2 Data

We have three data sets at our disposal: Hipparcos photometry, multicolour Geneva photometry and high-resolution spectroscopic data. The Geneva photometric observations were obtained with the Swiss telescope situated at La Silla in Chile, during several 3-weeks runs in the course of 1997. The spectroscopic data were obtained with the CAT/CES telescope of ESO in Chile, during 7 separate weeks of monitoring spread over 1996-1998. The spectral domain was [4115, 4135] Å in order to get the SiII-doublet with lines at $\lambda\lambda\,4128, 4130$ Å. The signal-to-noise ratio is about 400. The number of observations and the ranges of their Julian Dates are given in Table 1 for the Geneva photometry and the spectroscopy. For a complete description of the observations and data reductions we refer to Aerts et al. (1999) and De Cat (2001). We point out that the data published in this work is available upon request from the authors.

 

 

Table 1: Observing log for Geneva photometry (upper) and spectroscopy (lower).

Number of	JD
observations	2450000 +
	Start	End
32	485	503
69	541	583
7	588	601
27	163	170
15	188	194
13	272	277
4	490	498
4	513	528
6	571	576
8	633	638

In Aerts et al. (1999) some physical parameters of the star are given. They are:

$$\begin{eqnarray*}\left\{\begin{array}{lllll} \log T\rm _{eff} = 4.26 \pm 0.01,\\... ...,\\ M = 6.1~M_{\odot},\\ R = 3.6~R_{\odot}. \end{array}\right. \end{eqnarray*}$$

De Geus et al. (1989) found similar values for the parameters of the star: log $T\rm _{eff} = 4.27$, $\log g = 4.22$ and $\log L/L_{\odot} = 3$. In Borra et al. (1983), a photometric spectral type with observed UBV colors is given for the star, which is B2.5. With these parameters, HD 131120 is situated in the upper part of the SPB instability domain, close to the $\beta$ Cep instabilitsy domain (see e.g. Pamyatnykh 1999).