1. UV Ceti Stars Jessica Windschitl Atmospheres Spring 2007

2. Overview Red Dwarf System Gliese 623b (from NASA/HST)  History  Characteristics  UV Ceti flares  Atmospheres  Hydrogen  Magnetic Fields  Spots

3. 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

4. Stars with Flare UV Ceti Stars are Main Sequence M type Stars (Petterson 1989)

5. Recall… M dwarf = low mass = slow evolution = deep convection zones = low luminosity = low temperature = MOLECULES! Problems Already!

6. 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)

7. A “Typical” Flare 3 Phases  Pre-flare  45s  Flash phase  12s rise  18s decay  Slow Phase  35s rise  Several minute decay (Haupt & Schlosser 1974)

8. 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

9. Photo from NASA Jet Propulsion Laboratory

10. 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)

11. The Spectrum AD Leo

12. Hydrogen H alpha profile observed by Petterson and Coleman Note asymmetry of the line toward blue and central absorption

13. Hydrogen Flaring Non-Flaring Petterson & Coleman

14. 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

15. 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

16. 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!

17. 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.

18. THANK YOU