Observational templates of star cluster disruption

Carraro, G.; Marcos, R. de la Fuente; Villanova, S.; Bidin, C. Moni; Marcos, C. de la Fuente; Baumgardt, Holger; Solivella, G. R.

doi:10.1051/0004-6361:20066687

Cited by 20 publications

(21 citation statements)

References 37 publications

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“…NGC 1901 is a true representative of the terminal stage in the life of an open cluster, the OCR phase. Its current properties are compatible with NGC 1901 being what remains of a relatively small cluster with an original population of 500-750 stars (Villanova et al 2004b;Carraro et al 2007). …”

Section: Ngc 1901supporting

confidence: 61%

“…All of them have UBVI measurements with the exception of star #4, which does not have U. The CMDs for the detected stars clearly do not show any distinctive feature that can lead us to think about a group of stars with common properties, a physical ensemble as in the case of, e.g., NGC 1901 discussed in Carraro et al (2007). To guide the eye, and better clarify our conclusion, we over-impose in the same figure a solar metallicity isochrone taken from the Padova database (Girardi et al 2000), and adopting the set of parameters from Pavani et al (2007) Our photometric material simply suggests that what we see in the direction of NGC 6863 is nothing but random Galactic field.…”

Section: Photometrymentioning

confidence: 90%

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Not an open cluster after all: the NGC 6863 asterism in Aquila

Bidin

Marcos

et al. 2010

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Context. Shortly after birth, open clusters start dissolving; gradually losing stars into the surrounding star field. The time scale for complete disintegration depends both on their initial membership and location within the Galaxy. Open clusters undergoing the terminal phase of cluster disruption or open cluster remnants (OCRs) are notoriously difficult to identify. From an observational point, a combination of low number statistics and minimal contrast against the general stellar field conspire to turn them into very challenging objects. To make the situation even worst, random samples of field stars often display features that may induce to classify them erroneously as extremely evolved open clusters. Aims. In this paper, we provide a detailed study of the stellar content and kinematics of NGC 6863, a compact group of a few stars located in Aquila and described by the Palomar Observatory Sky Survey as a non existent cluster. Nonetheless, this object has been recently classified as OCR. The aim of the present work is to either confirm or disprove its OCR status by a detailed star-by-star analysis. Methods. The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC3 catalogue, and high resolution spectroscopy as well as results from extensive N-body calculations.Results. The spectra of the four brightest stars in this field clearly indicate that they are part of different populations. Their radial velocities are statistically very different and their spectroscopic parallaxes are inconsistent with them being part of a single, bound stellar system. Out of the four stars, only two of them have similar metallicity. The color magnitude diagram for the field of NGC 6863 does not show any clear signature typical of actual open clusters. Consistently, spatial scan statistics confirms the absence of any statistically significant, kinematically supported over-density at the purported location of NGC 6863. Conclusions. Our results show that the four brightest stars commonly associated to NGC 6863 form an asterism, a group of nonphysically associated stars projected together, leading to the conclusion that NGC 6863 is not a real open cluster.

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Section: Ngc 1901supporting

confidence: 61%

Section: Photometrymentioning

confidence: 90%

Not an open cluster after all: the NGC 6863 asterism in Aquila

Bidin

Marcos

et al. 2010

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“…The iron abundance [Fe/H] = 0.18(8) dex was derived by Luck (1994), as listed by Carrera & Pancino (2011). However, for the three investigated cluster stars, Luck et al (2000) present revised metallicities based on spectra with much higher Carraro et al (2007). The discrepancy for the prominent and well investigated Pleiades cluster could be due to the transformation of the overall metallicity Z to [Fe/H], assuming a correlation between the various abundance ratios.…”

