All Figures

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{4995fi01.ps} \end{figure}$ Figure 1: Effective temperatures as a function of spectral type for SMC objects studied in this paper. Dwarfs, giants and supergiants are denoted by, respectively, solid circles, triangles and squares. Shown with a solid line is the average $T_{\rm eff}$ relation for the dwarfs with spectral type later than O4. SMC dwarfs are found to be typically 3 to 4 kK hotter than the $T_{\rm eff}$ calibration for Galactic O-type dwarfs according to Martins et al. (2005a, dashed line). The dotted line corresponds to the SMC $T_{\rm eff}$ scale derived by Massey et al. (2005) for luminosity class V and III objects.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4995fi02.ps} \end{figure}$ Figure 2: Number of Lyman continuum ionising photons Q₀ as a function of spectral type. Different luminosity classes are shown using circles, triangles and squares for, respectively, IV-V, III and I-II class objects. Grey circles correspond to stars located on or left of the ZAMS. Indicated using a dashed line is the Galactic calibration for dwarfs from Martins et al. (2005a).
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{4995fi03.ps} \end{figure}$ Figure 3: Distribution of the analysed SMC objects in the $\log \mbox{$T_{\rm eff}$ }$ - $\log{{g}}_{\rm c}$ plane. Indicated with different symbols are luminosity class IV-V (circles), III (triangles) and I-II (squares). With exception of the subgiant NGC 346-026, the first group of objects are clearly separated from the more evolved objects. These more evolved objects seem to follow a trend of increasing surface gravity with increasing effective temperature.
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{4995fi04.ps} \end{figure}$ Figure 4: Comparison of spectroscopically determined masses with masses derived from the evolutionary tracks of Charbonnel et al. (1993) for $Z = 0.2~\mbox{$Z_{\odot}$ }$ . Luminosity classes IV-V, III and I-II are denoted by circles, triangles and squares, respectively. The dashed line corresponds to the one-to-one relation between the two mass scales. With exception of the two most massive objects, no systematic discrepancy between the spectroscopic and evolutionary masses is observed.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4995fi05.ps} \end{figure}$ Figure 5: Helium abundances as a function of surface gravity. Luminosity classes IV-V, III and I-II are denoted using circles, triangles and squares, respectively. Open symbols correspond to fast rotators ( $\mbox{$v_{\rm r}\sin i$ }> 250~\mbox{km~s$^{-1}$ }$ ). The average helium abundance of the investigated sample is 0.13. Shown with a dashed line is a measure for the initial $Y_{\rm He}$ , which is taken to be the average of the helium abundances of the dwarfs with a $Y_{\rm He}$ smaller than the sample average. Compared to this "initial'' abundance of 0.09 an increase in $Y_{\rm He}$ is visible for decreasing surface gravity.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{4995fi06.ps} \end{figure}$ Figure 6: HR-diagram of the analysed SMC sample. Different luminosity classes are distinguished using identical symbols as used in Fig. 5. Open symbols correspond to objects with a helium abundance of at least 0.12. Over-plotted in grey are the evolutionary tracks of Maeder & Meynet (2001) and Meynet & Maeder (2005) with $Z = 0.2~\mbox{$Z_{\odot}$ }$ and $\mbox{$v_{\rm r}$ }= 300~\mbox{km~s$^{-1}$ }$ . The ZAMS corresponding to these tracks is shown as a black solid line. The grey area in the top part of the diagram corresponds to the region in which the evolutionary models exhibit an enhancement of the surface helium abundance by ten percent or more.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{4995fi07.ps} \end{figure}$ Figure 7: The mass discrepancy (see also Fig. 4) as a function of surface helium abundance. To compute the discrepancy non-rotating tracks of Charbonnel et al. (1993) are used. Circles, triangles, and squares denote dwarfs, giants, and supergiants, respectively. The open circles indicate stars on or left of the ZAMS. The bulk of the stars have the initial helium abundance $\mbox{$Y_{\rm He}$ } = 0.09$ where the discrepancy seems random and of the order of the error. For helium-enriched stars the discrepancy always favours a higher $M_{\rm ev}$ , qualitatively consistent with models accounting for mixing decreasing the M/L-ratio and bringing helium to the surface. Quantitative predictions based on ZAMS stars of 20 $M_{\odot }$ (short-dashed, upper curve) and 30 $M_{\odot }$ (lower curve) for varying helium abundance show, however, a more modest effect than implied by our findings.
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In the text

