uv ceti stars jessica windschitl atmospheres spring 2007
TRANSCRIPT
UV Ceti StarsUV Ceti StarsJessica Windschitl
Atmospheres Spring 2007
OverviewOverview
Red Dwarf System Gliese 623b (from NASA/HST)
History
Characteristics
UV Ceti flares
Atmospheres
Hydrogen
Magnetic Fields
Spots
HistoryHistory
September 25, 1948 Flares observed on Luyten 726-8 By Joy & Humason or Luyten?
Luyten 726-8 (UV Ceti) becomes prototype for the flare stars
Initially various ideas for the cause of flaring (Gershberg 1967) Asteroids (Hertzsprung) Matter capture Surface nuclear reactions
Stars with FlareStars with Flare
UV Ceti Stars are Main Sequence M type Stars(Petterson 1989)
Recall…Recall…
M dwarf = low mass= slow evolution
= deep convection zones= low luminosity = low
temperature= MOLECULES!
Problems Problems Already!Already!
Other Characteristics Other Characteristics
Estimated 4.2x109 UV Ceti stars (Mirzoyan et. al. 1988)
Most are binaries
Majority are dMe stars
H, Ca, He lines indicate chromosphere
NLTE (Vardya 2003)
Can be observed from radio to x-ray (Petterson)
A “Typical” Flare A “Typical” Flare
3 Phases Pre-flare
45s
Flash phase 12s rise 18s decay
Slow Phase 35s rise Several minute
decay(Haupt & Schlosser 1974)
Image of a Flare Image of a Flare
GJ 3685A observed by GALEX on April 24, 2004
One of the Largest UV Flares ever observed
Consists of 2 flares occurring over a period of 20 minutes
Brightness increase of several orders of magnitude from quiescence
Photo from NASA Jet Propulsion Laboratory
The Atmosphere The Atmosphere
Chromosphere most significant region for flare stars
Ca H, K lines are weak (red stars!) Enhanced during flares
H lines indicate chromosphere in cool stars Also see lines similar to solar chromosphere
H- and molecular bands provide opacity (Vardya)
Line blanketing
Connection between Balmer emission and flaring? (Cram & Mullan 1979)
The SpectrumThe Spectrum
AD Leo
Hydrogen Hydrogen
H alpha profile observed by Petterson and Coleman
Note asymmetry of the line toward blue and central absorption
Hydrogen Hydrogen
Flaring
Non-Flaring
Petterson & Coleman
Magnetic Fields and Magnetic Fields and Rotation Rotation From solar studies, we know a little about flares (not
much!)
Flares are believed to be magnetic effects
Breaking and reconnecting of B field lines creates intense energy output
Convection and Rotation may play a role in both solar and stellar dynamos (Petterson)
TRACE
BY Draconis Syndrome BY Draconis Syndrome
Small scale luminosity fluctuations observed
Thought to be caused by starspots
Indicates stellar rotation
Rotations of 5-20 km/s measured (Petterson)
NSO/NOAO
In Conclusion In Conclusion
Flare stars are HARD to observe
Atmospheres of flare stars are HARD to model
Flares themselves are HARD to understand
Much work to be done!
ReferencesReferences
Cram, L.E. and Mullan, D.J. ApJ 234, pp 579-587, Dec. 1979.
Gershberg, R.E. Soviet Physics Uspekhi vol. 10 no. 3, 1967.
Haisch et. al. Ann. Reviews Astron. Astro. 1991.
Haupt, W. and Schlosser, W. Astron. & Astrophys. 37, pp 219-223, 1974.
Mauas, P. and Falchi, A. Astron. & Astrophys. 281, pp 129-138, 1994.
Mirzoyan et. al. Astrofizica vol. 29,1988.
Petterson, B.R. Solar Physics vol. 121 pp 299, 1989.
Petterson, B.R. and Coleman, L.A. ApJ 251, pp 571-582, Dec. 1981.
Vardya, M.S. Ann. Reviews Astron. Astro. 2003.
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