Wiyn Open Cluster Study. Lv. Astrometry and Membership in NGC 6819

Platais, I.; Gosnell, Natalie M.; Meibom, S.; Kozhurina-Platais, V.; Bellini, Andrea; Veillet, Christian; Burkhead, Martin S.

doi:10.1088/0004-6256/146/2/43

Cited by 35 publications

(80 citation statements)

References 34 publications

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“…For NGC 6819, new membership information from Platais et al (2011) has been included. References -1 van den Berg et al (2004), Geller et al (2015), 2 Gosnell et al (2012), Platais et al (2013) 3 van den Berg et al (2013), Platais et al (2011) …”

Section: Discussionmentioning

confidence: 99%

“…For NGC 6791, the emissivity was taken from van den Berg et al (2013), and for M 67 we updated the value for the new mass. We incorporated new counterpart and membership information from Platais et al (2013) in the numbers for NGC 6819; the range in emissivity reflects more and less conservative assumptions on which counterparts are cluster members or not. The conversion of the X-ray luminosities from the 0.2-10 keV band, as given in Gosnell et al (2012), to our adopted band of 0.3-7 keV was done assuming a 2 keV MeKaL model.…”

Section: Comparison With Other Old Open Clustersmentioning

confidence: 99%

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A Chandra X-Ray Census of the Interacting Binaries in Old Open Clusters—Collinder 261

Vats

Berg

2017

ApJ

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We present the first X-ray study of Collinder 261 (Cr 261), which at an age of 7 Gyr is one of the oldest open clusters known in the Galaxy. Our observation with the Chandra X-ray Observatory is aimed at uncovering the close interacting binaries in Cr 261, and reaches a limiting X-ray luminosity of L X ≈ 4 × 10 29 erg s −1 (0.3-7 keV) for stars in the cluster. We detect 107 sources within the cluster half-mass radius r h , and we estimate that among the sources with L X 10 30 erg s −1 , ∼26 are associated with the cluster. We identify a mix of active binaries and candidate active binaries, candidate cataclysmic variables, and stars that have "straggled" from the main locus of Cr 261 in the colour-magnitude diagram. Based on a deep optical source catalogue of the field, we estimate that Cr 261 has an approximate mass of 6500 M ⊙ , roughly the same as the old open cluster NGC 6791. The X-ray emissivity of Cr 261 is similar to that of other old open clusters, supporting the trend that they are more luminous in X-rays per unit mass than old populations of higher (globular clusters) and lower (the local neighbourhood) stellar density. This implies that the dynamical destruction of binaries in the densest environments is not solely responsible for the observed differences in X-ray emissivity.

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Section: Discussionmentioning

confidence: 99%

Section: Comparison With Other Old Open Clustersmentioning

confidence: 99%

A Chandra X-Ray Census of the Interacting Binaries in Old Open Clusters—Collinder 261

Vats

Berg

2017

ApJ

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“…Table 4 is from (Kalirai et al 2001) and 2MASS, respectively. This star has a proper-motion membership probability of 99% from Platais et al (2013). Though it has many spectroscopic observations from WIYN/Hydra, the source is a rapid rotator, and therefore reliable radial velocities are difficult to obtain (Hole et al 2009).…”

Section: Open Cluster Observationsmentioning

confidence: 99%

On the Origin of Sub-subgiant Stars. I. Demographics

Geller

Leiner

Bellini

et al. 2017

ApJ

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Sub-subgiants are stars observed to be redder than normal main-sequence stars and fainter than normal subgiant (and giant) stars in an optical color-magnitude diagram. The red straggler stars, which lie redward of the red giant branch, may be related and are often grouped together with the sub-subgiants in the literature. These stars defy our standard theory of single-star evolution, and are important tests for binary evolution and stellar collision models. In total, we identify 65 sub-subgiants and red stragglers in 16 open and globular star clusters from the literature; 50 of these, including 43 sub-subgiants, pass our strict membership selection criteria (though the remaining sources may also be cluster members). In addition to their unique location on the color-magnitude diagram, we find that at least 58% (25/43) of sub-subgiants in this sample are X-ray sources with typical 0.5-2.5 keV luminosities of order 10 30−31 erg s −1 . Their X-ray luminosities and optical-to-X-ray flux ratios are similar to those of RS CVn active binaries. At least 65% (28/43) of the sub-subgiants in our sample are variables, 21 of which are known to be radial-velocity binaries. Typical variability periods are 15 days. At least 33% (14/43) of the sub-subgiants are Hα emitters. These observational demographics provide strong evidence that binarity is important for sub-subgiant formation. Finally, we find that the number of sub-subgiants per unit mass increases toward lower-mass clusters, such that the open clusters in our sample have the highest specific frequencies of sub-subgiants.

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“…The WIYN Open Cluster Study (WOCS) obtained spectra for these clusters that were used to measure barium abundances to test the AGB mass transfer formation scenario for that cluster's blue straggler population. The Ba spectral order encompasses Na i D, which means those spectra can be analyzed to search for variable ISM absorption and check for spatial correlation with the differential reddening map suggested by Platais et al (2013) and Anthony-Twarog et al (2014).…”

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confidence: 99%

“…Evidence for differential reddening has been presented for NGC 6819 (the 2.5 Gyr Kepler cluster, Platais et al 2013;Anthony-Twarog et al 2014). The WIYN Open Cluster Study (WOCS) obtained spectra for these clusters that were used to measure barium abundances to test the AGB mass transfer formation scenario for that cluster's blue straggler population.…”

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confidence: 99%

No “Maunder Minimum” Candidates in M67: Mitigating Interstellar Contamination of Chromospheric Emission Lines

Curtis

2017

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The solar analogs of M67 let us glimpse the probable behavior of the Sun on time scales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun. Previous surveys of M67 observed that 15% of its Sun-like stars exhibited chromospheric activity levels below solar minimum, which suggest that these stars might be in activity-minimum states analogous to the Maunder Minimum. The activity diagnostic used, the HK index (relative intensities of the Ca ii H & K lines integrated over 1Å bandpasses), was measured from low-resolution spectra (R ≈ 5000), as is traditional and suitable for nearby, bright stars. However, for stars beyond the Local Bubble, the interstellar medium (ISM) imprints absorption lines in spectra at Ca ii H & K, which negatively bias activity measurements when these lines fall within the HK index bandpass. I model the ISM clouds in the M67 foreground with high-resolution spectra of blue stragglers and solar analogs. I demonstrate that ISM absorption varies across the cluster and must be accounted for on a star-by-star basis. I then apply the ISM model to a solar spectrum and broaden it to the lower spectral resolution employed by prior surveys. Comparing HK indices measured from ISM-free and ISM-contaminated spectra, I find that all stars observed below solar minimum can be explained by this ISM bias. I conclude that there is no compelling evidence for Maunder minimum candidates in M67 at this time.

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Wiyn Open Cluster Study. Lv. Astrometry and Membership in NGC 6819

Cited by 35 publications

References 34 publications

A Chandra X-Ray Census of the Interacting Binaries in Old Open Clusters—Collinder 261

A Chandra X-Ray Census of the Interacting Binaries in Old Open Clusters—Collinder 261

On the Origin of Sub-subgiant Stars. I. Demographics

No “Maunder Minimum” Candidates in M67: Mitigating Interstellar Contamination of Chromospheric Emission Lines

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