Hostname: page-component-586b7cd67f-t8hqh Total loading time: 0 Render date: 2024-11-30T12:44:05.708Z Has data issue: false hasContentIssue false
  • English
  • Français

Dissecting the EUV Spectrum of Capella

Published online by Cambridge University Press:  12 April 2016

Nancy S. Brickhouse
Nancy S. Brickhouse*
Affiliation:
Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138USA

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.

Extreme ultraviolet spectra of Capella, obtained at various orbital phases over the past two years by the EUVE satellite, show strong emission lines from a continuous distribution of temperatures (~ 105 − 107.3 K). In addition to the strong He II λ303.8, the spectra are dominated by emission lines of highly ionized iron. Strong lines of Fe IX, XV, XVI, and XVIII–XXIV are used to construct emission measure distributions for the individual pointings, which show several striking features, including a minimum near 106 K and a local maximum at 106.8 K. Furthermore, intensities of the highest temperature lines (Te > 107 K) show variations (factors of 2–3) at different orbital phases, while the lower temperature Fe lines show variations of about 30% or less. The low variability of most of the strong low temperature features motivates a detailed analysis of the summed spectrum. With ~ 280 ks of total exposure time, we have measured over 200 emission features with S/N ≥ 3.0 in the summed spectrum. We report here initial results from the analysis of this spectrum. We can now identify lines of Fe VIII and X–XIV, as well as a number of electron density and abundance diagnostic lines.

We also report here the first direct measurement of the continuum flux around ~ 100 Å in a cool star atmosphere with EUVE. The continuum flux can be predicted from the emission measure model based on Fe line emission, and demonstrates that the Fe/H abundance ratio is close to the solar photospheric value.

Type
III. Coronae of Cool Stars
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 105 - 112
Copyright
Copyright © Kluwer 1996

References

Anders, E., & Grevesse, N. 1989, Abundances of the Elements: Meteoritic and Solar, Geochim. Cosmochim. Acta, 53, 197 Google Scholar
Ayres, T.R. 1988, A Spectral Dissection of the Ultraviolet Emissions of Capella, ApJ, 331, 467 Google Scholar
Boyd, W., Jelinsky, P., Finley, D.S., Dupuis, J., Abbott, M., Christian, C., & Malina, R.F. 1994, In-Orbit Performance of the Spectrometers of the Extreme Ultraviolet Explorer, Proc. SPIE, 2280, 280 Google Scholar
Brickhouse, N.S., Raymond, J.C., & Smith, B.W. 1995a, New Model of Iron Spectra in the Extreme Ultraviolet and Application to SERTS, and EUVE, Observations: A Solar Active Region and Capella, ApJS, 97, 551 Google Scholar
Brickhouse, N.S., Dupree, A.K., & Raymond, J.C. 1995b, Analysis of the EUVE, Spectrum of Capella from the Transition Region to the Hot Corona, in progressGoogle Scholar
Cook, J.W., Cheng, C.-C., Jacobs, V.L., & Antiochos, S.K. 1989, Effect of Coronal Elemental Abundances on the Radiative Loss Function, ApJ, 338, 1176 Google Scholar
Davé, et al. 1987, Time-resolved spectra in the 80 Å Wavelength Region from Princeton Large Torus Tokamak Plasmas, J. Opt. Soc. Am., B4, 635 Google Scholar
Doschek, G.A., & Cowan, R.D. 1984, A Solar Spectral Line List Between 10 and 200 Å Modified for Application to High Spectral Resolution X-ray Astronomy, ApJS, 56, 67 Google Scholar
Drake, J.J., Laming, J.M., & Widing, K.G. 1995, Stellar Coronal Abundances. II. The First Ionization Potential Effect and Its Absence in the Corona of Procyon, ApJ, 443, 393 Google Scholar
Drake, S.A., Singh, K.P., White, N.E., & Simon, T. 1994, ASCA, X-ray Spectra of the Active Single Stars β Ceti and П1 Ursae Majoris, ApJ, 436, L87 Google Scholar
Dupree, A.K., Brickhouse, N.S., Doschek, G.A., Green, J.C., & Raymond, J.C. 1993, The Extreme Ultraviolet Spectrum of Alpha Aurigae Capella, ApJ, 418, L41 Google Scholar
Dupree, A.K., Brickhouse, N.S., & Hanson, G.J. 1995a, High Temperature Structure in Cool Binary Stars, these proceedingsGoogle Scholar
Dupree, A.K., Brickhouse, N.S., Doschek, G.A., Hanson, G.J., & Raymond, J.C. 1995b, EUVE Spectra of Alpha Aurigae Capella, at Different Phases, in preparationGoogle Scholar
Feldman, U. 1992, Elemental Abundances in the Upper Solar Atmosphere, Phys. Scripta, 46, 202 Google Scholar
Hurwitz, M., Bowyer, S., & Dupree, A.K. 1995, ORFEUS, Observations of Capella, in preparationGoogle Scholar
Landini, M., & Monsignori Fossi, B.C. 1993, Extreme Ultra Violet Plasma Diagnostic: a Test Using EUVE Calibration Data, A&A, 275, L17 Google Scholar
Lemen, J.R., Mewe, R., Schrijver, C.J., & Fludra, A. 1989, Coronal Activity in F-, G-, and K-Type Stars. III. The Coronal Differential Emission Measure Distribution of Capella, σ2 CrB, and Procyon, ApJ, 341, 471 Google Scholar
Linsky, J.L et al. 1993, Goddard High-Resolution Spectrograph Observations of the Local Interstellar Medium and the Deuterium/Hydrogen Ratio along the Line of Sight toward Capella, ApJ, 402, 694 Google Scholar
Linsky, J.L., Wood, B.E., Judge, P., Brown, A., Andrulis, C., & Ayres, T.R. 1995, The Transition Regions of Capella, ApJ, 442, 381 Google Scholar
Raymond, J.C. 1988, Radiation from Hot, Thin Plasmas, in Hot Thin Plasmas in Astrophysics, ed. Pallavicini, R., Dordrecht: Kluwer, 3 Google Scholar
Singh, K.P. 1994, private communicationGoogle Scholar
Stern, R.A., Lemen, J.R., Schmitt, J.H.M.M., & Pye, J.P. 1995, EUVE Observations of Algol: Detection of a Continuum and Implications for the Coronal [Fe/H] Abundance, ApJ, 444, L45 Google Scholar
Stratton, , et al. 1985, Relative Intensities of 2s2 2p* s 2p*+1 transitions in FI- to BI-like Ti, Cr, Fe, Ni, and Ge in a Tokamak Plasma: A Comparison of Experiment and Theory, Phys. Rev. A, 31, 2534 Google Scholar
Swank, J.H., White, N.E., Holt, S.S., & Becker, R.H. 1981, Two-Component X-ray Emission from RS Canum Venaticorum Binaries, ApJ, 246, 208 Google Scholar
Vedder, P.W., & Canizares, C.R. 1983, Measurement of Coronal X-ray Emission Lines from Capella, ApJ, 270, 666 Google Scholar
Vennes, S. et al. 1993, The First Detection of Ionized Helium in the Local ISM: EUVE, and IUE, Spectroscopy of the Hot DA White Dwarf GD 246, ApJ, 410, L119 Google Scholar
Zhang, H.L., Sampson, D.H., & Fontes, C.J. 1990, Relativistic Distorted-Wave Collision Strengths and Oscillator Strengths for the 85 Li-like Ions with 8 ≤ Z ≤ 92, At. Data Nucl. Data Tables, 44, 31 Google Scholar