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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