- ID:
- ivo://CDS.VizieR/J/AJ/106/1906
- Title:
- NGC 6611: A Cluster Caught in the Act
- Short Name:
- J/AJ/106/1906
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have combined optical CCD photometry and spectroscopy with infrared imaging photometry to study the young cluster NGC 6611. We use these data to derive improved values for the reddening law (R=3.75) and the distance modulus (m-M=11.5), and to construct a physical H-R diagram from which we can probe the ages, masses, and evolutionary states of this stellar ensemble. The H-R diagram shows a strong population of high-mass stars, the most massive of which has a mass of roughly 80 solar masses, similar to what we find in other Galactic and Magellanic Cloud clusters and associations. The age of the massive stellar population in NGC 6611 is approximately 2 million years, with an age spread of, perhaps, a million years, although the data are also consistent with there being no discernible age spread among the most massive stars. However, the H-R diagram does reveal that one star of somewhat lower mass (30 solar masses) must have formed approximately 6 million years ago. The upper end of the mass function of NGC 6611 is found to have a slope of Gamma=-1.1+/-0.3, indistinguishable from a Salpeter slope, and similar to what we have found in other Galactic associations, but shallower than what we have found in the Magellanic Clouds. Our most significant result, however, is that we catch this cluster in the act of forming intermediate mass (3-8 Solar masses) stars. This is the first well-established case where large numbers of intermediate-mass stars have been seen on their way to the zero-age main sequence. That intermediate mass pre-main sequence stars are indeed present is evidenced both by their location above the zero-age main sequence in the H-R diagram, and in some cases by their spectroscopic and infrared signatures of (possibly remnant protostellar) circumstellar material. The pre-main sequence population ranges from as young as 0.25 million years to at least 1 million years of age. We find an highly unusual number (27) of emission-line stars, which appear quite similar in their optical and infrared continuum and optical spectroscopic properties to "classical Be/Ae" stars (as opposed to Herbig Be/Ae stars). Our data are inconsistent with the traditional interpretation that these "classical Be/Ae" stars are slightly evolved stars undergoing mass loss. Instead, we offer the conjecture that these may be young stars whose circumstellar disks have become optically thin, and produce Balmer emission lines. The infrared data do indicate a number of stars, particularly amongst the embedded sample, whose colors are consistent with those of stars thought to be surrounded by optically thick circumstellar accretion disks. The identification of such disks around young massive stars continues to be rare, and implies that the disk survival times around intermediate and high mass stars are much shorter (< 0.5Myr) than those of disks surrounding lower mass stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/542/A68
- Title:
- NGC 3231, 7055 and 7127 BVRI photometry
- Short Name:
- J/A+A/542/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are often used as tracers for the formation and evolution of the Milky Way. But they can also be used to study distinct "local stellar populations" and all kind of stellar groups. All these studies crucially depend on their unambiguous detection and classification separating them from the fore- and background field population. Still more than one third of the catalogued galactic open clusters are unstudied to date. We have chosen three northern open cluster fields, namely NGC 3231, NGC 7055, and NGC 7127 which have been never studied before to shed more light on their true nature. We present Johnson-Cousins BVRI photometry down to V=19mag. After the transformation to the standard systems, colour-magnitude diagrams were generated. These diagrams were used to fit solar abundant isochrones to determine the distance modulus, reddening and apparent age of the main sequences. From the analysis of the colour-magnitude diagrams and the available proper motions we conclude that NGC 7055 and NGC 7127 are young, real, open clusters. NGC 3231, on the other hand, is probably a high galactic latitude open cluster remnant.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A73
- Title:
- NGC 6167 and NGC 6193 multi-photometry
- Short Name:
