Fundamental parameters and new variables of the galactic open cluster NGC 7128

We present UBV photometry of the highly reddened and poorly studied open cluster Berkeley 55, revealing an important population of B-type stars and several evolved stars of high luminosity. Intermediate-resolution far-red spectra of several candidate members confirm the presence of one F-type supergiant and six late supergiants or bright giants. The brightest blue stars are mid-B giants. Spectroscopic and photometric analyses indicate an age 50 ± 10 Myr. The cluster is located at a distance d ≈ 4 kpc, consistent with other tracers of the Perseus Arm in this direction. Berkeley 55 is thus a moderately young open cluster with a sizable population of candidate red (super)giant members, which can provide valuable information about the evolution of intermediate-mass stars.

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“…• 3), with DM = 13.0 ± 0.2 (4 kpc), is another likely tracer at some distance from Be 55 (Balog et al 2001).…”

Section: Cluster Parametersmentioning

confidence: 94%

The Young Open Cluster Berkeley 55

Negueruela

Marco

2012

The Astronomical Journal

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“…In a search for variable stars using CCD photometry, Jerzykiewicz et.al (1996) discovered two eclipsing binaries, one irregular red variable and three small-amplitude periodic variables in the cluster. The UBV CCD photometric data for 452 stars was taken from Balog et al (2001). The stars 1081 and 12 are found to show emission which are numbered as 1 and 2 respectively in our catalogue.…”

Section: Ngc 7128mentioning

confidence: 99%

Be phenomenon in open clusters: results from a survey of emission-line stars in young open clusters

Mathew

Subramaniam

Bhatt³

2008

Monthly Notices of the Royal Astronomical Society

102

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Emission‐line stars in young open clusters are identified to study their properties, as a function of age, spectral type and evolutionary state. 207 open star clusters were observed using the slitless spectroscopy method and 157 emission stars were identified in 42 clusters. We have found 54 new emission‐line stars in 24 open clusters, out of which 19 clusters are found to house emission stars for the first time. About 20 per cent clusters harbour emission stars. The fraction of clusters housing emission stars is maximum in both the 0–10 and 20–30 Myr age bin (∼40 per cent each). Most of the emission stars in our survey belong to Classical Be class (∼92 per cent) while a few are Herbig Be stars (∼6 per cent) and Herbig Ae stars (∼2 per cent). The youngest clusters to have Classical Be stars are IC 1590, NGC 637 and 1624 (all 4 Myr old) while NGC 6756 (125–150 Myr) is the oldest cluster to have Classical Be stars. The Classical Be stars are located all along the main sequence (MS) in the optical colour–magnitude diagrams (CMDs) of clusters of all ages, which indicates that the Be phenomenon is unlikely due to core contraction near the turn‐off. The distribution of Classical Be stars as a function of spectral type shows peaks at B1–B2 and B6–B7 spectral types. The Be star fraction [N(Be)/N(B+Be)] is found to be less than 10 per cent for most of the clusters and NGC 2345 is found to have the largest fraction (∼26 per cent). Our results indicate there could be two mechanisms responsible for the Classical Be phenomenon. Some are born Classical Be stars (fast rotators), as indicated by their presence in clusters younger than 10 Myr. Some stars evolve to Classical Be stars, within the MS lifetime, as indicated by the enhancement in the fraction of clusters with Classical Be stars in the 20–30 Myr age bin.

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“…A.1, the total number of CCD frames, total exposure time, the FWHM of the average stellar image, and the average airmass of the block. The transformation equations are based on the calibration of Crawford & Barnes (1970) and we followed the recipe from Balog et al (2001). Its four zero-point constants refer to the slopes for (b − y), m 1 , c 1 and β, respectively, while the three color-term coefficients are for V, m 1 and c 1 .…”

Section: Discussionmentioning

confidence: 99%

“…We adopted standard stars from the compilation of Hauck & Mermilliod (1998) and found only a total of eight stars within our field of view suitable for a zero-point calibration of the STELLA/WiFSIP data. The standard uvbyβ transformation was applied by following the procedure given in Balog et al (2001, and Table A.2. Figure 2a shows the de-reddened u − v vs. b − y color−color relation.…”

Section: Reddening Distance Metallicitymentioning

confidence: 99%

Stellar rotation, binarity, and lithium in the open cluster IC 4756

Strassmeier

Weingrill

Granzer

et al. 2015

A&A

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Context. An important aspect in the evolutionary scenario of cool stars is their rotation and the rotationally induced magnetic activity and interior mixing. Stars in open clusters are particularly useful tracers for these aspects because of their known ages. Aims. We aim to characterize the open cluster IC 4756 and measure stellar rotation periods and surface differential rotation for a sample of its member stars. Methods. Thirty-seven cluster stars were observed continuously with the CoRoT satellite for 78 days in 2010. Follow-up highresolution spectroscopy of the CoRoT targets and deep Strömgren uvbyβ and Hα photometry of the entire cluster were obtained with our robotic STELLA facility and its echelle spectrograph and wide-field imager, respectively. Results. We determined high-precision photometric periods for 27 of the 37 CoRoT targets and found values between 0.155 and 11.4 days. Twenty of these are rotation periods. Twelve targets are spectroscopic binaries of which 11 were previously unknown; orbits are given for six of them. Six targets were found that show evidence of differential rotation with ΔΩ/Ω in the range 0.04−0.15. Five stars are non-radially pulsating stars with fundamental periods of below 1 d, two stars are semi-contact binaries, and one target is a micro-flaring star that also shows rotational modulation. Nine stars in total were not considered members because of much redder color(s) and deviant radial velocities with respect to the cluster mean. Hα photometry indicates that the cluster ensemble does not contain magnetically over-active stars. The cluster average metallicity is -0.08 ± 0.06 (rms) and its logarithmic lithium abundance for 12 G-dwarf stars is 2.39 ± 0.17 (rms). Conclusions. The cluster is 890 ± 70 Myrs old with an average turn-off mass of 1.8 M and a solar or slightly subsolar metallicity. The distance modulus is 8. m 02 and the average reddening E(b − y) = 0. m 16. The cluster is masked by a very inhomogeneous foreground and background dust distribution and our survey covered 38% of the cluster. The average lithium abundance and the rotation periods in the range 1.7 to 11.4 d are consistent with the cluster age.

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Fundamental parameters and new variables of the galactic open cluster NGC 7128

Cited by 6 publications

References 23 publications

The Young Open Cluster Berkeley 55

The Young Open Cluster Berkeley 55

Be phenomenon in open clusters: results from a survey of emission-line stars in young open clusters

Stellar rotation, binarity, and lithium in the open cluster IC 4756

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