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

Abstract

We describe and analyze HST/STIS observations of the G2 V star α Centauri A (α 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 ±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 H2. For α 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., Si IV, C IV), infer the electron density from the O IV intersystem lines, and compare their differential emission measure distributions. One purpose of this study is to compare the α Cen A and solar UV spectra to determine how the atmosphere and heating processes in α 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.