Stellar Chromospheres

Stellar chromospheres and transition regions contain the moderate temperature (5,000-500,000 K) gas located between the photosphere and corona. These regions are best studied using the emission lines they emit in the ultraviolet. We are analyzing HST spectra of active late-type stars and binary systems to develop models for these stars consistent with the data. Of special interest are stars that flare, RS CVn-type binary systems, and hybrid-chromosphere stars. The above figure shows a portion of the far-ultraviolet spectra of seven dwarf stars observed with the Far Ultraviolet Explorer (FUSE) spacecraft and a comparison solar spectrum obtained with the SUMER instrument on SOHO. Important emission lines of H I (Lyman series), He II, C II, C III, O VI, and S VI formed in the chromospheres and transition regions of these stars between 8,000 K and 300,000 K are indicated. Also shown is the Fe XVIII line at 977 A formed in the coronae of these stars. We are analyzing these data to understand the dynamics and energy balance in these stellar atmospheres. The first papers from this work are listed below.

Research Objectives:

• Analyze high resolution stellar UV spectra obtained with the GHRS and STIS instruments on HST and FUSE.
• Determine the physical properties and structure of the chromospheres of active and quiescent late-type stars and binary systems.
• Determine the physical properties and structure of the chromospheres of premain sequence stars.
• Study flare dynamics and energetics using high resolution UV spectra.

Recent Publications:

• Pagano, I., Ayres, T.R., Lanzafame, A.C., Linsky, J.L., Montesinos, B., \& Rodon\`o, M.: 2005, "Key problems in cool-star astrophysics", Special Issue NUVA (Network for Ultraviolet Astronomy) (Kluwer Academic publ.), to appear
• Dupree, A.K., Lobel, A., Young, P.R., Ake, T.B., Linsky, J.L., and Redfield, S.: 2005, "A far-ultraviolet survey of luminous cool stars", Astrophysical Journal, 622, 629
• Redfield, S. and Linsky, J.L.: 2004, "Monitoring Altair's far-ultraviolet emission lines for variability over a stellar rotation period", Proceedings of the 13th Cool Stars Workshop, Ed. F. Favata, ESA SP-560, 903
• Linsky, J.L.: 2004, "Summary for Cool Stars 13: internal and external connections", Proceedings of the 13th Cool Stars Workshop, Ed. F. Favata, ESA SP-560, 367
• Pagano, I., Linsky, J.L., Valenti, J., and Duncan, D.K.: 2004, "HST/STIS High Resolution Echelle Spectra of Alpha Centauri (G2 V)", Astronomy and Astrophysics, 415, 331
• Redfield, S., et al.: 2002, "A FUSE spectroscopic survey of late-type dwarfs", Astrophysical Journal, 581, 626
• Simon, T., Ayres, T.R., Redfield, S., and Linsky, J.L.: 2002, "Limits on chromospheres and convection among main sequence A stars", Astrophysical Journal, 579, 800
• Bloomfield, D.S., Mathioudakis, M., Christian, D.J., Keenan, F.P., and Linsky, J.L.: 2002, "Opacity in the upper atmosphere of AU Mic", Astronomy and Astrophysics, 390, 219
• Linsky, J.L.: 2002, "Summary of the Twelfth Cool Stars Workshop: Insights, Mysteries, and Action Items", in Cool Stars 12, Proceedings of Cool Stars 12, to appear
• Young, P.R., Dupree, A.K., Wood, B.E., Redfield, S., Linsky, J.L., Ake, T.B., and Moos, H.W.: 2001, "FUSE observations of Capella", Astrophysical Journal Letters, 555, L121
• Robinson, R.D., Linsky, J.L., Woodgate, B.E., and Timothy, J.G.: 2001, "FUV observations of flares on the dM0e star AU Microscopii", Astrophysical Journal, 554, 368
• Linsky, J.L., Redfield, S., Ayres, T.R., Brown, A., and Harper, G.: 2001, "Cool star chromospheres and the Sun" in Eta Carinae and other Mysterious stars, ed. T. Gull, S. Johansson, and K. Davidson, ASP Conf. Series, 242, 257
• Ake, T.B., Dupree, A.K., Young, P.R., Linsky, J.L., Malina, R.F., Griffiths, N.W., and Siegmund, O.H.W.: 2000, "FUSE observations of the active cool star: AB Dor", Astrophysical Journal Letters, 538, L87
• Pagano, I., Rodono, M., Linsky, J.L., Neff, J.L., Walter, F.M., Kovari, Z., and Mathews, L.D.: 2001, "Spectral imaging maps of AR Lacertae. I. Results from IUE observations in 1994, October, Astronomy and Astrophysics, 365, 128
• Valenti, J.A., Johns-Krull, C.M., and Linsky, J.L.: 2000, "An IUE atlas of pre-main-sequence stars: I., coadded final archive spectra from the SWP camera", Astrophysical Journal Supplements, 129, 329
• Johns-Krull, C.M., Valenti, J.A., and Linsky, J.L.: 2000, "An IUE atlas of pre-main-sequence stars: II., Far UV accretion diagnostics in T Tauri stars", Astrophysical Journal, 539, 815
• Pagano, I., Linsky, J.L., Carkner, L., Robinson, R.D., Woodgate, B., and Timothy, G.: 2000, "HST/STIS echelle spectra of the dM1e star AU Microscopii outside of flares'', Astrophysical Journal, 532, 497
• Linsky, J.L. "Cool star chromospheres and the Sun", invited talk at the International Conference on Eta Carinae and other Mysterious Stars, Hven, Sweden, August 25, 2000, Astronomical Society of the Pacific Conference Series, 242, 247
• Linsky, J.L.: "Empirical constraints on stellar dynamos", invited talk at the Workshop on Astrophysical Dynamos, Aspen CO, June 14, 2000
• Linsky, J.L.: 2000, "The Wilson-Bappu relation between Ca II emission and stellar luminosities", Astrophysical Journal, 525, 776