UV Ceti Stars

1. UV Ceti Stars Jessica Windschitl Atmospheres Spring 2007

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

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 (Petterson 1989) UV Ceti Stars are Main Sequence M type Stars

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

6. 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)

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.

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