Outline of Types of Variable Stars

1. Intrinsic - Internal physical changes due to pulsations or eruptions
• Pulsating Stars - Size and/or shape of star changes or “vibrates”
1. Cepheid Variables- Period is one to seventy days, strict period-luminosity relationship
2. RR Lyrae - Short pulsation period from .05 to 1.2 days with light variations between .3 and 2 magnitudes
3. RV Tauri Stars - Alternating deep and shallow minima
4. Long-period Variables (LPVs)
• Mira type - Giant red variables with well defined periods ranging from 80 to 1000 days
• Semiregular - Giants are periodic with intervals of irregular light variation
• Eruptive (Cataclysmic) Stars - Binary system consisting of one giant, and one white dwarf star that leads to “outbursts” of activity
1. Supernovae - Sudden, dramatic, final magnitude increase as result of stellar explosion
2. Novae - Thermonuclear fusion explosion increases brightness and then fades
3. Recurrent Novae - System that has undergone two or more nova-like eruptions in recorded history
4. Dwarf Novae - Close binary system made up of a Sun-like star, white dwarf, and accretion disk surrounding the white dwarf
• U Geminorum - Well-defined quiescence at minimum then erupt by 2 to 6 mag. for 5 to 20 days
• Z Camelopardalis - Similar to U Gem except no well-defined quiescence and has “standstills” of brightness
• SU Ursae Majoris - Similar to U Gem except have short orbital periods of less than two hours, and have two distinct outbursts that are both short (duration one to two days, faint and more frequent) and long (duration ten to twenty days, bright and less frequent)
5. Symbiotic Stars - Semiperiodic nova-like outbursts of up to three magnitudes
6. R Coronae Borealis - Go into outburst by fading and then return to maximum brightness
2. Extrinsic- Eclipse or stellar rotation
• Eclipsing Binaries - Binary star systems with an orbital plane lying near the line-of-sight of the observer. Members periodically eclipse each other, blocking one another’s light, causing the system to appear fainter during an eclipse, on earth
• Rotating Variables - Rotating stars vary light output due to dark spots or bright spots on the star’s surface