排序方式： 共有50条查询结果，搜索用时 15 毫秒
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J. Ma R. de Grijs D. Chen S. van den Bergh Z. Fan Z. Wu H. Wu X. Zhou J. Wu Z. Jiang J. Chen 《Monthly notices of the Royal Astronomical Society》2007,376(4):1621-1629
Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, r c = 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc) , a tidal radius, r t = 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc) , and a concentration index c = log ( r t / r c ) = 2.01 ± 0.02 . The central surface brightness is 13.510 mag arcsec−2 . We also calculate the half-light radius, at r h = 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc) . The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log R h diagram as ω Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log R h plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. 相似文献
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Z. Fan J. Ma R. de Grijs X. Zhou 《Monthly notices of the Royal Astronomical Society》2008,385(4):1973-1988
Using metallicities from the literature, combined with the Revised Bologna Catalogue of photometric data for M31 clusters and cluster candidates [the latter of which is the most comprehensive catalogue of M31 clusters currently available, including 337 confirmed globular clusters (GCs) and 688 GC candidates], we determine 443 reddening values and intrinsic colours, and 209 metallicities for individual clusters without spectroscopic observations. This, the largest sample of M31 GCs presently available, is then used to analyse the metallicity distribution of M31 GCs, which is bimodal with peaks at [Fe/H]≈−1.7 and −0.7 dex. An exploration of metallicities as a function of radius from the M31 centre shows a metallicity gradient for the metal-poor GCs, but no such gradient for the metal-rich GCs. Our results show that the metal-rich clusters appear as a centrally concentrated spatial distribution; however, the metal-poor clusters tend to be less spatially concentrated. There is no correlation between luminosity and metallicity among the M31 sample clusters, which indicates that self-enrichment is indeed unimportant for cluster formation in M31.
The reddening distribution shows that slightly more than half of the GCs are affected by a reddening of E ( B − V ) ≲ 0.2 mag; the mean reddening value is E ( B − V ) = 0.28+0.23 −0.14 mag . The spatial distribution of the reddening values indicates that the reddening on the north-western side of the M31 disc is more significant than that on the south-eastern side, which is consistent with the conclusion that the north-western side is nearer to us. 相似文献
The reddening distribution shows that slightly more than half of the GCs are affected by a reddening of E ( B − V ) ≲ 0.2 mag; the mean reddening value is E ( B − V ) = 0.28
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Sarah L. Moll Richard de Grijs Sabine Mengel Linda J. Smith Paul A. Crowther 《Astrophysics and Space Science》2009,324(2-4):177-182
We present virial mass estimates of young massive clusters (YMCs) in the starburst galaxies NGC1140 and M83, determined from high spectral resolution VLT echelle spectroscopy and high spatial resolution Hubble Space Telescope imaging. The survivability of such clusters is important in testing the scenario that YMCs are potentially proto-globular clusters. As young clusters, they lie in the domain in which dynamical masses appear to overestimate true cluster masses, most likely due to the clusters not being virialised. We find that the dynamical mass of NGC1140-1 is approximately ten times greater than its photometric mass. We propose that the most likely explanation for this disparity is the crowded environment of NGC1140-1, rather than this being solely due to a lack of virial equilibrium. 相似文献
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Q. Liu R. de Grijs L. C. Deng Y. Hu I. Baraffe S. F. Beaulieu 《Monthly notices of the Royal Astronomical Society》2009,396(3):1665-1674
We use deep Hubble Space Telescope photometry of the rich, young (∼20- to 45-Myr old) star cluster NGC 1818 in the Large Magellanic Cloud to derive its stellar mass function (MF) down to ∼0.15 M⊙ . This represents the deepest robust MF thus far obtained for a stellar system in an extragalactic, low-metallicity ([Fe/H]≃−0.4 dex) environment. Combining our results with the published MF for masses above 1.0 M⊙ , we obtain a complete present-day MF. This is a good representation of the cluster's initial MF (IMF), particularly at low masses, because our observations are centred on the cluster's uncrowded half-mass radius. Therefore, stellar and dynamical evolution of the cluster will not have affected the low-mass stars significantly. The NGC 1818 IMF is well described by both a lognormal and a broken power-law distribution with slopes of Γ= 0.46 ± 0.10 and Γ≃−1.35 (Salpeter-like) for masses in the range from 0.15 to 0.8 M⊙ and greater than 0.8 M⊙ , respectively. Within the uncertainties, the NGC 1818 IMF is fully consistent with both the Kroupa solar neighbourhood and the Chabrier lognormal mass distributions. 相似文献
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