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Astron. Astrophys. 339, 840-845 (1998)

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2. Program stars and data analysis

2.1. Program stars

Our sample consists of single, binary and RS CVn stars with spectral type F-M, for which both the magnetic field strengths and ROSAT PSPC observations are available. We present the list of investigated stars in Table 1, columns (1) and (2) give sequence number and star name. The spectral type, B-V colour and adopted distance are given in columns (3), (4) and (5). Columns (6) and (7) give the magnetic field strength and the fill factor. In column (9), the S, B and R represent single, binary and RS CVn stars respectively.


[TABLE]

Table 1. Basic data of sample Stars
Col.(7) references are as follows:
1: Marcy 1984.
2: Saar 1990.
3: Mathys and Solansky 1989.
4: Saar 1996.


2.2. Data analysis

We use the data of the Roentgensatellite (ROSAT) with the position sensitive proportional counter (PSPC) to obtain pointed X-ray observations of selected program stars in the photon energy range 0.1 [FORMULA] 2.4keV. Using the EXSAS software, three different coronal models have been considered to fit the PSPC data.

Model 1. An isothermal plasma with intervening absorption and three adjustable parameters - the gas temperature T, the emission measure EM at the given temperature and the hydrogen column density [FORMULA]. The defaults Raymand-Smith full-code model is used in this model.

Model 2. A plasma consisting of two isothermal components with four adjustable parameters, [FORMULA], [FORMULA], [FORMULA] and [FORMULA]. The Raymand-Smith fast mode model is used.

Model 3. A plasma consisting of two isothermal components with intervening absorption and five adjustable parameters, [FORMULA], [FORMULA], [FORMULA], [FORMULA] and [FORMULA]. We use the Raymand-Smith fast mode model.

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© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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