Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...340..216m&link_type=abstract
Astronomy and Astrophysics, v.340, p.216-221 (1998)
Astronomy and Astrophysics
Astrophysics
4
Stars: Abundances, Stars: Activity, Stars: Coronae, Stars: Individual: Alpha Cen, Stars: Late Type, X-Rays: Stars
Scientific paper
We present the X-ray spectrum of the nearby binary alpha Cen AB (G2V + K1V) that has been obtained from observations with the low-energy concentrator (LECS) onboard the BeppoSAX X-ray astronomy satellite. SAX combines, in contrast to previous satellites, simultaneous coverage of the 0.1-10 keV energy range with sufficient spectral resolution to determine emission measure distributions and elemental abundances of soft coronal sources. The analysis of the spectrum using the SPEX plasma emission code shows a two-temperature structure of the corona which is confirmed by a differential emission measure analysis. It reveals a soft ( ~ 0.1 keV) component as detected previously by \hboxEUVE and ROSAT and a hard ( ~ 0.5 keV) component comparable to that seen by EINSTEIN, \hboxEUVE, and ASCA. The derived coronal Fe abundance of 0.7 +/- 0.3 (relative to solar photospheric) is consistent with the solar photospheric abundance but marginally (3hbox {\sigma^2 CrB}ma) different from the value of the metal-rich photosphere of alpha Cen. The abundance ratios Mg/Fe and Si/Fe are consistent (within 1hbox {\sigma^2 CrB}ma) with solar photospheric and coronal values, whereas the O/Fe ratio (3+/- 2) appears too high but the uncertainty is large. The X-ray flux in the 0.1-2.4 keV band is comparable to the average of previous observations with other instruments and to that derived from the ASCA observations if the different passbands of the instruments are taken into account. The two-temperature structure is reminiscent of recently determined emission measure distributions of the solar corona; the hotter component may be evidence for flare heating.
Favata Fabio
Guedel Manuel
Kaastra Jelle S.
Mewe Rolf
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