$\begin{figure} \par\includegraphics[width=9cm,clip]{4995fi08.ps} \end{figure}$ Figure 8: Modified wind momentum ( $D_{\rm mom}$ ) in units of ${\rm g~cm~s^{-2}}~\mbox{$R_{\odot}$ }$ as a function of luminosity for the analysed SMC sample. Luminosity classes are distinguished using identical symbols as in Fig. 5. Indicated using grey inverted triangles are upper limits. At $\log \mbox{$L_{\star}$ }/\mbox{$L_{\odot}$ }\approx 5.0$ the open symbol indicates the location NGC 346-033 would have if its true $v_{\infty }$ would be lower by a factor two compared to the adopted value. Using open squares modified wind momenta corrected for clumping are shown for the two supergiants with H $\alpha$ emission profiles. The upper and lower dashed lines correspond to the theoretical wind-momentum luminosity relations (WLR) as derived by Vink et al. (2000,2001) for Galactic and SMC metallicities. Shown with a dotted line is the empirical WLR constructed for objects with $\log \mbox{$L_{\star}$ }/\mbox{$L_{\odot}$ } \gtrsim 5.4$ .
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In the text

$\begin{figure} \par\includegraphics[width=14.1cm,clip]{4995fi09.ps} \end{figure}$ Figure 9: Comparison of $v_{\rm r}\sin i$ distributions. Left panel: cumulative distribution functions (cdf) of $v_{\rm r}\sin i$ for unevolved objects, i.e. luminosity class IV and V, and evolved objects, i.e. luminosity class I, II, III, in the SMC. The group of unevolved SMC objects are found to contain relatively both more fast rotators ( $\mbox{$v_{\rm r}\sin i$ }\gtrsim 100~\mbox{km~s$^{-1}$ }$ ) as well as more slow rotators ( $\mbox{$v_{\rm r}\sin i$ }\lesssim 50~\mbox{km~s$^{-1}$ }$ ) with respect to the group of evolved objects. Right panel: cdf of unevolved SMC objects and unevolved Galactic objects (Penny 1996). Compared to the Galactic sample the SMC sample contains a larger fraction of intermediately fast rotating stars ( $120 \gtrsim \mbox{$v_{\rm r}\sin i$ }\lesssim 190~\mbox{km~s$^{-1}$ }$ ).
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In the text

$\begin{figure} \par\includegraphics[width=14.2cm,clip]{4995fi10.ps} \end{figure}$ Figure 10: Left panel: cdfs of observed (solid line) and theoretical initial $v_{\rm r}\sin i$ distributions. Dotted and dashed lines, respectively, correspond to a constant $v_{\rm r}$ distribution, i.e. block function, and a single value $v_{\rm r}$ distribution. Right panel: filled areas indicate the one $\sigma$ probability distribution for theoretical $v_{\rm r}\sin i$ cdfs for the limited number of 21 objects, calculated from a constant $v_{\rm r}$ distribution with $\mbox{$v_{\rm min}$ } = 0~\mbox{km~s$^{-1}$ }$ and $v_{\rm max}$ of 200, 352 or 600 km s^-1. Shown with a dotted, dashed and dashed-dotted curve are, respectively, the best fitting block function, Gaussian and Maxwellian distribution cdf. See text and Fig. 11 for further comments and explanation.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4995fi11.ps} \end{figure}$ Figure 11: Best fitting model $v_{\rm r}$ distributions for the $v_{\rm r}\sin i$ distribution of the unevolved SMC objects. Shown with a dotted, dashed and dashed-dotted line are, respectively, the constant, the Gaussian and the Maxwellian distribution.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4995fi12.ps} \end{figure}$ Figure 12: Comparison of mass loss rates determined in this study using the optical spectrum with values determined from the UV spectrum. For the three objects with the lowest mass loss rates the values determined from the optical spectra correspond to upper limits.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{4995fi13.ps} \end{figure}$ Figure 13: Comparison of the programme stars located in NGC 346 with isochrones for zero age, 1, 2, 3, 4, 5 and 7 Myr derived from the non rotating evolutionary models of Charbonnel et al. (1993) (dashed lines) and models including rotation from Maeder & Meynet (2001) and Meynet & Maeder (2005) (dotted lines). For reference the tracks of the rotating models are also shown (grey lines, see Fig. 6 for initial masses of these tracks), where for clarity purpose only the blueward part of the evolution of the most massive tracks is plotted. Shown with identical symbols as in Fig. 5 are our programme stars, which are located in NGC 346. Luminosity class Vz objects are denoted using grey circles. See text for a discussion.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{4995fi14.ps} \end{figure}$ Figure 14: Age determination of the programme stars in NGC 346 using the non-rotating SMC models of Charbonnel et al. (1993) (open symbols) and those including rotation (Maeder & Meynet 2001; Meynet & Maeder 2005) (closed symbols). Circles, triangles, and squares denote dwarfs, giants, and supergiants, respectively. The horizontal axis gives the ID number of the star (see e.g. Table 3); the vertical axis the age in Myr. The lower limits (upwards pointing arrows) provide age estimates from tracks of chemically homogeneous evolution (Yoon et al. in preparation); see text for a discussion.
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In the text

