1,998 research outputs found
The age of 47Tuc from self-consistent isochrone fits to colour-magnitude diagrams and the eclipsing member V69
Our aim is to derive a self-consistent age, distance and composition for the
globular cluster Tucanae (Tuc; NGC104). First, we reevaluate the
reddening towards the cluster resulting in a nominal as
the best estimate. The of the components of the eclipsing binary
member V69 is found to be K from both photometric and spectroscopic
evidence. This yields a true distance modulus (random)(systematic) to Tuc when combined with existing measurements of
V69 radii and luminosity ratio. We then present a new completely
self-consistent isochrone fitting method to ground based and
cluster colour-magnitude diagrams and the eclipsing binary member V69. The
analysis suggests that the composition of V69, and by extension one of the
populations of Tuc, is given by [Fe/H], [O/Fe], and
on the solar abundance scale of Asplund, Grevesse & Sauval.
However, this depends on the accuracy of the model scale which is
50-75 K cooler than our best estimate but within measurement uncertainties. Our
best estimate of the age of Tuc is 11.8 Gyr, with firm () lower
and upper limits of 10.4 and 13.4 Gyr, respectively, in satisfactory agreement
with the age derived from the white dwarf cooling sequence if our determination
of the distance modulus is adopted.Comment: 19 pages, 8 figures, accepted for publication in MNRA
Responses of Russian Wheat Aphid (Homoptera: Aphididae) to Aphid Alarm Pheromone
In a series of laboratory tests, Russian wheat aphids, Diuraphis noxia (Mordvilko), responded to synthetic aphid alarm pheromone, (E)-β-farnesene, by removing stylets and leaving feeding sites or by crawling out of test arenas. Late instars and adults were more responsive than early instars. In dose-response assays, EC50 estimates ranged from 0.94 to 8.95 mg/ml among 3 experiments. In arenas, D. noxia also responded to the proximity of cornicle-damaged nymphs of either the green peach aphid, Myzus persicae (Sulzer), or of D. noxia, which suggests endogenous production of alarm pheromone by D. noxia. Combinations of (E)-β-farnesene and the aphid-pathogenic fungus Paecilomyces fumosoroseus (Wize) Brown & Smith did not enhance aphid mortality relative to controls treated with fungus only. Further studies involving appropriate formulations of (E)-β-farnesene are necessary before practical biorational strategies can be devised combining this semiochemical and biological control agent
Progress on the hybridization of cultivated lentil Lens culinaris Medik. and wild species Lens tomentosus Ladizinsky
Non-Peer ReviewedThe domestication of lentil has produced bottleneck effects resulting in a narrow genetic basis which has resulted in reduced levels of resistance to biotic and abiotic stresses relative to its wild relatives. Phenotypic variability studies have identified wild lentil germplasm with resistance to anthracnose (Colletotrichum spp.), ascochyta blight (Ascochyta lentis), stemphylium blight (Stemphylium botryosum) and Orobanche spp. root-holoparasitic infection. To increase genetic diversity and resistance to biotic and abiotic stresses in new cultivars, introgression of desirable genes from crop wild relatives is necessary. Current evidences suggest seven taxa in the genus Lens Mill.: L. culinaris (ssp. culinaris and ssp. orientalis), L. odemensis, L. ervoides, L. nigricans, L. tomentosus and L. lamottei. Morphologically, the wild lentil species L. tomentosus most resembles L. orientalis although it can be distinguished as having a hairy pod. Previous attempts of crossing cultivated lentil L. culinaris with the wild species L. tomentosus, have failed to produce viable seeds, as with time growing embryos are gradually degraded and shrivelled, and non-viable seeds are formed; consequently an embryo rescue technique has been employed with limited success. However, this technique is time consuming, and also requires controlled growing environments and highly skilled technical personal. Using very comprehensive phenotyping technique, we have crossed cultivated lentil cultivar ‘Indian head’ with L. tomentosus and successfully produced viable F1 generation and it has currently being evaluated for phenological and morphological characteristics. Our results suggest successful results can be achieved by selecting phenotypically resembling lentil species as parents as an initial step
Overexpression of Mcl-1 exacerbates lymphocyte accumulation and autoimmune kidney disease in lpr mice
Cell death by apoptosis has a critical role during embryonic development and in maintaining tissue homeostasis. In mammals,
there are two converging apoptosis pathways: the ‘extrinsic’ pathway, which is triggered by engagement of cell surface ‘death
receptors’ such as Fas/APO-1; and the ‘intrinsic’ pathway, which is triggered by diverse cellular stresses, and is regulated by prosurvival
and pro-apoptotic members of the Bcl-2 family of proteins. Pro-survival Mcl-1, which can block activation of the proapoptotic
