All Figures

$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fig1.eps}\end{figure}$ Figure 1: Schematic map of the observed field of IC 4996 (fov 6 $\hbox {$^\prime $ }$ $\times$ $6\hbox {$^\prime $ }$ ) with all stars measured in Johnson B and V, where 1 pixel (px) corresponds to 0.33 $\hbox {$^{\prime \prime }$ }$ . Identifiers refer to the objects discussed in the text.
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In the text

$\begin{figure} \par\includegraphics[width=6.4cm,clip]{5449fig2.eps}\end{figure}$ Figure 2: Schematic map of the observed field 1 of NGC 6530 (fov $\sim$ 13.5 $^\prime$ $\times$ 13.5 $^\prime$ ), South is at the top and East is to the left, with all stars measured in Johnson B and V, where 1 pixel (px) corresponds to 0.369 $^{\prime \prime }$ . The area marked with the solid lines corresponds to the overlapping region. Identifiers refer to the objects discussed in the text.
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In the text

$\begin{figure} \par\includegraphics[width=6.4cm,clip]{5449fig3.eps}\end{figure}$ Figure 3: Schematic map of the observed field 2 of NGC 6530, similar to Fig. 2.
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In the text

$\begin{figure} \par\includegraphics[width=6.5cm,clip]{5449fig4.eps}\end{figure}$ Figure 4: Amplitude spectrum of IC 4996 37 in the V filter; the identified frequency is marked with an arrow.
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In the text

$\begin{figure} \par\includegraphics[width=6.5cm,clip]{5449fig5.eps}\end{figure}$ Figure 5: Amplitude spectrum of IC 4996 40 in the V filter; the identified frequency is marked with an arrow.
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{5449fig6.eps}\end{figure}$ Figure 6: Amplitude spectrum of NGC 6530 5 in the V filter; "f1'' and "f2'' mark the identified frequencies.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fig7.eps}\end{figure}$ Figure 7: Amplitude spectrum of NGC 6530 82 in the V filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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In the text

$\begin{figure} \par\includegraphics[width=7.65cm,clip]{5449fig8.eps}\end{figure}$ Figure 8: Differential light curve of NGC 6530 85 with a five frequency multi-sine fit (solid line); top: V filter, bottom: B filter (shifted for better visibility).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fig9.eps}\end{figure}$ Figure 9: Amplitude spectra of NGC 6530 85 in both filters; the identified and sequentially prewhitened frequencies are marked with arrows.
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{5449fi10.eps}\end{figure}$ Figure 10: Amplitude spectrum of NGC 6530 263 in the V filter; the identified frequency is marked with an arrow.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi11.eps}\end{figure}$ Figure 11: Differential light curve of NGC 6530 278 with a nine frequency multi-sine fit (solid line); top: V filter, bottom: B filter (shifted for better visibility).
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In the text

$\begin{figure} \par\includegraphics[width=6.9cm,clip]{5449fi12.eps}\end{figure}$ Figure 12: Amplitude spectra of NGC 6530 278 in the V filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi13.eps}\end{figure}$ Figure 13: Amplitude spectrum of NGC 6530 281 in the B filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi14.eps}\end{figure}$ Figure 14: Differential light curve of IC 4996 67 in V ( top) and B filters ( bottom, shifted for better visibility). The solid line corresponds to the multi-sine fit with the two significant frequencies.
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In the text

$\begin{figure} \par\includegraphics[width=6.3cm,clip]{5449fi15.eps}\end{figure}$ Figure 15: Phase plots for IC 4996 80 in V ( top) and B ( bottom) filters with a frequency of 3.578 c/d.
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In the text

$\begin{figure} \par\includegraphics[width=7.25cm,clip]{5449fi16.eps}\end{figure}$ Figure 16: Differential light curve of IC 4996 95 in V with a multi-sine fit (solid line) of the two significant frequencies.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi17.eps}\end{figure}$ Figure 17: Differential light curves for IC 4996 104 in V ( top) and B ( bottom, shifted for better visibility) filters; the solid line corresponds to a multi-sine fit with the two significant frequencies.
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In the text