Section: Comparison With Spectroscopic Resultsmentioning

confidence: 97%

Towards a photometric metallicity scale for open clusters

Netopil

Paunzen

2013

A&A

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Context. Open clusters are a useful tool when investigating several topics connected with stellar evolution; for example the age or distance can be more accurately determined than for field stars. However, one important parameter, the metallicity, is only known for a marginal percentage of open clusters. Aims. We aim at a consistent set of parameters for the open clusters investigated in our photometric Δa survey of chemically peculiar stars. Special attention is paid to expanding our knowledge of cluster metallicities and verifying their scale. Methods. Making use of a previously developed method based on normalised evolutionary grids and photometric data, the distance, age, reddening, and metallicity of open clusters were derived. To transform photometric measurements into effective temperatures to use as input for our method, a set of temperature calibrations for the most commonly used colour indices and photometric systems was compiled. Results. We analysed 58 open clusters in total. Our derived metallicity values were in excellent agreement with about 30 spectroscopically studied targets. The mean value of the absolute deviations was found to be 0.03 dex, with no noticeable offset or gradient. The method was also applied using recent evolutionary models based on the currently accepted lower solar abundance value Z ∼ 0.014. No significant differences were found compared to grids using the former adopted solar value Z = 0.02. Furthermore, some divergent photometric datasets were identified and discussed. Conclusions. The method provides an accurate way of obtaining properly scaled metallicity values for open clusters. In light of present and future homogeneous photometric sky surveys, the sample of stellar clusters can be extended to the outskirts of the Milky Way, where spectroscopic studies are almost impossible. This will help for determining galactic metallicity gradients in more detail.

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“…Nevertheless, the possibility of an OCR remains open, and this kind of object is of great interest, because we are still lacking observational evidence of the last stages of the cluster dynamical evolution. Indeed, OCRs are very elusive and easily confused with random field fluctuations and, despite a large list of candidates (e.g., Pavani & Bica 2007;Bica et al 2001), only one genuine OCR has been to date spectroscopically confirmed (NGC 1901, Carraro et al 2007a). …”

Section: Discussionmentioning

confidence: 99%

Three Galactic globular cluster candidates

Bidin

Mauro

Geisler

et al. 2011

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Context. The census of Galactic globular clusters (GCs) is still incomplete, and about ten new objects are supposed to await discovery, hidden behind the crowded and reddened regions of the Galactic bulge and disk. Aims. We investigated the nature of three new GC candidates, discovered in the frames collected by the Vista Variables in the Via Lactea (VVV) near-infrared survey. They will be called VVV CL002, VVV CL003, and VVV CL004. Methods. We studied the results of point-spread-function near-infrared photometry from VVV data for the three objects and their surrounding fields, the proper motion information available in the literature and, when possible, we derived the cluster parameters by means of calibrated indices measured on the color-magnitude diagrams. Results. The evidence shows that VVV CL002 is a newly discovered, small, moderately metal-rich ([Fe/H] ≈ −0.4) Galactic GC. It is located at a Galactocentric distance of 0.7 ± 0.9 kpc, and it could be one of the nearest GC to the Galactic center. Its characteristics are more similar to those of low-mass, Palomar-like GCs than to more classical, old, and massive bulge GCs. VVV CL003 is the first star cluster discovered in the Galactic disk on the opposite side of the center with respect to the Sun, at a Galactocentric distance of ∼5 kpc. Its high metallicity ([Fe/H] ≈ −0.1) and location point to an open cluster, but a GC cannot be excluded. VVV CL004, on the contrary, is most probably only a random clump of field stars, as indicated by both its low statistical significance and by the impossibility to distinguish its stars from the surrounding field population. Conclusions. We claim the detection of i) a new Galactic GC, deriving an estimate of its basic parameters; ii) a stellar aggregate, probably an open cluster, in the disk directly beyond the Galactic center; and iii) an overdensity of stars, most probably an asterism.

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Observational templates of star cluster disruption

Cited by 20 publications

References 37 publications

Not an open cluster after all: the NGC 6863 asterism in Aquila

Not an open cluster after all: the NGC 6863 asterism in Aquila

Towards a photometric metallicity scale for open clusters

Three Galactic globular cluster candidates

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