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Variability Survey in the Open Cluster Stock 14 and the Surrounding Fields

Drobek D., Pigulski A., Shobbrook R. R., Narwid A.

Acta Astronomica

2013

Vol. 63, No. 3

339--368

We present the results of a photometric variability survey in the young open cluster Stock 14 and the surrounding fields. In total, we detected 103 variable stars of which 88 are new discoveries. We confirm short-period, low-amplitude light variations in two eclipsing members of the cluster, HD 101838 and HD 101794. In addition, we find two new β Cep stars of which one, HD 101993, is also a member. The sample of pulsating cluster members is supplemented by one multimode slowly pulsating B-type star and several single-mode candidates of this type. The other pulsating stars in our sample are mostly field stars. In particular, we found fourteen δ Sct stars including one γ Dor/δ Sct hybrid pulsator. From our UBV photometry we derived new parameters of Stock 14: the mean reddening E(B-V)=0.21±0.02 mag, the true distance modulus, 11.90±0.05 mag, and the age, 20±10 Myr. Finally, we use the new photometry to analyze changes of the 6.322-d orbital period of the bright eclipsing binary and the member of the cluster, V346 Cen. In addition to the known apsidal motion, we find that another effect, possibly light-time effect in a hierarchical system of a very long orbital period, affects these changes. The updated value of the period of apsidal motion for this system amounts to 306±4 yr. The open cluster Stock 14 was found to be a fairly good candidate for successful ensemble asteroseismology.

Variable Stars in the Open Cluster NGC 7044

Kopacki G., Drobek D., Kołaczkowski Z., Połubek G.

Acta Astronomica

2008

Vol. 58, No. 4

373--388

We present results of a search for variable stars in the intermediate-age open cluster NGC 7044. We found 23 variable stars in the observed field. One star turned out to be of the δ Sct type with two pulsational modes excited. From the position in the color-magnitude diagram we conclude that this star is a member of the cluster. Moreover, we found 13 eclipsing systems, of which five are W UMa stars, one is a β Lyr variable, six are β Per binaries showing detached configuration, and the last one is another probable β Per system. Using the period-luminosity-color relation for W UMa stars we established the membership of the contact binaries, finding four of them to be very probable cluster members. We estimated from these four stars an apparent distance modulus (m-M)_V of NGC 7044 to be 14.2±0.4 mag, which is smaller than previous determinations of this parameter. We were able to derive orbital period for only four β Per systems. For the remaining ones we observed only two or three eclipses. Finally, nine stars we found show irregular light changes. Most of them are red stars not belonging to the cluster. For the cluster core we determined a reddening map, which allowed us to construct a dereddened color-magnitude diagram of NGC 7044 with a narrow main sequence. By fitting a theoretical isochrone to this diagram we derived E(V-IC)=0.92 mag, (m-M)V=14.45 mag and log(τ/yr)=9.2.