$\begin{figure} \resizebox{17cm}{!}{ \includegraphics{fit_ngc346_001.ps} \incl... ...raphics{fit_ngc346_010.ps} \includegraphics{fit_ngc346_012.ps} } \end{figure}$ Figure A.1: Comparison of the observed line profiles of NGC 346-001, -007, -010 and -012 with best fitting synthetic line profiles obtained using the automated fitting method (grey lines). Wavelengths are given on the horizontal axis in Å. The vertical axis gives the normalised flux. Note that this axis is scaled differently for each line.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_ngc346_018.ps} \i... ...graphics{fit_ngc346_025.ps} \includegraphics{fit_ngc346_026.ps} } \end{figure}$ Figure A.2: Same as Fig. A.1, however, for NGC 346-018, -022, -025 and -026.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_ngc346_028.ps} \i... ...raphics{fit_ngc346_033.ps} \includegraphics{fit_ngc346_046.ps} } \end{figure}$ Figure A.3: Same as Fig. A.1, however, for NGC 346-028, -031, -033 and -046.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_ngc346_050.ps} \i... ...raphics{fit_ngc346_066.ps} \includegraphics{fit_ngc346_077.ps} } \end{figure}$ Figure A.4: Same as Fig. A.1, however, for NGC 346-050, -051, -066 and -077.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_ngc346_090.ps} \i... ...hics{fit_ngc346_097.ps} \includegraphics{fit_ngc346_107.ps} }\par \end{figure}$ Figure A.5: Same as Fig. A.1, however, for NGC 346-090, -093, -097 and -107.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_ngc346_112.ps} \i... ...} \par\resizebox{8.5cm}{!}{ \includegraphics{fit_ngc330_052.ps} } \end{figure}$ Figure A.6: Same as Fig. A.1, however, for NGC 346-112, NGC 330-031 and -052.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{ \includegraphics{fit_azv14.ps} \includ... ... \includegraphics{fit_azv26.ps} \includegraphics{fit_azv95.ps} } \end{figure}$ Figure A.7: Same as Fig. A.1, however, for AzV 14, 15, 26 and 95.

In the text

$\begin{figure} \par\resizebox{16.5cm}{!}{ \includegraphics{fit_azv243.ps} \inc... ...cludegraphics{fit_azv388.ps} \includegraphics{fit_azv469.ps} }\par\end{figure}$ Figure A.8: Same as Fig. A.1, however, for AzV 243, 372, 388 and 469. Shown with a dotted line for AzV 372 is the effect of an increase of the mass loss rate by 0.1 dex on the line profiles of H $\alpha$ and He II $\lambda$ 4686.

In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4995fi02.ps} \end{figure}$	Figure 2: Number of Lyman continuum ionising photons Q₀ as a function of spectral type. Different luminosity classes are shown using circles, triangles and squares for, respectively, IV-V, III and I-II class objects. Grey circles correspond to stars located on or left of the ZAMS. Indicated using a dashed line is the Galactic calibration for dwarfs from Martins et al. (2005a).
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4995fi11.ps} \end{figure}$	Figure 11: Best fitting model $v_{\rm r}$ distributions for the $v_{\rm r}\sin i$ distribution of the unevolved SMC objects. Shown with a dotted, dashed and dashed-dotted line are, respectively, the constant, the Gaussian and the Maxwellian distribution.
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4995fi12.ps} \end{figure}$	Figure 12: Comparison of mass loss rates determined in this study using the optical spectrum with values determined from the UV spectrum. For the three objects with the lowest mass loss rates the values determined from the optical spectra correspond to upper limits.
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