Probing the nature of possible open cluster remnants
  with the Southern Proper Motion Program

Carraro, G.; Dinescu, D. I.; Girard, Terrence M.; Altena, W. F. van

doi:10.1051/0004-6361:20042044

Cited by 9 publications

(15 citation statements)

References 16 publications

(31 reference statements)

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“…The statistical method (Table 2) also favors a non physical nature. These results point to NGC 6994 being a field fluctuation, in agreement with Carraro (2005) and Odenkirchen & Soubiran (2002). Composite open cluster CMDs have been a tool employed since Sandage (1958) and were useful for modeling stellar evolution.…”

Section: Proper Motionssupporting

confidence: 65%

“…Of these, 7 have been discussed in recent studies: (i) ESO 425 SC6 and ESO 425 SC15 were classified as non physical (Carraro et al 2005); (ii) NGC 1663 was found to be a remnant (Baume et al 2003); (iii) Ruprecht 3, NGC 1252 and NGC 1901 were found to be remnants (Pavani et al 2003); (iv) NGC 6994 (Bassino et al 2000;Carraro 2000;Ordenkirchen & Soubiran 2002) is discussed further in the present work.…”

Section: Object Selectionmentioning

confidence: 63%

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Characterization of open cluster remnants

Pavani

Bica

2007

A&A

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Context. Despite progress in the theoretical knowledge of open cluster remnants and the growing search for observational identifications in recent years, open questions still remain. The methods used to analyze open cluster remnants and criteria to define them as physical systems are not homogeneous. In this work we present a systematic method for studying these objects that provides a view of their properties and allows their characterization. Aims. Eighteen remnant candidates are analyzed by means of photometric and proper motion data. These data provide information on objects and their fields. We establish criteria for characterizing open cluster remnants, taking observational uncertainties into account. Methods. 2MASS J and H photometry is employed (i) to study structural properties of the objects by means of radial stellar density profiles, (ii) to test for any similarity between objects and fields with a statistical comparison method applied to the distributions of stars in the CMDs, and (iii) to obtain ages, reddening values, and distances from the CMD, taking an index of isochrone fit into account. The UCAC2 proper motions allowed an objective comparison between objects and large solid angle offset fields.Results. The objective analysis based on the present methods indicates 13 open-cluster remnants in the sample. Evidence of the presence of binary stars is found, as expected for dynamically evolved systems. Finally, we infer possible evolutionary stages among remnants from the structure, proper motion, and CMD distributions. The low stellar statistics for individual objects is overcome by means of the construction of composite proper motion and CMD diagrams. The distributions of remnants in the composite diagrams resemble the single-star and unresolved binary star distributions of open clusters.

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Section: Proper Motionssupporting

confidence: 65%

Section: Object Selectionmentioning

confidence: 63%

Characterization of open cluster remnants

Pavani

Bica

2007

A&A

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“…Observationally, Bica et al (2001) selected 35 groups that stand up against the mean Galactic stellar fields, and are located relatively high onto the Galactic plane. Regrettably, close scrutiny of the kinematics in some of them (Villanova et al 2004a;Carraro et al 2005;Carraro 2006) has shown that the contrast criterion is necessary but not sufficient for detecting a remnant. In fact, when dealing with the remnant of a physical group, one expects that the remains exhibit all the features of a physical group.…”

Section: Introductionmentioning

confidence: 99%

Observational templates of star cluster disruption

Carraro

Marcos

Villanova³

et al. 2007

A&A

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Context.Observations indicate that present-day star formation in the Milky Way disk takes place in stellar ensembles or clusters rather than in isolation. Bound, long-lived stellar groups are known as open clusters. They gradually lose stars and are severely disrupted in their final evolutionary stages, leaving an open cluster remnant made up of a few stars. Aims. In this paper, we study in detail the stellar content and kinematics of the poorly populated star cluster NGC 1901. This object appears projected against the Large Magellanic Cloud. The aim of the present work is to derive the current evolutionary status, binary fraction, age, and mass of this stellar group. These are fundamental quantities to compare with those from N-body models in order to study the most general topic of star cluster evolution and dissolution. Methods. The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC.2 catalog, and 3 epochs of high-resolution spectroscopy, as well as results from extensive N-body calculations. Results. The star group NGC 1901 is found to be an ensemble of solar metallicity stars, 400 ± 100 Myr old, with a core radius of 0.23 pc, a tidal radius of 1.0 pc, and a location at 400 ± 50 pc from the Sun. Out of 13 confirmed members, only 5 single stars have been found. Its estimated present-day binary fraction is at least 62%. The calculated heliocentric space motion of the cluster is not compatible with possible membership in the Hyades stream. Conclusions. Our results show that NGC 1901 is a clear prototype of an open cluster remnant characterized by a high value of the binary fraction and a significant depletion of low-mass stars. In light of numerical simulations, this is compatible with NGC 1901 being what remains of a larger system initially made of 500-750 stars.

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“…Unfortunately, subsequent analyses including positional, kinematic, photometric and spectroscopic information failed to confirm even the cluster status of some of the suggested candidates (Villanova et al 2004a;Carraro et al 2005). Again, negative results pointed out an already well known fact, that these objects are notoriously difficult to identify.…”

Section: Introductionmentioning

confidence: 96%

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

Bidin

Marcos

et al. 2010

A&A

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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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Probing the nature of possible open cluster remnants with the Southern Proper Motion Program

Cited by 9 publications

References 16 publications

Characterization of open cluster remnants

Characterization of open cluster remnants

Observational templates of star cluster disruption

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

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