Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-25T17:19:24.855Z Has data issue: false hasContentIssue false
  • English
  • Français

Cool Stars in the EUV: Spectral and Structural Variability

Published online by Cambridge University Press:  12 April 2016

Alexander Brown
Alexander Brown*
Affiliation:
Center for Astrophysics and Space Astronomy, University of Colorado, Campus Box 389, Boulder, CO 80309-0389, USA

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

EUV observations of RS CVn binaries and M dwarf flare stars are used to illustrate the variability of coronal emission seen in EUVE spectra and photometry. The EUVE emission line spectra show that the quiescent coronae of active stars are extremely hot (≥10 million K) and flares, which are even hotter, are common. Spectral sequences showing the evolution of flare temperature and density are presented. Very high coronal electron densities (log Ne ~ 13) have been detected during M dwarf flares. EUVE data for the RS CVn binary HR1099 are compared with those from simultaneous observations in other spectral regions, including X-ray (ASCA), ultraviolet (IUE), and radio (VLA, AT) data. These combined data show that the peak coronal temperature is above the sensitivity of EUVE and that the time of maximum flare brightness is spectral region dependent.

Type
III. Coronae of Cool Stars
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 89 - 96
Copyright
Copyright © Kluwer 1996

References

Ambruster, C.W., Brown, A., Pettersen, B., & Gershberg, R.E. 1994, EUVE observations of a flare on EV Lac, BAAS, 26, 866 Google Scholar
Bowyer, S. & Malina, R.F. 1991, The EUVE, mission, in Extreme Ultraviolet Astronomy, ed. Malina, R.F. & Bowyer, S., New York: Pergamon Press, 397 Google Scholar
Brown, A. 1994, Coronal and transition region spectroscopy of cool stars using EUVE, in Cool Stars, Stellar Systems, & The Sun: Eighth Cambridge Workshop, ed. Caillault, J.-P., ASP Conf. Ser., 64, 23 Google Scholar
Brown, A., Linsky, J.L., & Dempsey, R.C. 1994, EUVE coronal spectroscopy of the RS CVn binaries σ2 CrB and II Peg, BAAS, 26, 865 Google Scholar
Cully, S.L., Siegmund, O.H.W., Vedder, P.W., & Vallerga, J.V. 1993, Extreme Ultraviolet Explorer Deep Survey observations of a large flare on AU Microscopii, ApJL, 414, L49 Google Scholar
Cully, S.L., Fisher, G.H., Abbott, M.J., & Siegmund, O.H.W. 1994, A coronal mass ejection model for the 1992, July 15 flare on AU Microscopii observed by the Extreme Ultraviolet Explorer, ApJ, 435, L449 Google Scholar
Drake, J.J., Brown, A., Patterer, R.J., Vedder, P.W., Bowyer, S., & Guinan, E.F. 1994, Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?, ApJL, 421, L43 Google Scholar
Feldman, U., Mandelbaum, P., Seely, J.F., Doschek, G.A., & Gursky, H. 1992, The potential for plasma diagnostics from stellar extreme-ultraviolet observations, ApJS, 81, 387 Google Scholar
Hawley, S.L., et al. 1995, Simultaneous EUVE and Optical Observations of AD Leonis: Evidence for large Coronal Loops and the Neupert Effect in Stellar Flares, ApJ, in pressGoogle Scholar
Monsignori-Fossi, B.C., Landini, M. 1994, The EUV Spectrum of AU Microscopii: Temperature and density diagnostics from EUVE spectrometers observations, A&A, 284, 900 Google Scholar
Monsignori-Fossi, B.C., Landini, M., Del Zanna, G., & Drake, J.J. 1994, The EUV Spectrum of AT Mie. in Cool Stars, Stellar Systems, & The Sun: Eighth Cambridge Workshop, ed. Caillault, J.-P.., ASP Conf. Ser., 64, 44 Google Scholar
Monsignori-Fossi, B.C., Landini, M., Fruscione, A., & Dupuis, J. 1995, Extreme Ultraviolet Spectroscopy and Photometry of EQ Pegasi, A&A, in pressCrossRefGoogle Scholar
Pallavicini, R., Tagliaferri, G., & Stella, L. 1990, X-ray emission from solar neighbourhood flare stars: A comprehensive survey of EXOSAT results, A&A, 228, 403 Google Scholar