Issue
A&A
Volume 554, June 2013
Article Number A108
Number of page(s) 29
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361/201321065
Published online 12 June 2013

Online material

Appendix A: Eclipsing binaries

Table A.1

Eclipsing binaries in our field of view of NGC 3766.

thumbnail Fig. A.1

Folded light curves of the eclipsing binaries listed in Table A.1. The error bar displayed in red in the lower-left corner of each plot gives the mean error of the measurements. A zoom on the eclipses of candidate 50 (upper left most panel) is shown in Fig. A.3.

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thumbnail Fig. A.2

Light curve of the eclipsing binary candidate 50.

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thumbnail Fig. A.3

Folded light curve of the eclipsing binary candidate 50, zoomed on the first (left panel) and second (right panel) eclipse.

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The list of eclipsing binaries found in our FOV of NGC 3766 is provided in Table A.1. We give, in the order of the columns presented in the table, their identification number in our numbering scheme, their mean V′ magnitude, their colors, their period, their binarity type and their potential cluster membership. Membership is evaluated from the position of the star in the color–magnitude and color–color diagrams (Figs. 7 and 8, respectively, in the main body of the paper).

The folded light curves of the eclipsing binaries are shown in Fig. A.1.

The eclipsing binary system candidate 50 requires further discussion. Its light curve, displayed in Fig. A.2, shows only two eclipsing event candidates, that occurred respectively during the nights 2552.5 and 1858.5 d. The eclipse durations, if both events are indeed due to an eclipse, are of the order of several hours to half a day. The third dimming event, around 1410 d, spans two nights and seems less probably due to an eclipsing event. We therefore assume here that only the first two events are due to an eclipse. The first of them shows a very nice V-shape light curve, while the second one has only two sets of measurements on the brightening side of event.

It is difficult to estimate a period of an eclipsing binary with only two eclipses. Furthermore, and unfortunately, no B

or U′ measurement is available at the times of the two events. We therefore proceeded in the following way. We first determined the most probable period PV from the V′ light curve. No bright (i.e. at the out-of-eclipse level) measurement should be present at eclipse times, as easily checked in the folded light curves. This led to PV = 6.291223 d. We then search the smallest multiple nPV, n being an integer, for which the folded light curves in B′ and U′ are compatible with the two eclipses at their relevant phases. The final period is thereby estimated to P = 100.63957 d.

The folded light curve is shown in the upper-left panel of Fig. A.1, and a zoom on the two eclipses in Fig. A.3. The minima of the two eclipses are seen to be distant, in phase, by only 0.1 from each other, pointing to a very eccentric system.

To shed some further light on the binary nature of star 50, we took spectra of it with the Euler telescope. From its location on the MS in the HR diagram, we expected the star to be of spectral type around B3. Its spectra, however, showed the presence of many iron lines, thus revealing the presence of an A-type companion, possibly of spectral type A3. We thus conclude on a double system with a B-type primary and an A-type secondary. More observations are required to better characterize this system. We further note that this binary candidate 50 is also a member of group 2 stars.

Appendix B: Group 1 to 5 periodic variables

Table B.1

Periodic stars with secured frequencies in our FOV of NGC 3766.

The list of group 1 to 5 periodic variables with secured frequencies is provided in Table B.1. We give, in the order of the columns presented in the table, their identification number in our numbering scheme, their mean V′ magnitude and colors, the group to which they belong (as defined in Sect. 5), the period, amplitude, uncertainty on the amplitude, and S/N of each of their frequencies determined from their V′ time series (one line per period), and the star identification number given by McSwain & Gies (2005) and used in McSwain et al. (2008), if available.

The number of digits printed in Table B.1 for the periods is computed from the uncertainty εP on the period P, estimated with the formula, derived by Montgomery & Odonoghue (1999), (B.1)

where Nobs is the number of observations in the time series of duration Tobs, A is the amplitude and σnoise the mean uncertainty of the measurements. The uncertain digit is written in parenthesis.

The uncertainty on the amplitude is estimated, also from Montgomery & Odonoghue (1999), with the formula (B.2)The folded light curves of group 1 stars are shown in Figs. B.1 and B.2, of group 2 stars in Figs. B.3 to B.5, of group 3 stars in Figs. B.6 to B.9, and of group 4 stars in Figs. B.10 to B.12. The outliers seen in the folded light curve of star 49 (Fig. B.1) are due to an outburst occurring at the end of our observation campaign. It will be studied in more details in a forthcoming paper (Mowlavi et al., in prep.).

The light curves of the two LPV stars in our sample are shown in Fig. B.13.

thumbnail Fig. B.1

Folded light curves in V′ of the monoperiodic variables of group 1 (SPB candidates). The mean V′ magnitude has been subtracted from the light curves. Cyan lines represent a sine fit to the data using the frequency found by the period search algorithm. The star identification is written in the lower left corner of each figure, with the mean V′ magnitude in parenthesis. The period used to fold the data is written in the lower right corner of each figure.

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thumbnail Fig. B.2

Same as Fig. B.1, but for the multiperiodic variables of group 1 (SPB candidates). All significant frequencies are shown, one panel per frequency. The data shown for each frequency is the residual obtained by subtracting from the original data all earlier frequencies, from top to bottom panels. The period used to fold the data in each panel is written in the lower right corner of each panel.

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thumbnail Fig. B.3

Same as Fig. B.1, but for the monoperiodic variables of group 2.

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thumbnail Fig. B.4

Same as Fig. B.2, but for the biperiodic variables of group 2.

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thumbnail Fig. B.5

Same as Fig. B.2, but for the triperiodic variables of group 2.

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thumbnail Fig. B.6

Same as Fig. B.1, but for the monoperiodic variables of group 3 (δ Sct candidates).

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thumbnail Fig. B.7

Same as Fig. B.2, but for the biperiodic variables of group 3 (δ Sct candidates).

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thumbnail Fig. B.8

Same as Fig. B.2, but for the triperiodic variables of group 3 (δ Sct candidates).

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thumbnail Fig. B.9

Same as Fig. B.2, but for the multiperiodic variables of group 3 (δ Sct candidates) with more than three periods.

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thumbnail Fig. B.10

Same as Fig. B.1, but for the monoperiodic variables of group 4 (γ Dor candidates).

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thumbnail Fig. B.11

Same as Fig. B.2, but for the biperiodic variables of group 4 (γ Dor candidates).

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thumbnail Fig. B.12

Same as Fig. B.2, but for the multiperiodic variables of group 4 (γ Dor candidates) with more than two periods.

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thumbnail Fig. B.13

V′ light curves of the LPV stars 349 (top figure) and 1428 (bottom figure).

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© ESO, 2013

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