A CCD Photometric Survey of Variable Stars in the Field of NGC 188

Zhang, X. B.; Deng, Licai; Tian, Bing; Zhou, Xu

doi:10.1086/338846

Cited by 37 publications

(48 citation statements)

References 20 publications

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“…1 that contains the star. b Our best fit is the shorter period, but the longer period is also satisfactory and is near the periods listed by Kaluzny & Shara 1987 and by Zhang et al 2002. The light curve of WV 1 in Fig.…”

Section: Discussionsupporting

confidence: 76%

“…Comparison of our astrometric information (when available) with the coordinates provided by Zhang et al (2002) (which includes the information of the Kaluzny & Shara 1987 study) led us to identify one already known variable star in our sample, namely, WV 1, which corresponds to their V1. Visual inspection of the finding chart provided by the same study (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…NGC 188 is a rich open cluster that has been a popular target for numerous studies, primarily due to its advanced age (7.0 AE 0.5 Gyr; Sarajedini et al 1999, hereafter WOCS II), relatively close distance (M À m = 11.43 AE 0.08; von Hippel & Sarajedini 1998, hereafter WOCS I), and low reddening value [E(BÀV ) = 0.09 AE 0.02; WOCS II]. It has also been the object of intensive photometric monitoring (Baliunas & Guinan 1985;Kaluzny & Shara 1987;Zhang et al 2002), which led to the discovery of 19 variable stars in the vicinity of the cluster, 13 of which are W UMa type binaries: contact, solar-like systems found only in intermediate-age clusters with ages between 0.7 and 7 Gyr (Rucinski 1998).…”

Section: Introductionmentioning

confidence: 99%

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WIYN Open Cluster Study. XV. Photometric Monitoring of Open Clusters: New Variables in NGC 188

Kafka

Honeycutt

2003

Astron J

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Photometric monitoring of the central 17 0 Â 17 0 of the old open cluster NGC 188 with the WIYN 3.5 m telescope has resulted in the discovery of a number of new variable stars, down to 21.5 mag in V, 35 of which have well-determined periods. The variability types of the fainter stars of the sample (18-21.5 mag) remain uncertain. However, most of the brighter stars (15-18 mag) probably make up the low-luminosity extension of the already known W UMa population of NGC 188. We also report the discovery of two longer period variables on the subgiant branch of the cluster CMD, most likely FK Comae stars, which suggests that the cluster may provide significant insight on the formation and evolution of contact binary systems. Alternatively, these objects may represent a new kind of pulsation variables.

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Section: Discussionsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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WIYN Open Cluster Study. XV. Photometric Monitoring of Open Clusters: New Variables in NGC 188

Kafka

Honeycutt

2003

Astron J

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“…NGC 188 is well-known for its unusually high number of W UMa-type variable stars (Zhang et al 2002). Among the 19 variables listed by Zhang et al (2002) and the 25 variables with precise coordinates listed by Kafka & Honeycutt (2003), 22 are located in the EPIC field of view.…”

Section: Ngc 188 Observation and Source Identificationmentioning

confidence: 99%

“…NGC 188 also possesses other types of variables (Kaluzny & Shara 1987;Kaluzny 1990; Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Table 1 is only available in electronic form at http://www.edpsciences.org Mazur & Kaluzny 1990;Zhang et al 2002) and numerous probable blue stragglers (Leonard & Linneil 1992;Dinescu et al 1996).…”

Section: Introductionmentioning

confidence: 99%

X-ray observations of the old open stellar cluster NGC 188

Gondoin

2005

A&A

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Abstract. I present the analysis results from XMM-Newton observations of the old open stellar cluster NGC 188, which has an age of about 7 Gyr and a near solar metallicity. 58 X-ray sources were detected in the field of view of the EPIC MOS and pn cameras, and 46 sources are new X-ray detections. Visible counterparts were found for 20 sources including the variable star WV 28, the W UMa-type binaries V371 Cep and V372 Cep, and the red giant V11. 9 X-ray sources are identified with probable cluster non-members, while 43 X-ray sources are of unknown membership. X-ray emission was detected from 6 stars with high membership probability above a luminosity threshold of 10 30 erg s −1 . This indicates the presence of very active latetype stars in NGC 188 in spite of its old age. The HR diagram positions of two of these stars just above the main sequence are reminiscent of those for W Ursae Majoris-type contact binaries. Two other sources could be either members of close binary systems or the product of the coalescence of W UMa type binaries into single stars. One X-ray source in NGC 188 is located at the bottom of the red giant branch in an evolutionary status similar to that of an FK Comae-type star. Another X-ray source detected in NGC 188 has the HR diagram position of an M type star. Its X-ray to bolometric luminosity ratio, greater than the canonical 10 −3 saturation level, suggests that the star was flaring during XMM-Newton observations. M stars are most likely the most numerous X-ray sources in NGC 188 at lower X-ray luminosity thresholds.

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