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| Paper: |
Evolution of X-ray Activity of 1-3 M_odot Late-Type Stars in Early Post-Main-Sequence Phases |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
1146 |
| Authors: |
Pizzolato, N.; Maggio, A.; Sciortino, S. |
| Abstract: |
We present preliminary results on the variation of coronal X-ray emission during early post-main-sequence phases, for a sample of 83 late-type stars (D < 100 pc), with estimated masses in the range 1 - 3 M_odot using Hipparcos parallaxes and recent evolutionary tracks (Schaller et al. 1992). These stars were observed with the ROSAT/PSPC; source detection and evaluation of X-ray fluxes (or upper limits) were achieved with the wavelet transform algorithm of Damiani et al. (1997a,b). The aim of this work is to study the evolutionary history of X-ray activity in early post-main-sequence phases for stars with masses 1.5<M/M_odot<3.0 (inactive A-type stars on the main-sequence) with respect to lower mass solar-type stars. A trend of increasing X-ray luminosity with age for the higher mass stars is suggested by our ROSAT sample, and a similar evidence comes from two other independent samples: a sample of 24 stars observed with the {\it Einstein} satellite (Maggio et al. 1993), and a sample of 23 evolved stars extracted from the RIASS ``coronathon" (Ayres et al. 1995). The results of the present study may help to test the expectation that magnetic dynamo activity depends on the evolutionary phase through several possible ingredients, and in particular the rotation history of coronal X-ray sources during the main-sequence lifetime, and mass-dependent changes of the stellar internal structure. |
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