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J/A+A/554/A108          Periodic variables in NGC 3766        (Mowlavi+, 2013)

Stellar variability in open clusters. I. A new class of variable stars in NGC 3766. Mowlavi N., Barblan F., Saesen S., Eyer L. <Astron. Astrophys. 554, A108 (2013)> =2013A&A...554A.108M
ADC_Keywords: Clusters, open ; Stars, variable ; Photometry, CCD ; Photometry, Geneva ; Stars, A-type Keywords: Hertzsprung-Russell and C-M diagrams - stars: oscillations - open clusters and associations: individual: NGC 3766 - binaries: eclipsing - stars: variables: general Abstract: We analyze the population of periodic variable stars in the open cluster NGC3766 based on a 7-year multiband monitoring campaign conducted on the 1.2m Swiss Euler telescope at La Silla, Chili. The data reduction, light curve cleaning, and period search procedures, combined with the long observation time line, allowed us to detect variability amplitudes down to the mmag level. The variability properties were complemented with the positions in the color-magnitude and color-color diagrams to classify periodic variable stars into distinct variability types. We find a large population (36 stars) of new variable stars between the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is predicted to occur based on standard stellar models. The bulk of their periods ranges from 0.1 to 0.7d, with amplitudes between 1 and 4mmag for the majority of them. About 20% of stars in that region of the HR diagram are found to be variable, but the number of members of this new group is expected to be higher, with amplitudes below our mmag detection limit. The properties of this new group of variable stars are summarized and arguments set forth in favor of a pulsation origin of the variability, with g-modes sustained by stellar rotation. Potential members of this new class of low-amplitude periodic (most probably pulsating) A and late-B variables in the literature are discussed. We additionally identify 16 eclipsing binary, 13 SPB, 14 delta Sct, and 12 gamma Dor candidates, as well as 72 fainter periodic variables. All are new discoveries. We encourage searching for this new class of variables in other young open clusters, especially in those hosting a rich population of Be stars. Description: Coordinates, photometry and periods of variable stars detected in the open cluster NGC3766. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file tablea1.dat 65 16 Eclipsing binaries in our FOV of NGC 3766 tablea2.dat 96 228 Periodic stars with secured frequencies in our FOV of NGC3766
See also: J/ApJ/622/1052 : byHα photometry of NGC 3766 (McSwain+, 2005) Byte-by-byte Description of file: tablea1.dat
Bytes Format Units Label Explanations
1- 4 I4 --- GvaId [50/2663] Star identification number 6- 14 F9.6 h RAhour Right ascension in decimal hours (J2000.0) 16- 25 F10.6 deg DEdeg Declination in decimal degrees (J2000.0) 27- 32 F6.3 mag Vmag Not-calibrated Geneva CCD V band 34- 39 F6.3 mag B-V Not-calibrated Geneva CCD B-V color index 41- 46 F6.3 mag U-B Not-calibrated Geneva CCD U-B color index 48- 57 F10.6 d Per Period 58 A1 --- u_Per [)] Uncertainty flag on Per 60- 61 A2 --- Type [EABW] Type of binary star (EA, EB or EW) 63- 65 A3 --- Mmb [yes/no ] Potential cluster membership
Byte-by-byte Description of file: tablea2.dat
Bytes Format Units Label Explanations
1- 4 I4 --- GvaId [22/3525] Star identification number 5 A1 --- n_GvaId [*] * for eclipsing binaries 7- 15 F9.6 h RAhour Right ascension in decimal hours (J2000.0) 17- 26 F10.6 deg DEdeg Declination in decimal degrees (J2000.0) 28- 33 F6.3 mag Vmag Not-calibrated Geneva CCD V band 35- 40 F6.3 mag B-V Not-calibrated Geneva CCD B-V color index 41 A1 --- u_B-V [)] ) if the involved time series are not all good 43- 48 F6.3 mag U-B Not-calibrated Geneva CCD U-B color index 49 A1 --- u_U-B [)] ) if the involved time series are not all good 51- 53 A3 --- Grp Group of the variable (1-5) (1) 55- 65 F11.7 d Per Period 67- 75 F9.7 d e_Per Uncertainty on Per 77- 82 F6.2 mmag Amp Amplitude 84- 87 F4.2 mmag e_Amp Uncertainty on the amplitude 89- 92 F4.1 --- S/N Signal to noise ratio 94- 96 I3 --- MGid ? Star number given by McSwain et al. (2008ApJ...672..590M), <Cl* NGC 3766 MG NNN> in Simbad
Note (1): Groups as follows: 1 = V<12.5mag and P>1.1d. They are two magnitudes or more brighter than the most luminous delta Sct candidate. One fainter star at V=13.86mag is also added to this group (see Sect. 5.1). 2 = 11<V<14mag and 0.1d<P<1.1d. They fill the magnitude range between the delta Sct and group 1 stars. 3 = 14<V<14.9mag and P<0.1d. It is the group of delta Sct candidates. Two fainter stars at V≃15.3mag are also added to this group (see Sect. 5.3). 4 = 14.9<V<15.5mag and P>0.1d. One fainter star at V≃17mag is also added to this group (see Sect. 5.4). 5 = all other periodic variables, i.e. those fainter than V=15.5mag and the red giants that were excluded from the other groups.
Acknowledgements: Nami Mowlavi, Nami.Mowlavi(at)unige.ch
(End) Patricia Vannier [CDS] 11-Jun-2013
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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