All Figures

$\begin{figure} \par\includegraphics[angle=90,width=15.5cm,clip]{9399Fi01.ps} \end{figure}$ Figure 1: Left: colour-magnitude diagram of NGC 55. The targets selected for the spectroscopic study presented in this paper are marked with circles. Right: location of the target stars in NGC 55. Note that they are spread across the galaxy providing information from different points of NGC 55.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9399Fi02.ps} \end{figure}$ Figure 2: Observed fields of NGC 55. Each square represents approximately the FORS2 field of view ( $6\hbox {$.\mkern -4mu^\prime $ }8\times 6\hbox {$.\mkern -4mu^\prime $ }8$ ) in MXU mode. The image was taken from the DSS archive (http://archive.stsci.edu/cgi-bin/dss_form).
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In the text

$\begin{figure} \par\includegraphics[width=16.6cm,clip]{9399Fi03.ps} \end{figure}$ Figure 3: O-type supergiants in NGC 55. The most relevant transitions for spectral classification are shown.
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In the text

$\begin{figure} \par\includegraphics[width=16.6cm,clip]{9399Fi04.ps} \end{figure}$ Figure 4: Optical spectra of B-type supergiants in NGC 55.
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{9399Fi05.ps} \end{figure}$ Figure 5: Optical spectra of A-supergiants in NGC 55.
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{9399Fi06.ps} \end{figure}$ Figure 6: Three exceptional cases: a white dwarf ( top), an A5V detected in our sample probably belonging to the Milky Way halo ( middle) and an example of spectra dominated by H II emission ( bottom).
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{9399Fi07.ps} \end{figure}$ Figure 7: ``Exotic'' stars found in our survey of NGC 55. See Sect. 3.1 for a discussion of the morphology of each object.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9399Fi08.ps} \end{figure}$ Figure 8: Stellar radial velocities of NGC 55 blue stars as a function of the projected galactocentric distance (stars) and radial velocities measured from nebular emission (open circles). The galaxy's rotational curve derived by Puche et al. (1991) from H I regions (solid line) is included for comparison and there is good agreement with our results.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9399Fi09.ps} \end{figure}$ Figure 9: Spectra of objects with anomalous radial velocity.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9399Fi10.ps} \end{figure}$ Figure 10: V-band ( right) and H ${\alpha }$ ( left) images taken with FORS2. The position of the slits used to observe B_8 ( top) and C2_20 ( bottom) are marked on the image. B_8 is near large H II structures, while C2_20 is located close the centre of NGC 55.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.5cm,clip]{9399Fi11.ps} \end{figure}$ Figure 11: Example of metallicity determination: the spectra of two NGC 55 stars, C1_44 ( top) and A_25 ( bottom), are compared to objects from the Milky Way, LMC and SMC with similar spectral types. In these cases the strength of the silicon and magnesium lines of the NGC 55 stars is similar to the LMC stars.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{9399Fi12.ps} \end{figure}$ Figure 12: Metallicity distribution of B0-A0 supergiants in NGC 55. Left: location of the sample stars in the galaxy, the different symbols indicate their metallicity as shown in the plot. The star shows the optical centre of the galaxy. The average metallicity is close to the LMC. Right: the number of objects per metallicity bin normalised by the total of stars considered, as a function of projected galactocentric radio (degrees). The histogram hints a variation across the projected disk of NGC 55. The solid line represents the stars in each bin over the total, thus giving an idea of how large is the sample in each position bin. We have not plotted the objects with MW and LMC-MW metallicity for clarity, since there are only four of them.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi13.ps}\end{figure}$ Figure B.1: Digital spectral atlas of VLT-FORS2 observations of NGC 55. LBV candidates (LBVc), WRs and Of-stars.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi14.ps}\end{figure}$ Figure B.2: O-type supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi15.ps}\end{figure}$ Figure B.3: Late-O and B0 supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi16.ps}\end{figure}$ Figure B.4: B0 stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi17.ps}\end{figure}$ Figure B.5: B1 supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi18.ps}\end{figure}$ Figure B.5: continued.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi19.ps}\end{figure}$ Figure B.6: B2 supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi20.ps}\end{figure}$ Figure B.6: continued.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi21.ps}\end{figure}$ Figure B.7: Mid-B stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi22.ps}\end{figure}$ Figure B.7: continued.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi23.ps}\end{figure}$ Figure B.8: Late-B supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi24.ps}\end{figure}$ Figure B.8: continued.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi25.ps}\end{figure}$ Figure B.9: A0 supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi26.ps}\end{figure}$ Figure B.9: continued.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi27.ps}\end{figure}$ Figure B.10: Early-A stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi28.ps}\end{figure}$ Figure B.11: A2 supergiants in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi29.ps}\end{figure}$ Figure B.12: A2 and A3 stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi30.ps}\end{figure}$ Figure B.13: A3 stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi31.ps}\end{figure}$ Figure B.14: Mid-A stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi32.ps}\end{figure}$ Figure B.15: Late-A stars in NGC 55.
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In the text

$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi33.ps}\end{figure}$ Figure B.15: continued.
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In the text

$\begin{figure}\par\includegraphics[angle=0,width=15cm]{9399Fi34.ps} \end{figure}$ Figure C.1: FORS2 V-band preimaging of field A. The stars studied in this work are labelled and encircled.
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In the text

