排序方式: 共有34条查询结果,搜索用时 336 毫秒
1.
2.
3.
Mark A. Norris Ray M. Sharples Harald Kuntschner 《Monthly notices of the Royal Astronomical Society》2006,367(2):815-824
We present Gemini Multi-Object Spectrograph longslit spectroscopy of the isolated S0 galaxy NGC 3115. We have determined kinematical data and Lick/IDS absorption line-strength indices for the major axis out to around 9 kpc and for the minor axis out to around 5 kpc (around 2R e ). Using stellar population models which include the effects of variable [α/Fe] ratios, we derive metallicities, abundance ratios and ages for the stellar population of NGC 3115. We find that [α/Fe] remains fairly constant with increasing radius at around [α/Fe]= 0.17 for the major axis but increases rapidly for the minor axis to around [α/Fe]= 0.3 . We also find that to first order, this behaviour can be explained by a simple spheroid + disc model, where the spheroid has [α/Fe]= 0.3 and the disc shows close to solar abundance ratios. The disc also appears considerably younger than the spheroid, having an age of around 6 Gyr compared to 12 Gyr for the spheroid. We compare these results to those previously presented for the globular cluster system of NGC 3115. 相似文献
4.
5.
6.
Anouska Panton Claire Mahaffey Naomi Greenwood Joanne Hopkins David Montagnes Jonathan Sharples 《Ocean Dynamics》2012,62(2):295-306
Regions of freshwater influence (ROFIs) are dynamic areas within the coastal seas that experience cycles of stability driven
by density gradients and the spring-neap tidal cycle. As a result, pulses of biological production may occur on a more frequent
timescale than the classic seasonal cycle. Net community production (NCP) rates and chlorophyll a concentration are presented from a site within the ROFI of Liverpool Bay and compared to similar measurements made at a site
outside the ROFI during 2009. The influence of water column stability on biological production in the ROFI was also investigated
using high-frequency observations from a Cefas Smartbuoy. Both sites were autotrophic from spring to autumn before becoming
heterotrophic over winter. NCP at the inshore site was estimated to range from 30.8 to 50.4 gC m−2 year−1. A linear relationship detected between chlorophyll a and NCP from both sites was used to estimate metabolic balance over 1 year at the ROFI site using high-resolution chlorophyll
a concentrations from the Smartbuoy but was found to poorly replicate NCP rates compared to those derived from dissolved oxygen
fluxes. There was no clear biological response to periods of stratification within the ROFI, and it is proposed that changes
in light attenuation in the Liverpool Bay ROFI, driven not only by stratification but also by fluctuations in riverine sediment
load, most likely play an important role in controlling phytoplankton growth in this region. 相似文献
7.
M. A. Beasley R. M. Sharples T. J. Bridges D. A. Hanes S. E. Zepf K. M. Ashman D. Geisler 《Monthly notices of the Royal Astronomical Society》2000,318(4):1249-1263
We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately −1.6≤[Fe/H]≤0 dex. There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14.5±4 Gyr and the metal-rich population is 13.8±6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences. 相似文献
8.
9.
Volume Contents
Contents Volume 15 相似文献10.
Andrew Steele David t. Goddard Dave Stapleton Jan k. w. Toporski Vanessa Peters Virginia Bassinger George Sharples David d. Wynn‐Williams David s. Mckay 《Meteoritics & planetary science》2000,35(2):237-241
Abstract— Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite. 相似文献