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Richard De Grijs Robert W. O'Connell John S. Gallagher III 《Astrophysics and Space Science》2001,276(2-4):397-404
We present high-resolution optical and near-infrared HST observations of two adjacent regions in the fossil starburst region
inM82, M82 B1 and B2. The presence of both the active and the fossil starburst in M82 provides a unique physical environment
to study the stellar and dynamical evolution of star cluster systems. The cluster population in B2 is more heavily affected
by internal extinction than that in B1, amounting to an excess extinction in B2 of AV,excess≃1.1±0.3 mag. Preliminary age estimates date the cluster population in the fossil starburst between ∼2× 108 and ∼ 109 years. The radial luminosity profiles of the brightest clusters are more closely approximated by power laws than by a Gaussian
model, in particular in their wings, which favours a slow star formation scenario.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The dynamical mass of a star cluster can be derived from the virial theorem, using the measured half-mass radius and line-of-sight velocity dispersion of the cluster. However, this dynamical mass may be a significant overestimation of the cluster mass if the contribution of the binary orbital motion is not taken into account. Here, we describe the mass overestimation as a function of cluster properties and binary population properties, and briefly touch on the issue of selection effects. We find that for clusters with a measured velocity dispersion of σ los?10 km?s?1 the presence of binaries does not affect the dynamical mass significantly. For clusters with σ los?1 km?s?1 (i.e., low-density clusters), the contribution of binaries to σ los is significant, and may result in a major dynamical mass overestimation. The presence of binaries may introduce a downward shift of Δlog?(L V /M dyn)=0.05–0.4 (in solar units) in the log?(L V /M dyn) versus age diagram. 相似文献
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Enrique Pérez Richard de Grijs Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):79-81
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Richard J. Allison Simon P. Goodwin Richard J. Parker Simon F. Portegies Zwart Richard de Grijs M. B. N. Kouwenhoven 《Monthly notices of the Royal Astronomical Society》2009,395(3):1449-1454
We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that of random stars. If mass segregation is present, the MST length of the most massive stars will be shorter than that of random stars. This difference can be quantified (with an associated significance) to measure the degree of mass segregation. We test the method on simulated clusters in both 2D and 3D and show that the method works as expected.
We apply the method to the Orion Nebula Cluster (ONC) and show that the method is able to detect the mass segregation in the Trapezium with a 'mass segregation ratio (MSR)' ΛMSR = 8.0 ± 3.5 (where ΛMSR = 1 is no mass segregation) down to 16 M⊙ , and also that the ONC is mass segregated at a lower level (∼2.0 ± 0.5) down to 5 M⊙ . Below 5 M⊙ we find no evidence for any further mass segregation in the ONC. 相似文献
We apply the method to the Orion Nebula Cluster (ONC) and show that the method is able to detect the mass segregation in the Trapezium with a 'mass segregation ratio (MSR)' Λ
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Jun Ma ;Richard de Grijs ;Zhou Fan ;Soo-Chang Rey ;Zhen-Yu Wu ;Xu Zhou ;Jiang-Hua Wu ;Zhao-Ji Jiang ;Jian-Sheng Chen ;Kyungsook Lee ;Sangmo Tony Sohn 《天体物理学报》2009,(6):641-652
Mayall Ⅱ = G1 is one of the most luminous globular clusters （GCs） in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population （SSP） models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ～1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates （of order 10^7M⊙） indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster＇s exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, （1.65±0.63） × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently. 相似文献