- J/A+A/531/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Ara OB1a association is a nearby complex in the fourth Galactic quadrant where a number of young/embedded star clusters are projected close to more evolved, intermediate age clusters. It is also rich in interstellar matter, and contains evidences of the interplay between massive stars and their surrounding medium, like the rim HII region NGC 6188. We provide more solid estimates of the fundamental parameters (age and distance) of the two most prominent stellar clusters, NGC 6167 and NGC 6193, that may be used as a basis to study the star formation history of the region. The study is based on a photometric optical survey (UBVIHa) of NGC 6167 and NGC 6193 and their nearby field, complemented with public data from 2MASS-VVV, UCAC3 and IRAC-Spitzer in this region. We produced a uniform photometric catalogue and we estimated more robustly the fundamental parameters for NGC 6167, NGC 6193 and the IRAS 16375-4854 source. As a consequence, all of them are located at approximately the same distance from the Sun in the Sagittarius-Carina Galactic arm. However, the ages we estimated differ widely: NGC 6167 results to be an intermediate-age cluster (20-30Myr), NGC 6193 a very young one (1-5Myr) with PMS, H{alpha} emitters, and class II objects; and the IRAS 16375-4854 source is revealed as the youngest of the three containing several YSOs. These results support a picture in which Ara OB1a is a region where star formation has proceeded for several tens of Myr up to the present. The difference in ages of different stellar groups can be interpreted as a consequence of a triggered star formation process. Additionally, in the specific case of NGC 6193, an indication of possible non-coeval star formation was found.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/221
- Title:
- NGC 2849 and NGC 6134 UBVI photometry
- Short Name:
- J/MNRAS/430/221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry of two southern open clusters. As part of the Bologna Open Cluster Chemical Evolution project we obtained BVI and UBVI imaging for NGC 2849 and NGC 6134, respectively. By means of the synthetic colour-magnitude diagram method and using various evolutionary sets of stellar evolution tracks with various metallicities, we determined at the same time age, distance and reddening. We also determined an approximate metallicity for NGC 2849, for which the information is not available from sounder methods like high-resolution spectroscopy. NGC 2849 turned to be 0.85-1.0Gyr old with a solar metallicity. The foreground reddening is E(B-V)=0.28-0.32, and the true distance modulus (m-M)_0_=13.8-13.9. For NGC 6134 we did not obtain fully consistent answers from the V, B-V and V, V-I photometry, an unexpected problem, since both the metallicity and the reddening are known (from high-resolution spectroscopy and the U-B, B-V two colours diagram, respectively). This may either indicate a difficulty of current models (evolutionary tracks and/or models of atmosphere) to accurately reproduce colours, or be related to differences in the metal mixture assumed by the models and those of the clusters. Assuming the spectroscopic abundance and the colour excess [E(B-V)=0.35] from the U-B, B-V plot, we derived a best age between 0.82 and 0.95Gyr and a distance modulus 10.5.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/106
- Title:
- NGC5617 and Trumpler 22 stars BV mag and RV
- Short Name:
- J/MNRAS/453/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using photometry and high-resolution spectroscopy we investigate for the first time the physical connection between the open clusters NGC 5617 and Trumpler 22. Based on new CCD photometry we report their spatial proximity and common age of ~70Myr. Based on high-resolution spectra collected using the HERMES and UCLES spectrographs on the Anglo-Australian telescope, we present radial velocities and abundances for Fe, Na, Mg, Al, Si, Ca, and Ni. The measured radial velocities are -38.63+/-2.25km/s for NGC 5617 and -38.46+/-2.08km/s for Trumpler 22. The mean metallicity of NGC 5617 was found to be [Fe/H]=-0.18+/-0.02 and for Trumpler 22 was found to be [Fe/H]=-0.17+/-0.04. The two clusters share similar abundances across the other elements, indicative of a common chemical enrichment history of these clusters. Together with common motions and ages we confirm that NGC 5617 and Trumpler 22 are a primordial binary cluster pair in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/AJ/122/1486
- Title:
- NGC 2451A proper motions and membership
- Short Name:
- J/AJ/122/1486
