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Young Cluster (young + cluster)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The lithium depletion boundary and the age of NGC 2547

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
J. M. Oliveira
ABSTRACT We present the results of a photometric and spectroscopic survey of cool M dwarf candidates in the young open cluster NGC 2547. Using the 2dF fibre spectrograph, we have searched for the luminosity at which lithium remains unburned in an attempt to constrain the cluster age. The lack of a population of individual lithium-rich objects towards the faint end of our sample places a very strong lower limit to the cluster age of 35 Myr. However, the detection of lithium in the averaged spectra of our faintest targets suggests that the lithium depletion boundary lies at 9.5 < MI < 10.0 and that the cluster age is <54 Myr. The age of NGC 2547 judged from fitting isochrones to low-mass pre-main-sequence stars in colour,magnitude diagrams is 20,35 Myr using the same evolutionary models. The sense and size of the discrepancy in age determined by these two techniques is similar to that found in another young cluster, IC 2391, and in the low-mass pre-main-sequence binary system, GJ 871.1AB. We suggest that the inclusion of rotation or dynamo-generated magnetic fields in the evolutionary models could reconcile the two age determinations, but only at the expense of increasing the cluster ages beyond that currently indicated by the lithium depletion. Alternatively, some mechanism is required that increases the rate of lithium depletion in young, very low-mass fully convective stars. [source]

Probing evolutionary mechanisms in galaxy clusters: H I in Abell 1367

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
T.C. Scott
Abstract We are carrying out a programme of CO and interferometric H I observations in the nearby galaxy cluster Abell 1367. The aim is to better understand the processes driving the evolution of the ISM in late-type galaxies in the cluster environment. Abell 1367 is a dynamically young cluster. We have determined the H I content and g , i colour from AGES (Cortese 2008) and SDSS, respectively, of its bright late-type galaxies (spirals) in a volume centred on the NW subcluster. We use a combination of these characteristics, both of which are indicative of evolutionary history, to classify each spiral into one of four evolutionary states. This analysis revealed the cluster contains spirals in a wide range of evolutionary states. VLA D-array imaging centred on the NW subcluster indicates most galaxies in that field have their H I intensity maximum offset relative to its optical counterpart, implying a recent and strong disturbance. The direction of this offset is not always consistent with a simple scenario of ram pressure stripping by the cluster's high density intra-cluster medium (ICM) (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The Cepheid impostor HD 18391 and its anonymous parent cluster

ASTRONOMISCHE NACHRICHTEN, Issue 8 2009
D.G. Turner
Abstract New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small-amplitude variability at a level of ,V = 0.016 ± 0.002 is indicated, with a period of P = 123d.04 ± 0d.06. A weaker second signal may be present at P = 177d.84 ± 0d.18 with ,V = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of EB,V = 1.02 ± 0.003, is associated with heavily-reddened B-type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ,10, to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of rn = 3.5, and Rc = 14,, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid-like pulsation, provided that it follows the semi-period-luminosity relation expected of such objects. Its inferred luminosity as a cluster member is MV = ,7.76 ± 0.10, its age (9 ± 1) × 106 years, and its evolutionary mass ,19 M,. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period-luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On the properties of young multiple stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
E. J. Delgado-Donate
ABSTRACT We present numerical results on the properties of young binary and multiple stellar systems. Our analysis is based on a series of smoothed particle hydrodynamics (SPH) +N -body simulations of the fragmentation of small molecular clouds, which fully resolve the opacity limit for fragmentation. These simulations demonstrate that multiple star formation is a major channel for star formation in turbulent flows. We have produced a statistically significant number of stable multiple systems, with component separations in the range ,1,103 au. At the end of the hydrodynamic stage (0.5 Myr), we find that ,60 per cent of stars and brown dwarfs are members of multiples systems, with about a third of these being low-mass, weakly bound outliers in wide eccentric orbits. Our results imply that in the stellar regime most stars are in multiples (,80 per cent) and that this fraction is an increasing function of primary mass. After N -body integration to 10.5 Myr, the percentage of bound objects has dropped to about 40 per cent, this decrease arising mostly from very low-mass stars and brown dwarfs that have been released into the field. Brown dwarfs are never found to be very close companions to stars (the brown dwarf desert at very small separations), but one case exists of a brown dwarf companion at intermediate separations (10 au). Our simulations can accommodate the existence of brown dwarf companions at large separations, but only if the primaries of these systems are themselves multiples. We have compared the outcome of our simulations with the properties of real stellar systems as deduced from the infrared colour,magnitude diagram of the Praesepe cluster and from spectroscopic and high-resolution imaging surveys of young clusters and the field. We find that the spread of the observed main sequence of Praesepe in the 0.4,1 M, range appears to require that stars are indeed commonly assembled into high-order multiple systems. Similarly, observational results from Taurus and , Ophiuchus, or moving groups such as TW Hydrae and MBM 12, suggest that companion frequencies in young systems can indeed be as high as we predict. The comparison with observational data also illustrates two problems with the simulation results. First, low mass ratio (q < 0.2) binaries are not produced by our models, in conflict with both the Praesepe colour,magnitude diagram and independent evidence from field binary surveys. Secondly, very low-mass stars and brown dwarf binaries appear to be considerably underproduced by our simulations. [source]