YOUR most Important assets are TIME & ENERGY

1. YOUR most Important assets are TIME & ENERGY • To deploy this well requires some strategic thinking • So you should always have 3 questions in mind when listening to • Someone talking about their work • Why is this study Important / Interesting / Useful • Why is it being done here (ie at Arecibo) • Why is it being done now I hope you have got the answers for this talk by its end

2. Time Varying OH / IR Stars Murray Lewis

3. Introduction What are OH / IR Stars Their place in stellar evolution Some properties Examples of dramatic changes in OH 1612 MHz intensity Shell detachment and the time-scale for NIR-color evolution

4. General Refs. review Michael Feast in“Late Stages of Stellar Evolution” p33 or a thesis Peter te Lintel-Hekkert“The Evolution of OH/IR Stars & their Dynamical Properties”

10. Circumstellar Envelopes of Late-type Stars • Mira variables and OH/IR stars lose mass copiously to interstellar space • and so generate DUSTY circumstellar shells (CSs). • DUST • Reprocesses their luminosity to mid-IR radiation (5 - 100 µm) • Protects outflowing molecules against rapid photo-degradation by interstellar UV ==> chemical changes in the gas, and masers • CSs mediate the return of a star’s mass to space, and so are studied • to determine dM/dt, and its relation to the Galactic gas economy • for insight into Why/How mass-loss occurs • for the diversity of phenomena in these shells

11. Most stars lose mass before the SN stage is reached the mass losing stage is the red-giant stage if core mass reaches ~1.4 Mo --> SN otherwise star evolves through the planetary nebula phase to become a white dwarf HOW do we know? when dM/dt is large enough DUST forms in the outflowing wind intercepts stellar radiation and reradiates it in the IR == we see the IR signature, and often masers Masers may be SiO at 43 & 86 GHz, water at 22 GHz, and OH at 1.6 GHz

12. Pulsating RED GIANTS are the life-stage where the central ~0.55 - 0.6 Mo core is stabilzed against collapse by e-- degeneracy The core is a white dwarf (size == Earth) swaddled by a stellar atmosphere that reaches out almost to the orbit of Mars and pulsates (period is typically 200 - 1000 days) H-burning continues in an annular shell around the core L ~ 2,000 - 50,000 Lo Visual brightness changes around pulsation cycle by factors of 10 - 100 AND IR excess implies dM/dt > 0 (typically 10-7 to 10-4 M0/yr {most dust formation in our Galaxy is from red giants: ~50% of their mass is returned to the interstellar medium}

17. Stellar Evolution • Normal Main Sequence Stars • H-burning • Long-lived stage • Variable Stars • Particularly red giants • ∆L ~ 10 - 100 L • Periods 200 - 1000 days • White Dwarfs • Very hot & dense & tiny • Supported against collapse by e- degeneracy • Mass ~ 0.6 Mo • Super Novae • Once only catastrophe • L --> 10 9 Lo • rare

19. Stellar Evolution • Normal Main Sequence Stars • H-burning • Long-lived stage • Variable Stars • Particularly red giants • ∆L ~ 10 - 100 L • Periods 200 - 1000 days • White Dwarfs • Very hot & dense & tiny • Supported against collapse by e- degeneracy • Mass ~ 0.6 Mo • Super Novae • Once only catastrophe • L --> 10 9 Lo • rare

21. Stellar Evolution • Normal Main Sequence Stars • H-burning • Long-lived stage • Variable Stars • Particularly red giants • ∆L ~ 10 - 100 L • Periods 200 - 1000 days • White Dwarfs • Very hot & dense & tiny • Supported against collapse by e- degeneracy • Mass ~ 0.6 Mo • Super Novae • Once only catastrophe • L --> 10 9 Lo • rare

28. FV Boo 1985 1612 MHz

29. Period ~472 d

30. RED peak half-life 1.0 year

31. FV Boo

32. FV Boo

33. FV Boo

34. FV Boo

39. Comparison of model constant dM/dt shells with OH/IR stars

41. BLUE half-life 7.5 years