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide new evidence that NGC 2451A is undoubtedly a young open cluster, although sparsely populated. New cluster membership has been derived from relative proper motions of 5868 stars. In total, 136 stars down to V~15 5 have membership probability P{mu}>=2%. New CCD BV photometry indicates that about 70 stars are indeed main-sequence stars of NGC 2451A. This is also supported by our measurements of radial velocities. A total of 34 very likely cluster members yield a mean heliocentric radial velocity for NGC 2451A equal to +22.9km/s. The high quality of our BV photometry, a confirmation of cluster membership from proper motions and radial velocities, and a recently obtained metallicity estimate for several cluster stars allow us to perform a precise isochrone fit. The Yale isochrones, updated by the latest available input physics, have been fitted to the cluster's color-magnitude diagram, yielding a distance modulus V_0_-M_V_ in the range 6.35 to 6.38, which is in excellent agreement with the distance modulus (m-M)_0_=6.38 derived from the Hipparcos data recently by van Leeuwen and Robichon et al. (1998, Cat. <J/A+AS/130/157>). We have used the high-resolution spectra acquired using the Hydra multiobject spectrograph at the WIYN telescope (Kitt Peak, Arizona) in 1997 November and 1998 October.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/4185
- Title:
- NGC 2355 BVI photometry
- Short Name:
- J/MNRAS/453/4185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we analyse the evolutionary status and properties of the old open cluster NGC 2355, located in the Galactic anticentre direction, as a part of the long-term programme Bologna Open Clusters Chemical Evolution. NGC 2355 was observed with the Large Binocular Camera at the Large Binocular Telescope using the Bessel B, V, and Ic filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram method, as done in other papers of this series. Additional spectroscopic observations with the Fibre-fed Echelle Spectrograph at the Nordic Optical Telescope of three giant stars were used to determine the chemical properties of the cluster. Our analysis shows that NGC 2355 has metallicity slightly less than solar, with [Fe/H]=-0.06dex, age between 0.8 and 1Gyr, reddening E(B-V) in the range 0.14-0.19mag, and distance modulus (m-M)0 of about 11mag. We also investigate the abundances of O, Na, Al, {alpha}, iron-peak, and neutron capture elements, showing that NGC 2355 falls within the abundance distribution of similar clusters (same age and metallicity). The Galactocentric distance of NGC 2355 places it at the border between two regimes of metallicity distribution; this makes it an important cluster for the study of the chemical properties and evolution of the disc.
- ID:
- ivo://CDS.VizieR/J/PASP/117/22
- Title:
- NGC 6318 CCD BVI photometry
- Short Name:
- J/PASP/117/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD BVI photometry for the southern open cluster NGC 6318. The sample consists of 9876 stars measured in an area of 13.6'x13.6', extending down to V~21.5mag. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 8'.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.126
- Title:
- NGC 6819 CCD UBV photometry
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as E(B-V)=0.130+/-0.035mag and [Fe/H]=+0.051+/-0.020dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC 6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as mu_V=12.22+/-0.10mag, d=2309+/-106pc and t=2.4+/-0.2Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819 indicate that the cluster is orbiting in a slightly eccentric orbit of e=0.06 with a period of P_orb_=142Myr. The slope of the mass function estimated for the cluster is close to the one found for the stars in the solar neighbourhood.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/355.267
- Title:
- NGC 6811 CCD UBVRI photometry
- Short Name:
- J/other/ApSS/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1m telescope at the TIBITAK National Observatory (TUG). Using these photometric results, we determine the structural and astrophysical parameters of the cluster. The mean photometric uncertainties are better than 0.02 mag in the V magnitude and B-V, V-R, and V-I colour indices to about 0.03mag for U-B among stars brighter than magnitude V=18. Cluster member stars were separated from the field stars using the Galaxia model of Sharma et al. (2011ApJ...730....3S) together with other techniques. The core radius of the cluster is found to be r_c_=3.60arcmin. The astrophysical parameters were determined simultaneously via Bayesian statistics using the colour-magnitude diagrams V versus B-V, V versus V-I, V versus V-R, and V versus R-I of the cluster. The resulting most likely parameters were further confirmed using independent methods, removing any possible degeneracies. The colour excess, distance modulus, metallicity and the age of the cluster are determined simultaneously as E(B-V)=0.05+/-0.01mag, {mu}=10.06+/-0.08mag, [M/H]=-0.10+/-0.01dex and t=1.00+/-0.05Gyr, respectively. Distances of five red clump stars which were found to be members of the cluster further confirm our distance estimation.