$\begin{figure}\par\includegraphics[angle=0,width=15cm]{9399Fi35.ps} \end{figure}$ Figure C.2: Same as Fig. C.1. Target stars in field B.
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In the text

$\begin{figure}\par\includegraphics[angle=0,width=15cm]{9399Fi36.ps} \end{figure}$ Figure C.3: Same as Fig. C.1. Target stars in field C observed through mask C1.
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In the text

$\begin{figure}\par\includegraphics[angle=0,width=15cm]{9399Fi37.ps} \end{figure}$ Figure C.4: Same as Fig. C.1. Target stars in field C observed through mask C2.
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In the text

$\begin{figure}\par\includegraphics[angle=0,width=15cm]{9399Fi38.ps} \end{figure}$ Figure C.5: Same as Fig. C.1. Target stars in field D.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=15.5cm,clip]{9399Fi01.ps} \end{figure}$	Figure 1: Left: colour-magnitude diagram of NGC 55. The targets selected for the spectroscopic study presented in this paper are marked with circles. Right: location of the target stars in NGC 55. Note that they are spread across the galaxy providing information from different points of NGC 55.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9399Fi02.ps} \end{figure}$	Figure 2: Observed fields of NGC 55. Each square represents approximately the FORS2 field of view ( $6\hbox {$.\mkern -4mu^\prime $ }8\times 6\hbox {$.\mkern -4mu^\prime $ }8$ ) in MXU mode. The image was taken from the DSS archive (http://archive.stsci.edu/cgi-bin/dss_form).
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$\begin{figure} \par\includegraphics[width=16.6cm,clip]{9399Fi03.ps} \end{figure}$	Figure 3: O-type supergiants in NGC 55. The most relevant transitions for spectral classification are shown.
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$\begin{figure} \par\includegraphics[width=16.6cm,clip]{9399Fi04.ps} \end{figure}$	Figure 4: Optical spectra of B-type supergiants in NGC 55.
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$\begin{figure} \par\includegraphics[width=16.5cm,clip]{9399Fi05.ps} \end{figure}$	Figure 5: Optical spectra of A-supergiants in NGC 55.
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$\begin{figure} \par\includegraphics[width=16.5cm,clip]{9399Fi06.ps} \end{figure}$	Figure 6: Three exceptional cases: a white dwarf ( top), an A5V detected in our sample probably belonging to the Milky Way halo ( middle) and an example of spectra dominated by H II emission ( bottom).
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$\begin{figure} \par\includegraphics[width=16cm,clip]{9399Fi07.ps} \end{figure}$	Figure 7: ``Exotic'' stars found in our survey of NGC 55. See Sect. 3.1 for a discussion of the morphology of each object.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{9399Fi08.ps} \end{figure}$	Figure 8: Stellar radial velocities of NGC 55 blue stars as a function of the projected galactocentric distance (stars) and radial velocities measured from nebular emission (open circles). The galaxy's rotational curve derived by Puche et al. (1991) from H I regions (solid line) is included for comparison and there is good agreement with our results.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9399Fi09.ps} \end{figure}$	Figure 9: Spectra of objects with anomalous radial velocity.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{9399Fi10.ps} \end{figure}$	Figure 10: V-band ( right) and H ${\alpha }$ ( left) images taken with FORS2. The position of the slits used to observe B_8 ( top) and C2_20 ( bottom) are marked on the image. B_8 is near large H II structures, while C2_20 is located close the centre of NGC 55.
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$\begin{figure} \par\includegraphics[angle=90,width=8.5cm,clip]{9399Fi11.ps} \end{figure}$	Figure 11: Example of metallicity determination: the spectra of two NGC 55 stars, C1_44 ( top) and A_25 ( bottom), are compared to objects from the Milky Way, LMC and SMC with similar spectral types. In these cases the strength of the silicon and magnesium lines of the NGC 55 stars is similar to the LMC stars.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi13.ps}\end{figure}$	Figure B.1: Digital spectral atlas of VLT-FORS2 observations of NGC 55. LBV candidates (LBVc), WRs and Of-stars.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi14.ps}\end{figure}$	Figure B.2: O-type supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi15.ps}\end{figure}$	Figure B.3: Late-O and B0 supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi16.ps}\end{figure}$	Figure B.4: B0 stars in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi17.ps}\end{figure}$	Figure B.5: B1 supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi18.ps}\end{figure}$	Figure B.5: continued.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi19.ps}\end{figure}$	Figure B.6: B2 supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi20.ps}\end{figure}$	Figure B.6: continued.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi21.ps}\end{figure}$	Figure B.7: Mid-B stars in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi22.ps}\end{figure}$	Figure B.7: continued.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi23.ps}\end{figure}$	Figure B.8: Late-B supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi24.ps}\end{figure}$	Figure B.8: continued.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi25.ps}\end{figure}$	Figure B.9: A0 supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi26.ps}\end{figure}$	Figure B.9: continued.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi27.ps}\end{figure}$	Figure B.10: Early-A stars in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi28.ps}\end{figure}$	Figure B.11: A2 supergiants in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi29.ps}\end{figure}$	Figure B.12: A2 and A3 stars in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi30.ps}\end{figure}$	Figure B.13: A3 stars in NGC 55.
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$\begin{figure}\includegraphics[width=16.5cm,clip]{9399Fi31.ps}\end{figure}$	Figure B.14: Mid-A stars in NGC 55.
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