Variable Stars: Introduction

Pulsating Stars

These stars vary in luminosity caused by the star pulsating. The two forces at play are radiation pressure pushing outward and gravity squeezing inward. When the star is at its maximum diameter, radiation pressure is at a minimum, the temperature is low and gaseous velocity is zero. Gravity then makes the star contract, the pressure then increases, and so the temperature and the gaseous velocity. At its minimum diameter, the pressure will make the star “inflate.” The pressure and temperature and pressure will diminish and when the maximum diameter is reached, the whole process starts again. The repetition period is often vary irregular.

Cataclysmic Stars

The variations in luminosity in these stars increases abruptly following an eruption which effect all or part of the star’s atmosphere. This increase is accompanied by a rise in temperature and so by major variations in the spectra, when the maximum brightness has passed, the star dims and slowly cools.

Eclipsing Binary Stars

These stars vary in luminosity caused by occultation of one of a close pair of stars passes in front of the other, thus eclipsing it and reduce the total luminosity of the binary system.

Variable Stars: Principle Types of Variable Stars

Type Period Amplitude Number in Galaxy Remarks
Pulsating Variables
RR Lyrae0.2-1d0.5-1.56000Sp: A or F
Cepheids1-50d0.2-2.0About 700 in Milky Way,
1100 ea. in Megallanic Clouds,
more than 600 in Sculptor dwarf,
200 in Draco dwarf, 200 in Leo II
Sp:F or G, several types.
RV Tauri30-150d1.0-3.0100Sp: G or K
Semi-regular20-500d0.2-2.5SRA at least 1200, SRB 600,
Supergiants 60, Yellow (F, G, K) 50
Sp:M, C, S, several types
Long-period100-600d2.5-10more than 500Sp:M, C, or S
Irregularnon-periodic0.2-2.0 Sp:M, C, or S
Beta Canis Majoris0.1-0.5dLT 0.2more than 50Sp:B0-B4
Dwarf Cepheids0.05-0.25d0.5-1.0 Sp: A or F
Gamma Scutum0.05-0.2dLT 0.2more than 100Sp: A or F
Alpha Canum Venaticorum0.5-(100+)dLT 0.2 Sp: Peculiar A
ZZ Ceti1-15 minLT 0.05about 20 White Dwarfs
Cataclysmic Variables
Novae10-500d7-GT 15 Explosion of part of stellar atmosphere
Supernovae GT 20 Stellar explosion
Noviods   Several types
Dwarf Novae 2-6 Repeated explosions
Nebular Variables 1-4 Interaction with
gaseous nebula
Flare Stars 1-4  
Red Dwarfs 0.1-5 Sp: K or M. Flare stars
Eclipsing binary Variables
Algol Variables0.1-10000d0.1-3more than 3500All sp. present
Beta Lyrae0.5-200d0.1-1.5600Giants O, B and A
W Ursae Majoris0.2-1d0.2-1500Dwarfs F, G, or K