$\begin{figure} \par\includegraphics[width=6.9cm,clip]{5449fi18.eps}\end{figure}$ Figure 18: Amplitude spectrum of NGC 6530 13 in the V filter, where the significant frequency is indicated with an arrow.
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In the text

$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fi19.eps}\end{figure}$ Figure 19: Part of the light curve of NGC 6530 21 in the V ( top) and B filters ( bottom).
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In the text

$\begin{figure} \par\includegraphics[width=6.85cm,clip]{5449fi20.eps}\end{figure}$ Figure 20: Part of the differential light curve of NGC 6530 55 in the V ( top) and B filters ( bottom, shifted for better visibility).
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In the text

$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fi21.eps}\end{figure}$ Figure 21: Light curve of the suspected eclipsing binary NGC 6530 73 in the V (open circles) and B (solid circles) filters.
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In the text

$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fi22.eps}\end{figure}$ Figure 22: Observational HR diagram of all stars in the field of IC 4996: bona fide PMS pulsators (filled circles), candidate PMS pulsator (open circle), other variables (filled triangles), and other suspected variables (open triangles); the ZAMS values are taken from Schmidt-Kaler (solid line), and the borders of the classical instability strip (dashed lines) have been transformed into the M_V-(B-V)₀ plane.
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In the text

$\begin{figure} \par\includegraphics[width=6.65cm,clip]{5449fi23.eps}\vspace*{3mm} \includegraphics[width=6.65cm,clip]{5449fi24.eps}\end{figure}$ Figure 23: HR diagram of all measured stars in the field of IC 4996, where the stars have different symbols and sizes according to their expected amplitude noise levels; top: V filter, bottom: B filter; the values for the ZAMS (solid line) are taken from Schmidt-Kaler (1965).
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In the text

$\begin{figure} \par\includegraphics[width=6.6cm,clip]{5449fi25.eps}\end{figure}$ Figure 24: Observational HR diagram of all stars in the field of NGC 6530: bona fide PMS pulsators (filled circles), candidate PMS pulsator (open circle), other variables (filled triangles), and other suspected variables (open triangles); the ZAMS values are taken from Schmidt-Kaler (solid line) and the borders of the classical instability strip (dashed lines) have been transformed into the M_V-(B-V)₀ plane.
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In the text

$\begin{figure} \par\includegraphics[width=6.65cm,clip]{5449fi26.eps}\vspace*{3mm} \includegraphics[width=6.65cm,clip]{5449fi27.eps}\end{figure}$ Figure 25: HR diagram of all measured stars in the field of NGC 6530, where the stars have different symbols and sizes according to their expected amplitude noise level bins; top: V filter, bottom: B filter; the values for the ZAMS (solid line) are taken from Schmidt-Kaler (1965).
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In the text

