mass, and pulsation mode. The instability strip runs from the luminous Cepheids down through RR Lyrae and Delta Scuti stars, while long-period variables (Miras, semiregulars) occupy the red giant branch and asymptotic giant branch.
The pulsation period is set by the stellar mean density: more luminous (larger) stars pulsate with longer periods. This period-luminosity relation makes pulsators valuable distance indicators.
Light curve characteristics¶
- Strictly periodic (though some show amplitude/phase modulation)
- Light curve shape varies by subtype:
- Sawtooth (steep rise, slow decay): RR Lyrae ab, fundamental-mode Cepheids, Delta Scuti
- Sinusoidal: RR Lyrae c, overtone Cepheids, Miras
- Semiregular: LPV semiregulars with cycle-to-cycle amplitude variations
- Amplitude ranges from millimagnitudes (low-amplitude Delta Scuti) to several magnitudes (Miras)
- Bluer bands typically show larger amplitudes
Period ranges by subtype¶
| Subtype | Period Range | Amplitude | HR Diagram Location |
|---|---|---|---|
| Delta Scuti | 0.03-0.3 d | 0.05-0.3 mag | Main sequence / subgiant, A/F type |
| RR Lyrae | 0.2-1 d | 0.3-1.0 mag | Horizontal branch, A/F type |
| Cepheid | 1-100 d | 0.3-0.8 mag | Supergiant, F/G/K type |
| LPV (Mira) | 100-1000 d | >1 mag | AGB, M type |
| LPV (Semiregular) | 20-1000 d | 0.1-2 mag | RGB / AGB, K/M type |
References and further reading:¶
- Sterken & Jaschek, Light Curves of Variable Stars: A Pictorial Atlas
- Catelan & Smith, 2015, Pulsating Stars, Wiley-VCH
- Rimoldini et al., 2019, A&A 625 A97, Gaia Data Release 2: All-sky classification of high-amplitude pulsating stars arxiv:1811.03919