Presentation on theme: "UV Ceti Stars Jessica Windschitl Atmospheres Spring 2007."— Presentation transcript:
UV Ceti Stars Jessica Windschitl Atmospheres Spring 2007
Overview Red Dwarf System Gliese 623b (from NASA/HST) History Characteristics UV Ceti flares Atmospheres Hydrogen Magnetic Fields Spots
History 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 Flare UV Ceti Stars are Main Sequence M type Stars (Petterson 1989)
Recall… M dwarf = low mass = slow evolution = deep convection zones = low luminosity = low temperature = MOLECULES! Problems Already!
Other Characteristics Estimated 4.2x10 9 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)
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
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)
Magnetic Fields and 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 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 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!
References 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.