Open Clusters

DeepUBVandJHKphotometry of the stars in IC 1613 was used to investigate the stellar content in the H II regions of the northeast sector of the galaxy. The ages of nine of the associations outlined by Hodge (1978) were determined. A10 and A14 were found to be the youngest associations with ages of approximately 5 Myr, while A12, A18 and A19 were the oldest ones found, having a common age of approx. 20 Myr. Analysis of theoretical HR diagrams shows the presence of young massive stars in the associations, which have been born almost coeval. We have also found evidence of a difference between the slopes of the IMFs and differential LFs, between the group of associations embedded in gas and the group containing A12, A18 and A19, which are not affected by nebulosity.

Evolution of the gravitational contraction phase of stars having masses 0.3 < M/M⊙ < 1.5 were studied along with deuterium burning. The equation of state developed by Mihalas et al. (1988) and OPAL opacity tables were used in our investigation. The theoretical time lines were compared with observations.

As a result of the variability survey in Chi Persei and NGC6910, the number of Beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational properties, in particular the frequency spectra, of Beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B type stars in Chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of Beta Cep-type stars and maybe also for other B-type pulsators.

The northern Milky Way in the constellation of Cepheus (100° ≤ l ≤ 120°; 0° ≤ b ≤ 20°) contains several star forming regions. The molecular clouds of the Cepheus Flare region at b > 10°, are sites of low and intermediate mass star formation located between 200 and 450 pc from the Sun. Three nearby OB associations, Cep OB2, Cep OB3, Cep OB4, located at 600--800 pc, are eac= h involved in forming stars, like the well known high mass star forming regio= n S 140 at 900 pc. The reflection nebula NGC 7129 around 1 kpc harbors young, compact clusters of low and intermediate mass stars. The giant star forming complex NGC 7538 and the young open cluster NGC 7380, associated with the Perseus arm, are located at d > 2 kpc.

Aims: We look for new regions to search for substellar objects. Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, were explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to σ Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at similar galactic latitudes, as well as X-ray, mid-infrared, and spectroscopic data from the literature. Results: We compiled exhaustive lists of known young stars and new candidate members in the Ori OB1b association and of fore- and background sources. A total of 136 stars display features of extreme youth, like early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list another 74 known objects that might belong to the association. This catalogue can serve as input for characterising the stellar and high-mass substellar populations in the Orion Belt. Finally, we investigated the surface densities and radial distributions of young objects surrounding Alnilam and Mintaka and compared them with those in the σ Orionis cluster. We report on a new open cluster centred on Mintaka. Conclusions: Both regions can be analogues to the σ Orionis cluster, but more massive, more extended, slightly older, and less radially concentrated. Tables A.1 to A.18 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/485/931

We used both radial-velocity and proper-motion data to perform a rotation-curve solution on a combined sample of about 700 Population-I objects including young open clusters (lg A &lt; 8.1), classical Cepheids, and red supergiants. The distances of all objects are derived on a homogenized scale based on Kholopov&#39;s (1980) ZAMS, M_V (B-V)_0, PL relation for classical Cepheids by Berdnikov &

We have developed a methodology for the astrometric measurement of photographic plates making use of a CCD camera. In order to measure a complete 2°x 2° plate a mosaic of 8×8 frames with 50% overlap in both coordinates was taken. The detection and centering of stellar images was performed with SExtractor, and by means of our own software triple exposures were identified. A noticeable radial distortion produced by the optical system was found and corrected. The reduction to celestial coordinates was performed by means of the block-adjustment technique, using Tycho-2 as reference catalog. Differences with Tycho-2 suggest that the errors of CCD-based positions obtained from the CdC plate are between 0. and 0.. Completeness of the catalogs obtained is also discussed.

There is geological evidence that in the first few hundred Myr of the birth of the Solar System there was an epoch of strong bombardment caused by the collisions between growing planetesimals. Spitzer has the capability to probe that epoch in other stars by observing dust emission from debris disks around young solar system analogs. The MIPS GTO and FEPS

AI Crucis is a short-period semi-detached massive close binary (P = 1.41771d, Sp. = B 1.5) in the open cluster NGC 4103. It is a good astrophysical laboratory for investigating the formation and evolution of massive close binary stars via case A mass transfer. Orbital period variations of the system were analyzed based on one newly determined eclipse time and the others compiled from the literature. It is discovered that the orbital period of the binary is continuously increasing at a rate of dP/dt = +1.00(±0.04) × 10-7 d yr-1. After the long-term increase is subtracted from the O - C diagram, weak evidence indicates the presence of a cyclic oscillation with a period of 30.1 yr, which may reveal a very cool stellar companion in the system. The long-term period increase can be explained by mass transfer from the less massive component to the more massive one. This is in agreement with the semidetached configuration of the binary, indicating that the system is undergoing a slow mass-t...

