Kepler observations of the open cluster NGC 6819

Balona, L. A.; Medupe, T.; Abedigamba, O. P.; Ayane, Getinet Feleke; Keeley, L.; Matsididi, M.; Mekonnen, G.; Nhlapo, M. D.; Sithole, N.

doi:10.1093/mnras/stt148

Cited by 32 publications

(29 citation statements)

References 51 publications

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“…8). Additional measurements were done for the open clusters NGC 6866 (Balona et al 2013a) and NGC 6819 (Balona et al 2013b) showing rotational braking as well. The same author found several A-type stars showing signatures of spot-induced variability (Balona 2011(Balona , 2013, e.g., a beating pattern in the light curve, although this behavior was not expected because of their purely radiative atmospheres.…”

Section: Fig 16 Comparison Of Periods Frommentioning

confidence: 99%

Rotation and differential rotation of activeKeplerstars

Reinhold

Reiners

Basri

2013

A&A

353

397

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Context. The Kepler space telescope monitors more than 160 000 stars with an unprecedented precision providing the opportunity to study the rotation of thousands of stars. Aims. We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected that we interpreted as surface differential rotation (DR). We show how the absolute and relative shear (ΔΩ and α = ΔΩ/Ω, respectively) correlate with rotation period and effective temperature. Methods. Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were associated to different surface rotation periods. Our purely mathematical approach is capable of detecting different periods but cannot distinguish between the physical origins of periodicity. We ascribe the existence of different periods to DR, but spot evolution could also play a role. Because of the large number of stars the period errors are estimated statistically. We thus cannot exclude the existence of false positives among our periods.Results. In our sample of 40 661 active stars we found 24 124 rotation periods P 1 between 0.5 and 45 days, with a mean of P 1 = 16.3 days. The distribution of stars with 0.5 < B − V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate; the detection among older stars is incomplete probably because of our active sample selection. A second period P 2 within ±30% of the rotation period P 1 was found in 18 616 stars (77.2%). Attributing these two periods to DR we found that for active stars other than the Sun the relative shear α increases with rotation period, and slightly decreases with effective temperature. The absolute shear ΔΩ slightly increases from ΔΩ = 0.079 rad d −1 at T eff = 3500 K to ΔΩ = 0.096 rad d −1 at T eff = 6000 K. Above 6000 K, ΔΩ shows much larger scatter. The dependence of ΔΩ on rotation period is weak over a large period range. Conclusions. Latitudinal differential rotation measured for the first time in more than 18 000 stars provides a comprehensive picture of stellar surface shear. This picture is consistent with major predictions from mean-field theory, and seems to support these models. To what extent our observations are prone to false positives and selection bias has not been fully explored, and needs to be addressed using other data, including the full Kepler time coverage.

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Section: Fig 16 Comparison Of Periods Frommentioning

confidence: 99%

Rotation and differential rotation of activeKeplerstars

Reinhold

Reiners

Basri

2013

A&A

353

397

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“…M 67 is the oldest cluster for which stellar rotation periods have been attempted to be measured. The prior record holder was the 2.5 Gyr old NGC 6819, for which Balona et al (2013) and Meibom et al (2015) measured the rotation periods from the Kepler main mission data. Meibom et al (2015) determined a mean rotation period of 18.2 d for Sunlike stars in the cluster from data spanning 3.75 years.…”

Section: Discussionmentioning

confidence: 99%

Variability among stars in the M 67 field fromKepler/K2-Campaign-5light curves

González

2016

Mon. Not. R. Astron. Soc.

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We examine the photometric variability of stars in the M 67 field using Kepler/K2-Campaign-5 light curves. Variabilities and periods were determined for 639 stars. The mean photometric period of 28 single Sun-like members stars in M 67 is 23.4 ± 1.2 d. This corresponds to a gyro-age of 3.7 ± 0.3 Gyr, assuming the periods can be associated with rotation. The intrinsic variabilities of the solar analogs are greater than the Sun's variability, as measure from VIRGO fluxes. We also find evidence that the single cluster members have a different distribution of variability than the binary members.

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“…It is a moderately old cluster (≈ 2.5 Gyr; [1], [2], [4], [7]) with near-solar or slightly super-solar metallicity ([Fe/H]= +0.09 ± 0.03; [3]). A distance modulus of μ 0 = V 0 − M V = 12.36 mag and a reddening of E(B − V) = 0.16 from BV photometry and main-sequence fitting was obtained by [7] for this cluster.…”

Section: Mass Loss At the Tip Of The Rgbmentioning

confidence: 99%

“…For each of the stars in Fig.1, we used ν max , Δν and T eff to obtain log L/L and log M/M as was done by [1]. Since we know the approximate measurement errors in these three quantities, we derive approximate standard deviations σ(M)/M = 0.100, σ(L)/L = 0.200, σ(T eff )/T eff = 0.038.…”

Section: Mass Loss At the Tip Of The Rgbmentioning

confidence: 99%

Red Clump stars inKepleropen cluster NGC 6819

Abedigamba

Balona

Medupe

2015

EPJ Web of Conferences

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Abstract. We measure the large frequency separation, Δν, and the frequency of maximum amplitude, ν max , for 10 Red Clump (RC) single member (SM) stars in the Kepler open cluster NGC 6819. We derive luminosities and masses for each individual RC star. A comparison of the observations with an isochrone of Age = 2.5 Gyr, Z = 0.017 with no mass loss using a statistical techniques is made. A fractional mass loss of 5 ± 3 percent is obtained if we assume that no correction to Δν between RC and red-giant branch (RGB) is necessary. However, models suggest that an effective correction of about 1.9 percent in Δν is required to obtain the correct mass of RC stars owing to the different internal structures of stars in the two evolutionary stages. In this case we find that the mass loss in the red giant branch is not significantly different from zero. This finding confirms that of [6]. It is clear that the mass estimate obtained by asteroseismology is not sufficient to deduce the mass loss on the red giant branch. However, it is clearly only a few percent at most. [7] for this cluster. The objective of the work is to study the mass loss at the tip of the red giant branch (RGB) in this cluster. Article available at Mass loss at the tip of the RGB

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Kepler observations of the open cluster NGC 6819

Cited by 32 publications

References 51 publications

Rotation and differential rotation of activeKeplerstars

Rotation and differential rotation of activeKeplerstars

Variability among stars in the M 67 field fromKepler/K2-Campaign-5light curves

Red Clump stars inKepleropen cluster NGC 6819

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