Variable Stars and the Stories They Tell

1. Variable Stars and the Stories They Tell Mike Simonsen AAVSO C. E. Scovil Observatory

2. Stars: The Essential Building Blocks of the Universe

3. What is a Star? • Massive object, typically comprised of mostly Hydrogen gas • Balancing act between gravity’s contraction and nuclear burning’s expansion • Mass is the most important quantity of a star • Initial mass determines its life cycle

4. Variable Stars • Stars that vary in brightness • Time scales of seconds, hours, days, years or centuries • Understanding variable star behavior sheds light on other astronomical phenomena • General classifications or types

5. Pulsating variables • Light changes are related to the expansion and contraction of the star’s atmosphere • Miras (LPVs) • Cephieds (standard candles)

6. Eruptive variables • Novae • Dwarf Novae • Supernovae

7. Eclipsing variables • Eclipsing variables are not intrinsically variable • The change in brightness is due to a line of sight effect

8. Stellar Evolution:The Life Cycle of Stars

9. Star Birth • In the beginning a star condenses from a cloud of dusty interstellar gases • The life story of a star is the story of its perpetual attempt to contract As the pillars themselves are slowly eroded away by the ultraviolet light, small globules of even denser gas buried within the pillars are uncovered. These globules have been dubbed "EGGs." EGGs is an acronym for "Evaporating Gaseous Globules," but it is also a word that describes what these objects are. Forming inside at least some of the EGGs are embryonic stars — stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from whch they were drawing mass. Eventually, the stars themselves emerge from the EGGs as the EGGs themselves succumb to photoevaporation.

10. From A Cloud of Gas

11. A Star is Born

12. Orion NebulaNearby star forming region

13. Variable stars within one degree of M42

14. T Tauri type stars • T Tauri stars are named for the prototype of the class, T Tauri. These objects are pre-main sequence stars and have recently emerged from the opaque envelope of stellar formation. Having recently coalesced from their dusty and gaseous surroundings, these stars now become visible at optical wavelengths. • Our own Sun presumably passed through the T Tauri stage some 4 1/2 billion years ago. Therefore, these stars may be able to offer us a peak into the evolution of our own Sun, solar system, as well as other planetary systems.

15. Middle Age • As stars evolve to middle age, they, just like people, tend to swell at the waist. • The instability strip on the H-R diagram represents stars in transition from one phase of their lives to another. • Many M class stars are red giants. Pulsating variable stars, like Mira.

16. Old Age:Planetary Nebulae • Planetary nebulae are formed when a red giant star ejects its outer layers as clouds of luminescent gas, revealing the dense, hot, and tiny white dwarf star at its core. • 95% of all stars that we see in our own galaxy will ultimately become "planetary nebulae". This includes the Sun.

17. Our Future Sun

18. V838 Mon • Originally classified as a nova, V838 Mon may be an entirely new class of nova. Luminous Red Nova (LRN) • Other potential explanations: • Thermal pulse of a dying star • Thermonuclear event within a massive supergiant • Mergeburst • Planetary capture event

19. Binary Star Systems • Stars in close proximity to each other can influence the evolutionary development of their partner • Symbiotic variable stars and cataclysmic variables

20. Cataclysmic Variables

21. Death and Destruction

22. Seeding the Universe • All the heavy elements in the universe were created inside the bowels of stars that have long since blown up or blown off their atmospheres. • We are indeed “stardust”. • We owe our very existence to variable stars.

23. Modeling Larger Scale Phenomena • Accretion disks • Star formation • Planetary formation • Galaxy formation • Active galactic nuclei • Black holes

24. The Search For Life • Find extra terrestrial planets • Exoplanet searches • Exoplanet transit observations • Serendipitous discoveries of variable stars

25. Amateur Contributions to Science • AAVSO – American Association of Variable Star Observers • Monitor pulsating variables • Observing cataclysmic variables • Timing eclipsing variables and RR Lyrae stars • Chasing after GRB afterglows • Observing exoplanet transits

26. Be a Part of the ‘Story’

27. Thank you!