VStar, Citizen Sky and the intriguing Epsilon Aurigae

David BennFeb 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...

•Epsilon Aurigae (more later...)

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/

Citizen SkyVStar Team

•AAVSO staff

•myself (lead developer)

•other Citizen Sky participants

•See VStar About Box for credits

•Jan 2010 VStar AAS poster paper

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.

Yeah, that’s me hiding

Michael Umbricht(Brown University, Rhode Island;

tester, domain expert, evangelist)

VStarVStarVStarVStar

AAVSO AAVSO InternatioInternatio

nal nal DatabaseDatabase

AAVSO AAVSO InternatioInternatio

nal nal DatabaseDatabase

VSXVSX(Variable (Variable

Star Star Index)Index)

VSXVSX(Variable (Variable

Star Star Index)Index)

CSV, CSV, TSV TSV filesfiles

CSV, CSV, TSV TSV filesfiles

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)

U ScorpiiRecurrent Nova in outburst

Predicted by Dr Bradley SchaeferRapid 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

All U Sco data annotated with outbursts in VStar

1979

1987

1999 2010

2010 U Sco outburst

Jan 28

Jan 27

Feb 2

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

W Uma (W Ursae Majoris)Contact binary star

8 hour period!

http://www.citizensky.org/forum/w-uma-another-eclipsing-binary-star

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!

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

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

Capella & The Kids

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)

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

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)

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)

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

Text

Epsilon Aurigae: last eclipse

Epsilon Aurigae

By Nico Camargo and courtesy www.citizensky.org

By Brian Thieme and courtesy www.citizensky.org

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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

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.

•“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

VStar Links

•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://www.citizensky.org/forum/citizen-sky-or-eps-aur-posters-presented-january-2010-aas-meeting

Other Tools

•http://www.aavso.org/data/software/

•http://www.assa.org.au/sig/variables/software.asp

•http://www.peranso.com/

Epsilon Aurigae References

•Hopkins & Stencel, 2008, Epsilon Aurigae

•http://www.aavso.org/vstar/vsots/eps_aur.shtml

•http://www.citizensky.org/forum/history-and-evolution-disk-theory-epsilon-aurigae

•http://www.citizensky.org/forum/unanswered-questions-one-step-journey-thousand-steps

•http://www.citizensky.org/ (in general)

Epsilon Aurigae References

•See also http://www.spacedaily.com/reports/Close_Up_Photos_Of_Dying_Star_Show_Our_Sun_Fate_999.html

•http://media.skyandtelescope.com/documents/MysteryOfEpsilonAur.pdf

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

•http://www.springerlink.com/content/l7vr2674168p3760/

U Sco References

•http://www.skyandtelescope.com/news/83025892.html

•http://simostronomy.blogspot.com/

•https://sites.google.com/site/aavsocvsection/