proteins, Bax and Bak, appears critical for the survival and maintenance of multiple haemopoietic cell types. To
investigate the impact on haemopoiesis of simultaneously inhibiting both apoptosis pathways, we introduced the vavP-Mcl-1
transgene, which causes overexpression of Mcl-1 protein in all haemopoietic lineages, into Faslpr/lpr mice, which lack functional
Fas and are prone to autoimmunity. The combined mutations had a modest impact on myelopoiesis, primarily an increase in the
macrophage/monocyte population in Mcl-1tg/lpr mice compared with lpr or Mcl-1tg mice. The impact on lymphopoiesis was
striking, with a marked elevation in all major lymphoid subsets, including the non-conventional double-negative (DN) T cells
(TCRβ+
CD4–
CD8–
B220+
) characteristic of Faslpr/lpr mice. Of note, the onset of autoimmunity was markedly accelerated in Mcl-1tg/lpr
mice compared with lpr mice, and this was preceded by an increase in immunoglobulin (Ig)-producing cells and circulating
autoantibodies. This degree of impact was surprising, given the relatively mild phenotype conferred by the vavP-Mcl-1 transgene
by itself: a two- to threefold elevation of peripheral B and T cells, no significant increase in the non-conventional DN T-cell
population and no autoimmune disease. Comparison of the phenotype with that of other susceptible mice suggests that the
development of autoimmune disease in Mcl-1tg/lpr mice may be influenced not only by Ig-producing cells but also other
haemopoietic cell types
Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. I. Measurements, methods, and first results
Earlier measurements of the masses and radii of the detached eclipsing binary
V20 in the open cluster NGC 6791 were accurate enough to demonstrate that there
are significant differences between current stellar models. Here we improve on
those results and add measurements of two additional detached eclipsing
binaries, the cluster members V18 and V80. The enlarged sample sets much
tighter constraints on the properties of stellar models than has hitherto been
possible, thereby improving both the accuracy and precision of the cluster age.
We employed (i) high-resolution UVES spectroscopy of V18, V20 and V80 to
determine their spectroscopic effective temperatures, [Fe/H] values, and
spectroscopic orbital elements, and (ii) time-series photometry from the Nordic
Optical Telescope to obtain the photometric elements. The masses and radii of
the V18 and V20 components are found to high accuracy, with errors on the
masses in the range 0.27-0.36% and errors on the radii in the range 0.61-0.92%.
V80 is found to be magnetically active, and more observations are needed to
determine its parameters accurately. The metallicity of NGC 6791 is measured
from disentangled spectra of the binaries and a few single stars to be [Fe/H]=
+0.29 \pm 0.03 (random) \pm 0.07 (systematic). The cluster reddening and
apparent distance modulus are found to be E(B - V) = 0.160 \pm 0.025 and (m -
M)V = 13.51 \pm 0.06 . A first model comparison shows that we can constrain the
helium content of the NGC 6791 stars, and thus reach a more accurate age than
previously possible. It may be possible to constrain additional parameters, in
particular the C, N, and O abundances. This will be investigated in paper II.Comment: Accepted for publication in A&
The Victoria-Regina Stellar Models: Evolutionary Tracks and Isochrones for a Wide Range in Mass and Metallicity that Allow for Empirically Constrained Amounts of Convective Core Overshooting
Seventy-two grids of stellar evolutionary tracks, along with the capability
to generate isochrones and luminosity/color functions from them, are presented
in this investigation. Sixty of them extend (and encompass) the sets of models
reported by VandenBerg et al. (2000, ApJ, 532, 430) for 17 [Fe/H] values from
-2.31 to -0.30 and alpha-element abundances corresponding to [alpha/Fe] = 0.0,
0.3, and 0.6 (at each iron abundance) to the solar metallicity and to
sufficiently high masses (up to ~2.2 solar masses) that isochrones may be
computed for ages as low as 1 Gyr. The remaining grids contain tracks for
masses from 0.4 to 4.0 solar masses and 12 [Fe/H] values between -0.60 and
+0.49 (assuming solar metal-to-hydrogen number abundance ratios): in this case,
isochrones may be calculated down to ~0.2 Gyr. The extent of convective core
overshooting has been modelled using a parameterized version of the Roxburgh
(1989, A&A, 211, 361) criterion, in which the value of the free parameter at a
given mass and its dependence on mass have been determined from analyses of
binary star data and observed color-magnitude diagrams for several open
clusters. Because the calculations reported herein satisfy many empirical
constraints, they should provide useful probes into the properties of both
simple and complex stellar populations. [All of the model grids may be obtained
from the Canadian Astronomy Data Center
(http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/cvo/community/VictoriaReginaModels
).]Comment: Accepted for the ApJS (Feb. 2006); 39 pages including 14 figures, 3
table
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