All Tables

Table 1: Identification, spectral type, and photometric visual data of the studied objects. The $A_{\rm v}$ and $m_{\rm v}$ values for Orion stars are from Preibisch et al. (1999). The $M_{\rm v}$ values for these stars were calculated considering a distance $d \sim$ 450 $\pm$ 50 pc to the Orion nebula. Data for HD 214680 and HD 47839 are from Herrero et al. (1992). Photometric data for HD 149438 are from Humphreys (1978). Uncertainties in $m_{\rm v}$ , $A_{\rm v}$ , and $M_{\rm v}$ are 0.01, 0.03, and 0.3, respectively.
Table 2: SNR achieved for the different spectra for the three ranges observed with the INT+ IDS.
Table 3: Projected rotational velocity derived from the Fourier and FWHM analyses. References from the literature are: ^a Simón-Díaz et al. (2003), ^b Howarth et al. (1997), ^c McNamara & Larsson (1962), ^d Schönberner et al. (1988), ^e Killian et al. (1991).
Table 4: Stellar parameters derived from F ASTWIND analysis. Only an upper limit for log Q can be derived for these stars. The microturbulences considered for the HHe analysis in each star are shown in the corresponding fitting plots. A normal value for the He abundance was considered for all the stars ( $\epsilon$ = 0.09).
Table 5: Comparison of stellar parameters for HD 37020, HD 37023, HD 37042. The first values refer to the Cunha & Lambert (1992) determinations, the second values to this work. We see that there is excellent agreement for HD 37020, but poor agreement (specially for log g) for the other two stars.
Table 6: Comparison of masses and gravities derived from the evolutionary tracks and from quantitative analysis of the spectra. The quoted log $g_{\rm evol}$ values are given corrected to two decimal places to be consistent with the corresponding evolutionary masses. Note, however, that these are not an indication of the precision of these values, which we consider to be 0.1 dex.
Table 7: FEROS spectra used for the study of the spectral variability of $\theta ^1$ Ori C. All spectra were downloaded from the ESO- FEROS database except f85221, kindly provided by O. Stahl. The different phases were calculated from $\rm MJD_0$ -2.400.000,5 = 48832,5 (Stahl et al. 1996), and P = 15.422 days.
Table 8: Projected rotational velocities derived through Fourier and FWHM methods for some metal lines present in the spectrum of $\theta ^1$ Ori C. Values were derived at phase 0.972 (see explanation in text).
Table 9: Equivalent widths and derived line abundances for the set of O II lines used in our analysis. Line abundances refer to the microturbulence given in brackets for each star ( $\xi _t$ in km s^-1). Uncertainties in the line abundances come from the propagation of the uncertainties of the equivalent width measurements (see text). Some of the O II lines of the Orion stars have not been used, as they appear blended. O II $\lambda \lambda$ 4072, 4076, and 4078 lines were ruled out in the analysis of $\tau$ Sco due to the poor quality of the CASPEC spectrum in this region. Final oxygen abundances for each star were calculated through a weighted mean of the linear values. Errors represent the statistical deviation for these mean values.
Table 10: Oxygen abundances for the three B0.5V stars inside Orion nebula and the reference star $\tau$ Sco. Oxygen LTE and NLTE abundances derived by Cunha & Lambert (1994) for the Orion stars as well as those calculated by Esteban et al. (2004) for the nebula are also presented for comparison.
Table 11: Comparison of stellar parameters and abundances derived for $\tau$ Sco in previous studies found in the literature and in this work.
Table 12: Preliminary set of O II lines selected for the analysis, divided by multiplets. The spectrum of the low v sin i star $\tau$ Sco was used to identify the lines. The log gf values are from the NIST database.
Table 13: (Continued) Preliminary set of O II lines selected for the analysis, divided by multiplets. The spectrum of the low v sin i star $\tau$ Sco was used to identify the lines. The log gf values are from the NIST database.