The Case For Visual Observations of Variable Stars

1. The Case For Visual Observations of Variable Stars Presented to the Northwest Suburban Amateurs February 10, 2012 By Roger S. Kolman, Ph.D.

2. What Is The AAVSO? • American Association of Variable Star Observers. • Founded in 1911. • Cambridge, Massachusetts. • International non-profit organization. • 1200 members, 2500 observers.

3. What Does The AAVSO Do? • Observe, study and analyze variable stars. • Collect and archive variable star data for scientists, educators and the public to use. • Enable amateur astronomers to collaborate with professional astronomers. • Promote scientific education and research.

4. What Are 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). • Cepheids (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. 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.

9. Why Do We Observe Variables? • Most AAVSO observers start doing variables because they want to contribute to science. • In the end, they get hooked and stay because it is a lot of fun.

10. Methods of Observing Variables • Visual. • Photographic. • Photoelectric Photometry (Single Channel). • CCD (Multiple Channel). • Spectroscopy (Continuous Across Spectrum).

11. Advantages of Visual Observations • Short learning curve. • Observers already have skills. • Relatively inexpensive. • Naked Eye, binoculars, small telescopes. • Quick response. • See it, Estimate it, Report it. • More targets reached per session. • Find it, observe it, move on to next target.

12. Advantages of Visual Observations • Technology does not change with time. • Visual data provides self-consistent ongoing record. • For stars embedded in nebulae – differentiate. Examples – R Aqr, T Tau. • Can differentiate close doubles. • Professionals WANT them. • Over 5000 requests per year.

13. How Do Visual Observations and CCD Observations Compare? • Visual accuracy 0.1 magnitude. • Errors tend to randomize. • Signals can be tweaked out. • CCD accuracy 0.01 magnitude. • Not necessary for larger variations. • Depends on processing technique.

15. How Do Surveys Affect Us? • All Sky Automated Survey (ASAS-3) • Gives us new targets to observe. • Limited to 8.0 – 13.0 magnitude. • Avoids stars near horizon early evening & morning. • Avoids crowded star fields. • Not appropriate for rapidly changing and transient phenomena.

16. Program Stars For Visual Observers • The Bright Realm • Variables Near Deep Sky Objects • Legacy Stars • The Faint Realm • Rare Events • Transient Events • Campaign Targets • Away From Surveys

17. The Bright Realm • 100’s of Miras, Cepheids, 8th magnitude or brighter. • Under-observed – valuable work. • Example: Ed Oravec (right)

18. Variables Near Deep Sky Objects • W Her near M13. • EG And near M31. • CH UMa and R UMa near M81 & M82. • S Ori near M42. • While Visiting Old Friends – Observe a Variable – Make New Friends!

19. Legacy Stars • Regular observations for 100 years or more. • Increase frequency precision for stable periods. • Uncover long term changes in behavior.

20. Example - Mira

21. Example - Chi Cygni

22. Example – SS Cygni

23. Example – R CrB

24. Example - Betelgeuse

25. Finally – T UMi – Poster Boy ForEvolutionary Change!

26. The Faint Realm • Miras with minima < 13th magnitude. • Monitor Cataclysmic Variables with maxima <13th magnitude. • Monitor “Flickering” in CVs at minima. • Need dark skies/large aperture.

27. Rare Events & Transient Events • R CrB Stars in outburst • Only 23 known in this class • Recurrent Novae • Examples: RS Oph, T CrB • Galactic Novae • Nearly all events caught by visual observations

28. Campaign Targets • Requests from professional astronomers. • Multiband observations with space based instruments & large ground based telescopes.

29. Away From The Stare of Surveys • Low on the horizon • West after sunset • East before sunrise • Reduces gaps in data • Circumpolar Stars • Remotes have difficulty pointing near the poles. • Can only cover half of circumpolar region from site. • Milky Way • Quality results in crowded areas difficult because of pixel quality.

30. That Is Our Story… • Learn to star hop like a MONSTERobserving variable stars. • The most interesting things to look at are those that change. • The Sun, planets, comets. • VARIABLE STARS! • Are you looking for a challenge? • Do you need a motivation to get that telescope out of the closet? • Have fun, expand your horizons, and contribute to science. • Observing Variable Stars is Fun and Rewarding! • The AAVSO Wants YOU! • Visit aavso.org for more information

31. Be a Part of the ‘Story’