$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fig1.eps}\end{figure}$	Figure 1: Schematic map of the observed field of IC 4996 (fov 6 $\hbox {$^\prime $ }$ $\times$ $6\hbox {$^\prime $ }$ ) with all stars measured in Johnson B and V, where 1 pixel (px) corresponds to 0.33 $\hbox {$^{\prime \prime }$ }$ . Identifiers refer to the objects discussed in the text.
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$\begin{figure} \par\includegraphics[width=6.4cm,clip]{5449fig3.eps}\end{figure}$	Figure 3: Schematic map of the observed field 2 of NGC 6530, similar to Fig. 2.
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$\begin{figure} \par\includegraphics[width=6.5cm,clip]{5449fig4.eps}\end{figure}$	Figure 4: Amplitude spectrum of IC 4996 37 in the V filter; the identified frequency is marked with an arrow.
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$\begin{figure} \par\includegraphics[width=6.5cm,clip]{5449fig5.eps}\end{figure}$	Figure 5: Amplitude spectrum of IC 4996 40 in the V filter; the identified frequency is marked with an arrow.
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{5449fig6.eps}\end{figure}$	Figure 6: Amplitude spectrum of NGC 6530 5 in the V filter; "f1'' and "f2'' mark the identified frequencies.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fig7.eps}\end{figure}$	Figure 7: Amplitude spectrum of NGC 6530 82 in the V filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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$\begin{figure} \par\includegraphics[width=7.65cm,clip]{5449fig8.eps}\end{figure}$	Figure 8: Differential light curve of NGC 6530 85 with a five frequency multi-sine fit (solid line); top: V filter, bottom: B filter (shifted for better visibility).
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fig9.eps}\end{figure}$	Figure 9: Amplitude spectra of NGC 6530 85 in both filters; the identified and sequentially prewhitened frequencies are marked with arrows.
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{5449fi10.eps}\end{figure}$	Figure 10: Amplitude spectrum of NGC 6530 263 in the V filter; the identified frequency is marked with an arrow.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi11.eps}\end{figure}$	Figure 11: Differential light curve of NGC 6530 278 with a nine frequency multi-sine fit (solid line); top: V filter, bottom: B filter (shifted for better visibility).
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$\begin{figure} \par\includegraphics[width=6.9cm,clip]{5449fi12.eps}\end{figure}$	Figure 12: Amplitude spectra of NGC 6530 278 in the V filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi13.eps}\end{figure}$	Figure 13: Amplitude spectrum of NGC 6530 281 in the B filter; the identified and sequentially prewhitened frequencies are marked with arrows.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi14.eps}\end{figure}$	Figure 14: Differential light curve of IC 4996 67 in V ( top) and B filters ( bottom, shifted for better visibility). The solid line corresponds to the multi-sine fit with the two significant frequencies.
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$\begin{figure} \par\includegraphics[width=6.3cm,clip]{5449fi15.eps}\end{figure}$	Figure 15: Phase plots for IC 4996 80 in V ( top) and B ( bottom) filters with a frequency of 3.578 c/d.
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$\begin{figure} \par\includegraphics[width=7.25cm,clip]{5449fi16.eps}\end{figure}$	Figure 16: Differential light curve of IC 4996 95 in V with a multi-sine fit (solid line) of the two significant frequencies.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{5449fi17.eps}\end{figure}$	Figure 17: Differential light curves for IC 4996 104 in V ( top) and B ( bottom, shifted for better visibility) filters; the solid line corresponds to a multi-sine fit with the two significant frequencies.
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$\begin{figure} \par\includegraphics[width=6.9cm,clip]{5449fi18.eps}\end{figure}$	Figure 18: Amplitude spectrum of NGC 6530 13 in the V filter, where the significant frequency is indicated with an arrow.
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$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fi19.eps}\end{figure}$	Figure 19: Part of the light curve of NGC 6530 21 in the V ( top) and B filters ( bottom).
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$\begin{figure} \par\includegraphics[width=6.85cm,clip]{5449fi20.eps}\end{figure}$	Figure 20: Part of the differential light curve of NGC 6530 55 in the V ( top) and B filters ( bottom, shifted for better visibility).
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$\begin{figure} \par\includegraphics[width=6.55cm,clip]{5449fi21.eps}\end{figure}$	Figure 21: Light curve of the suspected eclipsing binary NGC 6530 73 in the V (open circles) and B (solid circles) filters.
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$\begin{figure} \par\includegraphics[width=6.65cm,clip]{5449fi23.eps}\vspace*{3mm} \includegraphics[width=6.65cm,clip]{5449fi24.eps}\end{figure}$	Figure 23: HR diagram of all measured stars in the field of IC 4996, where the stars have different symbols and sizes according to their expected amplitude noise levels; top: V filter, bottom: B filter; the values for the ZAMS (solid line) are taken from Schmidt-Kaler (1965).
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$\begin{figure} \par\includegraphics[width=6.65cm,clip]{5449fi26.eps}\vspace*{3mm} \includegraphics[width=6.65cm,clip]{5449fi27.eps}\end{figure}$	Figure 25: HR diagram of all measured stars in the field of NGC 6530, where the stars have different symbols and sizes according to their expected amplitude noise level bins; top: V filter, bottom: B filter; the values for the ZAMS (solid line) are taken from Schmidt-Kaler (1965).
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