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Astron. Astrophys. 340, 216-221 (1998)


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A BeppoSAX/LECS X-ray observation of [FORMULA] Centauri

R. Mewe 1, M. Güdel 2, F. Favata 3 and J.S. Kaastra 1

1 Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Paul Scherrer Institut, Würenlingen und Villigen, CH-5232 Villigen PSI, Switzerland
3 Astrophysics Division - Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands

Received 16 July 1998 / Accepted 15 September 1998

Abstract

We present the X-ray spectrum of the nearby binary [FORMULA] 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 ([FORMULA] 0.1 keV) component as detected previously by EUVE and ROSAT and a hard ([FORMULA] 0.5 keV) component comparable to that seen by EINSTEIN , EUVE , and ASCA . The derived coronal Fe abundance of 0.7 [FORMULA] 0.3 (relative to solar photospheric) is consistent with the solar photospheric abundance but marginally (3[FORMULA]) different from the value of the metal-rich photosphere of [FORMULA] Cen. The abundance ratios Mg/Fe and Si/Fe are consistent (within 1[FORMULA]) with solar photospheric and coronal values, whereas the O/Fe ratio (3[FORMULA] 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.

Key words: stars: abundances – stars: activity – stars: coronae – stars: individual: ff Cen – stars: late type – X-rays: stars

Send offprint requests to: R. Mewe, (R.Mewe@sron.nl)

© European Southern Observatory (ESO) 1998

Online publication: November 3, 1998

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