Binary stars in open clusters are very useful targets in constraining the nucleosynthesis process. The luminosities of the stars are known because the distances of the clusters are also known, so chemical peculiarities can be linked directly to the evolutionary status of a star. In addition, binary stars offer the opportunity to verify a relationship between them and the straggler population in both globular and open clusters. We carried out a detailed spectroscopic analysis to derive the atmospheric parameters for 16 red giants in binary systems and the chemical composition of 11 of them in the open clusters NGC 2360, NGC 3680, and NGC 5822. We obtained abundances of C, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employ the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code moog. The abundances of the light elements were derived using the spectral synthesis technique. We found that the stars NGC 2360-92 and 96, NGC 3680-34, and NGC 5822-4 and 312 are yellow straggler stars. We show that the spectra of NGC 5822-4 and 312 present evidence of contamination by an A-type star as a secondary star. For the other yellow stragglers, evidence of contamination is given by the broad wings of the Hα. Detection of yellow straggler stars is important because the observed number can be compared with the number predicted by simulations of binary stellar evolution in open clusters. We also found that the other binary stars are not s-process enriched, which may suggest that in these binaries the secondary star is probably a faint main-sequence object. The lack of any s-process enrichment is very useful in setting constraints for the number of white dwarfs in the open cluster, a subject that is related to the birthrate of these kinds of stars in open clusters and also to the age of a cluster. Finally, rotational velocities were also determined and their values were compared with those already determined for field giant stars.

Open clusters are important astrophysical laboratories to study the stellar formation and evolution and to verify the disk structure of the Milky Way. We present calculations of stellar atmospheric parameters and s-process abundances for nine giant stars in the galactic open clusters IC 4651 and IC 4725. These objects have their memberships confirmed from dynamic studies and chemical analysis. The high-resolution spectra are available in the FEROS ESO archive. We have applied a line by line analysis relative to Juno solar spectrum to determine the stellar atmospheric parameters and chemical abundances of Y II, Zr I, La II, Ce II, and Nd II under the local thermal equilibrium hypothesis. The obtained results were compared to the literature values. The derived s-process abundance pattern agrees with the most recent behaviors reported for giant stars in galactic open clusters. Résumé : Les amas ouverts constituent d'importants laboratoires pour étudier la formation et l'évolution stellaire et pour vérifier la structure en disque de la Voie lactée. Nous présentons des calculs des paramètres atmosphériques stellaires et d'abondances obtenues du processus s pour neuf étoiles géantes dans les amas ouverts galactiques IC 4651 et IC 4725. Ces objets ont vu leur nature confirmée par des études dynamiques et des analyses chimiques. Les spectres de haute résolution sont disponibles dans les archives de FEROS ESO. Nous appliquons une analyse relative raie par raie au spectre solaire de Juno pour déterminer les paramètres de l'atmosphère stellaire et les abondances stellaires en Y II, Zr I, Ce II et Nd II sous l'hypothèse de l'équilibre thermodynamique local (ETL/LTE). Les résultats obtenus sont comparés a ` ceux trouvés dans la littérature. Le patron d'abondance dérivé du processus s agrée avec les comportements les plus récents rapportés pour les étoiles géantes dans les amas ouverts de la galaxie. [Traduit par la Rédaction] Mots-clés : évolution stellaire, abondances stellaires, amas ouverts et associations stellaires, paramètres fondamentaux stellaires, atmosphère stellaire.

We present rotation periods for 71 single dwarf members of the open cluster NGC 6811 determined using photometry from NASA&#39;s Kepler mission. The results are the first from The Kepler Cluster Study, which combines Kepler&#39;s photometry with ground-based spectroscopy for cluster membership and binarity. The rotation periods delineate a tight sequence in the NGC 6811 color-period diagram from ~1 day

The Galactic calibration of the period-luminosity (PL) relation for classical Cepheids is examined using trigonometric, open cluster, and pulsation parallaxes, which help establish independent versions of the relationship. The calibration is important for the continued use of classical Cepheids in constraining cosmological models (by refining estimates for H_0), for defining zero-points for the SNe Ia and population II (Type II

A wide field proper motion study in Praesepe has provided a new view of an &quot;old&quot; open cluster. Multiple epoch point source positions from 2MASS and the PMM program&#x27;s digitized POSS database have determined proper motions for ~ 280,000 stars in the Praesepe field, covering over 100 square degrees, resulting in a total of ~ 1000 candidate members down to 0.1 Msun. We will discuss the observed dynamical properties of the cluster, including the radial dependence of the mass function and halo structure, and compare them with results from recent open cluster N body simulations. This presentation makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation.

