The example of xArae

The exoplanet-host star |x-Arae is a G5V star with a visual magnitude of V = 5.1, a Hipparcos parallax n = 65.5 ± 0.8 marcsec, which gives a distance to the Sun

Figure 40.2. These graphs display the error boxes for the position of the star i-Hor in the log g-log Teff diagram, as given by the three groups that observed this star (Table 40.1). The author's boxes which correspond to the chosen metallicity, in each graph, are emphasized with boldface lines. After Laymand and Vauclair (2006).

0 20 40 60 80 100 120 frequency modulo 120 |xHz

0 20 40 60 80 100 120 frequency modulo 129 p.Hz

Figure 40.3. Echelle diagrams for two possible models (OM1 and OM2) of the exoplanet-host star i-Hor, after Laymand and Vauclair (2006). Observations of this star were to be carried out with the HARPS spectrometer in November 2006.

0 20 40 60 80 100 120 frequency modulo 129 p.Hz

Figure 40.3. Echelle diagrams for two possible models (OM1 and OM2) of the exoplanet-host star i-Hor, after Laymand and Vauclair (2006). Observations of this star were to be carried out with the HARPS spectrometer in November 2006.

of 15.3 pc, and a luminosity of log(L/L0) = 0.28 ± 0.012. Spectroscopic observations by various authors gave five different effective temperatures and metal-licities; see references in Bazot et al. (2005). The HARPS observations allowed the identification of 43 oscillation modes of degrees l = 0 to l = 3 (Bouchy et al. 2005). From the analysis of the frequencies and comparison with models, the values Teii = 5813 ± 40 K and [Fe/H] = 0.32 ± 0.05 dex were derived: these values, which lie inside the spectroscopic boxes, were obtained with a much better precision than is available from spectroscopy.

For each evolutionary track, many models were computed inside the observed spectroscopic boxes in the HR diagram, but only those which could reproduce the observed echelle diagram were kept for subsequent tests (Figure 40.1). For these models the large separation Avl = vn+1j l — vn, l is exactly 90 i^Hz: a difference of only 0.5 |xHz completely destroys the fit with the observations.

We can see a clear difference between the overmetallic and the accretion cases for the lines l = 0 and l = 2: in the overmetallic case they come closer at large frequencies and even cross around v = 2.7 mHz, which does not happen in the accretion case. This behavior clearly appears in the representations of the small

Table 40.2. Observed parameters for HD 52265; see Soriano et al. (2006).

log g

authors

6,103 ± 52 4.28 ± 0.12 0.23 ± 0.05 Santos et al. (2004)

6,162 ± 22 4.29 ± 0.04 0.27 ± 0.02 Gonzalez etal. (2001)

6,076 ± 44 4.26 ± 0.06 0.19 ± 0.03 Fischer & Valentini (2005)

6,069 ± 15 4.12 ± 0.03 0.19 ± 0.03 Takeda et al. (2005)

6,179 ± 18 4.36 ± 0.03 0.24 ± 0.02 Gillon & Magain (2006)

separations; see specific figures in Bazot et al. (2005). I will come back to this important effect below, for another star. For |x-Arae it was not yet possible to decide which scenario was the best one, in spite of the very good data obtained, but we are still working on it.

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