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Issue A&A
Volume 415, Number 1, February III 2004
Page(s) 331 - 348
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20034002



A&A 415, 331-348 (2004)
DOI: 10.1051/0004-6361:20034002

HST/STIS high resolution echelle spectra of Centauri A (G2 V)

I. Pagano1, J. L. Linsky2, J. Valenti3 and D. K. Duncan4

1  INAF, Catania Astrophysical Observatory, via Santa Sofia 78, 95125 Catania, Italy
    e-mail: ipa@ct.astro.it
2  JILA, University of Colorado and NIST, Boulder, CO 80309-0440, USA
    e-mail: jlinsky@jila.colorado.edu
3  Space Telescope Science Institute, 3700 San Martin Dr. Baltimore, MD 21218, USA
    e-mail: valenti@stsci.edu
4  Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0389, USA
    e-mail: dduncan@colorado.edu

(Received 25 June 2003 / Accepted 9 October 2003)

Abstract
We describe and analyze HST/STIS observations of the G2 V star $\alpha$ Centauri A ( $\alpha$ Cen A , HD 128620 ), a star similar to the Sun . The high resolution echelle spectra obtained with the E140H and E230H gratings cover the complete spectral range 1133-3150 Å with a resolution of 2.6 km s -1, an absolute flux calibration accurate to $\pm 5$%, and an absolute wavelength accuracy of 0.6-1.3 km s -1. We present here a study of the E140H spectrum covering the 1140-1670 Å spectral range, which includes 671 emission lines representing 37 different ions and the molecules CO and H 2. For $\alpha$ Cen A and the quiet and active Sun , we intercompare the redshifts, nonthermal line widths, and parameters of two Gaussian representations of transition region lines (e.g., $\ion{Si}{iv}$, $\ion{C}{iv}$), infer the electron density from the $\ion{O}{iv}$ intersystem lines, and compare their differential emission measure distributions. One purpose of this study is to compare the $\alpha$ Cen A and solar UV spectra to determine how the atmosphere and heating processes in $\alpha$ Cen A differ from the Sun as a result of the small differences in gravity, age, and chemical composition of the two stars. A second purpose is to provide an excellent high resolution UV spectrum of a solar-like star that can serve as a proxy for the Sun observed as a point source when comparing other stars to the Sun .


Key words: stars: individual: $\alpha$ Cen A -- stars: chromospheres

Offprint request: I. Pagano, ipa@ct.astro.it

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