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Astron. Astrophys. 317, 701-706 (1997)

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2. The sample and observational data

The data sample selected for the present work has as main characteristic the high precision of the rotational velocities. In fact, we have selected all F-G-K subgiant stars listed in the Bright Star Catalog (Hoffleit & Jaschek 1982) northern of [FORMULA] and all the subgiant stars listed in the Catalog of Chromospherically Active Binary Stars of Strassmeier et al. (1988). The rotational velocities were obtained with the CORAVEL spectrometer (Baranne et al. 1979) at the Haute-Provence Observatory, France, and at the European Southern Observatory, Chile. For the Vsini values lower than about 50 km.s-1, CORAVEL measurements indicate a precision of about 1.0 km.s-1. However, for larger rotators we must be cautious about the analysis of the rotational velocities because the uncertainties may become important. For a complete discussion on the observational procedure, calibration and error analysis the reader is referred to De Medeiros & Mayor (1996).

We have combined our rotational velocity measurements with Lithium abundances available in the literature to analyse the link between rotation and Lithium contents. We have found Lithium abundances for a sample of 65 subgiant stars from which 34 are spectroscopic binaries: 12 stars were taken from Randich et al. (1993, 1994), 35 stars from Balachandran (1990), 7 stars from Pallavicini et al. (1987) and 6 stars from Duncan (1981). Because the Lithium abundances have been taken from different authors, we have compared the abundance values for those stars in common in the given sources. For four stars observed respectively by Randich et al. (1993) and Randich (1994) we find an excellent agreement with a mean of the difference of about 0.01 dex; for six stars with Lithium abundances from Pallavicini et al. (1987) and from Duncan (1981) the mean of the difference in the Lithium abundance is 0.27 dex, whereas for ten stars observed respectively by Balachandran (1990) and Duncan (1981) the mean of the difference is 0.20 dex, in the sense that both measurements from Pallavicini et al. (1987) and Balachandran (1990) are larger than the measurements from Duncan (1981). Despite the discrepancies between the measurements from Duncan (1981) and those given by Pallavicini et al. (1987) and Balachandran (1990), the comparison indicates, indirectly, a good agreement between the Lithium abundance values obtained respectively by Pallavicini et al. (1987) and Balachandran (1990). Further, the detailed error analysis made by Balachandran (1990) and Randich et al. (1993, 1994) indicates that their measurements have the same high quality. Let us recall that for the observations of Pallavicini et al. (1987), Balachandran (1990) and Randich et al. (1993, 1994) the signal-to-noise ratio was in most cases greater than 100.

Table 1 gives the measured rotational velocities as well as the Lithium abundances for the final list of 65 stars. Table 2 lists the orbital period and eccentricity available in the literature for 21 binary systems of the sample. The orbital period for the visual binary system HD 99028 and HD 150680 are respectively 192 yr and 34.487 yr.


[TABLE]

Table 1. Physical parameters for the programme stars



[TABLE]


[TABLE]

Table 2. Orbital parameters for subgiant binary systems


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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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