A BeppoSAX/LECS X-ray observation of alpha Centauri

We present the X-ray spectrum of the nearby binary a Cen AB (G2V + K1V) tha t has been obtained from observations with the low-energy concentrator (LEC S) onboard the BeppoSAX X-ray astronomy satellite. SAX combines, in contras t to previous satellites, simultaneous coverage of the 0.1-10 keV energy ra nge with sufficient spectral resolution to determine emission measure distr ibutions and elemental abundances of soft coronal sources. The analysis of the spectrum using the SPEX plasma emission code shows a two-temperature st ructure of the corona which is confirmed by a differential emission measure analysis. It reveals a soft (similar to 0.1 keV) component as detected pre viously by EUVE and ROSAT and a hard (similar to 0.5 keV) component compara ble to that seen by EINSTEIN, EWE, and ASCA. The derived coronal Fe abundan ce of 0.7 +/- 0.3 (relative to solar photospheric) is consistent with the s olar photospheric abundance but marginally (3 sigma) different from the val ue of the metal-rich photosphere of alpha Cen. The abundance ratios Mg/Fe a nd Si/Fe are consistent (within 1 sigma) with solar photospheric and corona l values, whereas the O/Fe ratio (3 +/- 2) appears too high but the uncerta inty 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 a re taken into account. The two-temperature structure is reminiscent of rece ntly determined emission measure distributions of the solar corona; the hot ter component may be evidence for flare heating.