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The Clusters AgeS Experiment (CASE). VI. Analysis of Two Detached Eclipsing Binaries in the Globular Cluster M55

Kaluzny J., Thompson I. B., Dotter A., Rozyczka M., Pych W., Rucinski S. M., Burley G. S.

Acta Astronomica

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2014

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Vol. 64, No. 1

11--26

EN

We present an analysis of the detached eclipsing binaries V44 and V54 belonging to the globular cluster M55. For V54 we obtain the following absolute parameters: Mp=0.726±0.015 Msun, Rp=1.006± 0.009 Rsun, Lp=1.38±0.07 Lsun for the primary, and Ms=0.555± 0.008 Msun, Rs=0.528±0.005 Rsun, Ls=0.16±0.01 Lsun for the secondary. The age and apparent distance modulus of V54 are estimated at 13.3-14.7 Gyr and 13.94±0.05 mag, respectively. This derived age is substantially larger than ages we have derived from the analysis of binary systems in 47 Tuc and M4. The secondary of V44 is so weak in the optical domain that only mass function and relative parameters are obtained for the components of this system. However, there is a good chance that the velocity curve of the secondary could be derived from near-IR spectra. As the primary of V44 is more evolved than that of V54, such data would impose much tighter limits on the age and distance of M55.

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The Clusters AgeS Experiment (CASE): The Blue Straggler Star M55-V60 Caught Amidst Rapid Mass Exchange

Rozyczka M., Kaluzny J., Thompson I. B., Rucinski S. M., Pych W., Krzeminski W.

Acta Astronomica

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2013

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Vol. 63, No. 1

67--78

EN

We analyze light and velocity curves of the eclipsing blue straggler V60 in the field of the globular cluster M55. We derive Mp=1.259± 0.025 Msun, Rp=1.102±0.021 Rsun, M bolp=3.03±0.09 mag for the primary and Ms=0.327±0.017 Msun, Rs=1.480±0.011 Rsun, Mbols=4.18±0.12 mag for the secondary. We measure an apparent distance modulus (m-M)V=14.04±0.09 mag. Based on the systemic velocity, distance, and proper motion of V60 we conclude that the system is a member of the cluster and argue that its present state is a result of rapid but conservative mass exchange which the binary is still undergoing. We report a peculiar blue excess on the ascending branch of the primary eclipse of V60 and discuss its possible origin.

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The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55

Kaluzny J., Thompson I. B., Krzeminski W., Zloczewski K.

Acta Astronomica

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2010

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Vol. 60, No. 3

245--260

EN

We report time-series photometry for 55 variable stars located in the central part of the globular cluster M55. The sample includes 28 newly identified objects of which 13 are eclipsing binaries. Three of these are detached systems located in the turn-off region on the cluster color-magnitude diagram. Two of them are proper motion (PM) members of M55 and are excellent candidates for a detailed follow-up study aimed at a determination of the cluster age and distance. Other detached binaries are located along the unevolved part of the cluster main sequence. Most of the variable stars are cluster blue straggler stars. This group includes 35 SX Phe stars, two contact binaries, and one semi-detached binary. V60 is a low mass, short period Algol with the less massive and cooler component filling its Roche lobe. The more massive component is an SX Phe variable star. The orbital period of V60 increases at a rate of dP/P=3.0×10-9. In addition to numerous variable blue stragglers we also report the detection of two red stragglers showing periodic variability. Both of these are PM members of M55. We note and discuss the observed paucity of contact binaries among unevolved main sequence stars in M55 and NGC 6752. This apparent paucity supports an evolution model in which the formation of contact binaries is triggered by stellar evolution at the main-sequence turn off.