1. VStar, Citizen Sky and the intriguing Epsilon Aurigae David Benn Feb 2010

2. Outline VStar multi-platform, open source, easy-to- use, variable star visualisation and analysis tool Citizen Sky collaboration between amateurs, professionals, educators to understand... Epsilon Aurigae (more later...)

3. Citizen Sky Under IYA, but continuing beyond Focus: current Epsilon Aurigae eclipse citizen (US) = volunteer or amateur 10-star tutorial, posts, teams, workshops http://www.citizensky.org/

5. Citizen Sky VStar Team AAVSO staff myself (lead developer) other Citizen Sky participants See VStar About Box for credits Jan 2010 VStar AAS poster paper

6. VStar Conversation with Arne Henden (AAVSO Director) at NACAA 2008. Java replacement for Grant Foster’s DOS program. Collaboration with AAVSO and Citizen Sky participants since May 2009. Early demo given in Aug 2009 at first Citizen Sky workshop at Alder Planetarium, Chicago. Frequent releases since Dec 2009; formal phase 1 release in near future.

8. Yeah, that’s me hiding

9. Michael Umbricht (Brown University, Rhode Island; tester, domain expert, evangelist)

12. VStarVStar AAVSO Internation al Database VSX (Variable Star Index) VSX CSV, TSV files

13. VStar Demo of VStar features using these stars: U Scorpii Chi Cygni W Uma Delta Dephei (added plot images on subsequent slides since I gave this talk for people not present at the ASSA meeting)

14. U Scorpii Recurrent Nova in outburst Predicted by Dr Bradley Schaefer Rapid magnitude rise and fall https://sites.google.com/site/aavsocvsection/ Not U Sco, but another similar system: Artist’s rendition of recurrent nova RS Oph Image credit: David Hardy and PPARC Barbara Harris Shawn Dvorak

15. All U Sco data annotated with outbursts in VStar 1979 1987 1999 2010

16. 2010 U Sco outburst Jan 28 Jan 27 Feb 2

17. Chi Cygni http://www.youtube.com/watch?v=hhMeumI36BM http://en.wikipedia.org/wiki/Chi_Cygni Mira type pulsating variable post-Asymptotic Giant Branch Star (late stage red giant) 5th to 13th magnitude period: ~407 days

20. W Uma (W Ursae Majoris) Contact binary star 8 hour period! http://www.citizensky.org/forum/w-uma-another-eclipsing-binary-star

23. VStar’s Future Period analysis, time panning (in database mode), better zoom control, search,... NACAA 2010 workshop and poster Use it! Free Citizen Sky sign up. Give feedback. Ask for features, fixes! It’s open source dude... Develop, test, document... Volunteers welcome!

24. Epsilon Aurigae Bright (~3rd mag) star in northern constellation Auriga. 11º altitude from SA on Dec 19 2009. Variability first noticed by Johann Fritsch, a German amateur in 1821. Distance: 625 parsecs

25. Epsilon Aurigae (circled) from Adelaide, 20 Dec 2009 at 0030

26. Capella & The Kids

27. Epsilon Aurigae Eclipsing binary variable inclination: 89º orbital separation: 18 to 20 AU period: 27.1 years duration: almost 2 years (more on this later)

28. Current Epsilon Aurigae eclipse began in August 2009 courtesy www.citizensky.org Minimum: December 2009 (maybe) Mid-eclipse: August 2010 Minimum light ends: March 2011 Eclipse ends: May 2011

29. Epsilon Aurigae Harlow Shapley (1928) concluded: primary F star being eclipsed by a companion of similar mass with little out-of-eclipse spectroscopic signature (i.e. an almost unseen companion)

30. Epsilon Aurigae Out-of-eclipse F-star magnitude variations 1984..1987: 96 days 2003..2004: sped up to 71 days 2007..2008: 65 days Out of Eclipse variations make it hard to determine when totality is reached; not completely understood. “Where’s my totality dude?” (Dr Bob, Citizen Sky)

31. Epsilon Aurigae Companion changing on timescale of decades 1901..1983 time of minimum increased from 313 to 445 days eclipse duration decreased from 720 to 640 days

32. Text

33. Epsilon Aurigae: last eclipse

34. Epsilon Aurigae

35. By Nico Camargo and courtesy www.citizensky.org By Brian Thieme and courtesy www.citizensky.org

36. Epsilon Aurigae Ludendorff (1912): companion: a swarm of meteorites Kuiper, Struve, Stromgren (1937): Primary F star eclipsed by large semi- transparent IR star Flat-bottomed light curve caused by scattering in IR star’s atmosphere. But, electron density too low to account for such scattering.

37. Epsilon Aurigae Schoenberg and Jung (1938) Proposed cool companion star. Permitted solid particles to cool during star’s convective process, before falling, reheating, and breaking apart. But, spherical shell of such particles wouldn’t lead to flattening during totality.

38. Epsilon Aurigae Kopal (1954) First to propose a flat semi-transparent disk as F-star’s companion: radius: ~6 AU opacity: 0.8 water or light hydrocarbons Good agreement with observations.

39. Epsilon Aurigae Huang (1965) First analytical model supporting disk as F-star’s companion. Gas block-like structure, physically and optically thick. Model agreed with light curve shape. Pointed to possible disk asymmetry. Subsequent theories extend or slightly modify Huang’s.