A sample of 160 UBVCCD observations of open star clusters near the galactic plane has been studied, and a catalogue of their properties obtained. The main photometrical properties have been re-estimated self consistently and the results have been compared with those of Lynga [Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, Stellar Data Centers, Observatoire de Strasbourg, France].

Astrometric properties of images obtained using MSCRED IRAF software package are investigated. CCD observations of M35 open cluster were taken in an observation run between October 10 and 17, 2004 at Belogradchick Observatory (Bulgaria) using the 60cm Cassegrain telescope endowed with a 1kX1k Apogee 47P CCD camera, ensuring to a field size of 6.16 square minutes, with a scale of 0.722arcsec/pixel in 2X2 binned mode. Dithered images are resampled and reansambled into a single larger image for which the World Coordinate System (WCS) solution is recomputed and investigated.

Presentamos los parámetros fundamentales de enrojecimiento, metalicidad, edad y distancia de los cúmulos abiertos poco estudiados Be 89, Ru 135 y Be 10, derivados de la fotometría CCD UBVRI. Los enrojecimientos interestelares se midieron en el diagrama color-color, y las metalicidades fotométricas se derivaron del exceso de ultravioleta de las estrellas tipo F. Las distancias y edades se obtuvieron ajustando isocronas a las secuencias observadas en cinco diagramas colormagnitud diferentes. Los promedios ponderados de los módulos de distancia y distancias heliocéntricas [(V0 ¿ MV ), d(kpc)] son: (11.m 90 ± 0.m 06, 2.4 ± 0.06) para Be 89, (9.m 58 ± 0.m 07, 0.81 ± 0.03) para Ru 135 y (11.m 16 ± 0.m 06, 1.7 ± 0.05) para Be 10, mientras que los promedios ponderados para las edades [log(A),A(Gyr)] son: (9.58 ± 0.06, 3.8 ± 0.6) para Be 89, (9.58 ± 0.06, 3.8 ± 0.7) para Ru 135 y (9.06 ± 0.05, 1.08 ± 0.08) para Be 10.

Con—rmatory evidence for changing light-curve amplitude of the former eclipsing and current SB2 system SS Lac in the Open Cluster NGC 7209 has been uncovered. Remeasured Harvard plate data and published and compiled data sets reveal that the depth of the primary minimum increased between the 1890s and 1902 and decreased in the 1920s and 1930s. A parabolic —tting of

We describe a variability study of the moderately old open cluster NGC 6819. We have detected 4 new detached eclipsing binaries near the cluster turnoff (one of which may be in a triple system). Several of these systems should be able to provide mass and radius information, and can therefore constrain the age of the cluster. We have also newly detected one possible detached binary member about 3.5 magnitudes below the turnoff. One EW-type binary (probably not a cluster member) shows unusually strong night-to-night light curve variations in sets of observations separated by 8 years. According to the best current information, the three brightest variables we detected (2 of them new) are cluster members, making them blue stragglers. One is a delta Scu pulsating variable, one is a close but detached binary, and the third contains a detached short period binary that shows total eclipses. In each case, however, there is evidence hinting that the system may have been produced through the i...

The model of magnetic braking of solar rotation considered by Charbonneau & MacGregor (1993) has been modified so that it is able to reproduce for the first time the rotational evolution of both the fastest and slowest rotators among solar-type stars in open clusters of different ages, without coming into conflict with other observational constraints, such as the time evolution of the atmospheric Li abundance in solar twins and the thinness of the solar tachocline. This new model assumes that rotation-driven turbulent diffusion, which is thought to amplify the viscosity and magnetic diffusivity in stellar radiative zones, is strongly anisotropic with the horizontal components of the transport coefficients strongly dominating over those in the vertical direction. Also taken into account is the poloidal field decay that helps to confine the width of the tachocline at the solar age. The model's properties are investigated by numerically solving the azimuthal components of the coupled momentum and magnetic induction equations in two dimensions using a finite element method