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VStar, Citizen Sky and the intriguing Epsilon Aurigae

VStar, Citizen Sky and the intriguing Epsilon Aurigae. David Benn Feb 2010. Outline. VStar multi-platform, open source, easy-to-use, variable star visualisation and analysis tool Citizen Sky collaboration between amateurs, professionals, educators to understand...

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VStar, Citizen Sky and the intriguing Epsilon Aurigae

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  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/

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

  5. 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.

  6. Yeah, that’s me hiding

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

  8. CSV, TSV files VStar AAVSO International Database VSX (Variable Star Index)

  9. 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)

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

  11. 1999 2010 1979 1987 All U Sco data annotated with outbursts in VStar

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

  13. 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 http://www.youtube.com/watch?v=hhMeumI36BM Chi Cygni

  14. http://www.citizensky.org/forum/w-uma-another-eclipsing-binary-starhttp://www.citizensky.org/forum/w-uma-another-eclipsing-binary-star W Uma (W Ursae Majoris)Contact binary star8 hour period!

  15. 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!

  16. 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

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

  18. Capella & The Kids

  19. 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)

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

  21. 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)

  22. 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)

  23. 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

  24. Text

  25. Epsilon Aurigae: last eclipse

  26. Epsilon Aurigae

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

  28. 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.

  29. 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.

  30. 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.

  31. 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.

  32. 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.

  33. 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.

  34. 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.

  35. 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.

  36. 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.

  37. 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.

  38. 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.

  39. http://www.nicolascretton.ch/Astronomy/images/HR_post_MS_sun_track.jpghttp://www.nicolascretton.ch/Astronomy/images/HR_post_MS_sun_track.jpg

  40. 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.

  41. http://www.skyandtelescope.com/news/80730537.html 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

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