41. Epsilon Aurigae Cameron (1971) Tried to explain why disk exists and is stable by suggesting a black hole in the system (paper in Nature). No evidence from X-ray studies.

42. Epsilon Aurigae Wilson (1971) Simulation of light curve from Huang’s model. Noted that a thick disk produces flat bottomed light curve during eclipse. 1955: mid-eclipse brightening. Proposed physically thin, optically thin disk with central opening.

43. Epsilon Aurigae Eggleton & Pringle (1985) Proposed binary star system inside disk to explain long-term disk stability. Suggested two mass models: High: F-star is super-giant. Low: F-star is more like AGB and disk is overflow remnant.

44. Epsilon Aurigae Schmidtke (1985) Considered possibility of gravitational lense as cause of ~0.2 magnitude mid- eclipse brightening. Found that even in high-mass case (Eggleton & Pringle) angle observed from Earth is not sufficient to explain mid-eclipse brightening.

45. Epsilon Aurigae Kemp & Henson (1983, 1986) Out-of-eclipse variation analysis (Henson) evidence of F-star non-radial pulsations In-eclipse variation analysis (Kemp) disk tilted with respect to orbit orbit crosses F-star just above star’s middle.

46. Epsilon Aurigae Ferluga (1990) Tweaked Huang’s model by proposing that disk is series of rings with Cassini- like division to explain mid-eclipse brightening. Doesn’t explain older observations. Instead, disk may be undergoing rapid changes. Investigation required.

47. Epsilon Aurigae Hoard et al (2010 AAS) Spitzer space telescope observations. F-star “only” 2 to 3 solar masses still nearly 300 suns across so, actually a post-Asymptotic Giant Branch star Companion Middle-B dwarf star, 15,000K, 5.9 solar masses.

48. http://www.nicolascretton.ch/Astronomy/images/HR_post_MS_sun_track.jpg

49. Epsilon Aurigae Hoard et al (2010 AAS) Disk: < 1 solar mass 550K 8 AU x 0.5 AU Better handle on physical characteristics, but questions remain.

50. In this artist's concept, Epsilon Aurigae (the supergiant star at right) is starting to be eclipsed by the dust disk circling a single, much dimmer B star. A new model explains the decades-old paradoxes of this system by assuming that its stars are relatively old, not young. NASA / JPL-Caltech http://www.skyandtelescope.com/news/80730537.html

51. Epsilon Aurigae Some open questions: What is the source of the out of eclipse variations? F-Star? Disk? What is the disk made of and exactly how massive? What is the interface between inner part of disk and the B star.

53. “The history of Epsilon Aurigae is basically the history of modern astrophysics” (Brian Kloppenborg). Many of the history slides above taken from Brian’s Citizen Sky disk history article (see references). A rare glimpse into early system formation. Small variations during totality can be used to map out disk structure. Epsilon Aurigae: Summary

54. VStar Links http://dbenn.wordpress.com/2009/08/21/ citizensky-workshop-and-vstar-software/ http://dbenn.wordpress.com/2009/08/21/ citizensky-workshop-and-vstar-software/ https://sourceforge.net/projects/vstar/ http://dbenn.wordpress.com/2009/12/31/ vstar-development-update/ http://dbenn.wordpress.com/2009/12/31/ vstar-development-update/ http://www.citizensky.org/forum/citizen- sky-or-eps-aur-posters-presented- january-2010-aas-meeting http://www.citizensky.org/forum/citizen- sky-or-eps-aur-posters-presented- january-2010-aas-meeting

55. Other Tools http://www.aavso.org/data/software/ http://www.assa.org.au/sig/variables/soft ware.asp http://www.assa.org.au/sig/variables/soft ware.asp http://www.peranso.com/

56. Epsilon Aurigae References Hopkins & Stencel, 2008, Epsilon Aurigae http://www.aavso.org/vstar/vsots/eps_au r.shtml http://www.aavso.org/vstar/vsots/eps_au r.shtml http://www.citizensky.org/forum/history- and-evolution-disk-theory-epsilon- aurigae http://www.citizensky.org/forum/history- and-evolution-disk-theory-epsilon- aurigae http://www.citizensky.org/forum/unanswe red-questions-one-step-journey- thousand-steps http://www.citizensky.org/forum/unanswe red-questions-one-step-journey- thousand-steps http://www.citizensky.org/ (in general) http://www.citizensky.org/

57. Epsilon Aurigae References See also http://www.spacedaily.com/reports/Close _Up_Photos_Of_Dying_Star_Show_Our _Sun_Fate_999.html http://www.spacedaily.com/reports/Close _Up_Photos_Of_Dying_Star_Show_Our _Sun_Fate_999.html http://media.skyandtelescope.com/docu ments/MysteryOfEpsilonAur.pdf http://media.skyandtelescope.com/docu ments/MysteryOfEpsilonAur.pdf http://www.skyandtelescope.com/news/8 0730537.html http://www.skyandtelescope.com/news/8 0730537.html http://www.springerlink.com/content/l7vr2 674168p3760/ http://www.springerlink.com/content/l7vr2 674168p3760/

58. U Sco References http://www.skyandtelescope.com/news /83025892.html http://www.skyandtelescope.com/news /83025892.html http://simostronomy.blogspot.com/ http://simostronomy.blogspot.com https://sites.google.com/site/aavsocvse ction/ https://sites.google.com/site/aavsocvse ction/