5 Atmospheric parameters and chemical composition

The UV (IUE) low resolution spectrum of HD 101584 matches well with that of an A6Ia star (HD 97534) (Fig. 9) indicating a $T_{\rm eff}$ of 8400 K (Lang 1992). The presence of CII lines at 6578 Å and 6582 Å indicates a $T_{\rm eff}$ > 8000 K. For $T_{\rm eff}$ $\le$ 8000 K the CII lines would be very weak or absent. The Paschen lines also indicates a low gravity (Fig. 10). The luminosity class Ia also indicates a very low gravity. From the analysis of several nitrogen lines around 7440 Å and 8710 Å we derived the microturbulence velocity $V_{\rm turb}=13$ km s^-1. We synthesised the spectral region from 4000 Å to 4700 Å (Fig. 11) with low gravity (log g =1.5) models of Kurucz (1993) with temperatures 8000 K, 8500 K and 9000 K. The best fit was found for $T_{\rm eff}=8500$ K, log g = 1.5, $V_{\rm T}=13$ km s^-1 and [Fe/H] = 0.0.

  

Figure 9: IUE low resolution spectrum of HD 101584 is compared with that the A6Ia star HD 97534. The dotted line corresponds to the spectrum of HD 97534 while the solid line is HD 101584

  

Figure 10: Observed and synthetic spectra in the Paschen line region. 1-observed, 2-$T_{\rm eff} = 8000$ K, log g=1.0, 3-($T_{\rm eff}$ = 8000 K, log g=2.0, 4-$T_{\rm eff}=8500$ K, log g=1.5. The peaks are FeI emission lines

  

Figure 11: Synthesis spectra for different models are compared with the observed spectrum. The observed spectrum is of 2.5 Å resolution taken at VBO kavalur. Observed spectrum matches well for $T_{\rm eff}=8500$ K, log g=1.5, $V_{\rm turb}=13$ km s-1 and [Fe/H] = 0.0

The line at 5876 Å was identified as a HeI line by Bakker et al. (1996a) who also state that the lines at 5047 Å and 5045 Å as due to HeI and NII respectively. However, we find that the 5047 and 5045 lines are in fact due to FeII. Except HeI 5876 Å, we have not found any other helium lines in the spectrum and nor have we found any NII or OII lines. In fact, Hibbert et al. (1991) indicate the presence of a CI line at 5876 Å. It is likely that the line at 5876 Å may be due to CI instead of HeI.

If we assume that the 5876 Å line is due to HeI then for a solar helium abundance and log g = 1.5, $T_{\rm eff} = 9000$ K is found. Since we do not see any other helium lines, if 5876 Å line is due to helium, it is likely that it may be formed in the stellar wind or in the chromosphere of the star. On the basis of the presence of this helium line Bakker et al. (1996a) suggested that HD 101584 is a B9II star of $T_{\rm eff}\ 12000$ K. On the basis of the analysis of our spectra we have not found any evidence for such a high temperature. We have also analysed the equivalent widths of absorption lines in the spectrum of HD 101584 given by Bakker et al. (1996a). The final abundances of some of the elements are listed in Table 2. The abundances listed in Table 2 show that the star is overabundant in carbon and nitrogen. It appears that the material processed by the triple alpha C-N and O-N cycle has reached the surface.

  

Table 1: List of emission lines detected in the high resolution spectrum of HD 101584

 

Table 1: continued

 

Table 1: continued